[Transcriber's notes]

This text is derived from an unedited version in the Internet Archive.

Page numbers are indicated by numbers enclosed in curly braces, e.g. {99}. They have been located where page breaks occurred in the original book.

Labels and text in a figure that are not mentioned in the figure description are included as a comma separated list, as in "(Figure text: cochlea, vestibule, 3 Canals)".

Lengthy footnotes and quotations are indented.

Obvious misspellings and typos are corrected but inconsistent spelling is not resolved, as in coordinate and coördinate.

Here are the appearances of the heading levels.

Here are the definitions of some unfamiliar words (to me).

amour propre: self-esteem; self-respect.

esprit de corps: camaraderie, bonding, solidarity, fellowship.

motility (motile): moving or capable of moving spontaneously.

unwonted: unusual.

[End Transcribers's notes]

BY
ROBERT S. WOODWORTH, Ph. D.
Professor of Psychology in Columbia University


NEW YORK
HENRY HOLT AND COMPANY
1921


COPYRIGHT, 1921
BY
HENRY HOLT AND COMPANY


Printed in the U.S.A.

A few words to the reader are in order. In the first place, something like an apology is due for the free way in which the author has drawn upon the original work of many fellow-psychologists, without any mention of their names. This is practically unavoidable in a book intended for the beginner, but the reader may well be informed of the fact, and cautioned not to credit the content of the book to the writer of it. The author's task has been that of selecting from the large mass of psychological information now available, much of it new, whatever seemed most suitable for introducing the subject to the reader. The book aims to represent the present state of a very active science.

Should the book appear unduly long in prospect, the longest and most detailed chapter, that on Sensation, might perfectly well be omitted, on the first reading, without appreciably disturbing the continuity of the rest.

On the other hand should any reader desire to make this text the basis of a more extensive course of reading, the lists of references appended to the several chapters will prove of service. The books and articles there cited will be found interesting and not too technical in style.

Much advantage can be derived from the use of the "Exercises". The text, at the best, but provides raw material. Each student's finished product must be of his own making. The exercises afford opportunity for the student to work over the material and make it his own.

A first or preliminary edition of this book, in mimeographed sheets, was in use for two years in introductory classes conducted by the author and his colleagues, and was subjected to exceedingly helpful criticism from both teachers and students. The revision of that earlier edition into the present form has been very much of a coöperative enterprise, and so many have coöperated that room could scarcely be found for all their names. Professor A. T. Poffenberger, Dr. Clara F. Chassell, Dr. Georgina I. Gates, Mr. Gardner Murphy, Mr. Harold E. Jones and Mr. Paul S. Achilles have given me the advantage of their class-room experience with the mimeographed book. Dr. Christine Ladd-Franklin has very carefully gone over with me the passages dealing with color vision and with reasoning. Miss Elizabeth T. Sullivan, Miss Anna B. Copeland, Miss Helen Harper and Dr. A. H. Martin have been of great assistance in the final stages of the work. Important suggestions have come also from several other universities, where the mimeographed book was inspected.

R. S. W.
Columbia University
August, 1921

Modern psychology is an attempt to bring the methods of scientific investigation, which have proved immensely fruitful in other fields, to bear upon mental life and its problems. The human individual, the main object of study, is so complex an object, that for a long time it seemed doubtful whether there ever could be real science here; but a beginning was made in the nineteenth century, following the lead of biology and physiology, and the work of the investigator has been so successful that to-day there is quite a respectable body of knowledge to assemble under the title of scientific psychology.

Psychology, then, is a science. It is the science of--what shall we say? "The science of the soul"--that is what the name means by derivation and ancient usage. "The science of the mind" has a more modern sound. "The science of consciousness" is more modern still. "The science of behavior" is the most recent attempt at a concise formula.

None of these formulas is wholly satisfactory. Psychology does not like to call itself the science of the soul, for that has a theological tang and suggests problems that have so far not seemed accessible to scientific investigation. Psychology does not like very well to call itself the science {2} of the mind, as the mind seems to imply some thing or machine, and there is no such thing to be observed (unless it be the brain and body generally), and, anyway, psychology is distinctly a study of actions rather than of things. Psychology does not like to limit itself to the study of consciousness, but finds it necessary to study also unconscious actions. As to "behavior", it would be a very suitable term, if only it had not become so closely identified with the "behavioristic movement" in psychology, which urges that consciousness should be entirely left out of psychology, or at least disregarded. "Behavior psychology", as the term would be understood to-day, means a part of the subject and not the whole.

[Footnote: A series of waggish critics has evolved the following: "First psychology lost its soul, then it lost its mind, then it lost consciousness; it still has behavior, of a kind."]

The best way of getting a true picture of psychology, and of reaching an adequate definition of its subject-matter, would be to inspect the actual work of psychologists, so as to see what kind of knowledge they are seeking. Such a survey would reveal quite a variety of problems under process of investigation, some of them practical problems, others not directly practical.

One line of question that always interests the beginner in psychology is as to how people differ--how different people act under the same circumstances--and why; and if we watch the professional psychologist, we often find him working at just this problem. He tests a great number of individuals to see how they differ, and tries to discover on what factors their differences depend, how far on heredity, how far on environment. The "psychologist" in such a place as the children's court {3} is a specialist whose duty it is to test the delinquent children that are brought before the court, with the special object of measuring the intelligence of each individual child and of helping in other ways to understand the child's peculiar conduct and attitude.

The "psychological examiner" in the Army, during the Great War, had the same general object in view. It was desirable to measure the intelligence of each recruit as he entered the service, since military experience had shown that men of low intelligence made poor soldiers, while those of high intelligence made the best officers and non-commissioned officers, provided they also possessed good physique and certain less measureable mental qualifications, such as courage and leadership.

The Army psychologists, like the court psychologist, were engaged in applying scientific knowledge to the practical problems of life; and there are many other applications of psychology, to education, to medicine, to business and other occupations, as well as to the art of right living. Scientific knowledge enables you to predict and control. Having devised scientific tests for intelligence, you can predict of a six-year-old boy who tests low, that he will not get much good from the regular classes in school; and thus you are in a position to control the education of this boy for his own best interests. In the Army, it happened during the earlier part of the war that some companies or regiments made much slower progress in training than others; and a whole Division was delayed for months because of the backwardness of a single regiment. When the psychological tests were introduced, these slow-learning units were found to contain a disproportionate number of men of low intelligence. From that time on, it was possible by aid of the tests to equalize the intelligence of different units when first formed, and thus insure equal {4} progress in training. This was a good example of "control".

Most of us are attracted by the practical use of a science, and some have no patience with any study that does not seem immediately practical. But really any science, however much it is applied, must remain fundamentally a pure science; that is, it must seek most of all to know and understand. Practical scientific knowledge was usually first obtained without any inkling of how it might be used. The science of electricity is the most striking example of this. It began as an attempt to understand certain curious phenomena, which seemed to be nothing but curiosities; yet when the knowledge of these phenomena had progressed to a certain point, abundant use was found for it. Much the same is true of psychology, which began as a pure science and only recently has found ways of applying its discoveries to practical affairs. So the student beginning the science, though properly desirous of making practical use of what he learns, should let himself be governed for the present by the desire to know and understand, confident that the more scientific (which is to say, the more complete, systematic and reliable) his knowledge is, the more available it will be for practical application.

Our science is not concerned entirely with differences between people, but asks also in what ways people are alike, and this is indeed its central problem. How do "we" observe, learn, remember, imagine, think? What sensations and feelings do we have, what emotions, what instincts, what natural and acquired impulses to action? How are our natural powers and impulses developed and organized as we grow up? Psychology is concerned with the child as well as the adult, and it is even concerned with the animal. It is concerned with the abnormal as well as the normal human being. So you will find books and {5} courses on animal psychology, child psychology, abnormal psychology. Now general psychology--or just plain "psychology"--has to do with the main laws and principles that hold in all these special fields.

A good definition of our science would distinguish it from other sciences, especially from those neighboring sciences with which it is in closest contact.

There is no difficulty in framing a good logical distinction here. Sociology studies the activities of a group of people taken as a whole, while psychology studies the activities of the individuals. Both might be interested in the same social act, such as an election, but sociology would consider this event as a unit, whereas psychology would break it up into the acts of the several voters. The distinction is clear enough theoretically, but breaks down often in practice, as sociology would like to know the motives that swayed individual voters, while psychology on its side is interested to know what decision was reached by the majority. All the social sciences, including economics and politics, have a psychological side, since they evidently are concerned to know the causes that govern human conduct. Social psychology studies the individual in his social relations.

Biology, being the science of living creatures, includes psychology, which studies these creatures on the mental side. The science of life includes the science of mental life. We may call psychology a part of biology, or we may call it one of the biological sciences. It has very close contact with several other branches of biology. Animal psychology overlaps that part of zoology which studies the behavior of animals. Genetic psychology, as it is sometimes called, i.e., the study of mental heredity. {6} and development, dovetails with the general biological science of genetics, so that we find biologists gathering data on the heredity of feeble-mindedness or of musical ability, while psychologists discuss the general theory of heredity.

That one of all the sciences that has the closest contacts with psychology is human and animal physiology. Broadly defined, physiology is that part of biology that studies functions or activities; and, so defined, it includes psychology as part of itself. In practice, psychology devotes itself to desire, thought, memory, and such "mental functions", while physiology concentrates its effort upon "bodily functions" like digestion and circulation. But this is only a rough distinction, which breaks down at many points.

Where shall we class sensation? Is it "mental" or "bodily"? Both sciences study it. Physiology is perhaps more apt to go into the detailed study of the action of the sense organs, and psychology to concern itself with the classification of sensations and the use made of them for recognizing objects or for esthetic purposes. But the line between the two sciences is far from sharp at this point.

Speech, also, lies in both provinces. Physiology has studied the action of the vocal organs and the location of the brain centers concerned in speech, while psychology has studied the child's process of learning to speak and the relation of speech to thought, and is more apt to be interested in stuttering, slips of the tongue, and other speech disturbances which are said to be "mental rather than physical".

It would be hard to mention any activity that is mental without being physical at the same time. Even thinking, which seems as purely mental as any, requires brain action; and the brain is just as truly a bodily organ as the heart or stomach. Its activity is bodily activity and lies properly within the field of physiology.

But it would be equally difficult to mention any function that is exclusively bodily, and not mental at the same time, in some degree. Take digestion for example: the pleasant anticipation of food will start the digestive juices flowing, before any food is physically in the stomach; while in anger or fear digestion comes to a sudden halt. Therefore we find physiologists interested in these emotions, and psychologists interested in digestion.

We do not find any clean separation between our science and physiology; but we find, on the whole, that psychology examines what are called "mental" activities, and that it studies them as the performances of the whole individual rather than as executed by the several organs.

Typically, the activities that psychology studies are conscious performances, while many of those falling to physiology are unconscious. Thus digestion is mostly unconscious, the heart beat is unconscious except when disturbed, the action of the liver is entirely unconscious. Why not say, then, that psychology is the study of conscious activities?

There might be some objection to this definition from the side of physiology, which studies certain conscious activities itself--speech, for example, and especially sensation.

There would be objection also from the side of psychology, which does not wish to limit itself to conscious action. Take the case of any act that can at first be done only with close attention, but that becomes easy and automatic after practice; at first it is conscious, later unconscious, but psychology would certainly need to follow it from the initial to the final stage, in order to make a complete study of the practice effect. And then there is the "unconscious", or the "subconscious mind"--a matter on which psychologists {8} do not wholly agree among themselves; but all would agree that the problem of the unconscious was appropriate to psychology.

For all the objections, it remains true that the typical mental process, the typical matter for psychological study, is conscious. "Unconscious mental processes" are distinguished from the unconscious activity of such organs as the liver by being somehow like the conscious mental processes.

It would be correct, then, to limit psychology to the study of conscious activities and of activities akin to these.

No one has objected so strenuously to defining psychology as the science of consciousness, and limiting it to consciousness, as the group of animal psychologists. By energetic work, they had proved that the animal was a very good subject for psychological study, and had discovered much that was important regarding instinct and learning in animals. But from the nature of the case, they could not observe the consciousness of animals; they could only observe their behavior, that is to say, the motor (and in some cases glandular) activities of the animals under known conditions. When then the animal psychologists were warned by the mighty ones in the science that they must interpret their results in terms of consciousness or not call themselves psychologists any longer, they rebelled; and some of the best fighters among them took the offensive, by insisting that human psychology, no less than animal, was properly a study of behavior, and that it had been a great mistake ever to define it as the science of consciousness.

It is a natural assumption that animals are conscious, but after all you cannot directly observe their consciousness, and you cannot logically confute those philosophers {9} who have contended that the animal was an unconscious automaton. Still less can you be sure in detail what is the animal's sensation or state of mind at any time; to get at that, you would need a trustworthy report from the animal himself. Each individual must observe his own consciousness; no one can do it from outside. The objection of the behaviorist to "consciousness psychology" arises partly from distrust of this method of inner observation, even on the part of a human observer.

Indeed, we can hardly define psychology without considering its methods of observation, since evidently the method of observation limits the facts observed and so determines the character of the science. Psychology has two methods of observation.

When a person performs any act, there are, or may be, two sorts of facts to be observed, the "objective" and the "subjective". The objective facts consist of movements of the person's body or of any part of it, secretions of his glands (as flow of saliva or sweat), and external results produced by these bodily actions--results such as objects moved, path and distance traversed, hits on a target, marks made on paper, columns of figures added, vocal or other sounds produced, etc., etc. Such objective facts can be observed by another person.

The subjective facts can be observed only by the person performing the act. While another person can observe, better indeed than he can himself, the motion of his legs in walking, he alone can observe the sensations in the joints and muscles produced by the leg movement. No one else can observe his pleased or displeased state of mind, nor whether he is thinking of his walking or of something quite different. To be sure, his facial expression, which is an objective fact, may give some clue to his thoughts and feelings, but "there's no art to read the mind's construction {10} in the face", or at least no sure art. One may feign sleep or absorption while really attending to what is going on around. A child may wear an angelic expression while meditating mischief. To get the subjective facts, we shall have to enlist the person himself as our observer.

This is observation by an individual of his own conscious action. It is also called subjective observation. Notice that it is a form of observation, and not speculation or reasoning from probabilities or from past experience. It is a direct observation of fact.

One very simple instance of introspection is afforded by the study of after-images. Look for an instant at the glowing electric bulb, and then turn your eyes upon a dark background, and observe whether the glowing filament appears there; this would be the "positive after-image". This simple type of introspection is used by physiology in its study of the senses, as well as by psychology; and it gives such precise and regular results that only the most confirmed behaviorists refuse to admit it as a good method of observation.

But psychology would like to make introspective observations on the more complex mental processes as well; and it must be admitted that here introspection becomes difficult. You cannot hope to make minute observations on any process that lasts over a very few seconds, for you must let the process run its natural course unimpeded by your efforts at observing it, and then turn your "mental eye" instantly back to observe it retrospectively before it disappears. As a matter of fact, a sensation or feeling or idea hangs on in consciousness for a few seconds, and can be observed in this retrospective way. There is no theoretical objection to this style of introspection, but it is practically difficult and {11} tricky. Try it on a column of figures: first add the column as usual, then immediately turn back and review exactly what went through your mind in the process of adding---what numbers you spoke internally, etc. Try again by introspecting the process of filling in the blanks in the sentence:

"Botany could not make use of introspection because ______ have probably no ________ processes."

At first, you may find it difficult to observe yourself in this way; for the natural tendency, when you are aiming at a certain result, is to reach the goal and then shift to something else, rather than to turn back and review the steps by which you reached the goal. But with practice, you acquire some skill in introspection.

One difficulty with introspection of the more complex mental processes is that individuals vary more here than in the simpler processes, so that different observers, observing each his own processes, will not report the same facts, and one observer cannot serve as a check upon another so easily as in the simpler introspection of after-images and other sensations, or as in the observations made in other sciences. Even well trained introspectionists are quite at variance when they attempt a minute description of the thought processes, and it is probable that this is asking too much of introspection. We mustn't expect it to give microscopic details. Rough observations, however, it gives with considerable certainty. Who can doubt, for example, that a well-practised act goes on with very little consciousness, or that inner, silent speech often accompanies thinking? And yet we have only introspection to vouch for these facts.

But to say, as used to be said, that psychology is purely an introspective science, making use of no other sort of observation, is absurd in the face of the facts.

We have animal psychology, where the observation is exclusively objective. In objective observation, the observer watches something else, and not himself. In animal psychology, the psychologist, as observer, watches the animal.

The same is true of child psychology, at least for the first years of childhood. You could not depend on the introspections of a baby, but you can learn much by watching his behavior. Abnormal persons, also, are not often reliable introspectionists, and the study of abnormal psychology is mostly carried on by objective methods.

Now how is it with the normal adult human being, the standard subject for psychology? Does he make all the observations on himself or may he be objectively observed by the psychologist? The latter, certainly. In fact, nearly all tests, such as those used in studying differential psychology, are objective. That is to say that the person tested is given a task to perform, and his performance is observed in one way or another by the examiner. The examiner may observe the time occupied by the subject to complete the task, or the quantity accomplished in a fixed time; or he may measure the correctness and excellence of the work done, or the difficulty of the task assigned. One test uses one of these measures, and another uses another; but they are all objective measures, not depending at all on the introspection of the subject.

What is true of tests in differential psychology is true of the majority of experiments in general psychology: the performer is one person, the observer another, and the observation is objective in character. Suppose, for example, you are investigating a memory problem; your method may be to set your subject a lesson to memorize under certain defined conditions, and see how quickly and well he learns it; then you give him another, equally difficult lesson to be learned under altered conditions, and observe whether he {13} does better or worse than before. Thus you discover which set of conditions is more favorable for memorizing, and thence can infer something of the way in which memorizing is accomplished. In the whole experiment you need not have called on your subject for any introspections; and this is a type of many experiments in which the subject accomplishes a certain task under known conditions, and his success is objectively observed and measured.

There is another type of objective psychological observation, directed not towards the success with which a task is accomplished, but towards the changes in breathing, heart beat, stomach movements, brain circulation, or involuntary movements of the hands, eyes, etc., which occur during the course of various mental processes, as in reading, in emotion, in dreaming or waking from sleep.

Now it is not true as a matter of history that either of these types of objective observation was introduced into psychology by those who call themselves behaviorists. Not at all; experiments of both sorts have been common in psychology since it began to be an experimental science. The first type, the success-measuring experiment, has been much more used than introspection all along. What the behaviorists have accomplished is the definitive overthrow of the doctrine, once strongly insisted on by the "consciousness psychologists", that introspection is the only real method of observation in psychology; and this is no mean achievement. But we should be going too far if we followed the behaviorists to the extent of seeking to exclude introspection altogether, and on principle. There is no sense in such negative principles. Let us accumulate psychological facts by any method that will give the facts.

Either introspective or objective observation can be employed in the experimental attack on a problem, which consists, as just illustrated in the case of memory, in controlling the conditions under which a mental performance occurs, varying the conditions systematically, and noting the resulting change in the subject's mental process or its outcome. Psychologists are inclined to regard this as the best line of attack, whenever the mental activity to be studied can be effectively subjected to control. Unfortunately, emotion and reasoning are not easily brought under control, and for this reason psychology has made slower progress in understanding them than it has made in the fields of sensation and memory, where good experimental procedure has been developed.

Another general line of attack worthy to be mentioned alongside of the experimental is the comparative method. You compare the actions of individuals, classes or species, noting likenesses and differences. You see what behavior is typical and what exceptional. You establish norms and averages, and notice how closely people cluster about the norm and how far individuals differ from it. You introduce tests of various sorts, by which to get a more precise measure of the individual's performance. Further, by the use of what may be called double comparison, or "correlation", you work out the relationships of various mental (and physical) traits. For example, when many different species of animals are compared in intelligence and also in brain weight, the two are found to correspond fairly well, the more intelligent species having on the whole the heavier brains; from which we fairly conclude that the size of the brain has something to do with intelligence. But when we correlate brain weight and intelligence in human individuals. {15} we find so many exceptions to the rule (stupid men with large brains and gifted men with brains of only moderate size) that we are forced to recognize the importance of other factors, such as the perfection of the microscopic structure of the brain.

Tests and correlations have become so prominent in recent psychological investigation that this form of the comparative method ranks on a par with the strict experimental method. A test is an experiment, in a way, and at least is often based upon an experiment; but the difference between the two lines of attack is that an experiment typically takes a few subjects into the laboratory and observes how their mental performances change with planfully changed conditions; whereas a test goes out and examines a large number of persons under one fixed set of conditions. An experiment belongs under what we called "general psychology", and a test under "differential psychology", since the first outcome of a test is to show how the individual differs from others in a certain respect. The results may, however, be utilized in various ways, either for such practical purposes as guiding the individual's choice of an occupation, or for primarily scientific purposes, such as examining whether intelligence goes with brain size, whether twins resemble each other as much mentally as they do physically, whether intellectual ability and moral goodness tend on the whole to go together, or not.

The genetic method is another of the general lines of attack on psychological problems. The object here is to trace the mental development of the individual, or of the race. It may be to trace the development either of mentality in general, or of some particular mental performance. It may be to trace the child's progress in learning to speak, or to follow the development of language in the human species, from the most primitive tongues up to those of the great {16} civilized peoples of to-day. It may be to trace the improvement of a performance with continued practice.

The value of the genetic method is easily seen. Usually the beginnings of a function or performance are comparatively simple and easy to observe and analyze. Also, the process of mental growth is an important matter to study on its own account.

The pathological method is akin to the genetic, but traces the decay or demoralization of mental life instead of its growth. It traces the gradual decline of mental power with advancing age, the losses due to brain disease, and the maladaptations that appear in insanity and other disturbances. Here psychology makes close contact with psychiatry which is the branch of medicine concerned with the insane, etc., and which in fact has contributed most of the psychological information derived from the pathological method.

The object of the pathological method is, on the one side, to understand abnormal forms of mental life, with the practical object of preventing or curing them, and on the other side, to understand normal mental life the better. Just as the development of a performance throws light on the perfected act, so the decay or disturbance of a function often reveals its inner workings; for we all know that it is when a machine gets out of order that one begins to see how it ought to work. Failure sheds light on the conditions of success, maladaptation throws into relief the mental work that has to be done by the normal individual in order to secure and maintain his good adaptation. According to the psychiatrists, mental disturbance is primarily an affair of emotion and desire rather than of intellect; and consequently they believe that the pathological method is of special importance in the study of the emotional life.

Having now made a rapid preliminary survey of the field of psychology, and of the aims and methods of the workers in this field, we ought to be in a position to give some sort of a definition.

We conclude, then: psychology is a part of the scientific study of life, being the science of mental life. Life consisting in process or action, psychology is the scientific study of mental processes or activities. A mental activity is typically, though not universally, conscious; and we can roughly designate as mental those activities of a living creature that are either conscious themselves or closely akin to those that are conscious. Further, any mental activity can also be regarded as a physiological activity, in which case it is analyzed into the action of bodily organs, whereas as "mental" it simply comes from the organism or individual as a whole. Psychology, in a word, is the science of the conscious and near-conscious activities of living individuals.

Psychology is not interested either in dead bodies or in disembodied spirits, but in living and acting individuals.

One word more, on the psychological point of view. In everyday life we study our acquaintances and their actions from a personal standpoint. That is, we evaluate their behavior according as it affects ourselves, or, perhaps, according as it squares or not with our standards of right and wrong. We always find something to praise or blame. Now, the psychologist has no concern with praise and blame, but is a seeker after the facts. He would know and understand human actions, rather than pass judgment on them. When, for example, he is introduced into the school or children's court, for the purpose of examining children that are "problems", his attitude differs considerably from that of the {18} teacher or officer of the law; for while they almost inevitably pass judgment on the child in the way of praise or blame, the psychologist simply tries to understand the child. The young delinquent brought into the laboratory of the court psychologist quickly senses the unwonted atmosphere, where he is neither scolded nor exhorted, but asked to lend his coöperation in an effort to discover the cause why his conduct is as it is. Now, this psychological attitude is not necessarily "better" than the other, but it is distinctly valuable in its place, as seen from the fact that the young delinquent often does coöperate. He feels that if the psychologist can find out what is the trouble with him, this may help. Nothing, indeed, is more probable; it is when we have the facts and trace out cause and effect that we are in a fair way to do good. Nothing is more humane than psychology, in the long run, even though the psychologist may seem unfeeling in the course of his investigation.

To the psychologist, conduct is a matter of cause and effect, of natural law. His business is to know the laws of that part of nature which we call human nature, and to use these laws, as fast as discovered, for solving the problems presented by the human individual or group. For him, even the most capricious conduct has its causes, even the most inexplicable has its explanation--if only the cause can be unearthed, which he does not pretend he can always actually accomplish, since causes in the mental realm are often very complex. No one can be a psychologist all of the time; no one can or should always maintain this matter-of-fact attitude towards self and neighbor. But some experience with the psychological attitude is of practical value to any one, in giving clearer insight, more toleration, better control, and even saner standards of living.

1. Outline the chapter. A sample outline of the briefer sort is here given:

A. Subject-matter of psychology: mental activities.

(1) A sub-class under vital activities.
(2) Activities of individuals, as distinguished from

(a) Activities of social groups (sociology).
(b) Activities of single organs (physiology).

(3) Either conscious, or closely related to conscious activities.
(4) May be activities of human or animal, adult or child, normal or abnormal individuals.

B. Problems of psychology:

(1) How individuals differ in their mental activities.
(2) How individuals are alike in their mental activities.
(3) Practical applications of either (1) or (2).

C. Methods of psychology:

(1) Methods of observing mental activities.

(a) Introspective, the observing by an individual of his own actions.
(b) Objective, the observation of the behavior of other individuals.

(2) General lines of attack upon psychological problems.

(a) Experimental: vary the conditions and see how the mental activity changes.
(b) Comparative: test different individuals or classes and see how mental activity differs, etc.
(c) Genetic: trace mental development.
(d) Pathological: examine mental decay or disturbance.

2. Formulate a psychological question regarding each of the following: hours of work, genius, crime, baseball.

3. Distinguish introspection from theorizing.

4. What different sorts of objective fact can be observed in psychology?

5. What is the difference between the physiology of hearing and the psychology of hearing?

6. State two reasons why it would be undesirable to limit psychology to the introspective study of consciousness.

{20}

7. What is the difference between an experiment and a test, (a) in purpose, (b) in method?

8. Compare the time it takes you to add twenty one-place numbers, arranged in a vertical column, and arranged in a horizontal line, (a) Is this introspective or objective observation? Why so? (b) Is it a test or an experiment? Why?

9. Write a psychological sketch of some one you know well, taking care to avoid praise and blame, and to stick to the psychological point of view.

Some of the good books on the different branches of psychology are the following:
On animal psychology:

Margaret F. Washburn, The Animal Mind, 2nd edition, 1917. John B. Watson, Behavior, 1914.

On child psychology:

Norsworthy and Whitley, The Psychology of Childhood, 1918.

On abnormal psychology:

A. J. Rosanoff, Manual of Psychiatry, 5th edition, 1920.

On applied psychology:

Hollingworth and Poffenberger, Applied Psychology, 1917.

On individual psychology, parts of:

E. L. Thorndike, Educational Psychology, Briefer Course, 1914, Daniel Starch, Educational Psychology, 1919.

Having the field of psychology open before us, the next question is, where to commence operations. Shall we begin with memory, imagination and reasoning, or with will, character and personality, or with motor activity and skill, or with feelings and emotions, or with sensation and perceptions? Probably the higher forms of mental activity seem most attractive, but we may best leave complicated matters till later, and agree to start with the simplest sorts of mental performance. Thus we may hope to learn at the outset certain elementary facts which will later prove of much assistance in unraveling the more complex processes.

Among the simplest processes are sensations and reflexes, and we might begin with either. The introspective psychologists usually start with sensations, because their great object is to describe consciousness, and they think of sensations as the chief elements of which consciousness is composed. The behaviorists would prefer to start with reflexes, because they conceive of behavior as composed of these simple motor reactions.

Without caring to attach ourselves exclusively to either introspectionism or behaviorism, we may take our cue just here from the behaviorists, because we shall find the facts of motor reaction more widely useful in our further studies than the facts of sensation, and because the facts of {22} sensation fit better into the general scheme of reactions than the facts of reaction fit into any general scheme based on sensation.

A reaction is a response to a stimulus. The response, in the simplest cases, is a muscular movement, and is called a "motor response". The stimulus is any force or agent that, acting upon the individual, arouses a response.

If I start at a sudden noise, the noise is the stimulus, and the forcible contraction of my muscles is the response. If my old friend's picture brings tears to my eyes, the picture (or the light reflected from it) is the stimulus, and the flow of tears is the response, here a "glandular" instead of a motor response.

One of the earliest experiments to be introduced into psychology was that on reaction time, conducted as follows: The experimenter tells his "subject" (the person whose reaction is to be observed) to be ready to make a certain movement as promptly as possible on receiving a certain stimulus. The response prescribed is usually a slight movement of the forefinger, and the stimulus may be a sound, a flash of light, a touch on the skin, etc. The subject knows in advance exactly what stimulus is to be given and what response he has to make, and is given a "Ready!" signal a few seconds before the stimulus. With so simple a performance, the reaction time is very short, and delicate apparatus must be employed to measure it. The "chronoscope" or clock used to measure the reaction time reads to the hundredth or thousandth of a second, and the time is found to be about .15 sec. in responding to sound or touch, about .18 sec. in responding to light.

Even the simple reaction time varies, however, from one {23} individual to another, and from one trial to another. Some persons can never bring their record much below the figures stated, while a few can get the time down to .10 sec, which is about the limit of human ability. Every one is bound to vary from trial to trial, at first widely, after practice between narrow limits, but always by a few hundredths of a second at the least. It is curious to find the elementary fact of variability of reaction present in such a simple performance.

What we have been describing is known as the "simple reaction", in distinction from other experiments that demand more of the subject. In the "choice reaction", there are two stimuli and the subject may be required to react to the one with the right hand and to the other with the left; for example, if a red light appears he must respond with the right hand, but if a green light appears, with the left. Here he cannot allow himself to become keyed up to as high a pitch as in the simple reaction, for if he does he will make many false reactions. Therefore, the choice reaction time is longer than the simple reaction time--about a tenth of a second longer.

The "associative reaction" time is longer still. Here the subject must name any color that is shown, or read any letter that is shown, or respond to the sight of any number by calling out the next larger number, or respond to any suitable word by naming its opposite. He cannot be so well prepared as for the simple, or choice reaction, since he doesn't know exactly what the stimulus is going to be; also, the brain process is more complex here; so that the reaction time is longer, about a tenth of a second longer, at the best, than the choice reaction. It may run up to two or three seconds, even in fairly simple cases, while if any serious thinking or choosing has to be done, it runs into many seconds and even into minutes. Here the brain process is very {24} complex and involves a series of steps before the required motor response can be made.

These laboratory experiments can be paralleled by many everyday performances. The runner starting at the pistol shot, after the preparatory "Ready! Set!", and the motorman applying the brakes at the expected sound of the bell, are making "simple" reactions. The boxer, dodging to the right or the left according to the blow aimed at him by his adversary, is making choice reactions, and this type is very common in all kinds of steering, handling tools and managing machinery. Reading words, adding numbers, and a large share of simple mental performances, are essentially associative reactions. In most cases from ordinary life, the preparation is less complete than in the laboratory experiments, and the reaction time is accordingly longer.

The simple reaction has some points of resemblance with the "reflex", which, also, is a prompt motor response to a sensory stimulus. A familiar example is the reflex wink of the eyes in response to anything touching the eyeball, or in response to an object suddenly approaching the eye. This "lid reflex" is quicker than the quickest simple reaction, taking about .05 second. The knee jerk or "patellar reflex", aroused by a blow on the patellar tendon just below the knee when the knee is bent and the lower leg hanging freely, is quicker still, taking about .03 second. The reason for this extreme quickness of the reflex will appear as we proceed. However, not every reflex is as quick as those mentioned, and some are slower than the quickest of the simple reactions.

A few other examples of reflexes may be given. The "pupillary reflex" is the narrowing of the pupil of the eye {25} in response to a bright light suddenly shining into the eye. The "flexion reflex" is the pulling up of the leg in response to a pinch, prick or burn on the foot. Coughing and sneezing are like this in being protective reflexes, and the scratching of the dog belongs here also.

There are many internal reflexes: movements of the stomach and intestines, swallowing and hiccoughing, widening and narrowing of the arteries resulting in flushing and paling of the skin. These are muscular responses; and there are also glandular reflexes, such as the discharge of saliva from the salivary glands into the mouth, in response to a tasting substance, the flow of the gastric juice when food reaches the stomach, the flow of tears when a cinder gets into the eye. There are also inhibitory reflexes, such as the momentary stoppage of breathing in response to a dash of cold water. All in all, a large number of reflexes are to be found.

Most reflexes can be seen to be useful to the organism. A large proportion of them are protective in one way or another, while others might be called regulative, in that they adjust the organism to the conditions affecting it.

Now comparing the reflex with the simple reaction, we see first that the reflex is more deep-seated in the organism, and more essential to its welfare. The reflex is typically quicker than the simple reaction. The reflex machinery does not need a "Ready" signal, nor any preparation, but is always ready for business. (The subject in a simple reaction experiment would not make the particular finger movement that he makes unless he had made ready for that movement.) The attachment of a certain response to a certain stimulus, rather arbitrary and temporary in the simple reaction, is inherent and permanent in the reflex. Reflex action is involuntary and often entirely unconscious.

Reflexes, we said, are permanent. That is because they {26} are native or inherent in the organism. You can observe them in the new-born child. The reflex connection between stimulus and response is something the child brings with him into the world, as distinguished from what he has to acquire through training and experience. He does acquire, as he grows up, a tremendous number of habitual responds that become automatic and almost unconscious, and these "secondary automatic" reactions resemble reflexes pretty closely. Grasping for your hat when you feel the wind taking it from your head is an example. These acquired reactions never reach the extreme speed of the quickest reflexes, but at best may have about the speed of the simple reaction. Though often useful enough, they are not so fundamentally necessary as the reflexes. The reflex connection of stimulus and response is something essential, native, closely knit, and always ready for action.

Seeing that the response, in reflex action, is usually made by a muscle or gland lying at some distance from the sense organ that receives the stimulus--as, in the case of the flexion reflex, the stimulus is applied to the skin of the hand (or foot), while the response is made by muscles of the limb generally--we have to ask what sort of connection exists between the stimulated organ and the responding organ, and we turn to physiology and anatomy for our answer. The answer is that the nerves provide the connection. Strands of nerve extend from the sense organ to the muscle.

But the surprising fact is that the nerves do not run directly from the one to the other. There is no instance in the human body of a direct connection between any sense organ and any muscle or gland. The nerve path from sense organ to muscle always leads through a nerve center. One {27} nerve, called the sensory nerve, runs from the sense organ to the nerve center, and another, the motor nerve, runs from the center to the muscle; and the only connection between the sense organ and the muscle is this roundabout path through the nerve center. The path consists of three parts, sensory nerve, center, and motor nerve, but, taken as a whole, it is called the reflex arc, both the words, "reflex" and "arc", being suggested by the indirectness of the connection.

Fig. 1.--The connection from the back of the hand, which is receiving a stimulus, and the arm muscle which makes the response. The nerve center is indicated by the dotted lines.

The nervous system resembles a city telephone system. What passes along the nerve is akin to the electricity that {28} passes along the telephone wire; it is called the "nerve current", and is electrical and chemical in nature.

Fig. 2.--(From Martin's "Human Body.") General view of the nervous system, showing brain, cord, and nerves.

All nerve connections, like the great majority of telephone connections, are effected through the centers, called "centrals" in {29} the case of the telephone. Telephone A is connected directly with the central, telephone B likewise, and A and B are indirectly connected, through the central switchboard. That is the way it is in the nervous system, with "nerve center" substituted for "central", and "sense organ" and "muscle or gland" for "telephones A and B."

Fig. 3.--Location of the cord, cerebrum and cerebellum. The brain stem continues the cord upward into the skull cavity. (Figure text: cerebrum, cerebellum, cord, tongue)

The advantage of the centralized system is that it is a system, affording connections between any part and any other, and unifying the whole complex organism.

The nerve centers are located in the brain and spinal cord. The brain lies in the skull and the cord extends from the brain down through a tube in the middle of the {30} backbone. Of the brain many parts can be named, but for the present it is enough to divide it into the "brain stem", a continuation of the spinal cord up along the base of the skull cavity, and the two great outgrowths of the brain stem, called "cerebrum" and "cerebellum". The spinal cord and brain stem contain the lower or reflex centers, while the cerebellum, and especially the cerebrum, contain the "higher centers". The lower centers are directly connected by nerves with the sense organs, glands and muscles, while the higher centers have direct connections with the lower and only through them with the sense organs, glands and muscles. In other words, the sensory nerves run into the cord or brain stem, and the motor nerves run out of these same, while interconnecting nerve strands extend between the lower centers in the cord and brain stem and the higher centers in the cerebrum and cerebellum.

The spinal cord contains the reflex centers for the limbs and part of the trunk, and is connected by sensory and motor nerves with the limbs and trunk. The brain stem contains the reflex centers for the head and also for part of the interior of the trunk, including the heart and lungs, and is connected with them by sensory and motor nerves. The nerve center that takes part in the flexion reflex of the foot is situated in the lower part of the cord, that for the similar reflex of the hand lies in the upper part of the cord, that for breathing lies in the lower or rear part of the brain stem, and that for winking lies further forward in the brain stem.

Big movements, such as the combined action of all four legs of an animal in walking, require cord and brain stem to work together, and throw into relief what is really true even of simpler reflexes, namely that a reflex is a coordinated movement, in the sense that different muscles cooperate in its execution.

{31}

We shall understand nerve action better if we know something of the way in which the nervous system is built. A nerve is not to be thought of as a unit, nor are the brain and cord to be thought of as mere masses of some peculiar substance.

Fig. 4.--A motor nerve cell from the spinal cord, highly magnified. (Figure text: dendrites, cell body, axon, termination of axon in muscle)

A nerve is a bundle of many slender insulated threads, just as a telephone cable, running along the street, {32} is a bundle of many separate wires which are the real units of telephonic communication. A nerve center, like the switchboard in a telephone central, consists of many parts and connections.

The whole nervous system is essentially composed of neurones. A neurone is a nerve cell with its branches. Most nerve cells have two kinds of branches, called the axon and the dendrites.

The nerve cell is a microscopic speck of living matter. Its dendrites are short tree-like branches, while its axon is often several inches or even feet in length. The axon is the "slender thread", just spoken of as analogous to the single telephone wire. A nerve is composed of axons. [Footnote: The axon is always protected or insulated by a sheath, and axon and sheath, taken together, are often called a "nerve fiber".] The "white matter" of the brain and cord is composed of axons. Axons afford the means of communication between the nerve centers and the muscles and sense organs, and between one nerve center and another.

The axons which make up the motor nerves are branches of nerve cells situated in the cord and brain stem; they extend from the reflex center for any muscle out to and into that muscle and make very close connection with the muscle substance. A nerve current, starting from the nerve cells in the reflex center, runs rapidly along the axons to the muscle and arouses it to activity.

The axons which make up the optic nerve, or nerve of sight, are branches of nerve cells in the eye, and extend into the brain stem. Light striking the eye starts nerve currents, which run along these axons into the brain stem. Similarly, the axons of the nerve of smell are branches of cells in the nose.

The remainder of the sensory axons are branches of nerve cells that lie in little bunches close alongside the cord or {33} brain stem. These cells have no dendrites, but their axon, dividing, reaches in one direction out to a sense organ and in the other direction into the cord or brain stem, and thus connects the sense organ with its "lower center".

Fig. 5.--Sensory and motor axons, and their nerve cells. The arrows indicate the direction of conduction. (Figure text: eye, brain stem, skin, cord, muscle)

Where an axon terminates, it broadens out into a thin plate, or breaks up into a tuft of very fine branches ( the "end-brush"), and by this means makes close contact with the muscle, the sense organ, or the neurone with which it connects.

Now let us consider the mode of connection between one neurone and another in a nerve center. The axon of one neurone, through its end-brush, is in close contact with the dendrites of another neurone. There is contact, but no actual growing-together; the two neurones remain distinct, and this contact or junction of two neurones is called a "synapse". The synapse, then, is not a thing, but simply a junction between two neurones.

Fig. 6.--The synapse between the two neurones lies just above the arrow.

The junction is good enough so that one of the two neurones, if itself active, can arouse the other to activity. The end-brush, when a nerve current reaches it from its own nerve cell, arouses the dendrites of the other neurone, and thus starts a nerve current running along those dendrites to their nerve cell and thence out along its axon.

Now here is a curious and significant fact: the dendrites are receiving organs, not transmitting; they pick up messages from the end-brushes across the synapse, but send out no messages to those end-brushes. Communication across a synapse is always in one direction, from end-brush to dendrites.

This, then, is the way in which a reflex is carried out, the pupillary reflex, for example. Light entering the eye starts a nerve current in the axons of the optic nerve; these axons terminate in the brain stem, where their end-brushes arouse the dendrites of motor nerve cells, and the axons of these {35} cells, extending out to the muscle of the pupil, cause it to contract, and narrow the pupil.

Or again, this is the way in which one nerve center arouses another to activity. The axons of the cells in the first center (or some of them) extend out of this center and through the white matter to the second center, where they terminate, their end-brushes forming synapses with the cells of the second center. Let the first center be thrown into activity, and immediately, through this connection, it arouses the second.

Fig. 7.--Different forms of synapse found in the cerebellum, "a" is one of the large motor cells of the cerebellum (a "Purkinje cell"), with its dendrites above and its axon below; and "b," "c" and "d" show three forms of synapse made by other neurones with this Purkinje cell. In "b," the arrow indicates a "climbing axon," winding about the main limbs of the Purkinje cell. In "c," the arrow points to a "basket"--an end-brush enveloping the cell body; while "d" shows what might be called a "telegraph-wire synapse." Imagine "d" superimposed upon "a": the axon of "d" rises among the fine dendrites of "a," and then runs horizontally through them; and there are many, many such axons strung among the dendrites. Thus the Purkinje cell is stimulated at three points: cell body, trunks of the dendrites, and twigs of the dendrites.

The "gray matter" comprises the nerve centers, lower and higher. It is made up of nerve cells and their dendrites, of the beginnings of axons issuing from these cells and of the terminations of incoming axons. The white matter, as was said before, consists of axons. An axon issues from the {36} gray matter at one point, traverses the white matter for a longer or shorter distance, and finally turns into the gray matter at another point, and thus nerve connection is maintained between these two points.

There are lots of nerve cells, billions of them. That ought to be plenty, and yet--well, perhaps sometimes they are not well developed, or their synapses are not close enough to make good connections.

Fig. 8.--A two-neurone reflex arc. (Figure text: stimulus, skin, sensory axon, bit of the spinal cord, motor axon, muscle)

Examined under the microscope, the nerve cell is seen to contain, besides the "nucleus" which is present in every living cell and is essential for maintaining its vitality and special characteristics, certain peculiar granules which appear to be stores of fuel to be consumed in the activity of the cell, and numerous very fine fibrils coursing through the cell and out into the axon and dendrites.

The reflex arc can now be described more precisely than before. Beginning in a sense organ, it extends along a sensory axon (really along a team of axons acting side by side) to its end-brush in a lower center, where it crosses a synapse and enters the dendrites of a motor neurone and so {37} reaches the cell body and axon of this neurone, which last extends out to the muscle (or gland). The simplest reflex arc consists then of a sensory neurone and a motor neurone, meeting at a synapse in a lower or reflex center. This would be a two-neurone arc.

Fig. 9.--A three-neurone arc, concerned in respiration. This also illustrates how one nerve center influences another. (Figure text: white matter, gray matter, lung, respiratory center in the brain stem, diaphragm, motor center in cord for the diaphragm)

Very often, and possibly always, the reflex arc really consists of three neurones, a "central" neurone intervening between the sensory and motor neurones and being connected through synapses with each. The central neurone plays an important rôle in coördination.

The internal structure of nerve centers helps us see how coördinated movement is produced. The question is, how {38} several muscles are made to work together harmoniously, and also how it is possible that a pin prick, directly affecting just a few sensory axons, causes a big movement of many muscles. Well, we find the sensory axon, as it enters the cord, sending off a number of side branches, each of which terminates in an end-brush in synaptic connection with the dendrites of a motor nerve cell.

Fig. 10.--Coördination brought about by the branching of a sensory axon. (Figure text: cord, sensory neurone, motor neurone)

Thus the nerve current from a single sensory neurone is distributed to quite a number of motor neurones. Where there are central neurones in the arc, their branching axons aid in distributing the excitation; and so we get a big movement in response to a minute, though intense stimulus.

But the response is not simply big; it is definite, coordinated, representing team work on the part of the muscles as distinguished from indiscriminate mass action. That means selective distribution of the nerve current. The axons of the sensory and central neurones do not connect with any and every motor neurone indiscriminately, but link up with selected groups of motor neurones, and thus harness together teams that will work in definite ways, producing {39} flexion of a limb in the case of one such team, and extension in the case of another. Every reflex has its own team of motor neurones, harnessed together by its outfit of sensory and central neurones. The same motor neurone may however be harnessed into two or more such teams, as is seen from the fact that the same muscle may participate in different reflex movements; and for a similar reason we believe that the same sensory neurone may be utilized in more than one reflex arc.

Fig. 11.--Coördination brought about by the branching of the axon of a central neurone. (Figure text: sensory, central, motor)

The most distinctive part of any reflex arc is likely to be its central neurones, which are believed to play the chief part in coördination, and in determining the peculiarities of any given reflex, such as its speed and rhythm of action.

Though the reflex is simple by comparison with voluntary movements, it is not the simplest animal reaction, for it is coördinated and depends on the nervous system, while the simplest animals, one-celled animals, have no nervous system, any more than they have muscles or organs of any {40} kind. Without possessing separate organs for the different vital functions, these little creatures do nevertheless take in and digest food, reproduce their kind, and move. Every animal shows at least two different motor reactions, a positive or approaching reaction, and a negative or avoiding reaction.

The general notion of a reaction is that of a response to a stimulus. The stimulus acts on the organism and the organism acts back. If I am struck by a wave and rolled over on the beach, that is passive motion and not my reaction; but if the wave stimulates me to maintain my footing, then I am active, I respond or react.

Now there is no such thing as wholly passive motion. Did not Newton teach that "action and reaction are equal"?--and he was thinking of stones and other inanimate objects. The motion of a stone or ball depends on its own weight and shape and elasticity as much as on the blow it receives. Even the stone counts for something in determining its own behavior.

A loaded gun counts for more than a stone, because of the stored energy of the powder that is set free by the blow of the hammer. The "reaction" of the gun is greater than the force acting on it, because of this stored energy that is discharged.

An animal reaction resembles the discharge of the gun, since there is stored energy in the animal, consisting in the chemical attraction between food absorbed and oxygen inspired, and some of this energy is utilized and converted into motion when the animal reacts. The stimulus, like the trigger of the gun, simply releases this stored energy.

The organism, animal or human, fully obeys the law of conservation of energy, all the energy it puts out being accounted for by stored energy it has taken in in food and oxygen. But at any one time, when the organism receives {41} a stimulus, the energy that it puts forth in reaction comes from inside itself.

There is another way in which the organism counts in determining its reaction. Not only does it supply the energy of the response, but its own internal arrangements determine how that energy shall be directed. That is to say, the organism does not blow up indiscriminately, like a charge of dynamite, but makes some definite movement. This is true even of the simplest animals, and the more elaborate the internal mechanism of the animal, the more the animal itself has to do with the kind of response it shall make to a stimulus. The nervous system of the higher animals, by the connections it provides between the stimulus and the stores of energy in the muscles, is of especial importance in determining the nature of the response.

Stimuli are necessary to arouse the activity of the organism. Without any stimulus whatever, it seems likely that the animal would relapse into total inactivity. It should be said, however, that stimuli, such as that of hunger, may arise within the organism itself. The stimulus may be external or internal, but some stimulus is necessary in order to release the stored energy.

In general, then, a reaction consists in the release by a stimulus of some of the stored energy of an animal, and the direction of that energy by the animal's own internal mechanism of nerves and muscles (and, we may add, bones and sinews) into the form of some definite response.

1. Outline of the chapter, being at the same time a "completion test". Complete the following outline by filling in the blank spaces (usually a single word will fill the blank, but sometimes two words will be better):

A. Definition: A reaction is a response to a ___________. The stimulus energy stored in the organism, and the __________ has a definite form determined by the organism's own machinery of ________ and ______. 

B. Among very prompt reactions are the reflex and the "simple reaction". The reflex differs from the "simple reaction" in that:

(1) It usually takes less________.

(2) It requires no___________,

(3) The machinery for it is ________in the organism.

C. The machinery for a reflex consists of:

(1) a________ organ.

(2) a ________nerve.

(3) a nerve ________,

(4) a _________nerve.

(5) a muscle or _________.

D. The sensory and motor nerves consist of ________ which are branches of ______. The cells for the motor nerves lie in the ________, and those for the sensory nerves lie in two cases in the _________, and in all other cases in bunches located close beside the _________or ________,

E. The neurone is the _______ of which the nervous ______ is composed. It consists of a ________ and of two sorts of branches, the ________ and the ________. Internally, the neurone shows a peculiar structure of ________ and ________.

F. Communication from one neurone to another occurs across a _____ called the synapse. The _________of an axon here comes into close contact with the ______or with the _________of another neurone. The communication takes place from the ________of the first neurone to the ___________ of the second.

G. The "nerve current" in a reflex therefore runs the following course: from the sense organ into a ________ axon, along this to its _________ in a nerve, and across a _________ there into the _________ of a neurone, and thence {43} out along the _______of this neurone to the ________or _________ that executes the reflex. This is a two-neurone _________, but often there is a third, ________neurone between the _________ and the _____________.

H. Coördination is effected by the ________ of the axons of the sensory and ________ neurones, by which means the nerve current is ______ to a team of ________ and so to a team of _________.

2. Is the reaction time experiment, as described in the text, an introspective or an objective experiment?

3. Mention two cases from common life that belong under the "simple reaction", two that belong under "choice reaction", and two that belong under the "associative reaction".

4. Arrange the reflexes mentioned in the text under the two heads of "protective" and "regulative".

5. Draw diagrams of (a) the neurone, (b) a synapse, (c) a reflex arc, and (d) a coördinated movement. Reduce each drawing to the simplest possible form, and still retain everything that is essential.

6. What part of the nervous system lies (a) in the forehead and top of the head, (b) in the very back of the head, (c) along the base of the skull, (d) within the backbone, (e) in the arm?

7. Using a watch to take the time, see how long it takes you to name the letters in a line of print, reading them in reverse order from the end of the line to the beginning. Compare with this time the time required to respond to each letter by the letter following it in the alphabet (saying "n" when you see m, and "t" when you see s, etc.). Which of these two "stunts" is more like reflex action, and how, nevertheless, does it differ from true reflex action?

8. The pupillary reflex. Describe the reaction of the pupil of the eye to light suddenly shining into the eye. This response can best be observed in another person, but you can observe it in yourself by aid of a hand mirror. On another person you can also observe the "crossed" pupillary reflex, by throwing the light into one eye only while you watch the other eye. What sort of connection do you suppose to exist between the two eyes, making this crossed reflex possible?

9. The lid reflex, or wink reflex, (a) Bring your hand suddenly close to another person's eye, and notice the response of the eyelid, (b) See whether you can get a crossed reflex here, (c) See whether your subject can voluntarily prevent (inhibit) the lid reflex, (d) See whether the reflex occurs when he gives the stimulus himself, by moving his own hand suddenly up to his eye. (e) What other stimulus, besides the visual one that you have been using, will arouse the same response?

C. Judson Herrick, in his Introduction to Neurology, 2nd edition, 1918, gives a fuller and yet not too detailed account of the neurone in Chapter III, and of reflex action in Chapter IV.

Percy G. Stiles, in his Nervous System and Its Conservation, 1915, discusses these matters in Chapters II, III and IV.

Ladd and Woodworth's Elements of Physiological Psychology, 1911, has chapters on these topics.

Having defined a reaction as an act of the individual aroused by a stimulus, there is no reason why we should not include a great variety of mental processes under the general head of reactions. Any mental process is an activity of the organism, and it is aroused by some stimulus, external or internal; therefore, it is a reaction.

I hear a noise--now, while the noise, as a physical stimulus, comes to me, my hearing it is my own act, my sensory reaction to the stimulus. I recognize the noise as the whistle of a steamboat--this recognition is clearly my own doing, dependent on my own past experience, and may be called a perception or perceptive response. The boat's whistle reminds me of a vacation spent on an island--clearly a memory response. The memory arouses an agreeable feeling--an affective response, this may be called. In its turn, this may lead me to imagine how pleasant it would be to spend another vacation on that island, and to cast about for ways and means to accomplish this result--here we have imagination and reasoning, aroused by what preceded just as the sensation was aroused by the physical stimulus.

In speaking of any mental process as an act of the individual, we do not mean to imply that he is always conscious {46} of his activity. Sometimes he feels active, sometimes passive. He feels active in hard muscular work or hard thinking, while he feels passive in reflex action, in sensation, and in simply "being reminded" of anything without any effort on his own part. But he is active in everything he does, and he does everything that depends on his being alive. Life is activity, and every manifestation of life, such as reflex action or sensation, is a form of vital activity. The only way to be inactive is to be dead.

But vital activity is not "self-activity" in any absolute sense, for it is aroused by some stimulus. It does not issue from the individual as an isolated unit, but is his response to a stimulus. That is the sense of calling any mental process a reaction; it is something the individual does in response to a stimulus.

To call a sensation a form of reaction means, then, that the sensation is not something done to the person, nor passively received by him from outside, but something that he himself does when aroused to this particular form of activity. What comes from outside and is received by the individual is the stimulus, and the sensation is what he does in response to the stimulus. It represents the discharge of internal stored energy in a direction determined by his own inner mechanism. The sensation depends on his own make-up as well as on the nature of the stimulus, as is especially obvious when the sensation is abnormal or peculiar. Take the case of color blindness. The same stimulus that arouses in most people the sensation of red arouses in the color-blind individual the sensation of brown. Now what the color-blind individual receives, the light stimulus, is the same as what others receive, but he responds differently, i.e., with a different sensation, because his own sensory apparatus is peculiar.

The main point of this discussion is that all mental {47} phenomena, whether movements, sensations, emotions, impulses or thoughts, are a person's acts, but that every act is a response to some present stimulus. This rather obvious truth has not always seemed obvious. Some theorists, in emphasizing the spontaneity and "self-activity" of the individual, have pushed the stimulus away into the background; while others, fixing their attention on the stimulus, have treated the individual as the passive recipient of sensation and "experience" generally. Experience, however, is not received; it is lived, and that means done; only, it is done in response to stimuli. The concept of reaction covers the ground.

While speaking of sensations and thoughts as belonging under the general head of reactions, it is well, however, to bear in mind that all mental action tends to arouse and terminate in muscular and glandular activity. A thought or a feeling tends to "express itself" in words or (other) deeds. The motor response may be delayed, or inhibited altogether, but the tendency is always in that direction.

To call all mental processes reactions means that it is always in order to ask for the stimulus. Typically, the stimulus is an external force or motion, such as light or sound, striking on a sense organ. There are also the internal stimuli, consisting of changes occurring within the body and acting on the sensory nerves that are distributed to the muscles, bones, lungs, stomach and most of the organs. The sensations of muscular strain and fatigue, and of hunger and thirst, are aroused by internal stimuli, and many reflexes are aroused in the same way.

Such internal stimuli as these are like the better known external stimuli in that they act upon sense organs; but it {48} seems necessary to recognize another sort of stimuli which act directly on the nerve centers in the brain. These may be called "central stimuli" and so contrasted with the "peripheral stimuli" that act on any sense organ, external or internal. To do this is to take considerable liberty with the plain meaning of "stimulus", and calls for justification. What is the excuse for thus expanding the notion of a stimulus?

The excuse is found in the frequent occurrence of mental processes that are not directly aroused by any peripheral stimulus, though they are plainly aroused by something else. Anything that arouses a thought or feeling can properly be called its stimulus. Now it often happens that a thought is aroused by another, just preceding thought; and it seems quite in order to call the first thought the stimulus and the second the response. A thought may arouse an emotion, as when the thought of my enemy, suddenly occurring to mind, makes me angry; the thought is then the stimulus arousing this emotional response.

If hearing you speak of Calcutta makes me think of India, your words are the stimulus and my thought the response. Well, then, if I think of Calcutta in the course of a train of thought, and next think of India, what else can we say than that the thought of Calcutta acts as a stimulus to arouse the thought of India as the response? In a long train of thought, where A reminds you of B and B of C and C of D, each of these items is, first, a response to the preceding, and, second, a stimulus to the one following.

There is no special difficulty with the notion of "central stimuli" from the physiological side. We have simply to think of one nerve center arousing another by means of the tract of axons connecting the two. Say the auditory center is aroused by hearing some one mention your friend's name, {49} and this promptly calls up a mental picture of your friend; here the auditory center has aroused the visual. What happens in a train of thought is that first one group of neurones is aroused to activity, and then this activity, spreading along the axons that extend from this group of neurones to another, arouses the second group to activity; and so on. The brain process may often be exceedingly complex, but this simple scheme gives the gist of it.

The way nerve currents must go shooting around the brain from one center or group of neurones to another, keeping it up for a long time without requiring any fresh peripheral stimulus, is remarkable. We have evidence of this sort of thing in a dream or fit of abstraction. Likely enough, the series of brain responses would peter out after awhile, in the absence of any fresh peripheral stimulus, and total inactivity ensue. But response of one brain center to nerve currents coming from another brain center, and not directly from any sense organ, must be the rule rather than the exception, since most of the brain neurones are not directly connected with any sense organ, but only with other parts of the brain itself. All the evidence we have would indicate that the brain is not "self-active", but only responsive; but, once thrown into activity at one point, it may successively become active at many other points, so that a long series of mental operations may follow upon a single sensory stimulus.

A "center" is a collection of nerve cells, located somewhere in the brain or cord, which gives off axons running to some other center or out to muscles or glands, while it also receives axons coming from other centers, or from sense organs. These incoming axons terminate in end-brushes and so form synapses with the dendrites of the local {50} nerve cells. The axons entering any center and terminating there arouse that center to activity, and this activity, when aroused, is transmitted out along the axons issuing from that center, and produces results where those axons terminate in their turn.

Fig. 12.--Side view of the left hemisphere of the brain, showing the motor and sensory areas (for the olfactory area, see Fig. 18). The visual area proper, or "visuo-sensory area," lies just around the corner from the spot marked "Visual," on the middle surface of the hemisphere, where it adjoins the other hemisphere. (Figure text: frontal lobe, parietal lobe, central fissure, occipital lobe, motor area, somesthetic area, auditory area, fissure of Sylvius, temporal lobe, brain stem, cerebellum)

The lower motor centers, called also reflex centers, are located in the cord or brain stem, and their nerve cells give rise to the axons that form the motor nerves and connect with the muscles and glands. A muscle is thrown into action by nerve currents from its lower motor center.

The principal higher motor center is the "motor area" of the brain, located in the cortex or external layer of gray matter, in the cerebrum. More precisely, the motor area is a long, narrow strip of cortex, lying just forward of what is called the "central fissure" or "fissure of Rolando".

If you run your finger over the top of the head from one side to the other, about halfway back from the forehead, the motor areas of the two cerebral hemispheres will lie close under the path traced by your finger.

Fig. 13.--(After Cajal.) Type of the brain cells that most directly control muscular movement. (Figure text: Axon. Giant pyramid cell from the motor area of the cerebral cortex, magnified 35 diameters. Cell body of same farther magnified)

The motor area in the right hemisphere is connected with the left half of the cord and so with the muscles of the left half of the body; the motor area of the left hemisphere similarly affects {52} the right half of the body. Within the motor area are centers for the several limbs and other motor organs. Thus, at the top, near the middle line of the head (and just about where the phrenologists located their "bump of veneration"!), is the center for the legs; next below and to the side is the center for the trunk, next that for the arm, next that for head movements, and at the bottom, not far from the ears, is the center for tongue and mouth.

Fig. 14.--The nerve path by which the motor area of the cortex influences the muscles. The upper part of this path, consisting of axons issuing from the giant pyramids of the motor area and extending down into the spinal cord, is the pyramidal tract. The lower part of the path consists of axons issuing from the motor cells of the cord and extending out to the muscles. The top of the figure represents a vertical cross-section of the brain, such as is given, on a larger scale, in Fig. 18. (Figure text: cortex, cord, muscles)

The largest nerve cells of all are found in the motor area, and are called, from their shape, the "giant pyramids". They have large dendrites and very long axons, which latter, {53} running in a thick bundle down from the cortex through the brain stem and cord, constitute the "pyramidal tract", the principal path of communication from the cerebrum to the lower centers. The motor area of the brain has no direct connection with any muscle, but acts through the pyramidal tract on the lower centers, which in turn act on the muscles.

The motor area is itself aroused to action by nerve currents entering it through axons coming from other parts of the cortex; and it is by way of the motor area that any other part of the cortex produces bodily movement. There are a few exceptions, as, for example, the movements of the eyes are produced generally by the "visual area" acting directly on the lower motor centers for the eye in the brain stem; but, in the main, any motor effect of brain action is exerted through the motor area. The motor area, as already mentioned, acts on the lower motor centers in the cord and brain stem, and these in turn on the muscles; but we must look into this matter a little more closely.

A lower motor center is a group of motor and central neurones, lying anywhere in the cord or brain stem, and capable of directly arousing a certain coördinated muscular movement. One such unit gives flexion of the leg, another gives extension of the leg, a third gives the rapid alternation of flexion and extension that we see in the scratching movement of the dog. Such a motor center can be aroused to activity by a sensory stimulus, and the resulting movement is then called a reflex.

The lower center can be aroused in quite another way, and that is by nerve currents coming from the brain, by way of the motor area and the pyramidal tract. Thus flexion of the leg can occur voluntarily as well as reflexly. The same {54} muscles, and the same motor neurones, do the job in either case. In the reflex, the lower center is aroused by a sensory nerve, and in the voluntary movement by the pyramidal tract.

The story is told of a stranger who was once dangling his legs over the edge of the station platform at a small backwoods town, when a native called out to him "Hist!" (hoist), pointing to the ground under the stranger's feet. He "histed" obediently, which is to say that he voluntarily threw into play the spinal center for leg flexion; and then, looking down, saw a rattler coiled just beneath where his feet had been hanging. Now even if he had spied the rattler first, the resulting flexion, though impulsive and involuntary, would still have been aroused by way of the motor area and the pyramidal tract, since the movement would have been a response to knowledge of what that object was and signified, and knowledge means action by the cerebral cortex, which we have seen to affect movement through the medium of the motor area. But if the snake had made the first move, the same leg movement on the man's part, made now in response to the painful sensory stimulus, would have been the flexion reflex.

Not only can the motor area call out essentially the same movements that are also produced reflexly, but it can prevent or inhibit the execution of a reflex in spite of the sensory stimulus for the reflex being present, and it can reinforce or facilitate the action of the sensory stimulus so as to assist in the production of the reflex. We see excellent examples of cerebral facilitation and inhibition in the case of the knee jerk. This sharp forward kick of the foot and lower leg is aroused by a tap on the tendon running in front {55} of the knee. Cross the knee to be stimulated over the other leg, and tap the tendon just below the knee cap, and the knee jerk appears. So purely reflex is this movement that it cannot be duplicated voluntarily; for, though the foot can of course be voluntarily kicked forward, this voluntary movement does not have the suddenness and quickness of the true reflex. For all that, the cerebrum can exert an influence on the knee jerk. Anxious attention to the knee jerk inhibits it; gritting the teeth or clenching the fist reinforces it. These are cerebral influences acting by way of the pyramidal tract upon the spinal center for the reflex.

Thus the cortex controls the reflexes. Other examples of such control are seen when you prevent for a time the natural regular winking of the eyes by voluntarily holding them wide open, or when, carrying a hot dish which you know you must not drop, you check the flexion reflex which would naturally pull the hand away from the painful stimulus. The young child learns to control the reflexes of evacuation, and gradually comes to have control over the breathing movements, so as to hold his breath or breathe rapidly or deeply at will, and to expire vigorously in order to blow out a match.

The coughing, sneezing and swallowing reflexes likewise come under voluntary control. In all such cases, the motor area facilitates or inhibits the action of the lower centers.

Another important effect of the motor area upon the lower centers consists in combining their action so as to produce what we know as skilled movements. It will be remembered that the lower centers themselves give coördinated movements, such as flexion or extension of the whole limb; but still higher coördinations result from cerebral control. {56} When the two hands, though executing different movements, work together to produce a definite result, we have coördination controlled by the cortex. Examples of this are seen in handling an ax or bat, or in playing the piano or violin. A movement of a single hand, as in writing or buttoning a coat, may also represent a higher or cortical coördination.

Fig. 15.--(From Starr.) Axons connecting one part of the cortex with another. The brain is seen from the side, as if in section. At "A" are shown bundles of comparatively short axons, connecting near-by portions of the cortex; while "B," "C," and "D" show bundles of longer axons, connecting distant parts of the cortex with one another. The "Corpus Callosum" is a great mass of axons extending across from each cerebral hemisphere to the other, and enabling both hemispheres to work together. "O. T." and "C. N." are interior masses of gray matter, which can be seen also in Fig. 18. "O. T." is the thalamus, about which more later.

Now it appears that the essential work in producing these higher coördinations of skilled movement is performed not by the motor area, but by neighboring parts of the cortex, which act on the motor area in much the same way as the motor area acts on the lower centers. Some of these {57} skilled-movement centers, or super-motor centers, are located in the cortex just forward of the motor area, in the adjacent parts of the frontal lobe. Destruction of the cortex there, through injury or disease, deprives the individual of some of his skilled movements, though not really paralyzing him. He can still make simple movements, but not the complex movements of writing or handling an instrument.

It is a curious fact that the left hemisphere, which exerts control over the movements of the right hand and right side of the body generally, also plays the leading part in skilled movements of either hand. This is true, at least, of right-handed persons; probably in the left-handed the right hemisphere dominates.

Motor power may be lost through injury at various points in the nervous system. Injury to the spinal cord, destroying the lower motor center for the legs, brings complete paralysis. Injury to the motor area or to the pyramidal tract does not destroy reflex movement, but cuts off all voluntary movement and cerebral control. Injury to the "super-motor centers" causes loss of skilled movement, and produces the condition of "apraxia", in which the subject, though knowing what he wants to do, and though still able to move his limbs, simply cannot get the combination for the skilled act that he has in mind.

Similar to apraxia is "aphasia" or loss of ability to speak. It bears the same relation to true paralysis of the speech organs that hand apraxia bears to paralysis of the hand. Through brain injury it sometimes happens that a person loses his ability to speak words, though he can still make vocal sounds. The cases differ in severity, some retaining the ability to speak only one or two words which {58} from frequent use have become almost reflex (swear words, sometimes, or "yes" and "no"), while others are able to pronounce single words, but can no longer put them together fluently into the customary form of phrases and sentences, and still others can utter simple sentences, but not any connected speech.

Fig. 16.--Side view of the left hemisphere, showing the location of the "speech centers." The region marked "Motor" is the motor speech center, that marked "Auditory" the auditory speech center, and that marked "Visual" the visual speech center. (Figure text: central fissure, motor area, auditory area, visual area, fissure of Sylvius, brain stem, cerebellum)

In pure cases of motor aphasia, the subject knows the words he wishes to say, but cannot get them out. The brain injury here lies in the frontal lobe in the left hemisphere, in right-handed people, just forward of the motor area for the mouth, tongue and larynx. This "motor speech center" is the best-known instance of a super-motor center. It coördinates the elementary speech movements into the combinations called words; and perhaps there is no other motor performance so highly skilled as this of speaking. It is acquired so early in life, and practised so constantly, that {59} we take it quite as a matter of course, and think of a word as a simple and single movement, while in fact even a short word, as spoken, is a complex movement requiring great motor skill.

There is some evidence that the motor speech center extends well forward into the frontal lobe, and that the front part of it is related to the part further back as this is to the motor area back of it. That is to say, the back of the speech center combines the motor units of the motor area into the skilled movements of speaking a word, while the more forward part of the speech center combines the word movements into the still more complex movement of speaking a sentence. It is even possible that the very front part of the speech center has to do with those still higher combinations of speech movements that give fluency and real excellence of speaking.

Besides the motor aphasia, just mentioned, there is another type, called sensory aphasia, or, more precisely, auditory aphasia. In pure auditory aphasia there is no inability to pronounce words or even to speak fluently, but there is, first, an inability to "hear words", sometimes called word deafness, and there is often also an inability to find the right words to speak, so that the individual so afflicted, while speaking fluently enough and having sense in mind, misuses his words and utters a perfect jargon. One old gentleman mystified his friends one morning by declaring that he must go and "have his umbrella washed", till it was finally discovered that what he wanted was to have his hair cut.

The cortical area affected in this form of aphasia is located a little further back on the surface of the brain than {60} the motor speech center, being close to the auditory area proper. The latter is a small cortical region in the temporal lobe, connected (through lower centers) with the ear, and is the only part of the cortex to receive nerve currents from the organ of hearing. The auditory area is, indeed, the organ of hearing, or an organ of hearing, for without it the individual is deaf. He may make a few reflex responses to loud noises, but, consciously, he does not hear at all; he has no auditory sensations.

In the immediate neighborhood of the auditory area proper (or of the "auditory-sensory area", as it may well be called), are portions of the cortex intimately connected by axons with it, and concerned in what may be called auditory perceptions, i.e., with recognizing and understanding sounds. Probably different portions of the cortex near the auditory-sensory center have to do with different sorts of auditory perception. At least, we sometimes find individuals who, as a result of injury or disease affecting this general region, are unable any longer to follow and appreciate music. They cannot "catch the tune" any longer, though they may have been fine musicians before this portion of their cortex was destroyed. In other cases, we find, instead of this music deafness, the word deafness mentioned just above.

The jargon talk that so often accompanies word deafness reminds us of the fact that speech is first of all auditory to the child. He understands what is said to him before he talks himself, and his vocabulary for purposes of understanding always remains ahead of his speaking vocabulary. It appears that this precedence of auditory speech over motor remains the fact throughout life, in most persons, and that the auditory speech center is the most fundamental of all the speech centers, of which there is one more not yet mentioned, used in reading.

Fig. 17.--(From Cajal.) Magnified sections through the cortex, to show the complexity of its inner structure. One view shows nerve cells and their dendrites, with only a few axons, while the other shows axons, outgoing and incoming, and some of their fine branches. Imagine one view superimposed upon the other, and you get some idea of the intricate interweaving of axons and dendrites that occurs in the cortex.

There is a visual-sensory area in the occipital lobe, at the back of the brain, that is connected with the eye in the same way as the auditory center is connected with the ear. Without it, the individual still shows the pupillary reflex to light, but has no sensations of sight. He is blind.

Fig. 18.--Vertical cross-section through the brain, showing the cortex on the outside, the thalamus and other interior masses of gray matter, some of the paths to and from the cortex, and the callosum or bridge of axons connecting the two cerebral hemispheres. The "Motor path" is the pyramidal tract, only the beginning of which is shown here, its further course being indicated in Fig. 14. (Figure text: tactile path, motor path, auditory path, callosum, thalamus, olfactory area)

This visual-sensory area occupies only a small portion of the occipital lobe, and yet practically the whole lobe is concerned with vision. Some portions of the lobe are concerned in perceiving words in reading, and without them the individual is "word blind". Other portions are concerned in perceiving (recognizing, understanding) seen objects, and without them the individual is "object blind". Other {63} portions are concerned in perceiving color relations, and still other portions in perceiving spatial relations through the sense of sight and so knowing where seen objects are and being able to guide one's movements by sight.

There is an olfactory area in a rather secluded part of the cortex, and this is related to the sense of smell in the same general way. Probably there is a similar taste center, but it has not been definitely located. Then there is a large and important area called the "somesthetic", connected with the body senses generally, i.e., chiefly with the skin and muscle senses. This area is located in a narrow strip just back of the central fissure, extending parallel to the motor area which lies just in front of the fissure, and corresponding part for part with it, so that the sensory area for the legs lies just behind the motor area for the legs, and so on. Destruction of any part of this somesthetic area brings loss of the sensations from the corresponding part of the body.

Just behind this direct sensory center for the body, in the parietal lobe, are portions of the cortex concerned in perceiving facts by aid of the body senses. Perception of size and shape by the sense of touch, perception of weight by the muscle sense, perception of degrees of warmth and cold by the temperature sense, are dependent on the parietal lobe and disappear when the cortex of this region is destroyed. It appears that there is a sort of hierarchy of centers here, as in the motor region and probably also in the visual and auditory regions. Skill in handling objects is partly dependent on the "feel" of the objects and so is impaired by injuries to the parietal lobe, as well as by injury to the frontal lobe; and knowing how to manage a fairly complex situation, as in lighting a fire when you have the various {64} materials assembled before you, seems also to depend largely on this part of the cortex.

Fig. 19.--Sensory path from the skin of any portion of the trunk or limbs. The path consists of three neurones, the cell body of the first lying just outside the spinal cord, that of the second lying in the cord, and that of the third lying in the thalamus. The last part of this path is the "Tactile path," shown in Fig. 18. (Figure text: cortex, thalamus, cord, skin)

As already indicated, no portion of the cortex, not even the sensory areas, is directly connected with any sense organ. The sensory axons from the skin, for example, terminate in the spinal cord, in what may be called the lowest sensory centers. Here are nerve cells whose axons pass up through the cord and brain stem to the thalamus or interbrain, where they terminate in a second sensory center. And cells here send their axons up to the somesthetic area of the cortex.

The thalamus is remarkable as an intermediate center for all the senses, except smell; but exactly what is accomplished by this big intermediate sensory center remains rather a mystery, though it certainly appears that the thalamus has something to do with feeling and emotion.

Regarding the cerebellum, there is much knowledge at hand, but it is difficult to give the gist of it in a few words. On the one hand, the cerebellum receives a vast number of axons from the lower sensory centers; while, on the other hand, it certainly has nothing to do with conscious sensation or perception. Its use seems to be motor. It has much to do with maintaining the equilibrium of the body, and probably also with maintaining the steadiness and general efficiency of muscular contraction. Though it has no known sensory or intellectual functions, it is very closely connected with the cerebrum, receiving a tremendous bundle of axons from different parts of the cerebrum, by way of the brain stem. Possibly these are related to motor activity. The phrenologists taught that the cerebellum was the center for the sexual instinct, but there is no evidence in favor of this guess.

Let a noise strike the ear and start nerve currents in along the auditory nerve, passing through the lowest and intermediate centers and reaching the auditory-sensory area of the cortex. When this last is aroused to activity, we have a sensation of sound, which is the first conscious reaction to the external stimulus. Axons running from the auditory-sensory to the near-by cortex give a perception of some fact indicated by the external stimulus, and this perception is a {66} second and higher conscious reaction, which, to be sure, ordinarily occurs so quickly after the first that introspection cannot distinguish one as first and the other as second; but the facts of brain injury, already mentioned, enable us to draw the distinction. The perceived fact may call up a mental image, or a recognition of some further fact less directly signified by the noise; these would be reactions of still higher order. Much of the cortex is apparently not very directly connected with either the sensory or the motor areas, and probably is concerned somehow in the recognition of facts that are only very indirectly indicated by any single sensory stimulus, or with the planning of actions that only indirectly issue in muscular movement.

On the sensory and intellectual side, the higher reactions follow the lower: sensation arouses perception and perception thought. On the motor side, the lower reactions are aroused by the higher. Thus the speech center arouses the motor centers for the speech organs, combining the action of these into the speaking of a word; and in a similar way, it seems, the intention to speak a sentence expressing a certain meaning acts as a stimulus to call up in order the separate words that make the sentence. A general plan of action precedes and arouses the particular acts and muscular movements that execute the plan.

1. Outline of the chapter. Fill in sub-topics under each of the following heads:

A. Mental processes of all kinds are reactions.
B. The stimulus that directly arouses a mental process is often "central".
C. Brain activities of all sorts influence the muscles by way of the motor area and the lower motor centers.
D. Brain action in skilled movement.
E. Brain action in speech.
F. Brain action in sensation.
G. Brain action in recognizing seen or heard objects.
H. Relations of reactions of different levels.

2. Define and illustrate these classes of stimuli:

A. Peripheral:

(1) External.
(2) Internal.

B. Central.

3. Show by a diagram how one cortical center arouses another. Compare the diagram in Fig. 9, p. 37.

4. Facilitation of the patellar reflex or "knee jerk". Let your subject sit with one leg hanging freely from the knee down. With the edge of your hand strike the patellar tendon just below the knee cap. (a) Compare the reflex movement so obtained with a voluntary imitation by the subject. Which is the quicker and briefer? (b) Apply a fairly strong auditory stimulus (a sudden noise) a fraction of a second before the tap on the tendon, and see whether the reflex response is reinforced, (c) Ask the subject to clench his fists or grit his teeth, and tap the tendon as he does so. Reinforcement? (d) Where is the reflex center for the patellar reflex, and whence comes the reinforcing influence?

5. Construct a diagram showing the different centers and connections involved in making the skilled movement of writing; and consider what loss of function would result from destruction of each of the centers.

Herrick's Introduction to Neurology, 1918, Chapter XX, on the "Functions of the Cerebrum".

Stile's Nervous System and Its Conservation, Chapters X, XI and XII.

One advantage of basing our psychology on reactions is that it keeps us "close to the ground", and prevents our discussions from sailing off into the clouds of picturesque but fanciful interpretation. Psychology is very apt to degenerate into a game of blowing bubbles, unless we pin ourselves down to hard-headed ways of thinking. The notion of a reaction is of great value here, just because it is so hard-headed and concrete. Whenever we have any human action before us for explanation, we have to ask what the stimulus is that arouses the individual to activity, and how he responds. Stimulus-response psychology is solid, and practical as well; for if it can establish the laws of reaction, so as to predict what response will be made to a given stimulus, and what stimulus can be depended on to arouse a desired response, it furnishes the "knowledge that is power". Perhaps no more suitable motto could be inscribed over the door of a psychological laboratory than these two words, "Stimulus-Response."

Such a motto would not frighten away the modern introspectionists, for they, no less than the behaviorists, could find a congenial home in a stimulus-response laboratory. They would begin by studying sensations, and, advancing to more complex responses, would observe the conscious processes entering into the response.

But, however useful the reaction may be as affording a sound basis for psychological study, we must not allow it to blind our eyes to any of the real facts of mental life; and, at first thought, it seems as if motives, interests and purposes did not fit into the stimulus-response program. Many hard-headed psychologists have fought shy of such matters, and some have flatly denied them any place in scientific psychology. But let us see.

S ---> R

Fig. 20.--The symbol of stimulus-response psychology. S means the stimulus, and R the response. The line between is the connection from stimulus to response.

Suppose we are looking out on a city street during the noon hour. We see numbers of people who--lunch over, nothing to do till one o'clock!--are standing or walking about, looking at anything that chances to catch their eye, waving their hands to friends across the street, whistling to a stray dog that comes past, or congregating about an automobile that has broken down in the crowded thoroughfare. These people are responding to stimuli, obviously enough, and there is no difficulty in fitting their behavior into the stimulus-response scheme.

But here comes some one who pays little attention to the sights and sounds of the street, simply keeping his eyes open enough to avoid colliding with any one else. He seems in a hurry, and we say of him, "He must have business on hand; he has to keep an appointment or catch a train". He is not simply responding to the stimuli that come to him, but has some purpose of his own that directs his movements.

Here is another who, while not in such a hurry, is not idling by any means, since he peers closely at the faces of the men, neglecting the women, and seems to be looking for some one in particular; or, perhaps, he neglects men and {70} women alike, and looks anxiously at the ground, as if he had lost something. Some inner motive shuts him off from most of the stimuli of the street, while making him extra responsive to certain sorts of stimuli.

Now it would be a great mistake to rule these purposeful individuals out of our psychology. We wish to understand busy people as well as idlers. What makes a man busy is some inner purpose or motive. He still responds to present stimuli--otherwise he would be in a dream or trance and out of all touch with what was going on about him--but his actions are in part controlled by an inner motive.

To complete the foundations of our psychology, then, we need to fit purpose into the general plan of stimulus and response. At first thought, purpose seems a misfit here, since--

First, a purpose is an inner force, whereas what arouses a response should be a stimulus, and typically an external stimulus. We do not wish to drop back into the old "self-activity" psychology, which thought of the individual as originating his acts from within himself. But if we could show that a purpose is itself an inner response to some external stimulus, and acts in its turn as a "central stimulus" to further reactions, this difficulty would disappear.

Second, while a typical reaction, like the reflex or the simple reaction of the experiment, is prompt and over with at once, a purpose persists. It keeps the busy man, in our illustration, hurrying all the way down the street and around the corner and how much farther we cannot say. It is very different from a momentary response, or from a stimulus that arouses a momentary response and nothing more.

Third, what persists, in purposive behavior, is the tendency {71} towards some end or goal. The purposeful person wants something he has not yet got, and is striving towards some future result. Whereas a stimulus pushes him from behind, a goal beckons to him from ahead. This element of action directed towards some end is absent from the simple response to a stimulus.

In short, we have to find room in our stimulus-response psychology for action persistently steered in a certain direction by some cause acting from within the individual. We must find room for internal states that last for a time and direct action. In addition, we sometimes, though not always, need to find room for conscious foreknowledge of the goal towards which the action is directed.

Fig. 21.--The stimulus-response scheme complicated to allow for the existence of T, an inner motive or tendency, which, aroused by an external stimulus, itself arouses a motor response. If the reaction-tendency were linked so firmly to a single response as to arouse that response with infallible certainty and promptness, then it would be superfluous for psychology to speak of a tendency at all. But often quite a series of responses, R1, R2, etc., follows upon a single stimulus, all tending towards the same end-result, such as escape; and then the notion of a "tendency" is by no means superfluous.

"Purpose" is not the best general term to cover all the internal factors that direct activity, since this word rather implies foresight of the goal, which demands the intellectual ability to imagine a result not present to the senses. This highest level of inner control over one's behavior had best be left for consideration in later chapters on imagination and will. There are two levels below this. In the middle level, the individual has an inner steer towards a certain result, though without conscious foresight of that result. At the lowest level, we can scarcely speak of the individual as being directed towards any precise goal, but still his {72} internal state is such as to predispose him for certain reactions and against other reactions.

The lowest level, that of organic states, is typified by fatigue. The middle level, that of internal steer, is typified by the hunting dog, striving towards his prey, though not, as far as we know, having any clear idea of the result at which his actions are aimed. The highest level, that of conscious purpose, is represented by any one who knows exactly what he wants and means to get.

No single word in the language stands out clearly as the proper term to cover all three levels. "Motives" would serve, if we agree at the outset that a motive is not always clearly conscious or definite, but may be any inner state or force that drives the individual in a given direction. "Wants" or "needs" might be substituted for "motives", and would apply better than "motives" to the lowest of our three levels. "Tendencies", or "tendencies to reaction", carries about the right meaning, namely that the individual, because of his internal state, tends towards a certain action. "Determining tendencies" (perhaps better, "directive tendencies") is a term that has been much used in psychology, with the meaning that the inner tendency determines or directs behavior. Much used also are "adjustment" and "mental set", the idea here being to liken the individual to an adjustable machine which can be set for one or another sort of work. Often "preparation" or "readiness for action" is the best expression.

Beginning at the lowest of our three levels, let us observe not even the simplest animal, but a single muscle. If we give a muscle electric shocks as stimuli, it responds to each shock by contracting. To a weak stimulus, the response is weak; {73} to a strong stimulus, strong. But now let us apply a long series of equal shocks of moderate intensity, one shock every two seconds. Then we shall get from the muscle what is called a "fatigue curve", the response growing weaker and weaker, in spite of the continued equality of the stimuli. How is such a thing possible? Evidently because the inner condition of the muscle has been altered by its long-continued activity. The muscle has become fatigued, and physiologists, examining into the nature of this fatigue, have found the muscle to be poisoned by "fatigue substances" produced by its own activity. Muscular contraction depends on the oxidation of fuel, and produces oxidized wastes, of which carbon dioxide is the best known; and these waste products, being produced in continued strong activity faster than the blood can carry them away, accumulate in the muscle and partially poison it. The "organic state" is here definitely chemical.

Fig. 22.--Fatigue curve of a muscle. The vertical lines record a series of successive contractions of the muscle, and the height of each line indicates the force of the contraction. Read from left to right.

This simple experiment is worth thinking over. Each muscular contraction is a response to an electric stimulus, but the force of the contraction is determined in part by the internal state of the muscle. Fatigue is an inner state of the muscle that persists for a time (till the blood carries away the wastes), and that predisposes the muscle towards a certain kind of response, namely, weak response. Thus the three characteristics of purposive behavior that seemed so {74} difficult to fit into the scheme of stimulus and response are all here in a rudimentary form.

But notice this fact also: the inner condition of muscular fatigue is itself a response to external stimuli. It is part and parcel of the total muscular response to a stimulus. The total response includes an internal change of condition, which, persisting for a time, is a factor in determining how the muscle shall respond to later stimuli. These facts afford, in a simple form, the solution of our problem.

Before leaving the muscle, let us take note of one further fact. If you examine the "fatigue curve" closely, you will see that a perfectly fresh muscle gains in strength from its first few responses. It is said to "warm up" through exercise; and the inner nature of this warming up has been found to consist in a moderate accumulation of the same products which, in greater accumulation, produce fatigue. The warmed-up condition is then another instance of an "organic state".

There will be more to say of "organic states" when we come to the emotions. For the present, do not the facts already cited compel us to enlarge somewhat the conception of a reaction as we left it in the preceding chapters? Besides the external response, there is often an internal response to a stimulus, a changed organic state that persists for a time and has an influence on behavior. The motor response to a given stimulus is determined partly by that stimulus, and partly by the organic state left behind by just preceding stimuli. You cannot predict what response will be made to a given stimulus, unless you know the organic state present when the stimulus arrives.

At the second level, the inner state that partly governs the response is more neural than chemical, and is directed {75} specifically towards a certain end-result. As good an instance as any is afforded by the "simple reaction", described in an earlier chapter. If the subject in that experiment is to raise his finger promptly from the telegraph key on hearing a given sound, he must be prepared, for there is no permanent reflex connection between this particular stimulus and this particular response. You tell your subject to be ready, whereupon he places his finger on the key, and gets all ready for this particular stimulus and response. The response is determined as much by his inner state of readiness as by the stimulus. Indeed, he sometimes gets too ready, and makes the response before he receives the stimulus.

The preparation in such a case is more specific, less a general organic state, than in the previous cases of fatigue, etc. It is confined for the most part to the nervous system and the sense organ and muscles that are to be used. In an untrained subject, it includes a conscious purpose to make the finger movement quickly when the sound is heard; but as he becomes used to the experiment he loses clear consciousness of what he is to do. He is, as a matter of fact, ready for a specific reaction, but all he is conscious of is a general readiness. He feels ready for what is coming, but does not have to keep his mind on it, since the specific neural adjustment has become automatic with continued use.

Examples of internal states of preparedness might be multiplied indefinitely, and it may be worth while to consider a few more, and try out on them the formula that has already been suggested, to the effect that preparation is an inner adjustment for a specific reaction, set up in response to some stimulus (like the "Ready!" signal), persisting for a time, and predisposing the individual to make the specified reaction whenever a suitable stimulus for it arrives. The preparation may or may not be conscious. It might be named "orientation" or "steer", with the meaning that {76} the individual is headed or directed towards a certain end-result. It is like so setting the rudder of a sailboat that, when a puff of wind arrives, the boat will respond by turning to the one side.

The runner on the mark, "set" for a quick start, is a perfect picture of preparedness. Here the onlookers can see the preparation, since the ready signal has aroused visible muscular response in the shape of a crouching position. It is not simple crouching, but "crouching to spring." But if the onlookers imagine themselves to be seeing the whole preparation--if they suppose the preparation to be simply an affair of the muscles--they overlook the established fact that the muscles are held in action by the nerve centers, and would relax instantly if the nerve centers should stop acting. The preparation is neural more than muscular. The neural apparatus is set to respond to the pistol shot by strong discharge into the leg muscles.

What the animal psychologists have called the delayed reaction is a very instructive example of preparation. An animal is placed before a row of three food boxes, all looking just alike, two of them, however, being locked while the third is unlocked. Sometimes one is unlocked and sometimes another, and the one which at any time is unlocked is designated by an electric bulb lighted above the door. The animal is first trained to go to whichever box shows the light; he always gets food from the lighted box. When he has thoroughly learned to respond in this way, the "delayed reaction" experiment begins. Now the animal is held while the light is burning, and only released a certain time after the light is out, and the question is whether, after this delay, he will still follow the signal and go straight to the right door. It is found that he will do so, provided the delay is not too long--how long depends on the animal. With rats the delay cannot exceed 5 seconds, with cats it can reach 18 {77} seconds, with dogs 1 to 3 minutes, with children (in a similar test) it increased from 20 seconds at the age of fifteen months to 50 seconds at two and a half years, and to 20 minutes or more at the age of five years.

Rats and cats, in this experiment, need to keep their heads or bodies turned towards the designated box during the interval between the signal and the release; or else lose their orientation. Some dogs, however, and children generally, can shift their position and still, through some inner orientation, react correctly when released. The point of the experiment is that the light signal puts the animal or child into a state tending towards a certain result, and that, when that result is not immediately attainable, the state persists for a time and produces results a little later.

In the delayed reaction, the inner orientation does little during the interval before the final reaction, except to maintain a readiness for making that reaction; but often "preparatory reactions" occur before the final reaction can take place. Suppose you whistle for your dog when he is some distance off and out of sight. You give one loud whistle and wait. Presently the dog swings around the corner and dashes up to you. Now, what kept the dog running towards you after your whistle had ceased and before he caught sight of you? Evidently he was directed towards the end-result of reaching you, and this directing tendency governed his movements during the process. He made many preparatory reactions on the way to his final reaction of jumping up on you; and these preparatory reactions were, of course, responses to the particular trees he had to dodge, and the ditches he had to jump; but they were at the same time governed by the inner state set up in him by your {78 } whistle. This inner state favored certain reactions and excluded others that would have occurred if the dog had not been in a hurry. He passed another dog on the way without so much as saying, "How d'ye do?" And he responded to a fence by leaping over it, instead of trotting around through the gate. That is to say, the inner state set up in him by your whistle facilitated reactions that were preparatory to the final reaction, and inhibited reactions that were not in that line.

A hunting dog following the trail furnishes another good example of a directive tendency. Give a bloodhound the scent of a particular man and he will follow that scent persistently, not turning aside to respond to stimuli that would otherwise influence him, nor even to follow the scent of another man. Evidently an inner neural adjustment has been set up in him predisposing him to respond to a certain stimulus and not to others.

The homing of the carrier pigeon is a good instance of activity directed in part by an inner adjustment, since, when released at a distance from home, he is evidently "set" to get back home, and often persists and reaches home after a very long flight. Or, take the parallel case of the terns, birds which nest on a little island not far from Key West. Of ten birds taken from their nests and transported on shipboard out into the middle of the Gulf of Mexico and released 500 miles from home, eight reappeared at their nests after intervals varying from four to eight days. How they found their way over the open sea remains a mystery, but one thing is clear: they persisted in a certain line of activity until a certain end-result was reached, on which this line of activity ceased.

One characteristic of tendencies that has not previously been mentioned comes out in this example. When a tendency has been aroused, the animal (or man) is tense and {79} restless till the goal has been reached, and then quiets down. The animal may or may not be clearly conscious of the goal, but he is restless till the goal has been attained, and his restlessness then ceases. In terms of behavior, what we see is a series of actions which continues till a certain result has been reached and then gives way to rest. Introspectively, what we feel (apart from any clear mental picture of the goal) is a restlessness and tenseness during a series of acts, giving way to relief and satisfaction when a certain result has been reached.

A hungry or thirsty animal is restless; he seeks food or drink, which means that he is making a series of preparatory reactions, which continues till food or drink has been found, and terminates in the end-reaction of eating or drinking.

The behavior of a hungry or thirsty individual is worth some further attention--for it is the business of psychology to interest itself in the most commonplace happenings, to wonder about things that usually pass for matters of course, and, if not to find "sermons in stones", to derive high instruction from very lowly forms of animal behavior. Now, what is hunger? Fundamentally an organic state; next, a sensation produced by this organic state acting on the internal sensory nerves, and through them arousing in the nerve centers an adjustment or tendency towards a certain end-reaction, namely, eating. Now, I ask you, if hunger is a stimulus to the eating movements, why does not the hungry individual eat at once? Why, at least, does he not go through the motions of eating? You say, because he has nothing to eat. But he could still make the movements; there is no physical impossibility in his making chewing and swallowing movements without the presence of food. {80} Speaking rationally, you perhaps say that he does not make these movements because he sees they would be of no use without food to chew; but this explanation would scarcely apply to the lower sorts of animal, and besides, you do not have to check your jaws by any such rational considerations. They simply do not start to chew except when food is in the mouth. Well, then, you say, chewing is a response to the presence of food in the mouth; and taking food into the mouth is a response to the stimulus of actually present food. The response does not occur unless the stimulus is present; that is simple.

Not quite so simple, either. Unless one is hungry, the presence of food does not arouse the feeding reaction; and even food actually present in the mouth will be spewed out instead of chewed and swallowed, if one is already satiated. Try to get a baby to take more from his bottle than he wants! Eating only occurs when one is both hungry and in the presence of food. Two conditions must be met: the internal state of hunger and the external stimulus of food; then, and then only, will the eating reaction take place.

Hunger, though a tendency to eat, does not arouse the eating movements while the stimulus of present food is lacking; but, for all that, hunger does arouse immediate action. It typically arouses the preparatory reactions of seeking food. Any such reaction is at the same time a response to some actually present stimulus. Just as the dog coming at your whistle was responding every instant of his progress to some particular object--leaping fences, dodging trees--so the dog aroused to action by the pangs of hunger begins at once to respond to present objects. He does not start to eat them, because they are not the sort of stimuli that produce this response, but he responds by dodging them or finding his way by them in his quest for food. The responses that the hungry dog makes to other objects than {81} food are preparatory reactions, and these, if successful, put the dog in the presence of food. That is to say, the preparatory reactions provide the stimulus that is necessary to arouse the end-reaction. They bring the individual to the stimulus, or the stimulus to the individual.

Fig. 23.--A stimulus arouses the tendency towards the end-reaction, R, but (as indicated by the dotted line), T is not by itself sufficient to arouse R; but T can and does arouse P, a preparatory reaction, and P (or some external result directly produced by P), coöperating with T, gives rise to R.

What we can say about the modus operandi of hunger, then, amounts to this: Hunger is an inner state and adjustment predisposing the individual to make eating movements in response to the stimulus of present food; in the absence of food, hunger predisposes to such other responses to various stimuli as will bring the food stimulus into play, and thus complete the conditions necessary for the eating reaction. In general, an aroused reaction-tendency predisposes the individual to make a certain end-reaction when the proper stimulus for that reaction is present; otherwise, it predisposes him to respond to other stimuli, which are present, by preparatory reactions that eventually bring to bear on the individual the stimulus required to arouse the end-reaction.

Let us apply our formula to one more simple case. While reading in the late afternoon, I find the daylight growing dim, rise and turn on the electric light. The stimulus that sets this series of acts going is the dim light; the first, inner response is a need for light. This need tends, by force of habit, to make me turn the button, but it does not make me execute this movement in the air. I only make this movement when the button is in reaching distance. My first {82} reaction, rising from my chair, is preparatory and brings the button close enough to act as a stimulus for the hand reaction. The button within reach is not by itself sufficient to arouse the turning reaction, nor is the need for light alone sufficient. The two conditions must be present together, and the preparatory reaction is such that, given the need, the other condition will be met and the reaction then aroused.

Very little need be added to our neural conception of a reaction in order to get a satisfactory conception of a tendency to reaction. Principally, we must add this fact, that a nerve center aroused to activity does not always discharge instantly and completely into the muscles, or into some other center, and come to rest itself. It does so, usually, in the case of a reflex, and in other momentary reactions; as when A makes you think of B, and B at once of C, and so on, each thought occupying you but a moment. But a tendency means the arousing of a nerve center under conditions which do not allow that center to discharge at once. The center remains in a condition of tension; energy is dammed up there, unable to find an outlet.

We have already seen what the conditions are that cause this damming up of energy. The center that is aroused tends to arouse in turn some lower motor center, but by itself does not have complete control over that lower center, since the lower center also requires a certain external stimulus in order to arouse it to the discharging point. Until the proper external stimulus arrives to complete the arousal of the lower center, the higher center cannot discharge its energy.

When there is an "organic state" present, such as hunger or thirst, this may act as a persistent stimulus to the sensory nerves and through them to the higher center in {83} question; and then we can readily understand how it is that the center remains active until the organic state is relieved. But where there is no such persistent organic stimulus, as there can scarcely be in the case of the bloodhound or of the man hurrying to a train or seeking in the crowd for a friend, there we have to suppose that a center, once aroused to activity and prevented from complete discharge, remains active by virtue of energy dammed up in itself. There is pretty good physiological evidence that this sort of thing is a fundamental fact; for there are certain rhythmical reflexes, like scratching or stepping, that, when started going by a momentary sensory stimulus, keep it up for a time after the stimulus has ceased. There seems to be no doubt that a nerve center, once aroused, may stay aroused for a time.

The "dammed-up energy" here is not to be confused with the "stored energy" spoken of under the head of reactions. We said, in that connection, that a stimulus released energy stored in the organism. That, however, was potential energy, dormant within the organism till aroused; but what we have here in mind is active or kinetic energy. Stored energy is like that of coal in the bin; dammed-up energy is like that of steam in the boiler.

Dammed-up energy in the nerve centers accounts for the persistence of a tendency to reaction after the stimulus has ceased. It accounts for the "delayed reaction" and similar cases. But how shall we account for preparatory reactions? We have a nerve center in an active state, tending to discharge into a certain lower motor center, but unable to do so because a peripheral stimulus is necessary, in addition, in order to arouse this lower center. Then we find the higher center discharging into other lower centers, and so giving rise to preparatory reactions. More precisely, what we find is that the higher center facilitates the response {84} of certain lower centers to their proper peripheral stimuli, while inhibiting the response of other lower centers to their appropriate stimuli. This is the same sort of thing that we observe in all control exerted by a higher center over a lower. It means that the higher center, besides its main line of connection with the lower center that will give the end-reaction, has minor lines of connection with certain other lower centers; some of these centers it facilitates and others it inhibits. These connections between the main and the subordinate centers may have been established by inborn nature, or by previous training, as will be explained in later chapters.

The action of the main center on the subordinate centers concerned in executing preparatory reactions does not relieve the tension in the main center. The dammed-up energy stays there till the proper stimulus is procured for arousing the end-reaction, and then escapes through its main channel of discharge, and the main center then finally comes to rest.

It may fairly be urged that no violence has been done to the general conception of a reaction by these additions, and also that with the additions the notion of a reaction has room for tendencies or inner adjustments. So that we conclude that stimulus-response psychology is adequate to the job, and will do justice to all forms of human behavior. It has a place for sensations, perceptions and thoughts, as we saw in the preceding chapter, and it has a place also for purposes, desires and motives generally.

In the present chapter, desirous of "keeping close to the ground", we have said little of distinctively human motives. That will come later. In general, a motive is a tendency towards a certain end-result or end-reaction, a tendency which is itself aroused by some stimulus, and which {85} persists for a time because its end-reaction is not at once made. The end-reaction is not made at once because it can only be aroused by an appropriate stimulus, acting in conjunction with the motive. But the motive, persisting in its inner activity, facilitates reactions to certain stimuli and inhibits others. The reactions it facilitates are preparatory to the end-reaction, in that they provide the necessary conditions for that reaction to occur, which means that they bring to bear on the individual the necessary stimulus which can arouse the end-reaction. The restlessness that characterizes an individual driven by an inner motive gives way to rest and satisfaction when the end-result is reached.

Motives range from the primitive or primal, like hunger, to the very advanced, such as zeal for a cause. They range from the momentary, illustrated by the need for more light in reading, to the great permanent forces of life, like amour propre and esprit de corps. But the permanent motives are not always active; they sleep and are awakened again by appropriate stimuli.

In everyday speech we are apt to use the words "motive" and "reason" interchangeably, as in asking some one what his "motive", or what his "reason" is for doing so and so. A motive, however, is not necessarily a reason, nor a reason a motive. A reason is thought-out and conscious, which a motive need not be. On the other hand, a reason does not become a motive unless it takes hold of us and arouses a genuine tendency towards the planned result. You may prove to me, logically, the desirability of a course of action, but your reasons do not necessarily make me desire it. You can give a child excellent reasons for studying his lessons, but you have to stir some real motive of child life in order to get action. In the highest type of conduct, to be sure, motive and reason pull together, reason showing the way to the goal at which motive is aimed.

1. Complete the following outline of the chapter, by filling in main headings to fit the subordinate headings that are given below:

A. _________

(1) It keeps close to the facts.
(2) It has room for introspective as well as behavior study.
(3) It can be applied practically.

B. _________

(1) A stimulus is typically external, a purpose internal.
(2) A stimulus typically acts for a moment, a purpose persists for some time.
(3) A stimulus is not directed towards a result, a purpose is so directed.

C. _________

(1) Organic or physiological states that predispose towards certain forms of behavior.
(2) Inner adjustments towards certain results, without foresight of the results.
(3) Conscious purpose.

D. _________

(1) They are aroused by stimuli.
(2) They persist for a time.
(3) They influence the response to other stimuli.

E. _________

(1) They are neural rather than chemical.
(2) They amount to a preparation or readiness for a certain response.
(3) They persist sometimes for only a few seconds, sometimes for many minutes at least.

F. _________

(1) A whole series of acts may be set going by a single stimulus.
(2) The series comes to an end when a certain result has been reached.
(3) Each act in the series is a response to some particular stimulus, and yet would not be aroused by that stimulus except for the active adjustment towards the end-result.
{87}
(4) The end-result cannot be reached until a particular stimulus helps the adjustment to arouse the end-reaction.
(5) The preliminary acts in the series bring the required stimulus that can give the end-reaction.

G. _______

(1) It may be kept active by a continuing peripheral stimulus.
(2) It may be unable to discharge fully because its main path of discharge is blocked.

H. ______

(1) The main center has minor connections with other centers, in addition to its main path of discharge.
(2) The persisting activity of the main center influences other centers by way of facilitation and inhibition.

2. Fill in the blanks in the following paragraph:

"A motive or (1) is a reaction that has not yet come off. It has been (2) by some stimulus, and it tends towards a certain (3), which however it is unable of itself to produce, but requires the assistance of another (4) which is not yet present. The motive gives rise to (5) responses, which, if (6), finally bring the required (7), and this, combined with the (8) arouses the (9), and so brings the whole (10) of acts to a close."

3. Cite cases illustrating the importance of preparatory adjustment

(a) for securing prompt reaction, and
(b) for securing keen observation.

4. Cite a case where some need or desire gives rise to a series of preparatory reactions.

5. Cite a case where a need or desire leads to the omission (inhibition) of acts that would otherwise have occurred.

6. What is meant by the last sentence in the chapter?

7. An experiment on the "delayed reaction". Take two sheets of paper, and on each write the letters A, B, C, D, E, and F, scattering them irregularly over the sheet. The task, in general, is now to take aim at one of the letters, while your hand, holding a pencil, is raised to the side of your head, and then to close the eyes and strike at the letter aimed for. First aim at A, and mark the point hit with an a, then the same with B, and so on. With the first sheet, strike as soon as you have got your aim and closed your eyes; but with the second sheet, aim, close your eyes, and count ten slowly before striking, keeping the eyes closed till the stroke has been made. Two sorts of observation should now be made: first, introspective--record at once what you can of the way you kept your aim during the delay. Second, objective--measure the errors, and determine how much the delay affected your aim. What conclusions can you draw from the experiment?

On the "delayed reaction", see Walter S. Hunter, "The Delayed Reaction in Animals and Children", Behavior Monographs, No. 6, 1913. A brief summary of this work can also be found in Hunter's General Psychology, 1919, pp. 31-33.

On the homing of pigeons and terns, see Watson and Lashley, An Historical and Experimental Study of Homing, published by the Carnegie Institution of Washington, 1915.

Interesting examples of changed organic states affecting the behavior of unicellular animals are given by Jennings in his Behavior of the Lower Organisms, 1906, and by Margaret F. Washburn in The Animal Mind, 2nd edition, 1917, pp. 246-257.

John Doe is a strongly built man, over six feet high, with big bones and muscles, erect, vigorous, with plenty of color in his face, dark-haired, blue-eyed, clean-shaven, with a scar on his cheek, broad face and large ears. He is easy-going, even-tempered, fond of children and also of women, rather slangy and even profane in his talk, has a deep, sonorous voice and can carry the bass in a chorus. He is handy with tools, can drive or repair an automobile, is a fairly good carpet salesman, but much prefers out-of-door work. Rather free in spending his money, he has never run into debt except on one occasion, which turned out badly for him. Which of these traits of John Doe are native and which are acquired? How far are his physical, mental and moral characteristics the result of his "original nature" and how far have they been ingrained in him or imposed upon him by his training and environment?

The distinction between native and acquired is clearest in the field of anatomy. Hair color and eye color are evidently native, and so, in the main, is the size of the body, though undoubtedly growth may be stunted by poor nutrition, and the individual fail to reach his "natural" height and weight. On the other hand, scars, tan, and the after-effects of disease or injury, are evidently acquired. Of movements, the native character of the reflexes has already been noted, and it is clear that skill in handling tools or {90} managing the voice is learned, though the individual may have a natural aptitude for these performances. Temperament and emotional traits we usually think of as belonging to a man's "nature", though we have to admit that a naturally cheerful disposition may be soured by ill treatment. On the other hand, while we reckon habits, such as profanity, or free spending, or an erect carriage, as belonging with the acquired traits, we know that some natures are prone to certain habits, and other natures to other habits. Thus the effects of "nature" and "experience" are almost inextricably interwoven in the behavior of an adult person.

Difficult as it certainly is to separate the native from the acquired in human action, the attempt must be made. We cannot dodge so fundamental a problem. Scientifically it is important as the starting-point of a genetic study; we must know where the individual starts in order to understand the course of his development. Practically it is important because there is reason to believe that native traits are deeply seated and not easily eradicated, even though they can be modified and specialized in different ways. If a habit is not simply a habit, but at the same time a means of gratifying some natural tendency, then it is almost imperative to find a substitute gratification in order to eliminate the habit. The individual's nature also sets limits beyond which he cannot be brought by no matter how much training and effort; and this is true of mental development as well as of physical.

"Native" means a little more than "congenital." A child may be born blind, having been infected by disease germs shortly before birth; he may be congenitally an idiot because of head injury during a difficult birth; or his mentality may have been impaired, during his uterine life, by {91} alcohol reaching his brain from a drunken mother. Such traits are congenital, but acquired. Native traits date back to the original constitution of the child, which was fully determined at the time when his individual life began, nine months before birth. The "fertilized ovum", formed by the combination of two cells, one from each of the parents, though microscopic in size and a simple sphere in shape, somehow contains the determiners for all the native or inherited traits of the new individual.

It is very mysterious, certainly. This microscopic, featureless creature is already a human individual, with certain of its future traits--those that we call "native"--already settled. It is a human being as distinguished from any other species, it is a white or colored individual, male or female, blonde or brunette, short or tall, stocky or slender, mentally gifted or deficient, perhaps a "born" musician or adventurer or leader of men. These and all other native traits are already determined and latent within it; and the only question, regarding such traits, is whether the environment is going to be such as to enable this young individual to live and mature and unfold what is latent within it.

For the first few months of the individual's existence, sheltered as it is within the mother's body, there is no chance for any acquisition, except of certain abnormalities such as were alluded to above. What occurs during this prenatal period is natural development, not learning or any effect of experience. The traits displayed by the new-born child are, accordingly, native traits. His breathing, crying, starting at a noise, squirming, stretching, grasping, sucking and swallowing, and other movements made from birth on, are to be counted as native reactions, that is to say, as {92} reactions executed by sensory, muscular and nervous machinery that have become ready for use by the mere process of natural growth. This is the first and clearest sign of a native trait, that it shall appear at birth.

But native traits continue to make their appearance as the child's development proceeds after birth. Inherited anatomical traits, like stature and build, hair color, beard, and shape of nose, though certainly determined by native constitution, do not fully make their appearance till maturity. In fact, what does maturity mean, except that the natural characteristics have finally reached their complete development? And it is as true of internal structure as of external, that natural development, far from being complete at birth, keeps on till maturity. The neurones continue to grow, and their synapses in the nerve centers to become closer knit, just by virtue of natural growth; and thus reflex arcs, and other reaction machinery, one by one reach the ready-to-use stage during the individual's growing-up, especially during the first few years. With the growth to a functional condition of their sensori-neuro-muscular mechanisms, mental and motor reactions that are native, though not present at birth, make their appearance. The native intelligence of the child gradually unfolds, likewise his special native "gifts" and his inherited emotional and impulsive traits.

Of course it is more difficult to make sure that a trait is native when it does not appear till some time after birth, for the chance of acquiring it by a process of learning has to be taken into account. If you can so control the conditions under which the young individual grows as to eliminate the possibility of learning a certain act, then you can {93} make sure whether the act is acquired or provided by the native constitution.

Take the question whether birds learn to fly or simply come to fly when their natural development has gone far enough. The newly hatched bird cannot fly; its muscles are not strong enough, its wings are not feathered, and its nerve mechanism for coördinating the wing movements has still some growth to make before being ready for use. But, under ordinary conditions, the young bird has some chance to learn flying, by watching the old birds fly and by trying and gradually getting the motion. The old birds, after a time, push the young ones from the nest and seem, to our eyes, to be teaching them to fly. Experiment enables us to decide the question. One of the earliest experiments in animal psychology was made by Spalding in 1873. He took newly hatched birds from the nest and shut each one separately in a little box that gave it no chance to stretch its wings or to see other birds fly. Here he fed and cared for them till the age at which flying usually begins, and then released them. Off they flew, skilfully managing wings and tail, swooping around the trees and soon disappearing from sight. A very successful experiment!--and conclusive. The little birds had had no chance to learn to fly, yet they flew. Flying must have come to them in the natural course of growth.

Compare with this experiment another one no less successful, though it turned out differently. To discover whether the song of the oriole is fixed by nature or learned by imitation, Scott took some little ones, just hatched, and brought them up away from older birds. After a time, when growth had advanced to a certain stage, the birds began {94} to sing. The elementary notes and rattles characteristic of the oriole made their appearance, but were combined in unusual ways, so that the characteristic song of the oriole did not appear, but a new song. When these birds had grown up in the laboratory, other new-hatched orioles were brought up with them, and adopted this new song; so that the laboratory became the center for a new school of oriole music. The experiment showed that the elements of the oriole's song were provided by nature, while the combination of these elements was acquired by imitation.

Probably this last is about the result one would get in the analogous case of human speech, if a similar experiment should be tried on children. Without an experiment, we have certain facts that point to a conclusion. The child uses his vocal organs from birth on; and before he reaches the age when he imitates the speech of others, he produces various vowels and consonants, and even puts them together into simple compounds, as "da-da" and "goo-goo." So far, deaf children do about the same as others, affording additional evidence that so much of speech is native. To get real speech, however, further combinations of the speech movements must be made, and the combinations (words) must have meaning attached to them. These higher achievements are evidently the result of learning, since the child uses the words that it hears spoken, and attaches the same meanings to them as people do about it. The child comes to speak the language of those about it, without regard to the speech of its ancestors. His "native language" is therefore acquired, though the elements of vocal utterance are truly native, and apparently are alike all over the world without regard to the various languages spoken.

As another example of this same general problem of distinguishing native from acquired reactions, and of the kind of evidence that throws light on the problem in the absence of direct experiment, let us consider the child's walking. Does the child learn to walk, or does it simply come to walk when its natural development has gone far enough? We think the child learns to walk because it begins very imperfectly and usually takes several weeks before it can be described as really walking of itself. We even think we teach it to walk, though when we examine our teaching we soon convince ourselves that we do not know how we walk, and that what we are doing with the baby is to stimulate and encourage him to walk, protect him from hurting himself, etc., rather than teaching him as we later teach the child to write. An experiment to settle the matter might be conducted along the lines of Spalding's experiment on the young birds. We might prevent the baby from making any attempt to walk till it had fully reached the normal age for walking, and then turn it loose and see whether it walked of itself.

Such an experiment has never been made under strict laboratory conditions; but here is a well-attested case that approximates to an experiment. A little girl of seven months, a very active child, seemed to want to get on her feet; but the doctor decided that her feet were too small to use, and directed that she be put back in long dresses. For four months she was kept in long dresses, and great care was exercised never to place her on the floor without them. Then, one day, she was set down without her dress, and immediately up she got and walked; and from that moment she was very agile on her feet.

Another rather different case, but tending towards the {96} same conclusion, is that of a little girl who, in contrast to the preceding, gave her parents some anxiety because, up to the age of seventeen months, she wouldn't walk. She would stand holding on, but not trust herself to her feet alone. One noon her father came in from his work and, removing his cuffs, laid them on the table. The little girl crept to the table, and raised herself to a standing position, holding on to the table. She then took a cuff in one hand, and inserted the other hand into it, thus, for the first time, standing unsupported. She put on the other cuff in like manner, and then marched across the room, as proud as you please. For a few days she could walk only with cuffs, but after that was able to dispense with them. There are a few other cases, differing in details, but agreeing on the main point, that the baby walked well on its first trial and went through nothing that could properly be interpreted as a process of learning.

It would really be very surprising if the human infant were left to learn locomotion for himself, while all other animals have this power by nature. Just because the human infant matures slowly, and learns a vast deal while maturing, is no reason for overlooking the fact that it does mature, i.e., that its native powers are gradually growing and reaching the condition of being ready for use. The most probable conception of "learning to walk," in the light of the evidence, is about as follows. At the age when the child's bones and muscles have become strong enough for walking, the nerve connections for coördinating this complex movement have also just about reached the stage of development when they are ready for business. The numerous synapses in the nerve centers that must be traversed by nerve currents in order to arouse the muscles to this particular act are not, we may suppose, all ready at the same instant, and it takes some little time for them to pass from {97} the stage when they will first conduct to the stage when, having grown more, they conduct perfectly. In other words, the neural mechanism for walking can function imperfectly before it can function perfectly. It takes several weeks of growth to pass from the barely functional condition to the fully functional condition; and it is during these weeks that the child seems to be learning to walk, while really his exercise of the partially developed neural mechanisms has no effect except to hasten their growth to some extent.

The fundamental sign or criterion of a native trait, in accordance with what we have been saying, is that it shall make its appearance when there has been no chance to acquire it through experience. This is the one perfect criterion; but unfortunately it cannot always be applied, especially with a slowly maturing and much-learning species such as the human. We need other criteria, and one of some value is the criterion of universality.

Consider, for example, the attraction between the sexes, and ask whether this represents a native tendency, or whether each individual acquires it, as he does his "native language", by learning from his elders. Before the body reaches sexual maturity, there has been abundant opportunity for the quick-learning child to observe sex attraction in older people. Yet it is highly improbable that the liking for the other sex which he begins to show strongly in youth is simply an acquired taste. It is improbable because the attraction between the sexes is so universal not only among mankind but among birds and mammals and, indeed, practically throughout the animal kingdom.

Fighting is a similar case. Not so universal as the sex instinct, it still appears almost universally among birds and mammals.

The human individual is an animal, and some of his native traits are universal among animals. He is a vertebrate, and some of his traits, though not present in all animals, are universal among vertebrates. He is a mammal, with mammalian traits; a primate, with primate traits; a man with human traits; a Chinaman or Indian or European with racial traits; belongs to a more or less definite stock or breed within the race, and possesses the traits that are common to members of that stock; and the same with family traits. The criterion of universality, in the light of these facts, comes down to this: that when all individuals having the same descent show a trait in common, that trait is to be regarded as belonging to their native constitution--unless evidence can be brought forward to the contrary.

Smoking is universal among many Malay peoples, but we know, as a historical fact, that it was introduced among them after the discovery of America, not very many generations ago. Superstition is universal among some peoples, but we see the superstitious beliefs and practices taught by the older to the younger generation. Similarly with any specific language. It may very well be true in such cases that the universal practice appeals to some native tendency of the people; but the specific practice is handed down by tradition and not by inheritance.

Though the universality of a trait creates a certain presumption in favor of its being native, the opposite is not always true, for a trait may be native and yet appear in only a fraction of those who have a common descent. Eye color is certainly native, and yet one of two brothers may have blue eyes and the other brown. Mental deficiency runs in families, but usually some members of such families have {99} normal mentality. Genius is almost certainly a native trait, but it is the reverse of universal. The fact is that, along with certain traits that appear in all, the native constitution of a stock provides also for traits that appear only sporadically. Enough has been said to show that the criterion of universality is one that needs to be applied with judgment.

Acquired traits are on the whole much less universal, much more individual, than native traits. They are readjustments of the individual to environmental conditions; and, as the environment varies, so the adjustments vary, even when native traits are the same. Acquired traits are often specializations of the native traits, as any specific language is a specialization of the vocal utterances that are native and common to all men, and as the peculiar gait of an individual is a specialization of the universal walking movement. The gait differs with the environmental differences to which the individual has adapted himself, and will be different in one who has been accustomed to walk over rough ground and in one whose walking has been done on the city streets.

Acquired traits are not independent of native, but are developed on the basis of the native traits. They are acquired not by laying aside native tendencies and working out something entirely new, but by acting in accordance with the native tendencies and making such readjustments as the environment demands. The acquisition of mental traits is accomplished by the process of learning, and we shall later have abundant occasion to examine it in more detail.

For the present, let us simply take a brief survey of the mental field, and notice what types of reactions are native and what acquired. On the motor side, the reflexes are native, while habitual and skilled movements are acquired. On the sensory side, nature provides the use of the sense organs and the sensations immediately resulting from their stimulation. The baby responds to touch, warmth, cold, sound and light as soon as it is born, or practically so, and undoubtedly has the corresponding sensations. In other words, the rudiments of seeing, hearing, etc., are provided by nature. But when we say, "I see a dog" we mean more than that we are getting certain visual sensations; we mean that we see a known object or known sort of object. This implies recognition of the object, either as an individual thing or as one of a class; and this the baby can scarcely be supposed to do at first. He sees the dog to the extent that he responds by visual sensations to the light coming from the dog, but not to the extent that he recognizes the dog as a dog. In short, the meanings of sensations are acquired, though the sensations themselves are native.

Things come to be known by use of the senses, and when thus known are not only recognized when present, but also remembered and thought of when they are not present to the senses. Such memories and items of knowledge, dependent as they are on experience, are to be reckoned among the acquired reactions. Ideas or conceptions of things also belong here.

Of the emotions, some are called "primary" or native--anger and fear are examples--while others result from the compounding of these primary emotions and are therefore acquired. As people and things come to be known, emotional reactions become attached to them, and give what {101} are often named "sentiments", such as love for this person, contempt for that one, family pride, patriotism. These sentiments, bound up as they are with knowledge and ideas, are certainly acquired.

Closely akin to the primary emotions are the native impulses, as the impulse to eat, to cry, to laugh, to escape from danger, to resist external compulsion and to overcome obstacles. The native impulses are the raw material out of which the numerous acquired desires of child and adult are formed. One sort of native impulse is the impulse to notice or pay attention to certain sorts of stimuli. These native interests of the child give birth to the various specialized interests of the adult. The baby's attention to a bright light represents a native interest; the older child's fixing his eyes on a dark brown piece of chocolate represents an acquired interest which has developed in a way that is easy to understand.

Finally, we must count among the native traits of the individual his inherited aptitudes for certain kinds of work. One child shows a natural aptitude for music, another for acting, another for mathematics, another for mechanical things, another for language, and so on. As any of these "natural gifts" is present in some degree in nearly all members of the human family, and not to anything like the same degree in animals, they are the characteristically human traits. It is on the basis of such native aptitudes that each individual proceeds, through the processes of learning, to build up his various acquired abilities, such as the ability to sing, to speak a certain language, to add, to work with tools, to perform athletic feats, and to take part in social activities of various sorts.

Our next task will be to examine more closely the native equipment of man, and after that to take up the process of learning, which is the way reactions are acquired. First the native, then the acquired. The acquired is based upon {102} the native. Acquired reactions are indeed so numerous that we cannot attempt even to list them all, let alone examine each one separately; but we can at least study the way in which they are acquired. Native reactions are much less numerous, so that the student may hope to obtain a fairly comprehensive survey of this field, though, of course, without much detail.

The general plan of this book, then, is as follows. Up to this point, it has been providing a stock of methods and general conceptions to serve as tools in psychological study: consciousness and behavior, the introspective and objective methods, reactions and tendencies to reaction, native and acquired, and the part played by the nervous system. Next comes a survey of reactions provided by the native constitution, and after that a study of the process of learning or acquiring reactions. Finally, there are several chapters devoted to such topics as imagination, reasoning and will, which are ways in which the individual utilizes his whole equipment, native and acquired, in meeting the exigencies of life.

1. Outline the chapter.

2. When does the individual come into existence as an individual? When does he begin to acquire traits? How long does he continue to unfold his native traits, and how long does he continue to acquire traits?

3. Which of the following elements of spoken language are native, and which acquired?

(a) Production of voice by the vocal cords and air blast from the lungs.
(b) Varying the voice in loudness.
(c) Varying the voice in pitch.
(d) Production of vowels by different positions of the mouth.
(e) Production of consonants by lip and tongue movements.
(f) Combination of vowels and consonants into words.
(g) Combination of words into idioms and grammatical sentences,
(h) Attachment of meanings to words.
(i) Sweet-toned voice.
(j) Nasal twang.
(k) Fluency in speaking.

4. In each of the following reactions, decide whether the connection of stimulus and response is probably native or acquired:

Edward L. Thorndike, in Chapter I of his Educational Psychology, Briefer Course, 1914, gives a general survey of the native factors in mental life and behavior.

Hollingworth and Poffenberger, in their Applied Psychology, 1917, devote Chapters II and III to the matter of mental heredity.

Norsworthy and Whitley, in their Psychology of Childhood, devote Chapters I and II to "original nature".

C. B. Davenport, in his Heredity and Eugenics, presents evidence of the importance of heredity in determining mental and moral traits.

Yerkes and Bloomfleld, in a short article in the Psychological Bulletin for 1910, Vol. 7, pp. 253-263, under the title, "Do Kittens Instinctively Kill Mice?", furnish a good illustration of the method employed in distinguishing native from acquired reactions.

Instinct is native behavior. It is contrasted with habit, knowledge, or anything in the way of learned reactions. When the mother wasp gathers a store of food suitable for young wasps, lays eggs beside the food and covers the whole with a wall of mud, we know that her behavior is instinctive because she has had no possible chance to learn from older wasps. She has never seen a wasp's nest made, for when the last preceding crop of nests was being made she was herself an unhatched egg. Therefore, she cannot possibly know the use of the nest with its eggs and store of food. She has no "reason" for building the nest, no ulterior purpose, but is impelled to build the nest, simply and solely for the sake of doing just that thing. Thus instinct is contrasted with calculated or reasoned action as well as with learned action. Calculated action is based on knowledge of cause and effect, and this knowledge is acquired by the individual in the course of his experience; but instinct is not based on the individual's experience, but only on his native constitution.

The case of the baby eating is exactly the same as that of the wasp. The baby has not learned to eat, he knows nothing of the use of food and therefore has no ulterior purpose in eating, he does not reason about the matter, but eats simply because hunger is a native impulse to eat. {106} Eating is an end in itself to a hungry baby, and not a means to some further end; and that is what eating continues to be even to the hungry adult, however much he may learn about the use of food in maintaining life. From a broad philosophical point of view, instinct may be seen to work towards some great end, such as the preservation of the individual or the propagation of the race, but from the individual's own point of view, it is directed simply towards the performance of some particular act, or the accomplishment of some particular result.

If instinct, as a collective term, means native behavior, "an instinct" is a unit of such behavior. Or, it is some unit of native organization that equips the individual to behave in a certain way. Different species of animals have different instincts, i.e., they are differently organized by nature. The differences of organization lie partly in the equipment of sense organs, partly in the equipment of motor organs, and partly in the nerves and nerve centers that, being themselves aroused by way of the sense organs, in turn arouse the motor organs.

The dependence of instinct on sensory equipment becomes clear when we think of animals possessing senses that human beings lack. The instinct of dogs to follow the scent depends on their keen sense of smell. Bees have something akin to a sense of taste in their feet, and follow their own trails by tasting them. Fishes have special sense organs along their sides that are stimulated by water currents, and it is in response to this stimulus that the fish instinctively keeps his head turned upstream.

The dependence of instinct on motor equipment is still more obvious. The flying instinct of birds depends on the possession of wings, and the swimming instinct of the seal depends on the fact that his limbs have the peculiar form of flippers. The firefly instinctively makes flashes of light, {107} and the electric eel instinctively discharges his electric organ and gives his enemy a shock.

But the core of an instinct is to be sought in the nerve centers, since it is there that the coördination of the muscles is accomplished. A wing or flipper would be of no use unless its muscles were excited to action by the nerve centers, and it would be of very little use unless the nerve centers were so organized as to arouse the muscles in a certain combination, and with a certain force and rhythm. In terms of the nervous system, an instinct is the activity of a team of neurones so organized, and so connected with muscles and sense organs, as to arouse certain motor reactions in response to certain sensory stimuli.

What we have said regarding instinct thus far could equally well be said of reflex action. A reflex is a native reaction, and it is taken care of by a team of neurones in the way just stated. We might speak of a reflex as "instinctive", using this adjective as equivalent to "native"; but we should shrink for some reason from speaking of the pupillary reflex to light as an instinct, or of the "knee jerk instinct", or the "swallowing instinct", or the "flexion instinct". There is some difference between the typical reflex and the typical instinct, though it is not very obvious what the difference is.

The typical reflex is a much simpler act than the typical instinct, but it is impossible to separate the two classes on this basis. At the best, this would be a difference of degree and not of kind. Among reflexes, some are simpler than others, but even the simplest is compound in the sense of being a coördinated movement. The knee jerk is simpler than the flexion reflex, and this is simpler than the scratch {108} reflex, which consists of a rapid alternation of flexion and extension by one leg, while the other is stiffly extended and supports the trunk. Coughing, which would be called a reflex rather than an instinct, consists of a similar alternation of inspiration and forced expiration, and swallowing consists of a series of tongue, throat and gullet movements. These compound reflexes show that we cannot accept the simple definition that is sometimes given for an instinct, that it is a compound of reflexes. Such a definition would place coughing and swallowing among the instincts, and so do violence to the ordinary use of the word. In point of complexity, we find a graded series ranging from the pupillary reflex at one extreme to the nesting or mating instinct at the other, and no sharp line can be drawn on this score between the reflexes and the instincts.

Another distinction has been attempted on the basis of consciousness. Typically, it may be said, a reflex works automatically and unconsciously, while an instinct is consciously impulsive. The reflex, accordingly, would be an unconscious reaction, the instinct a conscious reaction. But this distinction also breaks down on examination of cases. The pupillary reflex, to be sure, is entirely unconscious. But the flexion reflex is a little different. When unimpeded, it occurs so promptly that we are scarcely aware of the painful stimulus before the reaction has occurred. But let the reaction be hindered--either voluntarily or, for instance, by the foot being seized and held--and a strong conscious impulse is felt to pull the leg away; so that here the flexion reflex would belong among the instincts, according to the proposed distinction.

Similar remarks would apply equally well to coughing, since a strong impulse to cough is felt if the coughing movement is checked. Sneezing, a protective reflex, is usually a slow reaction, giving time for a conscious impulse to {109} sneeze before the reaction takes place. The same is true of scratching and of swallowing, and of a number of other reflexes. In short, it is impossible to draw a satisfactory line between reflexes and instincts on the basis of conscious impulse.

These cases point the way, however, to what is probably the best distinction. It was when the flexion reflex was delayed that it began to look like an instinct, and it was because sneezing was a slow response that it had something of the character of an instinct. Typically, a reflex is a prompt reaction. It occurs at once, on the occurrence of its stimulus, and is done with. What is characteristic of the instinct, on the contrary, is the persisting "tendency", set up by a given stimulus, and directed towards a result which cannot be instantly accomplished.

We would propose, then, to consider an instinct as an inner adjustment, or tendency to reaction. It is this, rather than just a reaction. When a stimulus promptly arouses a reaction, and that ends the matter, we speak of reflex action--provided, of course, the connection between stimulus and response is native. But when a stimulus sets up a tendency to a reaction that cannot be immediately executed, or towards an end-result which cannot immediately be reached, and when the tendency so aroused persists for a time in activity, and gives rise to preparatory reactions, then we speak of instinct.

The "broody" hen makes a good picture of instinct. When in this condition she responds to a nestful of eggs, as she does not at other times, by sitting persistently on them and keeping them covered. She is in a certain "organic state" that facilitates this response. In the absence {110} of any nestful of eggs, she shows a peculiar restless behavior that indicates to one who knows hens that this one "wants to set." The tendency that has been awakened in her cannot be satisfied by any momentary act, but persists and governs her actions for a considerable period.

The nesting instinct of birds affords a still more complete example. The end-result here, the finished nest, cannot be instantly had, and the pair of birds keep on gathering materials and putting them together until this end-result is present before their eyes. It is not necessary to suppose that the birds have any plan or mental image of what the nest is to be like; probably not. But their state, in the nest-building season, is such that they are impelled to build, and the tendency is not quieted till the completed nest is there.

The mating instinct, in unsophisticated members of the human species, is another perfect example. So is the hunting instinct in a dog; when this instinct is aroused, the animal makes a lot of movements of various sorts, responses to various particular stimuli, but evidently these movements are not sufficient to quiet the tendency, for they continue till the prey is captured. The behavior of a gregarious animal when separated from his fellows shows the same sort of thing. Take a young chick out of the brood and fence it away from the rest. It "peeps" and runs about, attacking the fence at different points; but such reactions evidently do not bring satisfaction, for it varies them until, if a way out of the inclosure has been left, it reaches the other chicks, when this series of acts terminates, and gives way to something quite different, such as pecking for food.

The persisting tendency does not produce the series of movements all by itself, but, as was explained in speaking of tendencies in general, coöperates with sensory stimuli in producing them. Clearly enough, the nest-building bird, {111} picking up a twig, is reacting to that twig. He does not peck at random, as if driven by a mere blind impulsion to peck. He reacts to twigs, to the crotch in the tree, to the half-built nest. Only, he would not react to these stimuli unless the nesting fit were on him. The nest-building tendency favors response to certain stimuli, and not to others; it facilitates certain reactions and inhibits others. It facilitates reactions that are preparatory to the end-result, and inhibits others.

Insects afford the best examples of very highly organized instincts. Their behavior is extremely regular and predictable, their progress towards the end-result of an instinct remarkably straightforward and sure. They make few mistakes, and do not have to potter around. By contrast, the instincts of mammals are rather loosely organized. Mammals are more plastic, more adaptable, and at the same time less sure; and this is notably true of man. It would be a mistake to suppose that man has few instinctive tendencies; perhaps he has more than any other creature. But his instinctive behavior has not the hard-and-fast, ready-made character that we see in the insects. Man is by all odds the most pottering, hem-and-hawing of animals. Instinct does not lead him straight to his goal, but makes him seek this way and that till he finds it. His powers of observation, memory and thought are drawn into the game, and thus instinct in man is complicated and partly concealed by learning and reasoning.

For example, when an insect needs a nest, it proceeds in orderly fashion to construct a nest of the pattern instinctive to that species of insect; but when a man needs a home, he goes about it in a variable, try-and-try-again {112} manner, scheming, experimenting, getting suggestions from other people, and finally producing--a dugout, a tree house; a wigwam, a cliff dwelling--something that differs altogether from many other human habitations, except in the fact that it is a habitation and thus satisfies a need which is undoubtedly as instinctive in man as in the insect.

A fully organized instinct is one where the necessary preparatory reactions are linked up closely with the main reaction-tendency, so that, once the main tendency is aroused to activity, the preparatory reactions follow with great sureness. The main team of neurones is closely connected with the subordinate teams that give the preparatory reactions; and these connections do not have to be acquired by experience and training, but are well formed by native growth. Just the right preparatory reactions are linked to the main tendency, so that the whole series of acts is run off with great regularity.

In a loosely organized instinct, the main tendency is not firmly linked with any specific preparatory reactions, but is loosely linked with a great many preparatory reactions, and so gives quite variable behavior, which, however, leads on the whole towards the main goal.

While a creature under the spell of a fully organized instinct is busy, one driven by a loosely organized instinct may be better described as restless. He tries this thing and that, and goes through the kind of behavior that is called "trial and error". A closely knit instinct, then, gives a perfectly definite series of preparatory reactions, while a loosely organized instinct gives trial and error behavior. We shall see later how trial and error furnishes a starting point for learning, and how, in an animal that can learn, those among the trial-and-error reactions that are actually preparatory to the end-result become firmly attached to the main tendency, so that what was by native constitution a loosely {113} organized instinct may become, through the individual's experience, a closely organized habit. If a man has occasion to build himself many homes, he comes, after a while, to build almost as uniformly and surely as an insect.

The theory of inheritance of acquired traits has gone by the board; biologists no longer accept it. Such traits as an individual's tanned skin acquired by living in the tropics, horny hands acquired by hard labor, immunity to measles acquired by having measles, big muscular development acquired by gymnastics, are not transmitted by heredity to the children of the individual who acquired these traits.

Nor are acquired behavior traits transmitted by heredity. Learned reactions are not so transmitted, knowledge is not, acquired skill is not. Learn to cook, to typewrite, or pilot an airplane as perfectly as possible, and your child will still have to learn all over again. You may make your experience valuable to him by teaching him, but not in the way of heredity.

Language affords a good test of this matter. A child's parents, and all his ancestors for many generations, may have spoken the same language, but that does not relieve the child of the necessity of learning that language. He does not inherit the language habits of his ancestors. He has no native tendency to say "dog", or "chien", or "hund", on sight of this animal. Here in America we have children born of stocks that have spoken foreign languages for many generations; but English becomes their "native tongue" after a generation or two here, that is to say, as soon as the child hears English from infancy.

In short, there is no likelihood whatever that any instinct {114} ever originated out of a habit or learned reaction. If we could believe it had so originated, that would furnish an easy explanation of the origin of an instinct; but it is contrary to all the known facts.

Some of the best-known instincts, such as feeding or mating--or hunting, or flight from danger, or the hibernation of frogs--are so essential for the survival of the individual or the propagation of the next generation that we tend to assume that all instinctive behavior has "survival value", value, that is, towards the survival of the individual or of the race. But this is an assumption, and it seems not to be borne out by actual observations of instinctive behavior, since, along with the definitely useful reactions, others occur that would seem to have no survival value. Perhaps the crowing of the rooster at dawn would be a case in point; or the elaborate bowing that is observed in some kinds of birds. And there are the less definite, rather random movements of squirming, kicking, running about, wrinkling up the face, etc., that appear in young animals. We may well hesitate before definitely asserting that these movements are of no use for survival, but at least their use is not obvious, and there is no reason for assuming that all instinctive behavior must necessarily be useful.

To be sure, the "struggle for existence" would eliminate individuals who behaved in ways that seriously handicapped them in procuring food or escaping from enemies; and therefore we should not expect to find really harmful instincts preserved in the race. But a mode of behavior might be neutral in this respect, or even slightly disadvantageous, and yet not be weeded out unless the struggle for existence were very keen.

The main point is that the psychologist should take instinctive behavior as he finds it, and not allow himself to be prejudiced by the assumption that instinct must necessarily be useful. That has to be shown in each case, not assumed at the outset.

You will hear it stated, by some, that there are just two instincts, and that all instinctive behavior belongs under the head of one or the other of these two. The one is the instinct to preserve one's individual life, and the other is the instinct to propagate the species. Mating, nesting and care of the young come under the reproductive instinct, while feeding, flight from danger, and shunning extreme heat or cold are modes of self-preservation. This seems logical enough, but it is very bad psychology. It amounts to a classification of native reactions from an external point of view, without any consideration of the way the individual is organized.

Perhaps the most obvious objection to these two supposedly all-inclusive instincts is found in what has just been said, to the effect that some instinctive behavior has no known survival value. This amounts to saying that some instincts do not serve either the preservation of the individual or the propagation of the species; and such a statement is probably true, especially of human instincts.

But even if this objection should not hold, there is another, more radical one. Neither of these two big "instincts" is a behavior unit in any sense. Take the "instinct of self-preservation", for example. It would certainly have to include both feeding and escape from danger. But feeding and flight from danger do not belong in a single series {116} of acts; they are two distinct series, and represent two distinct tendencies. So distinct are they that, as we shall see in the next chapter, they are antagonistic. If the danger-avoiding tendency is aroused, the whole feeding and digestive activity is checked for the time being. The two instincts are antagonistic, in their actual operation; throw one into action, and you throw the other out. It is only from an external point of view that the two can be classed together; in the organization of the individual they are entirely separate.

Not much different is the "instinct of reproduction". In birds, to be sure, there is a fairly continuous series of reactions, that begins with mating, continues with nesting, laying eggs and incubating them, and ends in the care of the young birds. But in mammals there is no such continuous series of reproductive acts, but mating comes to a close and an interval elapses in which there is no behavior going on that has anything to do with reproduction.

Before giving a detailed list of the various human instincts, we shall do well to consider emotion, which is closely bound up with instinct.

1. Outline the chapter.

2. Explain the differences between these three;

Action governed by instinct.
Action governed by habit.
Action governed by deliberation.

3. What is the objection to each of the following expressions?

(a) "The ex-soldier instinctively saluted when he met an officer in the street."
(b) "The bee knows by instinct how to construct the honeycomb."

4. Why is it so difficult to find a valid distinction between instinct and reflex action?

5. Why are instincts more universal and uniform than habits?

6. How is instinct an important matter to consider in a study of human motives?

7. Show how the behavior of a hungry child of six or eight years fits the picture of a "loosely organized instinct".

William James in his Principles of Psychology, 1890, has a very stimulating chapter on instinct, in Vol. II, pp. 383-441.

John B. Watson, in Chapters IV and V of his Behavior, 1914, gives a good account of the instincts of animals.

Joy, sorrow, fear, anger, amusement, disgust and curiosity illustrate the meaning of the term "emotion". An emotion is a "moved" or stirred-up state of mind. Or, since almost any such state of mind includes also elements that are cognitive, like recognition of present objects or memories of the past, we might better speak of emotion as the stirred-up-ness present in a state of mind. The emotional part of the total state may be so strong as to overshadow all other components, or it may have less intensity down to zero.

Such is emotion from the introspective point of view; but it can also be observed objectively, and in fact there is more to say about it objectively than introspectively. What appears to introspection as the scarcely analyzable state of anger appears to the external observer as clenched fists, flushed face, labored breathing, tense muscles, loud voice, and many other describable details. Anger is a state of the organism, or state of the individual, rather than simply a state of mind.

We shall have a more comprehensive definition, then, if we substitute "state of the individual" for "state of mind", and say that emotion is a stirred-up state of the individual. It is a conscious state, however; an "unconscious emotion" would be practically a contradiction in terms. Not but that a person may be angry without knowing it. He may be {119} "unconscious of the fact" that he is angry; which simply means that he is not introspectively observing himself and analyzing his mental state. But it is impossible that his organic state shall be all stirred up and his mental state meanwhile perfectly calm and intellectual. In short, an emotion is a conscious stirred-up state of the organism.

Something was said before about "organic states", under the general head of tendencies to reaction. Fatigue was an example. Now we could include fatigue under the term, "stirred-up state of the organism"; at least, if not precisely "stirred-up", it is uneasy. It is a deviation from the normal or neutral state. Also, it is often a conscious state, as when we speak of the "tired feeling"; not a purely cognitive state, either--not simply a recognition of the fact that we are fatigued--but a state of disinclination to work any longer. Though fatigue is thus so much like an emotion that it fits under our definition, it is not called an emotion, but a sensation or complex of sensations. After hard muscular work, the state of the muscles makes itself felt by "fatigue sensations", and the sum total of these, coming from many different muscles, makes up the complex sensation of fatigue. After prolonged mental work, there may be fatigue sensations from the eyes and perhaps from the neck, which is often fixed rigidly during strenuous mental activity; and there are perhaps other obscure fatigue sensations originating in other organs and contributing to the total sensation which we know as mental fatigue, or as general fatigue.

Many other organic states are akin to emotion in the same way. The opposite of fatigue, the "warmed-up" condition, brought on by a certain amount of activity after {120} rest, is a case in point. It is a deviation from the average or neutral condition, in the direction of greater readiness for activity. The warmed-up person feels ready for business, full of "ginger" or "pep"--in short, full of life. The name "euphoria" which means about the same as "feeling good", is given to this condition. Drowsiness is another of these emotion-like states; but hunger and thirst are as typical examples as any.

Now why do we hesitate to call hunger, fatigue and the rest by the name of emotions? For two reasons, apparently. There are two salient differences between an organic state such as hunger, and an emotion such as anger.

Hunger we call a sensation because it is localized; we feel it in the region of the stomach. Thirst we localize in the throat, muscular fatigue in the fatigued muscles, and there are several other organic states that come to us as sensations from particular organs. This is not entirely true of drowsiness or euphoria, but it is still less true of the emotions, which we feel as in us, rather than in any part of us. We "feel mad all over", and we feel glad or sorry all over. It is true that, traditionally, the heart is the seat of the emotions, which means, no doubt, that they are felt in the region of the heart more than elsewhere; and other ancient "seats", in the bowels or diaphragm, agree to this extent that they point to the interior of the trunk as the general location where the emotions are felt. But at best the location of emotions is much less definite than that of the sensations of fatigue or hunger.

The second difference between the emotions and the other organic states comes to light when we notice their causes. Thirst, as an organic state, is a lack of water resulting {121} from perspiration, etc.; hunger as an organic state results from using up the food previously eaten; fatigue results from prolonged muscular activity. Each of these organic states results naturally from some internal bodily process; while, on the contrary, the exciting cause of an emotion is usually something external which has nothing directly to do with the internal state of the body. Here I am, perfectly calm and normal, my organic state neutral, when some one insults me and throws me into a state of rage; this queer state seems to be inside me, specially in the trunk. Now how can the sound of the insulting person's voice produce any change in my insides? Evidently, by way of the auditory nerve, the brain and lower centers, and the motor nerves to the interior. While, then, organic states of the hunger class result directly from internal physiological processes, the organic state in an emotion is aroused by the brain, the brain itself being aroused by some stimulus, usually external.

But perhaps we are going too fast in assuming that there is any peculiar internal state in emotion. Possibly our subjective localization of anger in the trunk is all wrong, and everything there is going on as usual. At least, the question is squarely before us whether or not there is any internal bodily response in emotion.

Suppose we have a tame cat, that knows us well, and, after feeding her a good meal containing some substance that is opaque to the X-rays, suppose we place her on a table and pass X-rays through her body, so as to get a visible shadow of the stomach upon the plate of the X-ray machine. Well and good; the cat is contentedly digesting her meal, and the X-ray picture shows her stomach to be making rhythmical churning movements. In comes a fox {122} terrier and barks fiercely at the cat, who shows the usual feline signs of anger; but she is held in position and her stomach kept under observation--when, to our surprise, the stomach movements abruptly cease, not to begin again till the dog has been gone for perhaps fifteen minutes. The churning movements of the intestine cease along with those of the stomach, and, as other experiments show, even the gastric juice stops flowing into the stomach. The whole business of digestion halts during the state of anger. So anger is an organic state, without doubt. At least in cats--but the same is found to be true of man, and hence the excellent rule not to get angry on a full stomach.

Stomach-inhibition is not the only internal response during anger. The heart, so long regarded as the seat of the emotions, does beat more forcibly than usual; and the diaphragm, where the old Greeks located the emotions, does make extra-strong breathing movements. There are yet other and more curious changes that have recently been discovered by the physiologists.

Thus far, we have been considering muscular responses, but now we must turn our attention to the glands. The glands are often affected during emotion, as witness the shedding of tears in grief, sweating in anger, the dry mouth during fear due to inhibition of the salivary glands, and the stoppage of the gastric juice during anger, as just noted. These particular glands all pour out their secretions either upon the skin or upon the mucous membrane of the mouth, stomach, etc.; and such secretion is called "external" in distinction from the "internal secretion" of certain other glands which may be called the glands of internal secretion or the "endocrine glands". Internal secretions are {123} discharged into the blood vessels, and carried by the blood to all parts of the body, and they have important effects on the activity of various organs.

Of the endocrine glands, we will mention only two, which are known to play an important part in mental life.

The thyroid gland, situated in the lower part of the neck, is necessary for normal brain activity. Without its internal secretion, brain activity is very sluggish.

The adrenals, two little glands located near the kidneys (whence their name, though they have nothing to do with the kidney in function), have a close connection with such emotions as anger. In the normal or neutral state of the organism, the adrenal secretion oozes slowly into the blood, and has a tonic influence on the heart and muscles. But let an anger stimulus occur, and within a few seconds the adrenals are secreting rapidly; all the organs soon get a big dose of the adrenal secretion, and some of them are strongly affected by it. It hastens and strengthens the action of the heart, it causes the large veins inside the trunk to squeeze the blood lagging there back to the heart; and by these two means greatly quickens the circulation. It also affects the liver, causing it to discharge large quantities of stored sugar into the blood. Thus the muscles of the limbs get an unusual quantity of their favorite fuel supplied them, and also, by the increased circulation, an unusual quantity of oxygen; and they are enabled to work with unusual energy. The adrenal secretion also protects them in some way against fatigue.

While the adrenal secretion is thus exerting a very stimulating influence on the limb muscles, it is having just the opposite effect on the digestive organs; in fact it is having the effects described above as occurring there during anger. These inhibitory effects are started by the stomach nerves, but are continued by the action of the adrenal juice {124} on the stomach walls. The rapid secretion of the adrenal glands during anger is itself aroused by the nerve running to this gland.

There is a part of the nervous system called the "autonomic system", so called because the organs it supplies--heart, blood vessels, stomach, intestines and other internal organs, possess a large degree of "autonomy" or independence. The heart, it will be remembered, beats of itself, even when cut off altogether from any influence of the nerve centers; and the same is true in some measure of the other internal organs. Yet they are subject to the influence of the nerve centers, which reinforce and inhibit their activity. Each internal organ has a double supply of nerves, one nerve acting to reinforce the activity of the organ and the other to inhibit it; and both the reinforcing and the inhibiting nerves belong to the autonomic system.

The autonomic is not separate from the main nervous system, but consists of outgoing axons from centers in the cord and "medulla" (part of the brain stem). It has three divisions, one from the medulla, one from the middle reach of the cord, and one from the lower part of the cord; and these three divisions are related to three different emotional states. The upper division, from the medulla, favors digestion by promoting the flow of gastric juice and the churning movements of the stomach; and at the same time it seems to favor the comfortable, rather lazy state that is appropriate for digestion. The middle division (often called the "sympathetic", though the name is rather misleading to a student of psychology, as it has nothing to do with "sympathy") checks digestion, hastens the heart beat, and stimulates the adrenal glands to rapid secretion, thus giving {125} rise to the organic condition of anger. The lower division has to do with the bladder, rectum and sex organs, and is active during sex excitement, for one thing.

The lower centers in the medulla and cord that give rise to the autonomic nerves are themselves much under the influence of the higher, cerebral centers. Thus appetite for food, and the flow of gastric juice, can be aroused by the sight of good food, or by hearing or reading about food, or even by merely thinking of food; and both anger and sex appetite can be aroused in corresponding ways.

We should notice right here the antagonism that exists between the middle division of the autonomic and the other two. Suppose the upper division is active, as in comfortable digestion, when an angering stimulus supervenes; then, as we have seen, digestion halts, the upper autonomic is shunted out of action by the middle division. In the same way, sex appetite is shunted out by anger.

An emotion is often spoken of as a disturbance of the normal quiet state, and as if it represented a breakdown of the organism's machinery. Anger or fear is often a nuisance in civilized life, and any strong emotion is apt to disturb mental work or skilled manual work. But if we think ourselves back into a primitive condition of life, when anger means a fight, we see that the organic response in anger makes a first-class preparation for the fight. Rapid circulation, abundant muscular fuel, protection from fatigue--these are all positively useful; and the halting of digestion is useful also in relieving the circulation from taking care of an activity that can afford to wait.

What we have been calling the "organic state in anger" occurs also in fear of the strong type (as distinguished from {126} fear paralysis), and in certain other states that are not exactly either fear or anger, such as the state of a football player before the game, or the state of a student about to take an examination. It is the state of excitement or of being "all keyed up". So far as known, the organic response (including the adrenal secretion) is the same in these various instances of excitement: anger, fear, zeal and so on. When an individual is in this organic state, his muscles will work harder and longer than is otherwise possible; and thus are explained those remarkable cases of extraordinary strength and endurance in great emergencies, as in escaping from a fire or from a bombarded city.

The fear-anger state of the organism, being certainly a state of preparedness for attack or defense, suggests the following generalization: "Any emotion represents internal preparation for some type of overt action." This holds good, at least, for food appetite and sex appetite. Regarding the other emotions, we know too little of the internal responses that may occur, to judge whether or not they have any utility as preparatory reactions.

Though we know little of any internal response in many of the emotions, we almost always find some characteristic external movement, such as smiling, scowling, pouting, sneering, sobbing, screaming, shouting or dancing. By aid of such "expressive movements" we are sometimes able to judge the emotional state of another person. But what is the sense of these movements? At first thought, the question itself is senseless, the movements are so much a matter of course, while on second thought they certainly do seem odd. What sense is there is protruding the lips when sulky, {127} or in drawing up the corners of the mouth and showing the canine teeth in contempt? Perhaps they are just odd tricks of instinct--for we agreed in the preceding chapter not to assume all instinctive responses to be useful. Darwin, however, after studying a great many of these expressive movements, both in men and in animals, reached the conclusion that, if not of present utility, they were survivals of acts that had been useful earlier in the life of the individual or of the race.

Shaking the head from side to side, in negation or unwillingness, dates back to the nursing period of the individual's life, when this movement was made in rejecting undesired food. Directly useful in this case, it was carried over to analogous situations that aroused the child's reluctance.

Showing the teeth in scorn dates back, according to Darwin, to a prehuman stage of development, and is seen in its useful form in animals like the dog or gorilla that have large canine teeth. Baring the teeth in these animals is a preparation for using the teeth; and often, also, it frightens the enemy away and saves the bother of actually attacking "small fry". The movement, Darwin urges, has survived in the race, even after fighting with the teeth has largely disappeared.

Many other expressive movements are traced back in a similar way, though it must be admitted that the racial survivals are usually less convincing than those from the infancy of the individual. The nasal expression in disgust was originally a defensive movement against bad odors; and the set lips of determination went primarily with the set glottis and rigid chest that are useful in lifting heavy weights or in other severe muscular efforts. Such movements, directly useful in certain simple situations, become linked up with analogous situations in the course of the {128} individual's experience. Many of them, certainly, we can regard as preparatory reactions.

No one can doubt that some of the bodily changes that occur during an emotion make themselves felt as sensations. Try this experiment: pretend to be angry--it is not hard!--go through the motions of being angry, and notice what sensations you get. Some from the clenched fist, no doubt; some from the contorted face; some from the neck, which is stiff and quivering. In genuine anger, you could sense also the disturbed breathing, violent heart beat, hot face. The internal responses of the adrenal glands and liver you could not expect to sense directly; but the resulting readiness of the limb muscles for extreme activity is sometimes sensed as a feeling of tremendous muscular power.

Now lump together all these sensations of bodily changes, and ask yourself whether this mass of sensations is not identical with the angry state of mind. Think all these sensations away, and ask yourself whether any angry feeling remains. What else, if anything, can you detect in the conscious emotional state besides these blended sensations produced by internal and external muscular and glandular responses?

If you conclude that the conscious emotion consists wholly of these sensations, then you are an adherent of the famous James-Lange theory of the emotions; if you find any other component present in the emotion, you will find this theory unacceptable.

The American psychologist James, and the Danish psychologist Lange, independently of each other, put forward this theory in the early eighties of the last century, and it has ever since remained a great topic for discussion. According to the theory, the emotion is the way the body feels while executing the various internal and expressive movements that occur on such occasions. The "stirred-up state of mind" is the complex sensation of the stirred-up state of the body. Just as fatigue or hunger is a complex of bodily sensations, so is anger, fear or grief, according to the theory.

James says, we do not tremble because we are afraid, but are afraid because we tremble. By that he means that the conscious state of being afraid is composed of the sensations of trembling (along with the sensations of other muscular and glandular responses). He means that the mental state of recognizing the presence of danger is not the stirred-up state of fear, until it has produced the trembling and other similar responses and got back the sensations of them. "Without the bodily states following on the perception"--i.e., perception of the external fact that arouses the whole emotional reaction--"the latter would be purely cognitive in form, pale, colorless, destitute of emotional warmth. We might then see the bear, and judge it best to run, receive the insult, and deem it right to strike, but we should not actually feel afraid or angry."

It has proved very difficult to submit this theory to a satisfactory test. The only real test would be to cut off sensations from the interior of the trunk entirely; in which case, if the theory is right, the conscious emotion should fail to appear, or at least lack much of its "emotional warmth". Evidence of this sort has been slow in coming in. One or {130} two persons have turned up at nerve clinics, complaining that they no longer had any emotions, and were found to have lost internal bodily sensation. These cases strongly support the theory, but others have tended in the opposite direction. The fact that the internal response is the same in anger, and in fear of the energetic type, shows that the difference between these emotions must be sought elsewhere. Possibly sufficient difference could be found in the expressive movements, or in minor internal responses not yet discovered. If not, the theory would certainly seem to have broken down at this point.

In any case, there is no denying the service done by the James-Lange theory in calling attention to bodily sensations as real components of the conscious emotional state.

Most people are rather impatient with the James-Lange theory, finding it wholly unsatisfactory, though unable to locate the trouble precisely. They know the theory does not ring true to them, that is all. Now the trouble lies just here: what they mean by "being afraid" is "wanting to get away from the danger", what they mean by "being angry" is "wanting to strike the offending person", and in general what they mean by any of the named "emotions" is not a particular sort of "stirred-up conscious state", but an impulse towards a certain action or a certain result. Evidently it would be absurd to say we want to get away from the bear because we tremble, or that until we started to tremble we should be perfectly indifferent whether the bear got us or not.

The tendency to escape is aroused directly by the perception of danger; of that there can be no doubt. It does not depend on trembling, but for that matter neither does it depend on feeling afraid. Sometimes we recoil from a {131} sudden danger before experiencing any thrill of fear, and are frightened and tremble the next moment, after we have escaped. The stirred-up state develops more slowly than the tendency to escape. The seen danger directly arouses an adjustment towards the end-result of escape, and both the preparatory bodily responses and the feeling of fear develop after this adjustment has been set up. If the end-result is reached instantly, the preparatory reactions and the feeling may not develop at all, or they may put in an appearance after the main act is all over. There is nothing in all this that speaks either for or against the James-Lange theory.

These statements need further elucidation, however. Notice, first, that psychology makes a perfectly proper and important distinction between emotion and impulse. In terms of consciousness, emotion is "feeling somehow", and impulse is "wanting to do something". In behavior terms, emotion is an organic state, and impulse an adjustment of the nerve centers towards a certain reaction. An impulse is a conscious tendency.

Since emotion and impulse so often go together, common sense does not bother to distinguish them, and the common names for the "emotions" are more properly names of impulses. Fear means the impulse to escape, rather than any specific stirred-up state. Psychology has, indeed, made a mistake in taking over these names from common speech and trying to use them as names of specific emotional states. We were having some difficulty, a few moments ago, in finding any great distinction between fear and anger, considered as emotional states--just because we were overlooking the obvious fact that "fear" is an impulse to escape from something, while "anger" is an impulse to get at something and attack it. The adjustments are very different, but the organic states are much alike.

The organic state in fear or anger cannot generate the escape or fighting tendency, since the two tendencies are so different in spite of the likeness of the organic state. The tendencies are aroused directly by the perception of the dangerous or offensive object. The order of events is as follows. The stimulus that sets the whole process going is, let us say, a bear in the woods. First response: seeing the bear. Second response: recognizing the dangerous situation. Third response: adjustment towards escape. Fourth response (unless escape is immediate): internal preparatory reactions, adrenal, etc.; also, probably, external expressive movements and movements steered in the general direction of escape. Fifth response: conscious stirred-up state consisting of blended sensations of all these preparatory reactions. Sixth response (by good luck): definitive escape reaction. Seventh response: satisfaction and quiescence.

Fig. 24.--Here the stimulus-response diagram is complicated to take account of the emotional state. The ellipse here stands for the brain. S arouses T, a tendency towards the response R. But T also arouses P, a bodily state of preparedness, and sensations (E) of this bodily state, together with T, constitute the conscious state of the individual while he is tending towards the response, or end-result, R.

Typically, impulse generates emotion. The reaction tendency is primary and the emotion secondary.

But suppose the organic state of fear to be {133} present--never mind how it got there--might it not act like hunger or fatigue, and generate a fear impulse? Could it not be that a person should first be fearful, without knowing what he was afraid of and without really having anything to be afraid of; and then, as it were, find something to be afraid of, something to justify his frightened state? This may be the way in which abnormal fears sometimes arise: a naturally timid individual is thrown by some obscure stimulus into the state of fear, and then attaches this fear to anything that suggests itself, and so comes to be afraid of something that is really not very terrific, such as the number two, "I mustn't do anything twice, that would be dangerous; if I do happen to do it twice, I have to do it once more to avoid the danger; and for fear of inadvertently stopping with twice, it is best always to do everything three times and be safe." That is the report of a naturally timorous young man. We all know the somewhat similar experience of being "nervous" or "jumpy" after escaping from some danger; the organic fear state, once aroused, stays awhile, and predisposes us to make avoiding reactions. In the same way, let a man be "all riled up" by something that has happened at the office, and he is likely to take it out on his wife or children. Slightly irritating performances of the children, that would usually not arouse an angry reaction, do so this evening, because that thing at the office has "made him so cross."

In the same way, let a group of people get into a very mirthful state from hearing a string of good jokes, and a hearty laugh may be aroused by a feeble effort that at other times would have fallen flat.

In such cases, the organic state, once set up in response to a certain stimulus, persists after the reaction to that stimulus is finished and predisposes the individual to make the same sort of reaction to other stimuli.

Anger, fear, lust, the comfortable state appropriate to digestion, grief (the state of the weeping child), mirth or amusement, disgust, curiosity, the "tender emotion" (felt most strongly by a mother towards her baby), and probably a few others, are "primary emotions". They occur, that is to say, by virtue of the native constitution, and do not have to be learned or acquired through experience. They are native states of mind; or, as modes of behavior, they are like instincts in being native behavior.

One distinction between emotional and instinctive behavior is that the emotion consists of internal responses, while the instinct is directed outwards or at least involves action on external objects. Another distinction is that the emotional response is something in the nature of a preparatory reaction, while the instinct is directed towards the end-reaction.

The close connection of emotion and instinct is fully as important to notice as the distinction between them. Several of the primary emotions are attached to specific instincts: thus, the emotion of fear goes with the instinct to escape from danger, the emotion of anger goes with the fighting instinct, the emotion of lust with the mating instinct, tender emotion with the maternal instinct, curiosity with the exploring instinct. Where we find emotion, we find also a tendency to action that leads to some end-result.

It has been suggested, accordingly, that each primary emotion is simply the "affective" phase of an instinct, and that every instinct has its own peculiar emotion. This is a very attractive idea, but up to the present it has not been worked out very satisfactorily. Some instincts, such as that for walking, seem to have no specific emotion attached to them. Others, like anger and fear, resemble each other very {135} closely as organic states, though differing as impulses. The really distinct emotions (not impulses) are much fewer than the instincts.

The most important relationship between instinct and emotion is what we have seen in the cases of anger and a few others, where the emotion represents bodily readiness for the instinctive action.

We have been confining our attention in this chapter to the primary emotions. The probability is that the higher emotions, esthetic, social, religious, are derived from the primary in the course of the individual's experience.

Primary emotions become refined, first by modifications of the motor response, by which socially acceptable reactions are substituted for the primitive crying, screaming, biting and scratching, guffawing, dancing up and down in excitement, etc.; second by new attachments on the side of the stimulus, such that the emotion is no longer called out by the original simple type of situation (it takes a more serious danger, a subtler bit of humor, to arouse the emotional response); and third by combination of one emotion with another. An example of compound emotion is the blend of tenderness and amusement awakened in the friendly adult by the actions of a little child. Hate is perhaps a compound of anger and fear, and pity a compound of grief and tenderness. There are dozens of names of emotions in the language--resentment, reverence, gratitude, disappointment, etc.--which probably stand for compound emotions rather than for primary emotions, but the derivation of each one of them from the primary emotions is a difficult task. The emotional life cannot be kept apart from the life of ideas, for the individual is a good deal of a unit.

1. Outline the chapter.

2. Make a list of 20 words denoting various emotional states.

3. Trace the expressive facial movement of pouting back to its probable origin in the history of the individual.

4. What internal nerves are concerned with digestion? With fear?

5. Show by diagrams the differences between (a) the common-sense theory of the emotions, (b) the James-Lange theory, (c) the James-Lange theory modified to take full account of the reaction-tendency.

6. Make a list of objections to the James-Lange theory, and scrutinize each objection carefully, to see

(a) whether it really attacks the theory, or misconceives it.
(b) whether it carries much or little weight.

7. Act out several emotions, (a) by facial expression alone, and (b) by facial expression plus gestures, and let another person guess what emotion you are trying to express. How many times does he guess right under (a), and under (b)?

8. Discuss the relative practical importance of emotion and impulse.

For the James-Lange theory, see the chapter on the emotions by William James, in his Principles of Psychology, 1890, Vol. II, pp. 442-485.

For Darwin's views on expressive movements, see his Expression of the Emotions in Man and Animals, first published in 1872.

For pictures of facial expression in various emotions, see Antoinette Feleky, in the Psychological Review for 1914, Vol. 21, pp. 33-41.

For the internal physiological changes, see Walter B. Cannon's Bodily Changes in Pain, Hunger, Fear and Rage, 1915.

For an interesting and important view of the close connection between emotion and instinct, see William McDougall's Introduction to Social Psychology, Chapter II.

It would be a great mistake to suppose that instinct was important only in animal or child psychology, because the human adult governed his conduct entirely by reason and calculation of consequences. Man does not outgrow instinct, any more than he outgrows emotion. He does not outgrow the native reaction-tendencies. These primitive motives remain in force, modified and combined in various ways, but not eliminated nor even relegated to an unimportant place. Even in his most intelligent actions, the adult is animated by motives that are either plain instincts or else derivatives of the instincts. According to some of the leaders in psychology, he has no other motives than these; according to this book, as will be set forth later, there are "native likes and dislikes" (for color, tone, number, persons, etc.) to be placed beside the instincts as primary motives; but, according to either view, the instincts are extraordinarily important in the study of motivation, and a complete and accurate list of them is very much to be desired. Life is a great masquerade of the instincts, and it is not only entertaining to unmask them, but illuminating as well.

A complete account of an instinct would cover the following points: the stimulus that naturally arouses it, the end-result at which it is aimed, the preparatory reactions that occur, external and internal; and also, from the {138} introspective side, the conscious impulse, the peculiar emotional state (if any), and the special sort of satisfaction that comes when the end-result is reached. Further, we should know what modifications or disguises the instinct takes on in the course of experience--what new stimuli acquire the power of arousing it, what learned reactions are substituted for the native preparatory and final reactions, and what combinations occur between the instinct in question and other reaction-tendencies.

Besides all this, it would be very desirable to present convincing evidence that each instinct listed is a genuine instinct, a part of the native equipment, and not something built up by experience and training. It is rather absurd, the free and easy way in which an instinct is often assumed, simply to fit behavior which needs to be explained--a money getting instinct, for example, or a teacher-hating instinct. Since money and teachers do not exist in a state of nature, there can be no instincts specifically related to them; and it is incumbent on the psychologist to show how such acquired tendencies are derived from the native tendencies.

The full program outlined above being much too extensive to follow out completely in this chapter, we shall only mention a few salient points under each instinct. We shall try to point out the primitive behavior of the child, that reveals the instinct at its lowest terms, and give some hint also of its importance in adult behavior.

Of all the instincts, two groups or classes stand out from the rest: the responses to organic needs, and the responses to other persons. The first class includes eating, avoiding injury, and many others; the second class includes the herd instinct, the mating instinct and the parental instinct, these three and perhaps no others.

These two groups out, the rest are rather a miscellaneous collection, including the "random" or playful activity of young children, locomotion, vocalization, laughter, curiosity, rivalry and fighting. They might be named the "non-specific instincts", because the stimulus for each is not easy to specify, being sometimes another person, so that this group has great social importance, but sometimes being impersonal. This third class might also be called the "play instincts", since they are less essential than the other classes for maintaining the individual life or for propagating the species; and are, we may say, less concerned with the struggle for existence than with the joy of living.

Our classification then has three heads:

(1) Responses to organic needs,
(2) Responses to other persons,
(3) Play responses.

Something has already been said [Footnote: See above, pp. 79-81, 112.] of the manner in which an organic state, such as lack of water, acting on internal sensory nerves, arouses in the nerve centers an adjustment towards an end-result, and how, if the end-result cannot immediately be attained, preparatory reactions occur, the preparatory reactions being in some cases closely attached, by nature, to the main tendency, and in other cases only loosely attached so that the tendency leads to trial and error behavior. The reactions that are nearest to the end-result are likely to be closely attached to the main tendency, while those that are farther from the end-result are loosely attached. Thus, in the case of thirst, the drinking movement itself is about all, in man, that is purely instinctive, {140} and the way of getting water to the mouth, or the mouth to the water, is a matter for trial and error, and only becomes fixed as the result of a process of learning. Still less can we mention any specific water-seeking reactions, in the human being, that are provided by the native constitution. Yet the whole business of relieving thirst is directed by the native thirst-impulse, and to that extent is an instinctive activity. And shall we say that so simple a matter as meeting this organic need is below the dignity of psychology, and can have little influence on the behavior of mankind? Hardly, when we think of the rôle played by springs, wells and drinking places of all kinds in the life of the race, of aqueducts and reservoirs, of all the beverages that have been invented, and of all the people whose job it has been to provide and dispense them. To be sure, any beverage with a taste, or a "kick", is not simply a thirst-reliever, but makes some additional appeal, good or bad; but all this simply illustrates the way instincts become modified, by combination with other instincts, and by the learning and fixing of various preparatory reactions that were not provided, ready-made, in the native constitution. The drinking instinct, or thirst impulse, is a very good example of this whole class of organic instincts.

Here again, the reactions nearest to the end-result (food in the stomach) are provided by nature. Sucking and swallowing appear at birth, chewing with the appearance of the teeth; and the infant also makes what seem to be instinctive movements of seeking the breast, as well as movements of rejecting it when satiated and of spitting out bad-tasting food. Putting food (and other things) into the mouth by the hands seems almost instinctive, and yet it has to be fixed by trial and error. Anything like definite food-seeking behavior, amounting to a hunting instinct, scarcely gets a chance to show itself in {141} the human child, because his food is provided for him. In many animals, hunting is a highly organized instinct; thus, crouching, stalking, springing and teasing the mouse when caught, have been proved to be instinctive in young cats. Some animals have definite food-storing instincts also, and possibly food-storing shows the acquisitive or collecting tendency in its lowest terms. Possibly, that is to say, hunting and collecting, as well as disgust (primarily of bad-tasting or bad-smelling food), are originally parts of the food-getting behavior, having the general character of reactions preparatory to eating. However this may be, we can easily see the great importance of the hunger motive in human life; we have only to consider the matter in the same way as we considered thirst just above.

Breathing, obviously a native reaction, is ordinarily automatic and needs no preparatory reactions, simply because air is so easy to get. But let breathing be difficult, for any reason, and the stifling sensation is as impulsive as hunger or thirst. The stuffy air in a cave or in a hole under a haymow will lead a child to frantic escape. Possibly the delight in being out of doors which shows itself in young children, and is not lost in adults, represents a sort of air-hunting instinct, parallel to food-hunting. Closely connected with breathing is the function of circulation, automatic for the most part; and we should mention also the organic needs of waste-elimination, which give impulsive sensations akin to hunger and thirst, and lead to more or less organized instinctive reactions.

The warm-blooded animals, birds and mammals, have the remarkable power of keeping the body temperature constant (at 98-99 degrees Fahrenheit, in man, somewhat higher in birds), in spite of great variations in the external temperature to which the body is exposed, and in spite of great variations in the {142} amount of heat generated in the body by muscular exercise. Sweating and flushing of the skin are reactions to heat, and prevent the body temperature from rising; paling of the skin, shivering and general muscular activity are responses to cold and prevent the body temperature from falling. Shrinking from great heat or cold are also instinctive, while seeking shelter from the heat or cold is a preparatory reaction that is not definitely organized in the native constitution of man, but gives rise to a great variety of learned reactions, and plays a considerable part in life.

The "flexion reflex" of the arm or leg, which pulls it away from a pinch, prick or burn, is the type of a host of defensive reactions--winking, scratching, rubbing the skin, coughing, sneezing, clearing the throat, wincing, limping, squirming, changing from an uncomfortable position--most or all of them instinctive reactions. With each goes some sort of irritating sensation, as pain, itching, tickling, discomfort; and a conscious impulse to get rid of the irritation is often present. When the simpler avoiding reactions do not remove the irritating stimulus, they are repeated more vigorously or give way to some bigger reaction tending towards the same result. The climax of the avoiding reactions is flight or running away. Akin to flight are cowering, shrinking, dodging or warding off a blow, huddling into the smallest possible space, getting under cover, clinging to another person; and most or all of these, too, are instinctive reactions. With flight and the other larger danger-avoiding reactions there is often present, along with the impulse to escape, the stirred up organic and conscious state of fear.

The stimuli that arouse movements of escape are of two sorts: those that directly cause some irritating sensation, and those that are simply signs of danger. The smaller avoiding reactions--flexion reflex, coughing, etc.--are {143} aroused by stimuli that are directly painful or irritating; whereas flight, cowering, etc., are mostly responses to mere signs of danger. A "sign of danger" is usually seen or heard at some distance, not felt directly on or in the body. Now, while avoiding reactions are attached by nature to the irritating stimuli, it is not at all clear whether escape movements are natively attached to any signs of danger, or, if they are, to what particular signs of danger they are attached. What visual or auditory stimuli, that are not directly irritating, will arouse escape movements in a young child? For the youngest children, no such stimuli have been found. You can easily get avoiding reactions from a little baby by producing pain or discomfort; you can get the clinging response by letting the child slip when he is being held in your arms; and you get crying and shrinking on application of a loud, grating noise, such a noise as is irritating in itself without regard to what it may signify. But you cannot get any shrinking from stimuli that are not directly irritating.

For example, you get no sign of fear from a little child on suddenly confronting him with a furry animal. With older children, you do get shrinking from animals, but it is impossible to be sure that the older child has not learned to be afraid of them. I have seen a child of two years simply laugh when a large, strange dog came bounding towards him in the park; but a year later he would shrink from a strange dog. Whence the change? There are two possibilities: either a native connection between this stimulus and the shrinking response only reached its maturity when the child was about three years old--and there is nothing improbable in this--or else the child, though actually never bitten by a dog, had been warned against dogs by his elders or had observed his elders shrinking from dogs. Children do pick up fears in this way; for example, children who are {144} naturally not the least bit afraid of thunder and lightning may acquire a fear of them from adults who show fear during a thunderstorm.

On the whole, the danger-avoiding reactions are probably not linked by nature to any special signs of danger. While the emotion of fear, the escape impulse, and many of the escape movements are native, the attachment of these responses to specific stimuli--aside from directly irritating stimuli--is acquired. Fear we do not learn, but we learn what to fear.

We have the best of evidence that this is a native reaction, since the baby cries from birth on. He cries from hunger, from cold, from discomfort, from pain, and, perhaps most of all, as he gets a little older, from being thwarted in anything he has set out to do. This last stimulus gives the "cry of anger", which baby specialists tell us sounds differently from the cries of pain and of hunger. Still, there is so much in common to the different ways of crying that we may reasonably suppose there is some impulse, and perhaps some emotional state, common to all of them. The common emotion cannot be anger, or hunger, or discomfort or pain. To name it grief or sorrow would fit the crying of adults better than that of little children. The best guess is that the emotional state in crying is the feeling of helplessness. The cry of anger is the cry of helpless anger; anger that is not helpless expresses itself in some other way than crying; and the same is true of hunger, pain and discomfort. Crying is the reaction appropriate to a condition where the individual cannot help himself--where he wants something but is powerless to get it. The helpless baby sets up a wail that brings some one to his assistance; that is the utility of crying, though the baby, at first, does not have this result in view, but simply cries because he is hungry and helpless, uncomfortable and {145} helpless, thwarted and helpless. The child cries less as he grows older, because he learns more and more to help himself.

With the vocal element of crying goes movement of the arms and legs, which also has utility in attracting attention; but what may be the utility of shedding copious tears remains a mystery, in spite of several ingenious hypotheses that have been advanced to explain it.

That fatigue, primarily an organic state, gives rise to fatigue sensations and to a neural adjustment for rest--a disinclination to work any longer--and that drowsiness is a somewhat different organic state that gives an inclination to sleep--all this has been sufficiently set forth in earlier chapters. Going to sleep is a definite act, an instinctive response to the drowsy state. In the way of preparatory reactions, we find many interesting performances in birds and mammals, such as the curling up of the dog or cat to sleep, the roosting of hens, the standing on one leg of some birds; and we see characteristic positions adopted by human beings, but do not know how far these are instinctive and how far acquired. Closing the eyes is undoubtedly a native preparatory reaction for sleep.

Like the other responses to organic needs, rest and sleep figure pretty largely in the behavior of the adult, as in finding or providing a good place to sleep. Certainly if fatigue and sleep could be eliminated, as some over-enthusiastic workers have pretended to hope, life would be radically changed.

We are next to look for action and emotion aroused by persons, specifically--not by persons and things alike. Fear can be aroused by persons, but also by things. In a social animal, such as man, almost any instinct comes to have {146} social bearings. Eating and drinking become social matters, and all the organic instincts figure in the placing and making of a home. Home is a place of shelter against heat and cold, it is a refuge from danger, it is where you eat and where you sleep. It meets all these organic needs but--it is specially where "your people" are.

Home is a place where unlike persons foregather, male with female, adults with children, and thus it symbolizes the "family instincts", mating and child-care, which are responses to persons unlike in sex or age. But home also illustrates very well the herd instinct, which is a response to like persons, "birds of a feather flocking together". It is not the single home that illustrates this, but the almost universal grouping of homes into villages or cities.

It might be argued that a city or village was the result of economic causes, or, in the olden days, a means of protection against enemies, and not a direct satisfaction of any instinct in man to flock together. But often a family who know perfectly well that their economic advantage demands their remaining where they are, in some isolated country spot, will pull up stakes and accept an inferior economic status in the city, just because the country is too lonely for them. One woman, typical of a great many, declined to work in a comfortable and beautiful place in the country, because "she didn't want to see trees and rocks, she wanted to see people". There is no doubt that man belongs by nature with the deer or wolf rather than with solitary animals such as the lion. He is a gregarious creature.

The gregarious instinct does not by any manner of means account for all of man's social behavior. It brings men together and so gives a chance for social doings, but these doings are learned, not provided ready-made by the instinct. About all we can lay to the herd instinct is uneasiness when {147} alone, seeking company, remaining in company, and following the rest as they move from place to place. The feeling of loneliness or lonesomeness goes with being alone, and a feeling of satisfaction goes with being in company.

Probably there is one more fact that belongs under the herd instinct. A child is lonely even in company, unless he is allowed to participate in what the others are doing. Sometimes you see an adult who is gregarious but not sociable, who insists on living in the city and wishes to see the people, but has little desire to talk to any one or to take part in any social activities; but he is the exception. As a rule, people wish not only to be together but to do something together. So much as this may be ascribed to the instinct, but no more. "Let's get together and do something"--that is as far as the gregarious instinct goes. What we shall do depends on other motives, and on learning as well as instinct.

Attraction towards the opposite sex is felt by a small number of children, by most young people beginning from 15 to 20 years of age, by a minority not till a few years later, and, by a small number, never at all. On account of the late maturing of this instinct, in man, instinctive behavior is here inextricably interwoven with what has been learned. A definite organic and emotional state, lust, goes with this instinct. Preparatory reactions, called "courtship", are very definitely organized in many animals, and often quite elaborate. In man, courtship is elaborate enough, but not definitely organized as an instinct; and yet it follows much the same line as we observe in animal courtship. It begins with admiring attention to one of the opposite sex, followed by efforts to attract that one's attention by "display" (strutting, decoration of the person, demonstrating one's prowess, especially in opposition to rivals). Then the male takes an aggressive attitude, the {148} female a coy attitude; the male woos, the female hangs back, and something analogous to pursuit and capture takes place, except that the capture may be heartily accepted by both parties.

The "survival value" of this instinct is absolute; without it the race would not long survive. But it has "play value" also, it contributes to the joy of living as well as to the struggle for survival. There is much in social intercourse, and in literature and art, that is motivated by the sex impulse. Some would-be psychologists have been so much impressed by the wide ramifications of the sex motive in human conduct that they have attributed to it all play, all enjoyment, all the softer and lighter side of life, even all the spiritual side of life. One need only run over the long list of instincts, especially those that still remain to be mentioned, in order to be convinced of the one-sidedness of such a view. On the other hand, some moralists have been so deeply impressed by the difficulties that arise out of the sex motive, as to consider it essentially gross and bad; but this is as false as the other view. The sex impulse is like a strong but skittish horse that is capable of doing excellent work but requires a strong hand at the reins and a clear head behind. It is a horse that does not always pull well in a team; yet it is capable of fine teamwork. It can be harnessed up with other tendencies, and when so combined contribute some of its motive force to quite a variety of human activities.

In many species of animals, though not by any means in all, one or both of the parents stays by the young till some degree of maturity is reached. In some kinds of fish, it is the male that cares for the young; in birds it is often both parents. In mammals it is always the mother. Instinctively, the mammalian mother feeds, warms and defends her young. Just as {149} instinctively, the human mother does the same. This instinctive reaction to the little baby is attended by a strong emotion, called, for want of a better name, the "tender emotion".

The strongest stimulus to arouse this instinct is the little, helpless baby. The older child has to take second place with the mother, so soon as there is a little baby there. After a child is weaned, and after he is able to get about and do for himself to quite an extent, he has less hold on the maternal instinct. The love and care that he may still get is less a simple matter of instinct.

Though the little baby is the strongest stimulus to this instinct, older children and even adults, provided they are like the baby in being winsome and helpless in some way, may arouse the same sort of feeling and behavior, tender feeling and protective behavior. A pet animal may arouse the same tendency, and a "darling little calf" or a "cute little baby elephant" may awaken something of the same thrill. Even a young plant may be tended with a devotion akin to the maternal. The fact seems to be here, as with other instincts, that objects similar to the natural stimulus may arouse the same impulse and emotion. Love between the sexes is often a compound of sex attraction and the mothering instinct; and it is interesting to watch a happily mated couple each mothering the other.

But is it allowable to speak of this instinct as present in the male human being, or in any one not a mother? Undoubtedly the woman who has recently become a mother is most susceptible to the appeal of a little baby, but the response of other women and of girls to a baby is so spontaneous that we cannot but call it instinctive. Men and boys have no special desire to feed or cuddle a little baby, and are quite contented to leave the care of the baby mostly to the "women folks". But they do object strongly to seeing the {150} baby hurt or ill-treated, and will respond by protecting it. Also, they like to watch the baby act, and like to help it along in its efforts to do things. This may be instinctive in the man; at least it reminds us of the behavior of a mother cat or dog or horse, when she plays with her young and stimulates them to action. When the mother cat brings a live mouse for her half-grown kittens to practise on, she is acting instinctively, and probably a man is obeying the same instinct when he brings the baby a toy and derives pleasure from watching the baby's attempts to use it.

The parental instinct would thus seem to lie at the root of education, considered as an enterprise of adults directed towards getting the young to acquire the behavior of the race; and it also lies at the root of charity, the desire to protect the helpless.

Is there any instinct in the child answering to the parental, any "filial" instinct, as it were? Psychologists have usually answered no, but possibly they have been misled by the word "filial" and looked in the wrong direction. The parental instinct is an instinct to give, and the answering instinct would be one to take--not to give in return. It is probably not instinctive for the child to do for the parent, but is it not instinctive for the child to take from the parent, and to look to the parent for what he wants? It is not exactly "unnatural conduct" in a child to impose on his mother, as it would be in the mother to impose on the child; but would it not be unnatural in a child to take an unreceptive and distrustful attitude towards his mother?

Filial love is different. It is not purely instinctive, but depends on intelligence. It is only possible if the child has the intelligence to see the parent as something besides a parent--as some one needing care and protection--and if the child himself takes a parental attitude towards the parent. But that is a grown-up attitude, seldom taken by {151} young children. It is not the infantile instinct, which, if there is such an instinct, is the spring of trustful, docile, dependent, childlike and childish behavior.

Any instinct has "play value", but some have also "survival value" and so are serious affairs. Survival value characterizes the instincts we have already listed, both the responses to organic needs and the responses to other people. But there are other instincts with less of survival value, but no less of play value, and these we call the play instincts, without attaching any great importance to the name or even to the classification.

The kicking and throwing the arms about that we see in a well-rested baby is evidently satisfying on its own account. It leads to no result of consequence, except indeed that the exercise is good for the child's muscles and nerves. The movements, taken singly, are not uncoordinated by any means, but they accomplish no definite result, produce no definite change in external objects, and so seem random and aimless to adult eyes. It is impossible to specify the stimulus for any given movement, though probably stimuli from the interior of the body first arouse these responses. They are most apt to occur during the organic state of "euphoria", and tend to disappear during fatigue.

There is a counter-tendency to this tendency towards general activity, and that is inertia, the tendency towards inactivity or economy of effort. Most pronounced in fatigue, this also appears in lassitude and inert states that cannot be called fatigue because not brought on by excessive activity. After sleep, many people are inert, and require a certain amount of activity to "warm up" to the active condition. As the child grows older, the {152} "economy of effort" motive becomes stronger, and the random activity motive weaker, so that the adult is less playful and less responsive to slight stimuli. He has to have some definite goal to get up his energy, whereas the child is active by preference and just for the sake of activity.

During the first year or so of the child's life, his playful activity takes shape in several ways. First, out of the great variety of the random movements certain ones are picked out and fixed. This is the way with putting the hand into the mouth or drumming on the floor with the heels, and these instances illustrate the important fact that many learned acts develop out of the child's random activity. Without play activity there would be little work or accomplishment of the distinctively human type. Second, certain specific movements, those of locomotion and vocalization, appear with the ripening of the child's native equipment, and take an important place in his play. Third, his play comes to consist more and more of responses to external objects, instead of to internal stimuli as at first. The playful responses to external objects fall into two classes, according as they manipulate objects or simply examine them.

We have, then, a small group of instincts that is very closely related to the fundamental instinct of random activity.

Evidence has already been presented [Footnote: See p. 95.] indicating that walking is instinctive and not learned, so that the human species is no exception to the rule that every species has its instinctive mode of locomotion. Simpler performances which enter into the very complex movement of walking make their appearance separately in the infant before being combined into walking proper. Holding up the head, sitting up, kicking with an alternate motion of the {153} two legs, and creeping, ordinarily precede walking and lead up to it.

What is the natural stimulus to locomotion? It is as difficult to say as it is to specify the stimulus in other forms of playful activity. From the fact that blind children are usually delayed in beginning to walk, we judge that the sense of sight furnishes some of the most effective stimuli to this response. Often the impulse attending locomotion is the impulse to approach some seen object, but probably some satisfaction is derived simply from the free movement itself. There certainly is no special emotion going with locomotion. Locomotion has, of course, plenty of "survival value", and might have been included among the organic instincts.

Some of the other varieties of human locomotion, such as running and jumping, are probably native. Others, like hopping and skipping, are probably learned. As to climbing, there is some evolutionary reason for suspecting that an instinctive tendency in this direction might persist in the human species, and certainly children show a great propensity for it; while the acrobatic ability displayed by those adults whose business leads them to continue climbing is so great as to raise the question whether the ordinary citizen is right when he thinks of man as essentially a land-living or surface-living animal. As to swimming, the theory is sometimes advanced that this too is a natural form of locomotion for man, and that, consequently, any one thrown into deep water will swim by instinct. Experiments of this sort result badly, the victim clutching frantically at any support, and sometimes dragging down with him the theorist who is administering this drastic sort of education. In short, the instinctive response of a man to being in deep water is the same as in other cases of sudden withdrawal of solid support; it consists in clinging and is attended by the emotion of fear.

Crying at birth proves voice-production to be a native response, but we are more interested just here in the playful cooing and babbling that appear when the child is a few weeks or months old. This cheerful vocalization is also instinctive, in all probability, since the baby makes it before he shows any signs of responding imitatively to the voices of other people. It seems to be one form of the random activity that goes with euphoria. The child derives satisfaction not so much from the muscular activity of vocalization as from the sounds that he produces, so that deaf children, who begin to babble much like other children, lag behind them as the months go by, from not deriving this auditory satisfaction from the vocal activity. Though whistling, blowing a horn, shaking a rattle and beating a drum are not native responses, it is clear that the child naturally enjoys producing sounds of various sorts.

The baby's cheerful babbling is the instinctive basis on which his speech later develops through a process of learning.

While the first random activity of the baby has nothing to do with external objects, but simply consists of free movements of the arms and legs, after a time these give place to manipulation of objects. The baby turns things about, pulls and pushes them, drops them, throws them, pounds with them. Thus he acquires skill in handling things and also learns how things behave. This form of playful activity contains the germ of constructiveness and of inventiveness, and will come into view again under the head of "imagination."

Along with manipulation goes the examination of objects by the hand, the mouth, the eyes and ears, and all the senses. Listening to a sudden noise is one of the first exploratory reactions. Following a moving light with the eyes, fixing the eyes upon a {155} bright object, and exploring an object visually by looking successively at different parts of it, appear in the first few months of the baby's life. Exploration by the hands and by the mouth appear early. Sniffing an odor is a similar exploratory response. When the child is able to walk, his walking is dominated largely by the exploring tendency; he approaches what arouses his curiosity, and embarks on little expeditions of exploration. Similar behavior is seen in animals and is without doubt instinctive. With the acquisition of language, the child's exploration largely takes the form of asking questions.

The stimulus that arouses this sort of behavior is something new and unfamiliar, or at least relatively so. When an object has been thoroughly examined, it is dropped for something else. It is when the cat has just been brought into a strange house that she rummages all over it from garret to cellar. A familiar object is "taken for granted", and arouses little exploratory response.

Quite a group of conscious impulses and emotions goes with exploratory behavior. The feeling or impulse of curiosity is something that everybody knows; like other impulses, it is most strongly felt when the end in view cannot be immediately reached. When you are prevented by considerations of propriety or politeness from satisfying your curiosity, then it is that curiosity is most "gnawing". A very definite emotion that occurs on encountering something extremely novel and strange is what we know as "surprise", and somewhat akin to this is "wonder".

Exploration, though fundamentally a form of playful activity, has great practical value in making the child acquainted with the world. It contains the germ of seeking for knowledge. We shall have to recur to this instinct more than once, under the head of "attention" and again under "reasoning".

Manipulation and exploration go hand in hand and might be considered as one tendency rather than two. The child wishes to get hold of an object, that arouses his curiosity, and he examines it while handling it. You cannot properly get acquainted with an object by simply looking at it, you need to manipulate it and make it perform; and you get little satisfaction from manipulating an object unless you can watch how it behaves.

Just as playful activity in general is limited by the counter tendencies of fatigue and inertia, so the tendency to explore and handle the unfamiliar is held in check by counter tendencies which we may call "caution" and "contentment".

Watch an animal in the presence of a strange object. He looks at it, sniffs, and approaches it in a hesitating manner; suddenly he runs away for a short distance, then faces about and approaches again. You can see that he is almost evenly balanced between two contrary tendencies, one of which is curiosity, while the other is much like fear. It is not full-fledged fear, not so much a tendency to escape as an alertness to be ready to escape.

Watch a child just introduced to a strange person or an odd-looking toy. The child seems fascinated, and can scarcely take his eyes from the novel object, but at the same time he "feels strange", and cannot commit himself heartily to getting acquainted. There is quite a dose of caution in the child's make-up--more in some children than in others, to be sure--with the result that the child's curiosity gets him into much less trouble than might be expected. Whether caution is simply to be identified with fear or is a somewhat different native tendency, it is certainly a check upon curiosity.

By "contentment" we mean here a liking for the familiar, {157} which offsets to some extent the fascination of the novel. If you are perfectly contented, you are not inclined to go out exploring; and when you have had your fill of the new and strange, you like to get back to familiar surroundings, where you can rest in content. Just as playful behavior of all sorts decreases with increasing age, so the love for exploring decreases, and the elderly person clings to the familiar. But even children may insist in occupying their own particular chair, on eating from a particular plate, and on being sung to sleep always with the same old song. They are "little creatures of habit", not only in the sense that they readily form habits, but in the sense that they find satisfaction in familiar ways and things. Here we see the germ of a "conservative" tendency in human nature, which balances, to a greater or less extent, and may decidedly overbalance, the "radical" tendency of exploration.

We certainly must not omit this from our list of instincts, for, though it does not appear till some time after birth, it has all the earmarks of an instinctive response. If it were a learned movement, it could be made at will, whereas, as a matter of fact, few people are able to produce a convincing laugh except when genuinely amused, which means when the instinctive tendency to laugh is aroused by some appropriate stimulus. The emotion that goes with laughing may be called mirth or amusement, and it is a strongly impulsive state of mind, the impulse being simply to laugh, with no further end in view.

The most difficult question about laughter is to tell in general psychological terms what is the stimulus that arouses it. We have several ingenious theories of humor, which purport to tell; but they are based on adult humor, and we have as yet no comprehensive genetic study of laughter, tracing it up from its beginnings in the child. Laughing certainly belongs with the play instincts, and possibly the {158} stimulus is no more definite, at first, than that which arouses other playful activity. The baby seems to smile, at first, just from good spirits (euphoria). The stimuli that, a little later, arouse a burst of laughter have an element of what we may call "expected surprise" (as dropping a rattle and exploding with laughter when it bangs on the floor, and keeping this up time after time), and this element can still be detected in various forms of joke that are effective mirth-provokers in the adult. But why the child should laugh when tickled, at the same time trying to escape, is a poser. Many students of humor have subscribed to the theory that what makes us laugh is a sudden sense of our own superiority, thus attaching laughter to the self-assertive instinct, soon to be discussed. The laugh of victory, the laugh of defiance, the laugh of mockery, the sly or malicious laugh, support this theory, but can it be stretched to cover the laugh of good humor, the tickle laugh, or the baby's laugh in general? That seems very doubtful, and we must admit that we do not know the essential element in a laughter stimulus. One thing is fairly certain: that, while laughing is a native response, we learn what to laugh at, for the most part, just as we learn what to fear.

Hold the new-born infant's arms tightly against its sides, and you witness a very peculiar reaction: the body stiffens, the breath may be held till the face is "red with anger"; the child begins to cry and then to scream; the legs are moved up and down, and the arms, if they can be got free, make striking or slashing movements. In somewhat older children, any sort of restraint or interference with free movement may give a similar picture, except that the motor response is more efficient, consisting in struggling, striking, kicking, and biting. It is not so much pain as interference that gives this reaction. You get it if you take away a toy the child is playing with, or if you forbid {159} the child to do something he is bent on doing. In animals, the fighting response is made to restraint, to being attacked, or to being interfered with in the course of feeding, or mating, or in the instinctive care of the young. The mother lioness, or dog or cat or hen, is proverbially dangerous; any interference with the young leads to an attack by the mother. The human mother is no exception to this rule. In human adults, the tendency to fight is awakened by any interference with one's enterprises, by being insulted or got the better of or in any way set down in one's self-esteem.

In general, the stimulus to fighting is restraint or interference. Let any reaction-tendency be first aroused and then interfered with, and pugnacious behavior is the instinctive result.

The stimulus may be an inanimate object. You may see a child kick the door viciously when unable to open it; and grown-ups will sometimes tear, break or throw down angrily any article which they cannot make do as they wish. A bad workman quarrels with his tools. Undoubtedly, however, interference from other persons is the most effective stimulus.

The impulse so aroused is directed primarily towards getting rid of the restraint or interference, but also towards inflicting damage on the opponent; and with this impulse often goes the stirred-up organic and emotional state of anger. As brought out in the chapter on emotion, the organic state in anger is nearly or quite identical with that in fear of the active type; and the two states of the individual differ in respect to impulse rather than in respect to emotion. In fear, the impulse is to get away from the adversary, in anger to get at him. The emotion of anger is not always aroused in fighting, for sometimes there is a cold-blooded desire to damage the adversary.

The motor response, instinctively consisting of struggling, kicking, etc., as already described, becomes modified {160} by learning, and may take the form of scientific fistwork, or the form of angry talk, favored by adults. Or, the adversary may be damaged in his business, in his possessions, in his reputation, or in other indirect ways. The fighting spirit, the most stimulating of the emotions, gives energy to many human enterprises, good as well as bad. The successful reformer must needs be something of a fighter.

Thus far we have said nothing to justify our placing fighting here among the play instincts. Fighting against attack has survival value, fighting to protect the young has survival value, and, in general, the defensive sort of fighting has survival value, even though interference with play activity is just as apt to give this response as interference with more serious activities.

But there is more than this to the fighting instinct. The stimulus of interference is not always required. Consider dogs. The mere presence of another dog is often enough to start a scrap, and a good fighting dog will sally forth in search of a fight, and return considerably mauled up, which does not improve his chances for survival, to say the least. Fighting of this aggressive sort is a luxury rather than a necessity. It has play value rather than survival value. There can be no manner of doubt that pugnacious individuals, dogs or men, get more solid satisfaction from a good fight than from any other amusement. You see people "itching for a fight", and actually "trying to pick a quarrel", by provoking some other person who is strictly minding his own business and not interfering in the least. A battle of words usually starts in some such way, with no real reason, and a battle of words often develops into a battle of tooth and nail. Two women were brought before the judge for fighting, and the judge asked Mrs. Smith to tell how it started. "Well, it was this way, your honor. I met Mrs. Brown carrying a basket on her arm, and I says {161} to her, 'What have ye got in that basket?' says I. 'Eggs', says she. 'No!' says I. 'Yes!' says she. 'Ye lie!' says I. 'Ye lie!' says she. And a 'Whoop!' says I, and a 'Whoop!' says she; and that's the way it began, sir."

We have, then, to recognize aggressive fighting, in addition to defensive, and the aggressive sort certainly belongs among the play instincts.

The instincts that by acting counter to fighting hold it in check are several: laughter--a good laugh together allays hostility; or the parental instinct--a parent will stand treatment from his child that he would quickly resent from any one else; or self-assertion--"Too proud to fight!" But the most direct checks are afforded by inertia--"What's the use?"--and especially by fear and caution.

Fighting, both defensive and aggressive, has so close a connection with the more generalized self-assertive tendency that it might be included under that instinct. It may be regarded as a special form of self-assertive behavior, often complicated with the emotion of anger.

What then is this wonderful instinct of self-assertion, to which fighting and much of laughing are subordinate? "Assertiveness", "masterfulness", and the "mastery impulse" are alternative names. Of all the native tendencies, this is the one most frequently aroused, since there is scarcely a moment of waking (or dreaming) life when it is not more or less in action. It is so much a matter of course that we do not notice it in ourselves, and often not in other persons; and even clever psychological observers have seemed entirely blind to it, and given it no place in their list of instincts.

Self-assertion, like fighting, has two forms, the defensive and the aggressive, and in either case it may be a response to either people or things. That gives four varieties of self-assertive behavior, which may be labeled as follows:

1. Defensive reaction to things, overcoming obstruction, putting through what has been undertaken--the success motive.

2. Defensive reaction to persons, resisting domination by them--the independence motive.

3. Aggressive reaction to things--seeking for power.

4. Aggressive reaction to persons--seeking to dominate. We will take these up in order, beginning with the most elemental.

1. Overcoming obstruction. The stimulus here is much the same as that which induces fighting, but the response is simpler, without anger and without the impulse to do damage. Take hold of a baby's foot and move it this way or that, and you will find that the muscles of the leg are offering resistance to this extraneous movement. Obstruct a movement that the baby is making, and additional force is put into the movement to overcome the obstruction. An adult behaves in a similar way. Let him be pushing a lawn-mower and encounter unexpected resistance from a stretch of tough grass; involuntarily he pushes harder and keeps on going--unless the obstruction is too great. Let him start to lift something that is heavier than he thinks; involuntarily he "strains" at the weight, which means that a complex instinctive response occurs, involving a rigid setting of the chest with holding of the breath, and increased muscular effort. This instinctive reaction may be powerful enough to cause rupture.

Other than purely physical resistance is overcome by other self-assertive responses. When the child's toy will not do what he wants it to do, he does not give up at once, but tries again and puts more effort into his manipulation. When, in school, he is learning to write, and finds difficulty in producing the desired marks, he bends over the desk, twists his foot round the leg of his chair, screws up his face, {163} and in other ways reveals the great effort he is making. An adult, engaged in some piece of mental work, and encountering a distraction, such as the sound of the phonograph downstairs, may, of course, give up and listen to the music, but, if he is very intent on what he is doing, he puts more energy into his work and overcomes the distraction. When he encounters a baffling problem of any sort, he does not like to give it up, even if it is as unimportant as a conundrum, but cudgels his brains for the solution. As a general proposition, and one of the most general propositions that psychology has to present, we may say that obstruction of any sort, encountered in carrying out any intention whatever, acts as a stimulus to the putting of additional energy into the action.

Anger is often aroused by obstruction, but anger does not develop a tenth as often, in the course of the day, as the plain overcoming reaction. The impulse is not to do damage, but to overcome the obstruction and do what we have set out to do. The emotional state might sometimes be called "determination", sometimes "zeal"; but the most elementary state belonging here is effort. The feeling of effort is, partly at least, a sensation complex resulting from stiffening the trunk and neck, knitting the brows, and other muscular strains that have practical utility in overcoming physical resistance and that are carried over to the overcoming of other sorts of resistance, where they have no obvious utility. Effort is a simpler emotion than anger, and occurs much more frequently.

2. Resisting domination by other persons. The child shows from an early age that he "has a will of his own", and "wants his own way" in opposition to the commands of other persons. There is an independent spirit in man that is native rather than acquired. The strength of this impulse differs, to be sure, in different individuals, some {164} children being more "contrary" and others more docile; but there probably never was a child without a good dose of disobedience in his make-up. In order to have a nice, obedient child, you have to "break" him like a colt, though you can use reason as well as force in breaking a child. This process of "breaking" gives a habit of obedience to certain persons and along certain lines; but, outside of these limits, the child's independence is still there and ready to be awakened by any attempt to dominate him. In youth, with the sense of power that comes from attaining adult stature and muscular strength, the independent spirit is strengthened, with the result that you seldom see a youth, or an adult, who can take orders without at least some inner opposition and resentment.

3. Seeking for power over things. The self-assertive response to things is not limited to overcoming the obstructions offered by things to the accomplishment of our purposes; but we derive so much positive satisfaction from overcoming obstruction and mastering things that we go out in search of things to master. The child's manipulation has an element of masterfulness in it, for he not only likes to see things perform, but he likes to be the one that makes them perform. If he has a horn, he is not satisfied till he can sound it himself. The man with his automobile is in the same case. When it balks, he is stimulated to overcome it; but when it runs smoothly for him, he has a sense of mastery and power that is highly gratifying. Chopping down a big tree, or moving a big rock with a crowbar, affords the same kind of gratification; and so does cutting with a sharp knife, or shooting with a good bow or gun, or operating any tool or machine that increases one's power. Quite apart from the utility of the result accomplished, any big achievement is a source of satisfaction to the one who has done it, because it gives play to aggressive self-assertion. Many {165} great achievements are motived as much by the zest for achievement as by calculation of the advantages to be secured.

4. Seeking to dominate other people. The individual not simply resists domination by other people, but he seeks to dominate them himself. Even the baby gives orders and demands obedience. Get a number of children together, and you will see more than one of them attempt to be the leader in their play. Some must necessarily be followers just now, but they will attempt to take the lead on another occasion. The "born leader" is perhaps one who has an exceptionally strong dose of masterfulness in his make-up, but he is, still more, one who has abilities, physical or mental, that give him the advantage in the universal struggle for leadership.

Besides giving orders and taking the lead, there are other ways in which the child finds satisfaction for his instinct to dominate. Showing off is one, bragging is one, doing all the talking is one; and, though in growing older and mixing with people the child becomes less naive in his manner of bragging and showing off, he continues even as an adult to reach the same end in more subtle ways. Going about to win applause or social recognition is a seeking for domination. Anything in which one can surpass another becomes a means of self-assertion. One may demonstrate his superiority in size, strength, beauty, skill, cleverness, virtue, good humor, coöperativeness, or even humility, and derive satisfaction from any such demonstration. The impulse to dominate assumes literally a thousand disguises, more rather than less.

Rivalry and emulation, sometimes accorded a separate place in a list of the instincts, seem well enough provided for under the general head of self-assertion. They belong on the social side of assertive behavior, i.e., they are responses to other people and aim at the domination of other {166} people or against being dominated by them. But the struggle for mastery, in rivalry, does not take the form of a direct personal encounter. Compare wrestling with a contest in throwing the hammer. In wrestling the mastery impulse finds a direct outlet in subduing the opponent, while in throwing the hammer each contestant tries to beat the other indirectly, by surpassing him in a certain performance. This you would call rivalry, but wrestling is scarcely rivalry, because the struggle for mastery is so direct. Rivalry may seek to demonstrate superiority in some performance, or to win the favor of some person or social group, as in the case of rivals in love.

When we speak of "emulation", we have in mind the sort of behavior observed when one child says, "See what I can do!" and the other counters with, "Pooh! I can do that, too". Or, the first child wins applause by some performance, and we then notice the second child attempting the same. It is a case of resisting the indirect domination of another, by not letting him surpass us in performance or in social recognition.

Thwarted self-assertion deserves special mention, as the basis for quite a number of queer emotional states. Shame, sulkiness, sullenness, peevishness, stubbornness, defiance, all go with wounded self-assertion under different conditions. Envy and jealousy belong here, too. Shyness and embarrassment go with self-assertion that is doubtful of winning recognition. Opposed to all these are self-confidence, the cheerful state of mind of one who seeks to master some person or thing and fully expects to do so, and elation, the joyful state of one who has mastered.

Is there any counter-tendency that limits self-assertion and holds it in check? Inertia and fear of course have this effect, but is there any specific instinct precisely opposite to self-assertion? A difficult question, not {167} yet to be answered with any assurance; but there is some evidence of a native submissive or yielding tendency. Two forms may be distinguished: yielding to obstruction, and yielding to the domination of other persons.

Giving up, in the face of obstacles, is certainly common enough, but at first thought we should say that the individual was passive in the matter, and simply forced to yield, as a stone is brought to a stop when it strikes a wall. In reality, giving up is not quite so passive as this. There is no external force that can absolutely force us to give up, unless by clubbing us on the head or somehow putting our reactive mechanism out of commission. As long as our brain, nerves and muscles are able to act, no external force can absolutely compel us to cease struggling. Since, then, we do cease struggling before we are absolutely out of commission, our giving up is not a purely passive affair, but our own act, a kind of reaction; and no doubt a native reaction. Further, when struggling against a stubborn obstacle, we sometimes feel an impulse to give up, and giving up brings relief.

The ability to give up is not a mere element of weakness in our nature, but is a valuable asset in adapting ourselves to the environment. Adaptation is called for when the reaction first and most naturally made to a given situation does not meet the requirements of the situation. A too stubborn assertiveness means persistence in this unsuitable reaction, and no progress towards a successful issue; whereas giving up the first plan of attack, and trying something else instead, is the way towards success. Some people are too stubborn to be adaptable.

The docility of the child, who believes whatever is told him, has in it an element of submissiveness. There is submissiveness also in the receptive attitude appropriate in observation and forming opinions--the attitude of looking for the facts and accepting them as they are rather than seeking {168} to confirm one's own prepossessions. Bias is self-assertive, impartiality is submissive to some degree.

Yielding to the domination of other persons often occurs unwillingly, and then comes under the head of "thwarted self-assertion"; but the question is whether it ever occurs willingly and affords satisfaction to the individual who yields. We certainly yield with good grace to one who so far outclasses us that competition with him is unthinkable. An adult may arouse the submissive response in a child; and the social group, by virtue of its superior power and permanence, may arouse it in the individual adult. Hero worship seems a good example of willing submission, agreeable to the one who submits. There are persons who are "lost" without a hero, without some one to lean on, some one to tell them what to do and even what to believe. This looks much like the "filial" or "infantile" instinct that was mentioned before as a possibility, and the dependent spirit in an adult possibly represents a continuation of the infantile attitude into adult life.

Some behavior that looks submissive is really self-assertion in disguise. There are two forms of self-assertion that are specially likely to be taken for submission. Wounded or thwarted self-assertion is one. Shame and envy are like submission in this respect, that they involve an absence of self-confidence or self-assurance, but they do not afford the satisfaction of willing submission, nor the relief of giving up the struggle against obstacles. So far from being genuinely submissive, they are states in which the self is making a violent and insistent demand for justification or social recognition. The other form of self-assertion which looks like submission occurs when a person identifies himself with a superior individual or with a social group. He will then boast of the prowess of his hero or of the prestige of his group, whether it be his family, his school, {169} his town or his country. Now, boasting cannot by any stretch of the imagination be regarded as a sign of submissiveness; it is a sign of assertiveness, and nothing else. What has happened here is that the individual, having identified himself with his hero or his group, finds in their greatness a means of asserting himself as against other individuals who have not the good fortune to be so identified. This transferred self-assertion is a strong element in loyalty and public spirit, and plays a large and useful part in public affairs.

1. Make an outline of the chapter, in the form of a table, which shall show for each instinct: (a) the natural stimulus, (b) the native motor response, (c) the end-result that the instinct tends towards, in its adult as well as its native condition, and (d) the emotion, if any, that goes with the activity of the instinct.

2. An adult tendency or propensity may be simply an unmodified instinct, or it may be derived from instincts by combination, etc. Try to identify each of the following as an instinct, or to analyze it into two or more instincts:

(a) Love for adventure.
(b) Patriotism.
(c) A father's pride in his children.
(d) Love for travel.
(e) Insubordination.
(f) Love for dancing.

3. Which of the instincts are most concerned in making people work?

4. Show how self-assertion finds gratification in the life-work of

an actor.
a physician.
a housekeeper.
a teacher.
a railroad engineer.

5. Arrange the following impulses and emotions in the order of the frequency of their occurrence in your ordinary day's work and play:

(a) Fear.
(b) Anger.
(c) Disgust
(d) Curiosity.
(e) Self-assertion.
(f) Submission.
(g) The tendency to protect or "mother" another.

6. How do "practical jokes" lend support to the view that laughter is primarily aroused by a sense of one's own superiority?

7. Get together a dozen jokes or funny stories, and see how many of them can be placed with the practical jokes in this respect.

8. Mention some laughter-stimuli that do not lend support to the theory mentioned in Exercise 6.

9. What instincts find outlet in (a) dress, (b) automobiling, (c) athletics, (d) social conversation?

McDougall's Social Psychology gives, in Chapters III and IV, an inventory of the instinctive equipment of mankind, and in Chapter V attempts to analyze many complex human emotions and propensities into their native elements.

Thorndike, in his Educational Psychology, Briefer Course, 1914, Chapters, II-V, attempts a more precise analysis of stimulus and response.

Watson's Psychology from the Standpoint of a Behaviorist, 1919, attempts in Chapter VI to show that there are only three primary emotions, fear, rage and love; and in Chapter VII gives a critical review of the work on human instincts.

H. C. Warren, in Chapter VI of his Human Psychology, 1919, gives a brief survey of the reflexes and instincts.

Feeling is subjective and unanalyzed. It is conscious, and an "unconscious feeling" would be a contradiction in terms. But, while conscious, it is not cognitive; it is not "knowing something", even about your subjective condition; it is simply "the way you feel". As soon as you begin to analyze it, and say, "I feel badly here or there, in this way or in that", you know something about your subjective condition, but the feeling has evaporated for the instant. In passing over into definite knowledge of facts, it has ceased to be feeling.

Feeling is an undercurrent of consciousness, or we might call it a background. The foreground consists of what you are taking notice of or thinking about, or of what you are intending to do; that is to say, the foreground is cognitive or impulsive, or it may be both at once, as when we are intent on throwing this stone and hitting that tree. In the background lies the conscious subjective condition. Behind facts observed and acts intended lies the state of the individual's feeling, sometimes calm, sometimes excited, sometimes expectant, sometimes gloomy, sometimes buoyant.

The number of different ways of feeling must be very great, and it would be no great task to find a hundred different words, some of them no doubt partly synonymous, to complete the sentence, "I feel _______". All the {173} emotions, as "stirred-up states of mind", belong under the general head of the feelings.

But when the psychologist speaks of the feelings, he usually means the elementary feelings. An emotion is far from elementary. If you accept the James-Lange theory, you think of an emotion as a blend of organic sensations; and if you reject that theory, you would still probably agree that such an emotion as anger or fear seems a big, complex state of feeling. It seems more complex than such a sensation as red, warm, or bitter, which are called elementary sensations because no one has ever succeeded in decomposing them into simpler sensations. Now, the question is whether any feelings can be indicated that are as elementary as these simple sensations.

No one has ever been able to break up the feelings of pleasantness and unpleasantness into anything simpler. "Pleasure" and "displeasure" are not always so simple; they are names for whole states of mind which may be very complex, including sensations and thoughts in addition to the feelings of pleasantness and unpleasantness. "Pain" does not make a satisfactory substitute for the long word "unpleasantness", because "pain", as we shall see in the next chapter, is properly the name of a certain sensation, and feelings are to be distinguished from sensations. Red, warm and bitter, along with many others, are sensations, but pleasantness and unpleasantness are not sensations.

How, then, do the elementary feelings differ from sensations? In the first place, sensations submit readily to being picked out and observed, and in fact become more vivid when they are brought into the "foreground", while feelings grow vague and lose their character when thus singled {174} out for examination. Attend to the noises in the street and they stand out clearly, attend to the internal sensation of breathing and it stands out clearly, but attend to your pleasant state of feeling and it retreats out of sight.

In the second place, sensations are "localized"; you can tell pretty well where they seem to come from. Sensations of light, sound and smell are localized outside the body, sensations of touch are localized on the skin (or sometimes outside), taste sensations are localized in the mouth, organic and muscular sensations in some part of the body. On the other hand, pleasantness and unpleasantness are much less definitely localized; they seem to be "in us", without being in any special part of us.

In the third place, feelings differ from sensations in having no known sense organs. There is no special sense organ or set of sense organs for the feeling of pleasantness or unpleasantness, as there is for warmth or cold. Some sensations are pleasant, to be sure, and some unpleasant; but there is no one kind of sense organ that has the monopoly of either sort of feeling.

The pleasantness or unpleasantness characteristic of many sensations is called their "feeling-tone", and sensations that are markedly pleasant or unpleasant are said to have a strong or pronounced feeling-tone. Bitter is intrinsically unpleasant, sweet pleasant, the salty taste, when not too strong, neither one nor the other, so that it has no definite feeling-tone. Odors, as well as tastes, usually have a rather definite feeling-tone. Of sounds, smooth tones are pleasant, grating noises unpleasant. Bright colors are pleasant, while dull shades are sometimes unpleasant, sometimes merely indifferent or lacking in feeling-tone. Pain is usually unpleasant, moderate warmth and cold pleasant, simple touch {175} indifferent. Very intense sensations of any kind are likely to be unpleasant.

The statements made above as to the subjectivity and non-localization of feeling do not apply altogether to the feeling-tone of sensations. The pleasantness or unpleasantness of a sensation is localized with the sensation and seems to belong to the object rather than to ourselves. The unpleasantness of a toothache seems to be in the tooth rather than simply "in us". The pleasantness of a sweet taste is localized in the mouth, and we even think of the sweet substance as being objectively pleasant. We say that it is a "pleasant day", and that there is a "pleasant tang in the air", as if the pleasantness were an objective fact.

By arguing with a person, however, you can get him to admit that, while the day is pleasant to him, and the tang in the air pleasant to him, they may be unpleasant to another person; and he will admit that a sweet substance, ordinarily pleasant, is unpleasant when he has had too much of sweet things to eat. So you can make him realize that pleasantness and unpleasantness depend on the individual and his condition, and are subjective rather than objective. Show a group of people a bit of color, and you will find them agreeing much better as to what color that is than as to how pleasant it is. Feeling-tone is subjective in the sense that people disagree about it.

1. Pleasantness might represent a general organic state, and unpleasantness the contrary state, each state being an internal bodily response to pleasant or unpleasant stimuli, and making itself felt as an unanalyzable compound of vague internal sensations.

This theory of feeling is certainly attractive, and it would {176} account very well for all the facts so far stated, for the subjectivity of feeling, for its lack of localization, and for the absence of specific sense organs for the feelings. It would bring the feelings into line with the emotions. But the real test of the theory lies just here: can we discover radically different organic states for the two opposite feelings?

Numerous experiments have been conducted in the search for such radically different organic states, but thus far the search has been rather disappointing. Arrange to record the subject's breathing and heart beat, apply pleasant and unpleasant stimuli to him, and see whether there is any characteristic organic change that goes with pleasant stimuli, and an opposite change with unpleasant stimuli. You should also obtain an introspective report from your subject, so as to be sure that the "pleasant stimuli" actually gave a feeling of pleasantness, etc. Certain experiments of this sort have indicated that with pleasantness goes slower heart beat and quicker breathing, with unpleasantness quicker heart beat and slower breathing. But not all investigators have got these results; and, anyway, it would be impossible to generalize to the extent of asserting that slow heart beat always gave a pleasant state of feeling, and rapid heart beat an unpleasant; for there is slow heart beat during a "morning grouch", and rapid during joyful expectation. Or, in regard to breathing, try this experiment: hasten your breathing and see whether a feeling of pleasantness results; slacken it and see whether unpleasantness results. The fact is that pleasantness can go with a wide range of organic states, so far as these are revealed by heart beat and breathing; and the same with unpleasantness. If there is any organic fact definitely characteristic of either state of feeling, it is a subtle fact that has hitherto eluded observation.

2. Pleasantness might represent smooth and easy brain action, unpleasantness slow and impeded brain action. According to this theory, unimpeded progress of nerve currents through the brain is pleasant, while resistance encountered at the brain synapses is unpleasant. A stimulus is pleasant, then, because the nerve currents started by it find smooth going through the brain centers, and another stimulus is unpleasant because it finds the going poor.

While this theory looks good in some ways, and fits some cases very well--as the great unpleasantness of blocked reaction, where you cannot make up your mind what to do--there are two big objections to it. The first objection is found in the facts of practice. Practising any reaction makes it more and more smooth-running and free from inner obstruction, and should therefore make it more and more pleasant; but, as a matter of fact, practising an unfamiliar act of any sort makes it more pleasant for a time only, after which continued practice makes it automatic and neither pleasant nor unpleasant. The smoothest reactions, which should give the highest degree of pleasant feeling according to the theory, are simply devoid of all feeling.

The second objection lies in the difficulty of believing unpleasant stimuli to give slow, impeded reactions. On the contrary, the instinctive defensive reactions to unpleasant stimuli are very quick, and give no sign of impeded progress of nerve currents through the brain centers.

3. There is one fact, not yet taken into account, that may point the way to a better theory. Feeling is impulsive. In pleasantness, the impulse is to "stand pat" and let the pleasant state continue; in unpleasantness, the impulse is to end the state. The impulse of pleasantness is directed towards keeping what is pleasant, and the impulse of unpleasantness is directed towards getting rid of the unpleasant. In indifference there is no tendency either to keep or to be {178} rid of. These facts are so obvious as scarcely to need mention, yet they may be the core of this whole matter of feeling. Certainly they are the most important facts yet brought out as relating feeling to conduct.

Putting this fact into neural terms, we say that pleasantness goes with a neural adjustment directed towards keeping, towards letting things stay as they are; while unpleasantness goes with an adjustment towards riddance. Bitter is unpleasant because we are so organized, by native constitution, as to make the riddance adjustment on receiving this particular stimulus. In plain language, we seek, to be rid of it, and that is the same as saying it is unpleasant. Sweet is pleasant for a similar reason.

There is some evidence that these adjustments occur in that part of the brain called the thalamus. [Footnote: See p. 65.]

Laying aside now the difficult question of the organic and cerebral nature of the feelings, we turn to the simpler question of the stimuli that arouse them. A very important fact immediately arrests our attention. There are two different kinds of stimuli for pleasantness, and two corresponding kinds for unpleasantness. The one kind is typified by sweet and bitter, the other by success and failure. Some things are pleasant (or unpleasant) without regard to any already awakened desire, while other things are pleasant (or unpleasant) only because of such a desire. A sweet taste is pleasant even though we were not desiring it at the moment, and a bitter taste is unpleasant though we had no expectation of getting it and no desire awakened to avoid it. On the other hand, the sight of our stone hitting the tree is pleasant only because we were aiming at the tree, and {179} the sight of the stone going to one side of the tree is unpleasant just for the same reason.

Some things we want. Because we like them; Some things we like. Because we want them.

We want candy, because we like the sweet taste; but we like a cold drink because and when we are thirsty and not otherwise. Thirst is a want for water, a state of the organism that impels us to drink; and when we are in this state, we like a drink, a drink is pleasant then. How absurd it would be to say that we were thirsty because we liked to drink! when the fact is that we like to drink because we are thirsty. The desire to drink must first be aroused, and then drinking is pleasant.

What is true of thirst is true of hunger, or of any organic need. The need must first be aroused, and then its satisfaction is pleasant. This applies just as well to fighting, laughing, fondling a baby, and to all the instincts. It gives you no pleasure to strike or kick a person, or to swear at him, unless you are first angry with him. It gives you no pleasure to go through the motions of laughing unless you "want to laugh", i.e., unless you are amused. It gives you no pleasure to fondle the baby unless you love the baby. Let any instinct be first aroused, and then the result at which the instinct is aimed causes pleasure, but the same result will cause no pleasure unless the instinct has been aroused.

The same can be said of desires that are not exactly instinctive. At a football game, for example, when one of the players kicks the ball and it sails between the goal posts, half of the spectators yell with joy, while the other half {180} groan in agony. Why should the appearance of a ball sailing between two posts be so pleasant to some, and unpleasant to others? This particular appearance is by itself neither pleasant nor unpleasant, but because the desire to see this happen has been previously aroused in the partisans of one team, and the desire that it should not happen in the partisans of the other, therefore it is that the pleasantness or unpleasantness occurs. First arouse any desire, and then you can give pleasure by gratifying it, displeasure by thwarting it. This is the pleasure of success, and the unpleasantness of failure.

Pleasures of this class may be named secondary, because they depend upon pre-aroused desires.

Though many of the most intense pleasures and displeasures of life are of the secondary type, this fact must not blind us to the existence of the primary pleasures and displeasures, typified by sweet and bitter. Any sensation with a pronounced feeling-tone is a primary pleasure or displeasure. We like or dislike it just for itself, and without regard to the gratification of any pre-aroused instinct or desire.

There are natural likes and dislikes--apart from the satisfaction of instincts--and there are others that are acquired. In other words, there are native tastes and acquired tastes. Individuals differ considerably in their native tastes, and still more in their acquired tastes. Liking for sweets is native, liking for fragrant odors is native, but liking for lemonade, or black coffee, or olives, or cheese, is acquired, and not acquired by everybody. Liking for bright colors is native, but liking for subdued colors, and the special pleasure in color harmonies, are acquired. So we might {181} run through the list of the senses, finding under each some sensations with native feeling-tone, and other sensations that acquire feeling-tone through experience.

Some people have a native liking for numbers and other facts of a mathematical nature. We say of such a one that he has a natural taste for mathematics. Another has a natural dislike for the same. Some have a taste for things of the mechanical sort, others fight shy of such things. Some have a natural taste for people, being sociable creatures--which means more than being gregarious--while others are little interested in mixing with people, observing their ways, and the give and take of friendly intercourse.

Now the question arises whether these native likes and dislikes, for odors, colors, tones, numbers, machinery, and people, are really independent of the instincts. Some psychologists have insisted that all the interest and satisfaction of life were derived from the instincts, laying special stress on the instincts of curiosity and self-assertion.

With respect to our "natural liking for mathematics", these psychologists would argue as follows: "First off, curiosity is aroused by numbers, as it may be by any novel fact; then the child, finding he can do things with numbers, gratifies his mastery impulse by playing with them. He encounters number problems, and his mastery impulse is again aroused in the effort to solve the problems. Later, he is able to 'show off' and win applause by his mathematical feats, and thus the social form of self-assertion is brought into play. This particular child may have good native ability for mathematics, and consequently his mastery impulse is specially gratified by this kind of activity; but he has no real direct liking for mathematics, and all his industry in this field is motivated by curiosity and especially by self-assertion."

The instinct psychologists have a strong case here, as {182} they would have also in regard to the liking for machinery. Still, the mathematical individual would not be convinced, for he would testify that numbers, etc., made a direct appeal to him. Numbers, geometric forms, and algebraic transformations are fascinating to him, and there is something beautiful, to his mind, in the relationships that are discovered. The same could be said of the liking for plant or animal life that appears in the "born biologist". If the objects of the world make a direct appeal to the man whose mind is attuned to them, then his interest and zeal in studying them are not wholly derived from the instincts. The instincts come into play, truly enough, in all scientific work, and add impetus to it, but the primary motive is a direct liking for the kind of facts studied.

"Primary likes and dislikes" are still more clearly in evidence in the arts than in the sciences. Take the color art, for example. There can be no manner of doubt that bright colors are natively pleasant. Can we explain the liking for color as derived from satisfaction of the instincts? Is it due simply to curiosity? No, for then the color would no longer be attractive after it had ceased to be a novelty. Is color liked simply for purposes of self-display? No, this would not explain our delight in the colors of nature. Or do color effects constitute problems that challenge the mastery impulse? This might fit the case of intricate color designs, but not the strong, simple color effects that appeal to most people. There is no escape from the conclusion that color is liked for its own sake, and that this primary liking is the foundation of color art.

Music, in the same way, is certainly based on a primary liking for tones and their combinations, as well as for rhythm. Novel effects also appeal to curiosity, musical performance is a means of display to the performer, and the problem set by a piece of music to the performer in the {183} way of execution, and to the listener in the way of understanding and appreciation, gives plenty of play to the mastery impulse. Besides, music gets associated with love, tenderness, war and religion; but none of the impulses thus gratified by music is the fundamental reason for music, since without the primary taste for tone and rhythm there would be no music to start with, and therefore no chance for these various impulses to find an outlet in this direction.

Still another field of human activity, in which native likes and dislikes play their part alongside of the instincts, is the field of social life. The gregarious instinct brings individuals together into social groups, and probably also makes the individual crave participation in the doings of the group. The sex instinct lends a special interest to those members of the group who are of the opposite sex, and the parental instinct leads the adults to take a protective attitude towards the little children. Also, it is probably due to the parental instinct that any one spontaneously seeks to help the helpless. Self-assertion has plenty of play in a group, both in the way of seeking to dominate and in the way of resisting domination; and the submissive tendency finds an outlet in admiring and following those who far surpass us. Thwarted self-assertion accounts for many of the dislikes that develop between the members of a group. But none of these instincts accounts for the interest in personality, or for the genuine liking that people may have for one another.

Let a group of persons of the same age and sex get together, all equals for the time being, no one seeking to dominate the rest, no one bowing to another as his superior nor chafing against an assumed superiority which he does not admit, no one in a helpless or unfortunate condition that arouses the pity of the rest. What an uninteresting affair! No instincts called into play except bare gregariousness! {184} On the contrary, such a group affords almost or quite the maximum of social pleasure. It affords scope for comradeship and good fellowship, which are based on a native liking for people, and not on the instincts.

Enough has perhaps been said to convince the reader that, besides the things we like for satisfaction of our instinctive needs and cravings, there are other things that we "just naturally like"--and the same with dislikes--and that these primary likes and dislikes have considerable importance in life.

Pleasantness and unpleasantness are the only feelings generally accepted as elementary, though several others have been suggested.

This author suggested that there were three pairs of feelings: pleasantness and unpleasantness; tension and its opposite, release or relief; and excitement and its opposite, which may be called numbness or subdued feeling. Thus there would be three dimensions of feeling, which could be represented by the three dimensions of space, and any given state of feeling could be described by locating it along each of the three dimensions. Thus, one moment, we may be in a pleasant, tense, excited state; another moment in a pleasant, relieved and subdued state; and another moment in an unpleasant, tense and subdued state, etc. As each feeling can also exist in various degrees, the total number of shades of feeling thus provided for would be very great, indeed.

Though this theory has awakened great interest, it has not won unqualified approval. Excitement and the rest are real enough states of feeling--no one doubts that--but the question is whether they are fit to be placed alongside of pleasantness and unpleasantness as elementary feelings. It {185} appears rather more likely that they are blends of sensations. In the excited states that have been most carefully studied, that is to say, in fear and anger, there is that big organic upstir, making itself felt as a blend of many internal sensations. Tension may very probably be the feeling of tense muscles, for tension occurs specially in expectancy, and the muscles are tense then.

Whether elementary or not, these feelings are worthy of note. It is interesting to examine the striving for a goal and the attainment of the goal with respect to each "dimension" of feeling. Striving is tense, attainment brings the feeling of release. Striving is often excited, but fatigue and drowsiness (seeking for rest) are numb, and self-assertion may be neutral in this respect, as in "cool assumption". Reaching the goal may be excited or not; all depends on the goal, whether it be striking your opponent or going to sleep. On the other hand, reaching the goal is practically always pleasant (weeping seems an exception here), while striving for a goal is pleasant or unpleasant according as progress is being made towards the goal, or stiff obstruction encountered.

The feeling of familiarity, and its opposite, the feeling of strangeness or newness, also have some claim to be considered here. The first time you see a person, he seems strange, the next few times he awakens in you the feeling of familiarity, after which he becomes so much a matter of course as to arouse no definite feeling of this sort, unless, indeed, a long time has elapsed since you saw him last; in this case the feeling of familiarity is particularly strong.

The feelings of doubt or hesitation, and of certainty or assurance, also deserve mention as possibly elementary.

1. Outline the chapter.

2. Complete the sentence, "I feel_____" in 20 different ways (not using synonyms), and measure the time required to do this.

3. What can be meant by speaking in psychology of only two feelings, when common speech recognizes so many?

4. If the states of mind designated by the words, "feeling sure", or "feeling bored", are compound states, what elements besides the feelings of pleasantness and unpleasantness may enter into the compounds?

5. Attempt an analysis of the "worried feeling", by your own introspection, i.e., try to discover elementary feelings and sensations in this complex state of mind.

6. Following Wundt's three-dimensional scheme of feeling, analyze each of the following states of mind (for example, a child just admitted to the presence of the Christmas tree would be in a state of mind that is pleasant, tense, and excited):

(a) Watching a rocket go up and waiting for it to burst.
(b) Just after the rocket has burst.
(c) Waiting for the dentist to pull.
(d) Just after he has pulled.
(e) Enjoying a warm bed.
(f) Lying abed after waking, not quite able as yet to decide to get up.
(g) Seeing an automobile about to run down a child.

7. Make a list of six primary dislikes, and a list of six dislikes that are dependent on the instincts.

For a much fuller treatment of the subject, see E. B. Titchener, Textbook of Psychology, 1909, pp. 225-264.

With reflex action, instinct, emotion and feeling, the list of native mental activities is still incomplete. The senses are provided by nature, and the fundamental use of the senses goes with them. The child does not learn to see or hear, though he learns the meaning of what he sees and hears. He gets sensation as soon as his senses are stimulated, but recognition of objects and facts comes with experience. Hold an orange before his open eyes, and he sees, but the first time he doesn't see an orange. The adult sees an object, where the baby gets only sensation. "Pure sensation", free from all recognition, can scarcely occur except in the very young baby, for recognition is about the easiest of the learned accomplishments, and traces of it can be seen in the behavior of babies only a few days old.

Sensation is a response; it does not come to us, but is aroused in us by the stimulus. It is the stimulus that comes to us, and the sensation is our own act, aroused by the stimulus. Sensation means the activity of the receiving organ (or sense organ), of the sensory nerves, and of certain parts of the brain, called the sensory centers. Without the brain response, there is apparently no conscious sensation, so that the activity of the sense organ and sensory nerve is preliminary to the sensation proper. Sensation may be called the first response of the brain to the external stimulus. It is usually only the first in a series of brain {188} responses, the others consisting in the recognition of the object and the utilization of the information so acquired.

Sensation, as we know it in our experience, goes back in the history of the race to the primitive sensitivity (or irritability) of living matter, seen in the protozoa. These minute unicellular creatures, though having no sense organs--any more than they have muscles or digestive organs--respond to a variety of stimuli. They react to mechanical stimuli, as a touch or jar, to chemical stimuli of certain kinds, to thermal stimuli (heat or cold), to electrical stimuli, and to light. There are some forces to which they do not respond: magnetism, X-rays, ultraviolet light; and we ourselves are insensitive to these agents, which are not to be called stimuli, since they arouse no response.

In the development of the metazoa, or multicellular animals, specialization has occurred, some parts of the body becoming muscles with the primitive motility much developed, some parts becoming digestive organs, some parts conductors (the nerves) and some parts becoming specialized receptors or sense organs. A sense organ is a portion of the body that has very high sensitivity to some particular kind of stimulus. One sense organ is highly sensitive to one stimulus, and another to another stimulus. The eye responds to very minute amounts of energy in the form of light, but not in other forms; the ear responds to very minute amounts of energy in the form of sound vibrations, the nose to very minute quantities of energy in certain chemical forms.

There is only one thing that a sense organ always and necessarily contains, and that is the termination of a sensory nerve. Without that, the sense organ, being isolated, would have no effect on the brain or muscles or any other {189} part of the body, and would be entirely useless. The axons of the sensory nerve divide into fine branches in the sense organ, and thus are more easily aroused by the stimulus.

Besides the sensory axons, two other things are often found in a sense organ--sometimes one of the two, sometimes the other and sometimes both. First, there are special sense cells in a few sense organs; and second, in most sense organs there is accessory apparatus which, without being itself sensitive, assists in bringing the stimulus to the sense cells or sensory nerve ends.

Fig. 25.--Diagram of the taste end-organ. Within the "Taste bud" are seen two sense cells, and around the base of these cells are seen the terminations of two axons of the nerve of taste. (Figure text: surface of tongue, taste bud, pit)

Sense cells are present only in the eye, ear, nose and mouth--always in very sheltered situations. The taste cells are located in little pits opening upon the surface of the tongue. In the sides of these pits can be found little flask-shaped chambers, each containing a number of taste cells. The taste cell has a slender prolongation that protrudes from the chamber into the pit; and it is this slender tip of the cell that is exposed to the chemical stimulus of the {190} tasting substance. The stimulus arouses the taste cell, and this in turn arouses the ending of the sensory axon that twines about the base of the cell at the back of the chamber. The taste cell, or its tip, is extra sensitive to chemical stimuli, and its activity, aroused by the chemical stimulus, in turn arouses the axon and so starts a nerve current to the brain stem and eventually to the cortex.

Fig. 26.--The olfactory sense cells and their brain connections. (Figure text: axon to brain cortex, dendrites, synapses in brain stem, axons of sense cells sense cells in nose.)

The olfactory cells, located in a little recess in the upper and back part of the nose, out of the direct air currents going toward the lungs, are rather similar to the taste cells. They have fine tips reaching to the surface of the mucous membrane lining the nasal cavity and exposed to the chemical stimuli of odors. The olfactory cell has also a long slender branch extending from its base through the bone into the skull cavity and connecting there with dendrites of nerve cells. This central branch of the olfactory cell is, in fact, an axon; and it is peculiar in being an axon growing from a sense cell. This is the rule in invertebrates, but in vertebrates the sensory axon is regularly an outgrowth of a {191} nerve cell, and only in the nose do we find sense cells providing their own sensory nerve.

Fig. 27.--Sense cells and nerve cells of the retina. Light, reaching the retina from the interior of the eyeball (as shown in Fig. 28), passes through the nearly transparent retina till stopped by the pigment layer, and then and there arouses to activity the tips of the rods and cones. The rods and cones pass the impulse along to the bipolar cells and these in turn to the optic nerve cells, the axons of which extend by way of the optic nerve to the thalamus in the brain. (Figure text: pigment layer, rods, cones, light, bipolar Cells, optic Nerve Cells)

In the eye, the sense cells are the rods and cones of the retina. These are highly sensitive to light, or, it may be, to chemical or electrical stimuli generated in the pigment of the retina by the action of light. The rods are less highly developed than the cones. Both rods and cones connect at their base with neurones that pass the activity along through the optic nerve to the brain.

The internal ear contains sense cells of three rather similar kinds, all being "hair cells", Instead of a single {192} sensitive tip, each cell has a number of fine hair-tips, and it is these that first respond to the physical stimulus. In the cochlea, the part of the inner ear concerned with hearing, the hairs are shaken by sound vibrations that have reached the liquid in which the whole end-organ is immersed. In the "semicircular canals", a part of the inner ear that is concerned not with sound but with rotary movements of the head, we find hair cells again, their hair-tips being matted together and so located as to be bent, like reeds growing on the bottom of a brook, by currents of the liquid filling the canals. In the "vestibule", the central part of the inner ear, the hair-tips of the sense cells are matted together, and in the mat are imbedded little particles of stony matter, called the "otoliths". When the head is inclined in any direction, these heavy particles sag and bend the hairs, so stimulating them; and the same result occurs when a sudden motion up or down or in any direction is given to the head. Around the base of the sense cells, in any of these parts of the internal ear, are twined the fine endings of sensory axons, which are excited by the activity of the sense cells, and pass the activity on to the brain.

Every sense except the "pain sense" has more or less of this. The hairs of the skin are accessory to the sense of touch. A touch on a hair is so easily felt that we often think of the hairs as sensitive; but really it is the skin that is sensitive, or, rather, it is the sensory axon terminating around the root of the hair in the skin. The tongue can be thought of as accessory apparatus serving the sense of taste, and the breathing apparatus as accessory to the sense of smell, "tasting" being largely a tongue movement that brings the substance to the taste cells, and "smelling" of anything being largely a series of little inspiratory movements that carry the odor-laden air to the olfactory part of the nasal cavity.

But it is in the eye and the ear that the highest development of accessory sense apparatus has taken place. All of the eye except the retina, and all of the ear except the sense cells and the sensory axons, are accessory.

Fig. 28.--Horizontal cross section through the right eyeball. (Figure text: cornea, ciliary muscle, retina, choroid. sclerotic, Optic Nerve)

The eye is an optical instrument, like the camera. In fact, it is a camera, the sensitive plate being the retina, which differs indeed from the ordinary photographic plate in recovering after an exposure so as to be ready for another. Comparing the eye with the camera, we see that the eyeball corresponds to the box, the outer tough coat {194} of the eyeball (the "sclerotic" coat) taking the place of the wood or metal of which the box is built, and the deeply pigmented "choroid" coat, that lines the sclerotic, corresponding to the coating of paint used to blacken the inside of the camera box and prevent stray light from getting in and blurring the picture. At the front of the eye, where light is admitted, the sclerotic is transformed into the transparent "cornea", and the choroid into the contractile "iris", with the hole in its center that we call "the pupil of the eye".

Fig. 29.--Diagram to show the course of the sound waves through the outer and middle ear and into the inner ear. The arrow is placed within the "meatus," and points in the direction taken by the sound waves. See text for their further course. (Figure text: cochlea, vestibule, semicircular canal, ossicles, Eustachian, ear drum)

The iris corresponds to the adjustable diaphragm of the camera. Just behind the pupil is the lens of the eye, which also is adjustable by the action of a little muscle, called the "ciliary muscle". This muscle corresponds to the focussing mechanism of the camera; by it the eye is focussed on near or far objects. The eye really {195} has two lenses, for the cornea acts as a lens, but is not adjustable. The "aqueous and vitreous humors" fill the eyeball and keep it in shape, while still, being transparent, they allow the light to pass through them on the way to the retina. The retina is a thin coat, lying inside the choroid at the back of the eyeball, and having the form of a hollow hemisphere. The light, coming through the pupil and traversing the vitreous humor, strikes the retina from the inside of the eyeball. Other accessory apparatus of the eye includes the lids, the tear glands, and the muscles that turn the eyeball in any direction.

Fig. 30.--Two views of the internal ear. These views show the shape of the internal ear cavity. The sense organs lie inside this cavity. Notice how the three semi-circular canals lie in three perpendicular planes. (Figure text: cochlea, vestibule, 3 Canals)

The ear is about as complex a piece of mechanism as the eye. We speak of the "outer", "middle" and "inner" ear. The outer, in such an animal as the horse, serves as a movable ear trumpet, catching the sound waves and concentrating them upon the ear drum, or middle ear. The human external ear seems to accomplish little; it can be cut off without noticeably affecting hearing. The most essential part of the external ear is the "meatus" or hole that allows the sound waves to pass through the skin to the tympanic membrane or drum head. The sound waves throw this membrane into vibration, and the vibration is transmitted, by an assembly of three little bones, across the air-filled cavity {196} of the middle ear to an opening leading to the water-filled cavity of the inner ear. This opening from the middle to the inner ear is closed by a membrane in which one end of the assembly of little bones is imbedded, as the other end is imbedded in the tympanic membrane; and thus the vibrations are transmitted from the tympanic membrane to the liquid of the inner ear. Once started in this liquid, the vibrations are propagated through it to the sense cells of the cochlea and stimulate them in the way already suggested.

Fig. 31.--A small sample of the sense cells of the cochlea. The hairs of the sense cells are shaken by the vibration of the water, and pass the impulse back to the end-brushes of the auditory axons, The tectorial membrane looks as if it might act as a damper, but may be concerned, as "accessory apparatus," in the stimulation of the hair cells. The basilar membrane consists in part of fibers extending across between the ledges of bone; these fibers are arranged somewhat after the manner of piano strings, and have suggested the "piano theory" of hearing, to be mentioned later in the chapter. (Figure text: water space, membrane, Tectorial membrane, bone, soft tissue, basilar membrane, auditory axons to brain stem, nerve cells of auditory nerves, auditory hair cells with end brushes of auditory axons)

Further study of the accessory apparatus of the eye and ear can be recommended as very interesting, but the little that has been said will serve as an introduction to the study of sensation.

Prominent among the psychological problems regarding sensation is that of analysis. Probably each sense gives comparatively few elementary sensations, and many blends or compounds of these elements. To identify the elements is by no means a simple task, for under ordinary circumstances what we get is a compound, and it is only by carefully controlling the stimulus that we are able to get the elements before us; and even then the question whether these are really elementary sensations can scarcely be settled by direct observation.

Along with the search for elementary sensations goes identification of the stimuli that arouse them, and also a study of the sensations aroused by any combination of stimuli. Our task now will be to ask these questions regarding each of the senses.

Rough and smooth, hard and soft, moist and dry, hot and cold, itching, tickling, pricking, stinging, aching are skin sensations; but some of these are almost certainly compounds. The most successful way of isolating the elements out of these compounds is to explore the skin, point by point, with weak stimuli of different kinds. If a blunt metal point, or the point of a lead pencil, a few degrees cooler than the skin, is passed slowly over the skin, at most points no sensation except that of contact arises, but at certain points there is a clear sensation of cold. Within an area an inch square on the back of the hand, several of these cold spots can be found; and when the exploration is carefully made, and the cold spots marked, they will be found to give the same sensation every time. Substitute a metal point a few {198} degrees warmer than the skin, and a few spots will be found that give the sensation of warmth, these being the warmth spots. Use a sharp point, like that of a needle or of a sharp bristle, pressing it moderately against the skin, and you get at most points simply the sensation of contact, but at quite a number of points a small, sharp pain sensation arises. These are the pain spots. Finally, if the skin is explored with a hair of proper length and thickness, no sensation at all will be felt at most points, because the hair bends so readily when one end of it is pressed against the skin as not to exert sufficient force to arouse a sensation; but a number of points are found where a definite sensation of touch or contact is felt; these are the touch spots.

No other varieties of "spots" are found, and the four sensations of touch, warmth, cold and pain are believed to be the only elementary skin sensations. Itch, stinging and aching seem to be the same as pain. Tickle is touch, usually light touch or a succession of light touches. Smooth and rough are successions of touch sensations. Moist is usually a compound of smooth and cold. Hard and soft combine touch and the muscular sensation of resistance.

Hot and cold require more discussion. The elementary sensations are warmth and coolness, rather than hot and cold. Hot and cold are painful, and the fact is that strong temperature stimuli arouse the pain spots as well as the warmth or cold spots. Hot, accordingly, is a sensation compounded of warmth and pain, and cold a sensation composed of coolness and pain. More than this, when a cold spot is touched with a point heated well above the skin temperature (best to a little over 100 Fahrenheit), the curious fact is noted that the cold spot responds with its normal sensation of cold. This is called the "paradoxical cold sensation". From this fact it is probable that a hot object excites the cold sensation, along with those of warmth and {199} pain; so that the sensation of heat is a blend of the three. Another curious fact is that a very cold object produces a burning sensation indistinguishable from that of a hot object; so that the sensation of great cold, like that of heat, is probably a blend of the three elementary sensations of warmth, cold and pain.

Fig. 32.--Diagram of various sorts of sensory end-organ found in the skin.

A is a hair end-organ; the sensory axons can be seen coiling around the root of the hair; evidently a touch on the hair, outside, would squeeze the coiled axon and stimulate it. The hair is a bit of "accessory apparatus."

B is a touch corpuscle, consisting of a coiled axon-end surrounded by a little cone of other tissue.

C is an end-bulb, presumably belonging to the temperature sense. It has, again, a coiled axon-end surrounded by other tissue. The "coils" are really much more finely branched than the diagram shows.

D is a free-branched nerve end, consisting simply of a branched axon, with no accessory apparatus. It is the pain-sense organ.

E is a corpuscle of a type found in the subcutaneous tissue, as well as in more interior parts of the body. It contains an axon-end surrounded by a layered capsule.

The stimulus that arouses the touch sensation is a bending of the skin. That which arouses warmth or cold is of {200} course a temperature stimulus, but, strange as it may seem, the exact nature of the effective stimulus has not been agreed upon. Either it is a warming or cooling of the skin, or it is the existence of a higher or lower temperature in the skin than that to which the skin is at the moment "adapted". This matter will become clearer when we later discuss adaptation. The stimulus that arouses the pain sensation may be mechanical (as a needle prick), or thermal (heat or cold), or chemical (as the drop of acid), or electrical; but in any case it must be strong enough to injure or nearly to injure the skin. In other words, the pain sense organ is not highly sensitive, but requires a fairly strong stimulus; and thus it is fitted to give warning of stimuli that threaten injury.

Several kinds of sensory end-organ are found in the skin. There is the "spherical end-bulb", into which a sensory axon penetrates; it is believed to be the sense organ for cold. There is the rather similar "cylindrical end-bulb" believed to be the sense organ for warmth. There is the "touch corpuscle", found in the skin of the palms and soles, and consisting, like the end-bulbs, of a mass of accessory cells with a sensory axon ramifying inside it; this is an end-organ for the sense of touch. There is the hair end-organ, consisting of a sensory axon coiled about the root of the hair; this, also, is a touch receptor. Finally, there is the "free-branched nerve end", consisting simply of the branching of a sensory axon, with no accessory apparatus whatever; and this is the pain receptor. Perhaps the pain receptor requires no accessory apparatus because it does not need to be extremely sensitive.

Now since we find, in the skin, "spots" responsive to four quite different stimuli, giving four quite different sensations, and apparently provided with different types of end-organs, it has become customary to speak of four skin senses in place of the traditional "sense of touch". We {201} speak of the pain sense, the warmth sense, the cold sense, and the pressure sense, which last is the sense of touch proper.

Analysis has been as successful in the sense of taste as in cutaneous sensation. Ordinarily we speak of an unlimited number of tastes, every article of food having its own characteristic taste. Now the interior of the mouth possesses the four skin senses in addition to taste, and many tastes are in part composed of touch, warmth, cold or pain. A "biting taste" is a compound of pain with taste proper, and a "smooth taste" is partly touch. The consistency of the food, soft, tough, brittle, gummy, also contributes, by way of the muscle sense, to the total "taste". But in addition to all these sensations from the mouth, the flavor of the food consists largely of odor. Food in the mouth stimulates the sense of smell along with that of taste, the odor of the food reaching the olfactory organ by way of the throat and the rear passage to the nose. If the nose is held tightly so as to prevent all circulation of air through it, most of the "tastes" of foods vanish; coffee and quinine then taste alike, the only taste of each being bitter, and apple juice cannot be distinguished from onion juice.

But when the nose is excluded, and when cutaneous and muscular sensations are deducted, there still remain a few genuine tastes. These are sweet, sour, bitter and salty--and apparently no more. These four are the elementary taste sensations, all others being compounds. The papillae of the tongue, with their little "pits" already spoken of, correspond to the "spots" of the skin, with this difference, however, that the papillae do not each give a single sensation. Some of them give only two, some only three of the four tastes; and the bitter taste is aroused principally from {202} the back of the tongue, the sweet from the tip, the sour from the sides, the salty from both tip and sides.

The stimulus to the sense of taste is something of a chemical nature. The tasteable substances must be in solution in order to penetrate the pits and get to the sensitive tips of the taste cells. If the upper surface of the tongue is first dried, a dry lump of sugar or salt laid on it gives no sensation of taste until a little saliva has accumulated and dissolved some of the substance.

Exactly what is the chemical agent that produces a given taste sensation is a problem of some difficulty. Many different substances give the sensation of bitter, and the question is, what there is common to all these substances. The sweet taste is aroused not only by sugar, but by glycerine, saccharine, and even "sugar of lead" (lead acetate). The sour taste is aroused by most acids, but not by all, and also by some substances that are not chemically acids. Thus the chemistry of taste stimuli involves something not as yet understood.

Though there is this uncertainty regarding the stimulus, on the whole the sense of taste affords a fine example of success achieved by experimental methods in the analysis of complex sensations. At the same time it affords a fine example of the fusion of different sensations into characteristic blends. The numerous "tastes" of every-day life, though found on analysis to be compounded of taste, smell, touch, pain, temperature and muscle sensations, have the effect of units. The taste of lemonade, for example, compounded of sweet, sour, cold and lemon odor, has the effect of a single characteristic sensation. It can be analyzed, but it ordinarily appears as a unit. This is true generally of blends; indeed, what we mean by blending is that, while the component sensations are still present and can be found by careful attention, they are not simply present together {203} but are compounded into a characteristic total. Each elementary sensation entering into the blend gives up some of its own quality, as, in the case of lemonade, neither the sweet nor the sour is quite so distinct and obtrusive as either would be if present alone. The same is true of the lemon odor, and it is true generally of the odor components that enter into the "tastes" of food. Were the odor components in these tastes as clear and distinct as they are when the same substance is smelled outside the mouth, we could not fail to notice that the "tastes" were largely composed of odor. The obtrusive thing about a blend is the total effect, not the elementary sensations that are blended.

The great variety of odors long resisted every attempt at psychological analysis, largely because the olfactory end-organ is so secluded in position. You cannot apply stimuli to separate parts of it, as you can to the skin or tongue. But, recently, good progress has been made, [Footnote: By Henning.] by assembling almost all possible odors, and becoming thoroughly acquainted with them, not as substances, but simply as odors, and noting their likenesses and differences. It seems possible now to state that there are six elementary odors, as follows:

1. Spicy, found in pepper, cloves, nutmeg, etc.
2. Flowery, found in heliotrope, etc.
3. Fruity, found in apple, orange oil, vinegar, etc.
4. Resinous, found in turpentine, pine needles, etc.
5. Foul, found in hydrogen sulphide, etc.
6. Scorched, found in tarry substances.

These being the elements, there are many compound odors. The odor of roasted coffee is a compound of resinous and scorched, peppermint a compound of fruity and spicy.

Each elementary odor corresponds to a certain characteristic in the chemical constitution of the stimulus.

The sense of smell is extremely delicate, responding to very minute quantities of certain substances diffused in the air. It is extremely useful in warning us against bad air and bad food. It has also considerable esthetic value.

The term "organic sensation" is used to cover a variety of sensations from the internal organs, such as hunger, thirst, nausea, suffocation and less definite bodily sensations that color the emotional tone of any moment, contributing to "euphoria" and also to disagreeable states of mind. Hunger is a sensation aroused by the rubbing together of the stomach walls when the stomach, being ready for food, begins its churning movements. Careful studies of sensations from the internal organs reveal astonishingly little of sensation arising there, but there can be little doubt that the sensations just listed really arise where they seem to arise, in the interior of the trunk.

Little has been done to determine the elementary sensations in this field; probably the organic sensations that every one is familiar with are blends rather than elements.

Of the tremendous number and variety of visual sensations, the great majority are certainly compounds. Two sorts of compound sensation can be distinguished here: blends similar to those of taste or smell, and patterns which scarcely occur among sensations of taste and smell, though they are found, along with blends, in cutaneous sensation. Heat, compounded of warmth, cold and pain sensations, is an {205} excellent example of a blend, while the compound sensation aroused by touching the skin simultaneously with two points--or three points, or a ring or square--is to be classed as a pattern. In a pattern, the component parts are spread out in space or time (or in both at once), and for that reason are more easily attended to separately than the elements in a blend. Yet the pattern, like the blend, has the effect of a unit. A spatial pattern has a characteristic shape, and a temporal pattern a characteristic course or movement. A rhythm or a tune is a good example of a temporal pattern.

Visual sensations are spread out spatially, and thus fall into spatial patterns. They also are in constant change and motion, and so fall into temporal patterns, many of which are spatial as well. The visual sensation aroused, let us say in a young baby, by the light entering his eye from a human face, is a spatial pattern; the visual sensation aroused by some one's turning down the light is a pure temporal pattern; while the sensation from a person seen moving across the room is a pattern both spatial and temporal. Finding the elements of a visual pattern would mean finding the smallest possible bits of it, which would probably be the sensations due to the action of single rods and cones, just as the smallest bit of a cutaneous sensation would be due to the exciting of a single touch spot, warmth spot, cold spot or pain spot.

Analyzing a visual blend is quite a different job. Given the color pink, for example, let it be required to discover whether this is a simple sensation or a blend of two or more elementary sensations. Studying it intently, we see that it can be described as a whitish red, and if we are willing to accept this analysis as final, we conclude that pink is a blend of the elementary sensations of white and red. Of the thousands and thousands of distinguishable hues, shades {206} and tints, only a few are elements and the rest are color blends; and our main problem now is to identify the elements. Notice that we are not seeking for the physical elements of light, nor for the primary pigments of the painter's art, but for the elementary sensations. Our knowledge of physics and painting, indeed, is likely to lead us astray. Sensations are our responses to the physical stimulus, and the psychological question is, what fundamental responses we make to this class of stimuli.

Suppose, without knowing anything of pigments or of the physics of light, we got together a collection of bits of color of every shade and tint, in order to see what we could discover about visual sensations. Leaving aside the question of elements for the moment, we might first try to classify the bits of color. We could sort out a pile of reds, a pile of blues, a pile of browns, a pile of grays, etc., but the piles would shade off one into another. The salient fact about colors is the gradual transition from one to another. We can arrange them in series better than we can classify them. They can be serially arranged in three different ways, according to brightness or intensity, according to color-tone, and according to saturation.

The intensity series runs from light to dark. We can arrange such a series composed entirely of reds or blues or any other one color; or we can arrange the whole collection of bits of color into a single light-dark series. It is not always easy to decide whether a given shade of one color is lighter or darker than a given shade of a different color; but in a rough way, at least, every bit of whatever color would have its place in the single intensity series. An intensity series can, of course, be arranged in any other sense as well as in sight.

The color-tone series is best arranged from a collection consisting entirely of full or saturated colors. Start the {207} series with any color and put next to this the color that most resembles it in color-tone, i.e., in specific color quality; and so continue, adding always the color that most resembles the one preceding. If we started with red, the next in order might be either a yellowish red or a bluish red. If we took the yellowish red and placed it beside the red, then the next in order would be a still more yellowish red, and the series would run on to yellow and then to greenish yellow, green, bluish green, blue, violet, purple, purplish red, and so back to red. The color-tone series returns upon itself. It is a circular series.

Fig. 33.--The color circle. R, Y, G and B, stand for the colors red, yellow, green and blue. The shaded portion corresponds to the spectrum or rainbow. Complementary colors (see later) lie diametrically opposite to each other on the circumference.

A saturation series runs from full-toned or saturated colors to pale or dull. Since we can certainly say of a pale blue that it is less saturated than a vivid red, etc., we could, theoretically, arrange our whole collection of bits of color in a single saturation series, but our judgment would be very uncertain at many points. The most significant saturation series confine themselves to a single color-tone, {208} and also, as far as possible, to a constant brightness, and extend from the most vivid color sensation obtainable with this color-tone and brightness, through a succession of less and less strongly colored sensations of the same tone and brightness, to a dead gray of the same brightness. Any such saturation series terminates in a neutral gray, which is light or dark to match the rest of the particular saturation series.

White, black and gray, which find no place in the color-tone series, give an intensity series of their own, running from white through light gray and darker and darker gray to black, and any gray in this series may be the zero point in a saturation series of any color-tone.

A three-dimensional diagram of the whole system of visual sensations can be built up in the following way. Taking all the colors of the same degree of brightness, we can arrange the most saturated, in the order of their color-tone, around the circumference of a circle, put a gray of the same brightness at the center of this circle, and then arrange a saturation series for each color-tone extending from the most saturated at the circumference to gray at the center. This would be a two-dimensional diagram for colors having the same brightness. For a greater brightness, we could arrange a similar circle and place it above the first, and for a smaller brightness, a similar circle and place it below the first, and we could thus build up a pile of circles, ranging from the greatest brightness at the top to the least at the bottom. But, as the colors all lose saturation when their brightness is much increased, and also when it is much decreased, we should make the circles smaller and smaller toward either the top or the bottom of the pile, so that our three-dimensional diagram would finally take the form of a double cone, with the most intense white, like that of sunlight, at the upper point, with dead black at the lower point, {209} and with the greatest diameter near the middle brightness, where the greatest saturations can be obtained. The axis of the double cone, extending from brightest white to dead black, would give the series of neutral grays. All the thousands of distinguishable colors, shades and tints, would find places in this scheme.

Fig. 34.--The color cone, described in the text. Instead of a cone, a four-sided pyramid is often used, so as to emphasize the four main colors, red, yellow, green and blue, which are then located at the corners of the base of the pyramid. (Figure text: white, black, R, B, G, Y)

Not every one gets all these sensations. In color-blindness, the system is reduced to one or two dimensions, instead of three. There are two principal forms of color-blindness: total, very uncommon; and red-green blindness, fairly {210} common. The totally color-blind individual sees only white, black, and the various shades of gray. His system of visual sensations is reduced to one dimension, corresponding to the axis of our double cone.

Red-green blindness, very uncommon in women, is present in three or four percent of men. It is not a disease, not curable, not corrected by training, and not associated with any other defect of the eye, or of the brain. It is simply a native peculiarity of the color sense. Careful study shows that the only color sensations of the red-green blind person are blue and yellow, along with white, black and the grays. His color circle reduces to a straight line with yellow at one end and blue at the other. Instead of the color circle, he has a double saturation series, reaching from saturated yellow through duller yellows to gray and thence through dull blues to saturated blue. What appears to the normal eye as red, orange or grass green appears to him as more or less unsaturated yellow; and what appears to the normal eye as greenish blue, violet and purple appears to him as more or less unsaturated blue. His color system can be represented in two dimensions, one for the double saturation series, yellow-gray-blue, and the other for the intensity series, white-gray-black.

Color-blindness, always interesting and not without some practical importance (since the confusions of the color-blind eye might lead to mistaking signals in navigation or railroading), takes on additional significance when we discover the curious fact that every one is color-blind--in certain parts of the retina. The outermost zone of the retina, corresponding to the margin of the field of view, is totally color-blind (or very nearly so), and an intermediate zone, between this and the central area of the retina that sees all the colors, is red-green blind, and delivers only blue and yellow sensations, along with white, black and gray. Take {211} a spot of yellow or blue and move it in from the side of the head into the margin of the field of view and then on towards the center. When it first appears in the margin, it simply appears gray, but when it has come inwards for a certain distance it changes to yellow. If a red or green spot is moved in similarly, it first appears gray, then takes on a faint tinge of yellow, and finally, as it approaches the center of the field of view, appears in its true color. The outer zone gets only black and white, the intermediate zone gets, in addition to these, yellow and blue, and the central area adds red and green (and with them all the colors).

Fig. 35.--Color cones of the retina. F is the fovea, or central area of clearest vision. (Figure text: all colors, white-black & yellow-blue, white-black)

Now as to the question of elements, let us see how far we can go, keeping still to the sensations, without any reference to the stimulus. If a collection of bits of color is presented to a class of students who have not previously studied this matter, with the request that each select those colors that seem to him elementary and not blends, there is practically unanimous agreement on three colors, red, yellow and blue; and there are some votes for green also, but almost none for orange, violet, purple, brown or any other colors. {212} except white and black. That white and black are elementary sensations is made clear by the case of total color-blindness, since in this condition there are no other visual sensations from which white and black could be compounded, and these two differ so completely from each other that it would be impossible to think of white as made up of black, or black of white. Gray, on the other hand, appears like a blend of black and white. In the same way, red-green blindness demonstrates the reality of yellow and blue as elementary sensations, since neither of them could be reduced to a blend of the other with white or black; and there are no other colors present in this form of color vision to serve as possible elements out of which yellow and blue might be compounded. That white, black, yellow and blue are elementary sensations is therefore clear from the study of visual sensations alone; and there are indications that red and green are also elements.

Thus far, we have said nothing of the stimulus that arouses visual sensations. Light, the stimulus, is physically a wave motion, its vibrations succeeding each other at the rate of 500,000000,000000 vibrations, more or less, per second, and moving through space with a speed of 186,000 miles per second. The "wave-length", or distance from the crest of one wave to the crest of the next following, is measured in millionths of a millimeter.

The most important single step ever taken towards a knowledge of the physics of light, and incidentally towards a knowledge of visual sensations, was Newton's analysis of white light into the spectrum. He found that when white light is passed through a prism, it is broken up into all the colors of the rainbow or spectrum. Sunlight consists of a {213} mixture of waves of various lengths. At one end of the spectrum are the long waves (wave-length 760 millionths of a millimeter), at the other end are the short waves (wavelength 390), and in between are waves of every intermediate length, arranged in order from the longest to the shortest. The longest waves give the sensation of red, and the shortest that of violet, a slightly reddish blue.

Outside the limits of the visible spectrum, however, there are waves still longer and shorter, incapable of arousing the retina, though the very long waves, beyond the red, arouse the sensation of warmth from the skin, and the very short waves, beyond the violet, though arousing none of the senses, do effect the photographic plate. Newton distinguished seven colors in the visible spectrum, red, orange, yellow, green, blue, indigo and violet; but there is nothing specially scientific about this list, since physically there are not seven but an unlimited number of wave-lengths included in the spectrum, varying continuously from the longest at the red end to the shortest at the violet; while psychologically the number of distinguishable colors in the spectrum, though not unlimited, is at least much larger than seven. Between red and orange, for instance, there are quite a number of distinguishable orange-reds and reddish oranges.

If now we ask what differences in the stimulus give rise to the three kinds of difference in visual sensation that were spoken of previously, we find that color-tone depends on the wave-length of the light, brightness on the energy of the stimulus, i.e., on the amplitude of the vibration, and saturation on the mixture of long and short wave-lengths in a complex light-stimulus--the more mixture, the less saturation.

These are the general correspondences between the light stimulus and the visual sensation; but the whole relationship is much more complex. Brightness depends, not only on the energy of the stimulus, but also on wave-length. The {214} retina is tuned to waves of medium length, corresponding to the yellow, which arouse much brighter sensation than long or short waves of the same physical energy. Otherwise put, the sensitivity of the retina is greatest for medium wavelengths, and decreases gradually towards the ends of the spectrum, ceasing altogether, as has been said, at wavelengths of 760 at the red end and of 390 at the violet end.

Saturation, depending primarily on amount of mixture of different wave-lengths, depends also on the particular wavelengths acting, and also on their amplitude. So, the red and blue of the spectrum are more saturated than the yellow and green; and very bright or very dim light, however homogeneous, gives a less saturated sensation than a stimulus of medium strength.

Color-tone depends on the wave-length, as has been said, but this is far from the whole truth; the whole truth, indeed, is one of the most curious and significant facts about color vision. We have said that each color-tone is the response to a particular wave-length. But any color-tone can be got without its particular wave-length being present at all; all that is necessary is that wave-lengths centering about this particular one shall be present. A mixed light, consisting of two wave-lengths, the one longer and the other shorter than the particular wave which when acting alone gives a certain color-tone, will give that same color-tone. For example, the orange color resulting from the isolated action of a wave-length of 650 is given also by the combined action of wave-lengths of 600 and 700, in amounts suitably proportioned to each other.

A point of experimental technique: in mixing colored lights for the purpose of studying the resulting sensations, we do not mix painter's pigments, since the physical {215} conditions then would be far from simple, but we mix the lights themselves by throwing them together either into the eye, or upon a white screen. We can also, on account of a certain lag or hang-over in the response of the retina, mix lights by rapidly alternating them, and get the same effect as if we had made them strike the retina simultaneously.

By mixing a red light with a yellow, in varying proportions, all the color-tones between red and yellow can be got--reddish orange, orange and yellowish orange. By mixing yellow and green lights, we get all the greenish yellow and yellowish green color-tones; and by mixing green and blue lights we get the bluish greens and greenish blues. Finally, by mixing blue and red lights, in varying proportions, we get violet, purple and purplish red. Purple has no place in the spectrum, since it is a sensation which cannot be aroused by the action of any single wave-length, but only by the mixture of long and short waves.

To get all the color-tones, then, we need not employ all the wave-lengths, but can get along with only four. In fact, we can get along with three. Red, green and blue will do the trick. Red and green lights, combined, would give the yellows; green and blue would give the greenish blues; and red and blue would give purple and violet.

The sensation of white results--to go back to Newton--from the combined action of all the wave-lengths. But the stimulus need not contain all the wave-lengths. Four are enough; the three just mentioned would be enough. More surprising still, two are enough, if chosen just right. Mix a pure yellow light with a pure blue, and you will find that you get the sensation of white--or gray, if the lights used are not strong.

[Footnote: When you mix blue and yellow pigments, each absorbs part of the wave-lengths of white light, and what is left after this double absorption may be predominantly green. This is absolutely different from the addition of blue to yellow light; addition gives white, not green.]

Lights, or wave-lengths, which when acting together on the retina give the sensation of white or gray, are said to be complementary. Speaking somewhat loosely, we sometimes say that two colors are complementary when they mix to produce white. Strictly, the colors--or at least the color sensations--are not mixed; for when yellow and blue lights are mixed, the resulting sensation is by no means a mixture of blue and yellow sensations, but the sensation of white in which there is no trace of either blue or yellow. Mixing the stimuli which, acting separately, give two complementary colors, arouses the colorless sensation of white.

Blue and yellow, then, are complementary. Suppose we set out to find the complementary of red. Mixing red and yellow lights gives the color-tones intermediate between these two; mixing red and green still gives the intermediate color-tones, but the orange and yellow and yellowish green so got lack saturation, being whitish or grayish. Now mix red with bluish green, and this grayishness is accentuated, and if just the right wave-length of bluish green is used, no trace of orange or yellow or grass green is obtained, but white or gray. Red and bluish green are thus complementary. The complement of orange light is a greenish blue, and that of greenish yellow is violet. The typical green (grass green) has no single wave-length complementary to it, but it does give white when mixed with a compound of long and short waves, which compound by itself gives the sensation of purple; so that we may speak of green and purple as complementary.

Returning now to the question of elementary sensations, which we laid aside till we had examined the relationship of the sensations to the stimulus, we need to be on our guard against physics, or at least against being so much impressed with the physics of light as to forget that we are concerned with the response of the organism to physical light--a matter on which physics cannot speak the final word.

Fig. 36.--(After König.) The color triangle, a map of the laws of color mixture. The spectral colors are arranged in order along the heavy solid line, and the purples along the heavy dotted line. The numbers give the wave-lengths of different parts of the spectrum. Inside the heavy line are located the pale tints of each color, merging from every side into white, which is located at the point W.

Suppose equal amounts of two spectral colors are mixed: to find from the diagram the color of the mixture. Locate the two colors on the heavy line, draw a straight line between these two points, and the middle of this line gives the color-tone and saturation of the mixture. For example, mix red and yellow: then the resulting color is a saturated reddish yellow. Mix red (760) and green (505): the resulting yellow is non-saturated, since the straight line between these two points lies inside the figure. If the straight line joining two points passes through W, the colors located at the two points are complementary.

Spectral colors are themselves not completely saturated. The way to get color sensations of maximum saturation is first to stare at one color, so as to fatigue or adapt the eye for that color, and then to turn the eye upon the complementary color, which, under these conditions, appears fuller and richer than anything otherwise obtainable. The corners, R, G, and B, denote colors of maximum saturation, and the whole of the triangle outside of the heavy line is reserved for super-saturated color sensations.

Physics tells us of the stimulus, but we are concerned with the response. The facts of color-blindness and color mixing show very clearly that the response does not tally in all respects with the stimulus. Physics, then, is apt to confuse the student at this point and lead him astray. Much impressed with the physical discovery that white light is a mixture of all wave-lengths, he is ready to believe the sensation of white a mixed sensation. He says, "White is the sum of all the colors", meaning that the sensation of white is compounded of the sensations of red, orange, yellow, green, blue and violet--which is simply not true. No one can pretend to get the sensations of red or blue in the sensation of white, and the fact of complementary colors shows that you cannot tell, from the sensation of white, whether the stimulus consists of yellow and blue, or red and bluish green, or red, green and blue, or all the wave-lengths, the response being the same to all these various combinations. Total color-blindness showed us, when we were discussing this matter before, that white was an elementary sensation, and nothing that has been said since changes that conclusion.

Consider black, too. Physics says, black is the absence of light; but this must not be twisted to mean that black is the absence of all visual sensation. Absence of visual sensation is simply nothing, and black is far from that. It is a sensation, as positive as any, and undoubtedly elementary.

From the point of view of physics, there is no reason for considering any one color more elementary than any other. Every wave-length is elementary; and if sensation tallied precisely with the stimulus, every spectral color-tone would be an element. But there are obvious objections to such a view, such as: (1) there are not nearly as many {219} distinguishable color-tones as there are wave-lengths; (2) orange, having a single wave-length, certainly appears to be a blend as truly as purple, which has no single wave-length; and (3) we cannot get away from the fact of red-green blindness, in which there are only two color-tones, yellow and blue. In this form of color vision (which, we must remember, is normal in the intermediate zone of the retina), there are certainly not as many elementary responses as there are wave-lengths, but only one response to all the longer waves (the sensation of yellow), one response to all the shorter waves (the sensation of blue), one response to the combination of long and short waves (the sensation of white), and one response to the cessation of light (the sensation of black). These four are certainly elementary sensations, and there are probably only a few more.

There must be at least two more, because of the fact that two of the sure elements, yellow and blue, are complementary. For suppose we try to get along with one more, as red. Then red, blended with yellow, would give the intervening color-tones, namely, orange with reddish and yellowish orange; and red blended with blue would give violet and purple; but yellow and blue would only give white or gray, and there would be no way of getting green. We must admit green as another element. The particular red selected would be that of the red end of the spectrum, if we follow the general vote; and the green would probably be something very near grass green. We thus arrive at the conclusion that there are six elementary visual responses or sensations: white and black, yellow and blue, red and green.

It is a curious fact that some of these elementary sensations blend with each other, while some refuse to blend. White and black blend to gray, and either white or black or both together will blend with any of the four elementary colors or with any possible blend of these four. Brown, for {220} example, is a grayish orange, that is, a blend of white, black, red and yellow. Red blends with yellow, yellow with green, green with blue, and blue with red. But we cannot get yellow and blue to blend, nor red and green. When we try to get yellow and blue to blend, by combining their appropriate stimuli, both colors disappear, and we get simply the colorless sensation of white or gray. When we try to get red and green to blend, both of them disappear and we get the sensation of yellow.

Of the most celebrated theories of color vision, the oldest, propounded by the physicists Young and Helmholtz, recognized only three elements, red, green and blue. Yellow they regarded as a blend of red and green, and white as a blend of all three elements. The unsatisfactory nature of this theory is obvious. White as a sensation is certainly not a blend of these three color sensations, but is, precisely, colorless; and no more is the yellow sensation a blend of red and green. Moreover, the theory cannot do justice either to total color-blindness, with its white and black but no colors, or to red-green blindness, with its yellow but no red or green.

The next prominent theory was that of the physiologist Hering. He did justice to white and black by accepting them as elements; and to yellow and blue likewise. The fact that yellow and blue would not blend he accounted for by supposing them to be antagonistic responses of the retina; when, therefore, the stimuli for both acted together on the retina, neither of the two antagonistic responses could occur, and what did occur was simply the more generic response of white. Proceeding along this line, he concluded that red and green were also antagonistic responses; but just here {221} he committed a wholly unnecessary error, in assuming that if red and green were antagonistic responses, the combination of their stimuli must give white, just as with yellow and blue. Accordingly, he was forced to select as his red and green elementary color-tones two that would be complementary; and this meant a purplish (i.e., bluish) red, and a bluish green, with the result that his "elementary" red and green appear to nearly every one as compounds and not elements. It would really have been just as easy for Hering to suppose that the red and green responses, antagonizing each other, left the sensation yellow; and then he could have selected that red and green which we have concluded above to have the best claim.

A third theory, propounded by the psychologist, Dr. Christine Ladd-Franklin, is based on keen criticism of the previous two, and seems to be harmonious with all the facts. She supposes that the color sense is now in the third stage of its evolution. In the first stage the only elements were white and black; the second stage added yellow and blue; and the third stage red and green. The outer zone of the retina is still in the first stage, and the intermediate zone in the second, only the central area having reached the third. In red-green blind individuals, the central area remains in the second stage, and in the totally color-blind the whole retina is still in the first stage.

In the first stage, one response, white, was made to light of whatever wave-length. In the second stage, this single response divided into two, one aroused by the long waves and the other by the short. The response to the long waves was the sensation of yellow, and that to the short waves the sensation of blue. In the third stage, the yellow response divided into one for the longest waves, corresponding to the red, and one for somewhat shorter waves, corresponding to the green. Now, when we try to get a blend of red and green {222} by combining red and green lights, we fail because the two responses simply unite and revert to the more primitive yellow response; and similarly when we try to get the yellow and blue responses together, they revert to the more primitive white response out of which they developed.

But, since no one can pretend to see yellow as a reddish green, nor white as a bluish yellow, it is clear that the just-spoken-of union of the red and green responses, and of the yellow and blue responses, must take place below the level of conscious sensation. These unions probably take place within the retina itself. Probably they are purely chemical unions.

Fig. 37.--The Ladd-Franklin theory of the evolution of the color sense. (Figure text: Stage 1--white, Stage 2--yellow blue, Stage 3--red green blue)

The very first response of a rod or cone to light is probably a purely chemical reaction. Dr. Ladd-Franklin, carrying out her theory, supposes that a light-sensitive "mother substance" in the rods and cones is decomposed by the action of light, and gives off cleavage products which arouse the vital activity of the rods and cones, and thus start nerve currents coursing towards the brain.

In the "first stage", she supposes, a single big cleavage product, which we may call W, is split off by the action of {223} light upon the mother substance, and the vital response to W is the sensation of white.

In the second stage, the mother substance is capable of giving off two smaller cleavage products, Y and B. Y is split off by the long waves of light, and B by the short waves, and the vital response to Y is the sensation of yellow, that to B the sensation of blue. But suppose that, chemically, Y + B = W: then, if Y and B are both split off at the same time in the same cone, they immediately unite into W, and the resulting sensation is white, and neither yellow nor blue.

Fig. 38.--The cleavage products, in the three stages of the color sense. The "mother substance" is not represented in the diagram, but only the cleavage products which, according to the Ladd-Franklin theory, are the direct stimuli for the color sensations. (Figure text: 1--white, 2--yellow blue, 3--red green blue)

Similarly, in the third stage, the mother substance is capable of giving off three cleavage products, R, G and B; and there are three corresponding vital responses, the sensations of red, green and blue. But, chemically, R + G = Y; and therefore, if R and G are split off at the same time, they unite chemically into Y and give the sensation of yellow. If R, G and B are all split off at the same time, they unite chemically as follows: R + G = Y, and Y + B = W; and therefore the resulting sensation is that of white.

This theory of cleavage products is in good general agreement with chemical principles, and it does justice to all the facts of color vision, as detailed in the preceding pages. It should be added that "for black, the theory supposes that, {224} in the interest of a continuous field of view, objects which reflect no light at all upon the retina have correlated with them a definite non-light sensation--that of black." [Footnote: Quotation from Dr. Ladd-Franklin.]

Sensory adaptation is a change that occurs in other senses also, but it is so much more important in the sense of sight than elsewhere that it may best be considered here. The stimulus continues, the sensation ceases or diminishes--that is the most striking form of sensory adaptation. Continued action of the same stimulus puts the sense into such a condition that it responds differently from at first, and usually more weakly. It is much like fatigue, but it often is more positive and beneficial than fatigue.

The sense of smell is very subject to adaptation. On first entering a room you clearly sense an odor that you can no longer get after staying there for some time. This adaptation to one odor does not prevent your sensing quite different odors. Taste shows less adaptation than smell, but all are familiar with the decline in sweet sensation that comes with continued eating of sweets.

All of the cutaneous senses except that for pain are much subject to adaptation. Continued steady pressure gives a sensation that declines rapidly and after a time ceases altogether. The temperature sense is usually adapted to the temperature of the skin, which therefore feels neither warm nor cool. If the temperature of the skin is raised from its usual level of about 70 degrees Fahrenheit to 80 or 86, this temperature at first gives the sensation of warmth, but after a time it gives no temperature sensation at all; the warmth sense has become adapted to the temperature of 80 degrees; and now a temperature of 70 will give the sensation of cool. {225} Hold one hand in water at 80 and the other in water at 66, and when both have become adapted to these respective temperatures, plunge them together into water at 70; and you will find this last to feel cool to the warm-adapted hand and warm to the cool-adapted. There are limits to this power of adaptation.

The muscle sense seems to become adapted to any fixed position of a limb, so that, after the limb has remained motionless for some time, you cannot tell in what position it is; to find out, you have only to move it the least bit, which will excite both the muscle sense and the cutaneous pressure sense. The sense of head rotation is adaptable, in that a rotation which is keenly sensed at the start ceases to be felt as it continues; but here it is not the sense cells that become adapted, but the back flow that ceases, as will soon be explained.

To come now to the sense of sight, we have light adaptation, dark adaptation, and color adaptation. Go into a dark room, and at first all seems black, but by degrees--provided there is a little light filtering into the room--you begin to see, for your retina is becoming dark-adapted. Now go out into a bright place, and at first you are "blinded", but you quickly "get used" to the bright illumination and see objects much more distinctly than at first; for your eye has now become light-adapted. Remain for some time in a room illuminated by a colored light (as the yellowish light of most artificial illuminants), and by degrees the color sensation bleaches out so that the light appears nearly white.

Dark adaptation is equivalent to sensitizing the retina for faint light. Photographic plates can be made of more or less sensitiveness for use with different illuminations; but the retina automatically alters its sensitivity to fit the illumination to which it is exposed.

You will notice, in the dark room, that while you see light and shade and the forms of objects, you do not see colors. The same is true out of doors at night. In other words, the kind of vision that we have when the eye is dark-adapted is totally color-blind. Another significant fact is that the fovea is of little use in very dim light. These facts are taken to mean that dim-light vision, or twilight vision as it is sometimes called, is rod vision and not cone vision; or, in other words, that the rods and not the cones have the great sensitiveness to faint light in the dark-adapted eye. The cones perhaps become somewhat dark-adapted, but the rods far outstrip them in this direction. The fovea has no rods and hence is of little use in very faint light. The rods have no differential responsiveness to different wave-lengths, remaining still in the "first stage" in the development of color vision, and consequently no colors are seen in faint light.

Rod vision differs then from cone vision in having only one response to every wave-length, and in adapting itself to much fainter light. No doubt, also, it is the rods that give to peripheral vision its great sensitivity to moving objects.

After-images, which might better be called after-sensations, occur in other senses than sight, but nowhere else with such definiteness. The main fact here is that the response outlasts the stimulus. This is true of a muscle, and it is true of a sense organ. It takes a little time to get the muscle, or the sense organ, started, and, once it is in action, it takes a little time for it to stop. If you direct your eyes towards the lamp, holding your hand or a book in front of them as a screen, remove the screen for an {227} instant and then replace it, you will continue for a short time to see the light after the external stimulus has been cut off. This "positive after-image" is like the main sensation, only weaker. There is also a "negative after-image", best got by looking steadily at a black-and-white or colored figure for as long as fifteen or twenty seconds, and then directing the eyes upon a medium gray background. After a moment a sensation develops in which black takes the place of white and white of black, while for each color in the original sensation the complementary color now appears.

Fig. 39.--The visual response outlasts the stimulus. The progress of time is supposed to be from left to right in the diagram. After the stimulus ceases, the sensation persists for a time, at first as a positive after-image, and then as a negative after-image, a sort of back swing. (Figure text: stimulus, sensory response)

This phenomenon of the negative after-image is the same as that of color adaptation. Exposing the retina for some time to light of a certain color adapts the retina to that color, bleaches that color sensation, and, as it were, subtracts that color (or some of it) from the gray at which the eyes are then directed; and gray (or white) minus a color gives the complementary color.

Contrast is still another effect that occurs in other senses, but most strikingly in vision. There is considerable in common between the negative after-image and contrast; indeed, {228} the negative after-image effect is also called "successive contrast". After looking at a bright surface, one of medium brightness appears dark, while this same medium brightness would seem bright after looking at a dark surface. This is evidently adaptation again, and is exactly parallel to what was found in regard to the temperature sense. After looking at any color steadily, the complementary color appears more saturated than usual; in fact, this is the way to secure the maximum of saturation in color sensation. These are examples of "successive contrast".

"Simultaneous contrast" is something new, not covered by adaptation, but gives the same effects as successive contrast. If you take two pieces of the same gray paper, and place one on a black background and the other on white, you will find the piece on the black ground to look much brighter than the piece on the white ground. Spots of gray on colored backgrounds are tinged with the complementary colors. The contrast effect is most marked at the margin adjoining the background, and grows less away from this margin. Any two adjacent surfaces produce contrast effects in each other, though we usually do not notice them any more than we usually notice the after-images that occur many times in the course of the day.

Sound, like light, is physically a wave motion, though the sound vibrations are very different from those of light. They travel 1,100 feet a second, instead of 186,000 miles a second. Their wave-length is measured in feet instead of in millionths of a millimeter, and their vibration frequencies are counted in tens, hundreds and thousands per second, instead of in millions of millions. But sound waves vary among themselves in the same three ways that we {229} noticed in light waves: in amplitude, in wave-length (or vibration rate), and in degree of mixture of different wave-lengths.

Difference of amplitude (or energy) of sound waves produces difference of loudness in auditory sensation, which thus corresponds to brightness in visual sensation. Sounds can be arranged in order of loudness, as visual sensations can be arranged in order of brightness, both being examples of intensity series such as can be arranged in any kind of sensation.

Difference of wave-length of sound waves produces difference in the pitch of auditory sensation, which thus corresponds to color in visual sensation. Pitch ranges from the lowest notes, produced by the longest audible waves, to the highest, produced by the shortest audible waves. It is customary, in the case of sound waves, to speak of vibration rate instead of wave-length, the two quantities being inversely proportional to each other (in the same conducting medium). The lowest audible sound is one of about sixteen vibrations per second, and the highest one of about 30,000 per second, while the waves to which the ear is most sensitive have a vibration rate of about 1,000 to 4,000 per second. The ear begins to lose sensitiveness as early as the age of thirty, and this loss is most noticeable at the upper limit, which declines slowly from this age on.

Middle C of the piano (or any instrument) has a vibration rate of about 260. Go up an octave from this and you double the number of vibrations per second; go down an octave and you halve the number of vibrations. Of any two notes that are an octave apart, the upper has twice the vibration rate of the lower. The whole range of audible notes, from 16 to 30,000 vibrations, thus amounts to about eleven octaves, of which music employs about eight octaves, finding little use for the upper and lower extremes of the {230} pitch series. The smallest step on the piano, called the "semitone", is one-twelfth of an octave; but it must not be supposed that this is the smallest difference that can be perceived. A large proportion of people can observe a difference of four vibrations, and keen ears a difference of less than one vibration; whereas the semitone, at middle C, is a step of about sixteen vibrations.

Mixture of different wave-lengths, which in light causes difference of saturation, may be said in sound to cause difference of purity. A "pure tone" is the sensation aroused by a stimulus consisting wholly of waves of the same length. Such a stimulus is almost unobtainable, because every sounding body gives off, along with its fundamental waves, other waves shorter than the fundamental and arousing tone sensations of higher pitch, called "overtones". A piano string which, vibrating as a whole, gives 260 vibrations per second (middle C), also vibrates at the same time in halves, thus giving 520 vibrations per second; in thirds, giving 780 per second; and in other smaller segments. The whole stimulus given off by middle C of the piano is thus a compound of fundamental and overtones; and the sensation aroused by this complex stimulus is not a "pure tone" but a blend of fundamental tone and overtones. By careful attention and training, we can "hear out" the separate overtones from the total blend; but ordinarily we take the blend as a unit (just as we take the taste of lemonade as a unit), and hear it simply as middle C of a particular quality, namely the piano quality. Another instrument will give a somewhat different combination of overtones in the stimulus, and that means a different quality of tone in our sensation. We do not ordinarily analyze these complex blends, but we distinguish one from another perfectly well, and thus can tell whether a piano or a cornet is playing. The difference between different instruments, which we have spoken of as a {231} difference in quality or purity of tone, is technically known as timbre; and the timbre of an instrument depends on the admixture of shorter waves with the fundamental vibration which gives the main pitch of a note.

Akin to the timbre of an instrument is the vowel produced by the human mouth in any particular position. Each vowel appears to consist, physically, of certain high notes produced by the resonance of the mouth cavity. In the position for "ah", the cavity gives a certain tone; in the position for "ee" it gives a higher tone. Meanwhile, the pitch of the voice, determined by the vibration of the vocal cords, may remain the same or vary in any way. The vowel tones differ from overtones in remaining the same without regard to the pitch of the fundamental tone that is being sung or spoken, whereas overtones move up or down along with their fundamental. The vowels, as auditory sensations, are excellent examples of blends, in that, though compounds, they usually remain unanalyzed and are taken simply as units. What has been said of the vowels applies also to the semi-vowels and continuing consonants, such as l, m, n, r, f, th, s and sh.

Other consonants are to be classed with the noises. Like a vowel, and like the timbre of an instrument, a noise is a blend of simple tones; but the fundamental tone in a noise-blend is not so preponderant as to give a clear pitch to the total sound, while the other tones present are often too brief or too unsteady to give a tonal effect.

The two senses of sight and hearing have many curious differences, and one of the most curious appears in mixing different wave-lengths. Compare the effect of throwing two colored lights together into the eye with the effect of {232} throwing two notes together into the ear. Two notes sounded together may give either a harmonious blend or a discord; now the discord is peculiar to the auditory realm; mixed colors never clash, though colors seen side by side may do so to a certain extent. A discord of tones is characterized by imperfect blending (something unknown in color mixing), and by roughness due to the presence of "beats" (another thing unknown in the sense of sight). Beats are caused by the interference between sound waves of slightly different vibration rate. If you tune two whistles one vibration apart and sound them together, you get a tone that swells once a second; tune them ten vibrations apart and you get ten swellings or beats per second, and the effect is rough and disagreeable.

Aside from discord, a tone blend is really not such a different sort of thing from a color blend. A chord, in which the component notes blend while they can still, by attention and training, be "heard out of the chord", is quite analogous with such color blends as orange, purple or bluish green. At the same time, there is a curious difference here. By analogy with color mixing, you would expect two notes, as C and E, when combined, to give the same sensation as the single intermediate note D. Nothing of the kind! Were it so, music would be very different from what it is, if indeed it were possible at all. But the real difference between the two senses at this point is better expressed by saying that D does not give the effect of a combination of C and E, or, in general, that no one note ever gives the effect of a combination or blend of notes higher and lower than itself. Homogeneous orange light gives the sensation of a blend of red and yellow; but there is nothing like this in the auditory sphere. In light, some wave-lengths give the effect of simple colors, as red and yellow; and other wave-lengths the effect of blends, as greenish yellow or bluish {233} green; but in sound, every wave-length gives a tone which seems just as elementary as any other.

There is nothing in auditory sensation to correspond to white, no simple sensation resulting from the combined action of all wave-lengths. Such a combination gives noise, but nothing that seems particularly simple. There is nothing auditory to correspond with black, for silence seems to be a genuine absence of sensation. There are no complementary tones like the complementary colors, no tones that destroy each other instead of blending. In a word, auditory sensation tallies with its stimulus much more closely than visual sensation does with its; and the main secret of this advantage of the sense of hearing is that it has a much larger number of elementary responses. Against the six elementary visual sensations are to be set auditory elements to the number of hundreds or thousands. From the fact that every distinguishable pitch gives a tone which seems as simple and unblended as any other, the conclusion would seem to be that each was an element; and this would mean thousands of elements. On the other hand, the fact that tones close together in pitch sound almost alike may mean that they have elements in common and are thus themselves compounds; but still there would undoubtedly be hundreds of elements.

Both sight and hearing are served by great armies of sense cells, but the two armies are organized on very different principles. In the retina, the sense cells are spread out in such a way that each is affected by light from one particular direction; and thus the retina gives excellent space information. But each retinal cell is affected by any light that happens to come from its particular direction. Every cone, in the central area of the retina, makes all the elementary visual responses and gives all the possible color sensations; so it is not strange that the number of visual {234} elements is small. On the other hand, the ear, having no sound lens, has no way of keeping separate the sounds from different directions (and accordingly gives only meager indications of the direction of sound); but its sense cells are so spread out as to be affected, some by sound of one wavelength, others by other wave-lengths. The different tones do not all come from the same sense cells. Some of the auditory cells give the low tones, others the medium tones, still others the high tones; and since there are thousands of cells, there may be thousands of elementary responses.

The most famous theory of the action of the inner ear is the "piano theory" of Helmholtz. The foundation of the theory is the fact that the sense cells of the cochlea stand on the "basilar membrane", a long, narrow membrane, stretched between bony attachments at either side, and composed partly of fibers running crosswise, very much as the strings of a piano or harp are stretched between two side bars. If you imagine the strings of a piano to be the warp of a fabric and interwoven with crossing fibers, you have a fair idea of the structure of the basilar membrane, except for the fact that the "strings" of the basilar membrane do not differ in length anywhere like as much as the strings of the piano must differ in order to produce the whole range of notes. Now, a piano string can be thrown into "sympathetic vibration", as when you put on the "loud pedal" (remove the dampers from the strings) and then sing a note into the piano. You will find that the string of the pitch sung has been thrown into vibration by the action of the sound waves sung against it.

Now suppose the strings of the basilar membrane to be tuned to notes of all different pitches, within the range of {235} audible vibrations: then each string would be thrown into sympathetic vibration whenever waves of its own vibration rate reached it by way of the outer and middle ear; and the sense cells standing over the vibrating fibers would be shaken and excited. The theory is very attractive because it would account so nicely for the great number of elementary tone sensations (there are over 20,000 fibers or strings in the basilar membrane), as well as for various other facts of hearing--if we could only believe that the basilar membrane did vibrate in this simple manner, fiber by fiber. But (1) the fabric into which the strings of the membrane are woven would prevent their vibrating as freely and independently as the theory requires; (2) the strings do not differ in length a hundredth part of what they would need to differ in order to be tuned to all notes from the lowest to the highest, and there is no sign of differences in stretch or in loading of the strings to make up for their lack of difference in length; and (3) a little model of the basilar membrane, exposed to sound waves, is seen to be thrown into vibration, indeed, and into different forms of vibration for waves of different length, but not by any means into the simple sort of vibration demanded by the piano theory. This theory is accordingly too simple, but it probably points the way towards some truer, more complex, conception.

The fact that there are many elementary sensations of hearing is the chief reason why the art of tones is so much more elaborate than the art of color; for while painting might dispute with music as to which were the more highly developed art, painting depends on form as well as color, and there is no art of pure color at all comparable with music, which makes use simply of tones (and noises) with their combinations and sequences.

It is a remarkable fact that some parts of the inner ear are not connected with hearing at all, but with quite another sense, the existence of which was formerly unsuspected. The two groups of sense cells in the vestibule--the otolith organs--were formerly supposed to be the sense organ for noise; but noise now appears to be a compound of tones, and its organ, therefore, the cochlea. The semicircular canals, from their arrangement in three planes at right angles to each other, were once supposed to analyze the sound according to the direction from which it came; but no one could give anything but the vaguest idea of how they might do this, and besides the ear is now known to give practically no information regarding the direction of sound, except the one fact whether it comes from the right or left, which is given by the difference in the stimulation received by the two ears, and not by anything that exists in either ear taken alone.

The semicircular canals have been much studied by the physiologists. They found that injury to these structures brought lack of equilibrium and inability to walk, swim or fly in a straight course. If, for example, the horizontal canal in the left ear is destroyed, the animal continually deviates to the left as he advances, and so is forced into a "circus movement". They found that the compensatory movements normally made in reaction to a movement impressed on the animal from without were no longer made when the canals were destroyed. They found that something very much like these compensatory movements could be elicited by direct stimulation of the end-organs in the canals or of the sensory nerves leading from them. And they found that little currents of the liquid filling the canals acted as a stimulus to these end-organs and so aroused the {237} compensatory movements. They were thus led to accept a view that was originally suggested by the position of the canals in space.

Fig. 40.--How the sense cells in a semicircular canal are stimulated by a water current. This current is itself an inertia back-flow, resulting from a turning of the head in the opposite direction. (Figure text: water current, nerve to brain)

Each "semicircular" canal, itself considerably more than a semicircular tube, opens into the vestibule at each end and thus amounts to a complete circle. Therefore rotating the head must, by inertia, produce a back flow of the fluid contents of the canal, and this current, by bending the hairs of the sense cells in the canal, would stimulate them and give a sensation of rotation, or at least a sensory nerve impulse excited by the head rotation.

When a human subject is placed, blindfolded, in a chair that can be rotated without sound or jar, it is found that he can easily tell whenever you start to turn him in either direction. If you keep on turning him at a constant speed, he soon ceases to sense the movement, but if then you stop him, he says you are starting to turn him in the opposite {238} direction. He senses the beginning of the rotary movement because this causes the back flow through his canals; he ceases to sense the uniform movement because friction of the liquid in the slender canal soon abolishes the back flow by causing the liquid to move with the canal; and he senses the stopping of this movement because the liquid, again by inertia, continues to move in the direction it had been moving just before when it was keeping pace with the canal. Thus we see that there are conscious sensations of rotation from the canals, and that these give information of the starting or stopping of a rotation, though not of its steady continuance. Excessive stimulation of the canals gives the sensation of dizziness.

The otolith organs in the vestibule are probably excited, not by rotary movements, but by sudden startings and stoppings of rectilinear motion, as in an elevator; and also by the pull of gravity when the head is held in any position. They give information regarding the position and rectilinear movements of the head, as the canals do of rotary head movements. Both are important in maintaining equilibrium and motor efficiency.

The muscle sense is another sense of bodily movement; it was the "sixth sense", so bitterly fought in the middle of the last century by those who maintained that the five senses that were enough for our fathers ought to be enough for us, too. The question was whether the sense of touch did not account for all sensations of bodily movement. It was shown that there must be something besides the skin sense, because weights were better distinguished when "hefted" in the hand than when simply laid in the motionless palm; and it was shown that loss of skin sensation in an arm or leg interfered much less with the coördinated movements of the limb than did the loss of all the sensory nerves to the limb.

Fig. 41.--(From Cajal.) A "tendon spindle," very similar to the muscle spindle spoken of in the text, but found at the tendinous end of a muscle instead of embedded in the muscle substance itself, "a" indicates the tendon, and "e" the muscle fibers; "b" is a sensory axon, and "c" its end-brush about the spindle. Let the tendon become taut in muscular contraction, and the fine branches of the sensory axon will be squeezed and so stimulated.

Later, the crucial fact was established {239} that sense organs (the "muscle spindles") existed in the muscles and were connected with sensory nerve fibers; and that other sense organs existed in the tendons and about {240} the joints. This sense accordingly might better be called the "muscle, tendon and joint sense", but the shorter term, "muscle sense", bids fair to stick. The Greek derivative, "kinesthesis", meaning "sense of movement", is sometimes used as an equivalent; and the corresponding adjective, "kinesthetic", is common.

The muscle sense informs us of movements of the joints and of positions of the limbs, as well as of resistance encountered by any movement. Muscular fatigue and soreness are sensed through the same general system of sense organs. This sense is very important in the control of movement, both reflex and voluntary movement. Without it, a person lacks information of where a limb is to start with, and naturally cannot know what movement to make; or, if a movement is in process of being executed, he has no information as to how far the movement has progressed and cannot tell when to stop it. Thus it is less strange than it first appears to learn that "locomotor ataxia", a disease which shows itself in poor control of movement, is primarily a disease affecting not the motor nerves but the sensory nerves that take care of the muscle sense.

1. Outline the chapter, rearranging the material somewhat, so as to state, under each sense, (a) what sense cells, if any, are present in the sense organ, (b) what accessory apparatus is present in the sense organ, (c) what stimuli arouse the sense, (d) what are the elementary responses of the sense, (e) peculiar blends occurring within the sense or between this sense and another, (f) what can be said regarding adaptation of the sense, and (g) what can be said regarding after-images of the sense.

2. Classify the senses according as they respond to stimuli (a) internal to the body, (b) directly affecting the surface of the body, (c) coming from a distance.

3. What distinctive uses are made of each sense?

4. Explore a small portion of the skin, as on the back of the hand, for cold spots, and for pain spots.

5. Try to analyze the smooth sensation obtained by laying the finger tip on a sheet of paper, and the rough sensation obtained by laying the finger tip on the surface of a brush, and to describe the difference in terms of the elementary skin sensations.

6. Is the pain sense a highly developed sense, to judge from its sense organ? Is it highly specialized? highly sensitive? How does its peculiarity in these respects fit it for its use?

7. Separation of taste and smell. Compare the taste of foods when the nostrils are held closed with the taste of the same food when the nostrils are opened.

8. Make a complete analysis of the sensations obtained from chocolate ice cream in the mouth.

9. Peripheral vision. (a) Color sense. While your eyes are looking rigidly straight ahead, take a bit of color in the hand and bring it slowly in from the side, noticing what color sensation you get from it when it can first be seen at all, and what changes in color appear as it moves from the extreme periphery to the center of the field of view, (b) Form sense. Use printed letters in the same way, noticing how far out they can be read, (c) Sense of motion. Notice how far out a little movement of the finger can be seen. Sum up what you have learned of the differences between central and peripheral vision. What is the use of peripheral vision?

10. Light and dark adaptation. Go from a dimly lighted place into bright sunlight, and immediately try for an instant to read with the sun shining directly upon the page. Remaining in the sunlight, {242} repeat the attempt every 10 seconds, and notice how long it takes for the eye to become adapted to the bright light. Having become light-adapted, go back into a dimly lighted room, and see whether dark-adaptation takes more or less time than light-adaptation.

11. Color adaptation. Look steadily at a colored surface, and notice whether the color fades as the exposure continues. Try looking at the color with one eye only, and after a minute look at the color with each eye separately, and notice whether the saturation appears the same to the eye that has been exposed to the color, and to the eye that has been shielded.

12. Negative after-images. Look steadily for half a minute at a black cross upon a white surface, and then turn the eyes upon a plain gray surface, and describe what you see. (b) Look steadily for half a minute at a colored spot upon a white or gray background, and then turn the eyes upon a gray background, and note the color of the after-image of the spot. Repeat with a different color, and try to reach a general statement as to the color of the negative after-image.

13. Positive visual after-images. Look in the direction of a bright light, such as an electric light, holding the hand as a screen before the eyes, so that you do not see the light. Withdraw the hand for a second, exposing the eyes to the light, and immediately screen the eyes again, and notice whether the sensation of the light outlasts the stimulus.

14. Tactile after-images. Touch the skin lightly for an instant, and notice whether the sensation ends as soon as the stimulus is removed. If there is any after-image, is it positive or negative?

15. Tactile adaptation. Support two fingers on the edge of a table, and lay on them a match or some other light object. Let this stimulus remain there, motionless, and notice whether the tactile sensation remains steady or dies out. What is the effect of making slight movements of the fingers, and so causing the stimulus to affect fresh parts of the skin?

16. Temperature sense adaptation. Have three bowls of water, one quite warm, one cold, one medium. After holding one hand in the warm water and the other in the cold, transfer both simultaneously to the medium water and compare the temperature sensations got by each hand from this water. State the result in terms of adaptation.

17. Overtones. These can be quite easily heard in the sound of a large bell. What use does the sense of hearing make of overtones?

For a somewhat fuller discussion of the topic of sensation, see Warren's Human Psychology, 1919, pp. 151-214; and for a much fuller discussion, see Titchener's Textbook of Psychology, 1909, pp. 46-224.

For a really thorough consideration of the facts and theories of color vision, see J. Herbert Parsons, An Introduction to the Study of Colour Vision, 1915.

For a more complete statement of the Ladd-Franklin theory, see the article on "Vision", in Baldwin's Dictionary of Philosophy and Psychology, 1902.

For a recent study that has revolutionized the psychology of the sense of smell, see Der Geruch, by Hans Henning, 1916, or a review of the same by Professor Gamble in the American Journal of Psychology, 1921, Vol. 32, pp. 290-296.

For an extensive discussion of the "Psychology of Sound", sec the book with this title by Henry J. Watt, 1917.

For a full account of taste, see Hollingworth and Poffenberger's Sense of Taste, 1917.

"Attention!" shouts the officer as a preliminary to some more specific command, and the athletic starter calls out "Ready!" for the same purpose. Both commands are designed to put the hearer in an attitude of readiness for what is coming next. They put a stop to miscellaneous doings and clear the way for the specific reaction that is next to be called for. They nullify the effect of miscellaneous stimuli that are always competing for the hearer's attention, and make him responsive only to stimuli coming from the officer. They make the hearer clearly conscious of the officer. They arouse in the hearer a condition of keen alertness that cannot be maintained for more than a few seconds unless some further command comes from the officer. In all these ways "attention" in the military sense, or "readiness" in the athletic sense, affords a good picture of the psychology of attention. Attention is preparatory, selective, mobile, highly conscious. To attend to a thing is to be keenly conscious of that thing, it is to respond to that thing and disregard other things, and it is to expect something more from that thing.

Attention is, in a word, exploratory. To attend is to explore, or to start to explore. Primitive attention amounts to the same as the instinct of exploration. Its natural stimulus is anything novel or sudden, its "emotional state" is curiosity or expectancy, and its instinctive reaction consists {245} of exploratory movements. Its inherent impulse is to explore, examine, or await.

Attention belongs fundamentally among the native forms of behavior. The child does not have to learn to attend, though he must learn to attend to many things that do not naturally get his attention. Some stimuli naturally attract attention, and others attract attention only because of previous experience and training. In considering the whole subject of attention, then, we shall in part be dealing with native responses, and in part with responses that are acquired. But the great laws of attention, which will come to light in the course of the chapter, are at the same time general laws of reaction, and belong under the head of native characteristics.

We can attend to anything whatever, but are more likely to attend to some things than to others. As stimuli for attention, some objects are much more effective than others, and the question is, in what way one object has the advantage over another. There are several ways, several "factors of advantage", we may call them.

Change is the greatest factor of advantage. A steady noise ceases after a while to be noticed, but let it change in any respect and immediately it arrests attention. The ticking of the clock is a good example: as long as it keeps uniformly on, it is unnoticed, but if it should suddenly beat faster or louder or in a different key, or even if it should stop altogether, it would "wake us up" with a start. The change in the stimulus must not be too gradual if it is to be effective, it must have a certain degree of suddenness. It may be a change in intensity, a becoming suddenly stronger or weaker; or it may be change in quality, as in tone, or {246} color, or odor; or it may be a change in position, a movement in space. When one who is holding our arm gives it a sudden squeeze to attract our attention, that is a change of intensity; when we step from the bank into the water, the sudden change from warmth to cold, that gets our attention without fail, is a change of quality; and something crawling on the skin attracts attention by virtue of its motion. Anything moving in the field of view is also an unfailing stimulus to attention.

Strength, or high intensity of a stimulus, is another important factor of advantage. Other things being equal, a strong stimulus will attract attention before a weak one. A loud noise has the advantage over a low murmur, and a bright flash of light over a faint twinkle.

In the case of visible objects, size has about the same effect as intensity. The large features of the landscape are noticed before the little details. The advertiser uses large type, and pays for big space in the newspaper, in the effort to attract the attention of the reader.

[Footnote: Often he pays more than the space is worth; at least doubling the size of his "ad" will not, on the whole, double the amount of attention he gets, or the number of readers whose attention he will catch. The "attention value" of an advertisement has been found by Strong to increase, not as fast as the increase in space, but about as the square root of the space occupied.]

Another similar factor is repetition. Cover a billboard with several copies of the same picture, and it attracts more attention than a single one of the pictures would. Repeat a "motive" in the decoration of a building, and it is more likely to be noticed. Repeat a cry or call several times, and after a while it may be noticed, though not at first. The "summation of stimuli" has much the same effect as increasing the intensity of a single stimulus.

If, however, a stimulus is repeated or continued for a long time, it will probably cease to hold attention, because of its {247} monotony, or, in other words, because it lacks the element of change.

Striking quality is an advantage, quite apart from the matter of intensity. Saturated colors, though no stronger in intensity of light than pale colors, are stronger stimuli for attention. High notes are more striking than low. Itch, tickle and pain get attention in preference to smooth touch. "Striking" cannot be defined in physical terms, but simply refers to the fact that some kinds of stimulus get attention better than others.

Definite form has the advantage over what is vague. A small, sharply defined object, that stands out from its background, attracts the eye more than a broad, indefinite expanse of light such as the sky. In the realm of sound, "form" is represented by rhythm or tune, and by other definite sequences of sound, such as occur in the jingles that catch the little child's ear.

The factors of advantage so far mentioned are native, and a stimulus possessing one or more of them is a natural attention-stimulus. But the individual also learns what is worth noticing, and what is not, and thus forms habits of attention, as well as habits of inattention. The automobile driver forms the habit of attending to the sound of his motor, the botanist forms the habit of noticing such inconspicuous objects as the lichens on the tree trunks. On the other hand, any one forms the habit of not noticing repeated stimuli that have no importance for him. Move into a house next the railroad, and at first you notice every train that passes; even at night you awake with a start, dreaming that some monster is pursuing you; but after a few days the trains disturb you very little, night or day. The general rule covering attention habits is this: anything that you have to work with, or like to play with, acquires the power to attract your attention, while anything that you do nothing {248} with loses whatever hold on your attention it may have possessed by virtue of its intensity, quality, etc.

Besides these permanent habits of attention, there are temporary adjustments determined by the momentary interest or desire. Stimuli relevant to the momentary interest have an unwonted hold upon attention, while things out of line with this interest may escape attention altogether, even though the same things would ordinarily be noticed. What you shall notice in the store window is governed by what you are looking for as much as by the prominence of the object in the total display. When you are angry with a person, you notice bad points about him that you usually overlook, and any aroused desire adjusts or "sets" attention in a similar way. The desire or interest of the moment facilitates attention to certain stimuli and inhibits attention to others, and is thus an important factor of advantage.

The interest of the moment is often represented by a question. Ask yourself what spots of red there are in the field of view, and immediately various red spots jump out and strike the eye; ask yourself what pressure sensations you are getting from the skin, and immediately several obtrude themselves. A question sets attention towards whatever may furnish an answer.

To sum up, we may say that three general factors of advantage determine the power of any stimulus to attract attention. There is the native factor, consisting of change, intensity, striking quality, and definite form; there is the factor of habit, dependent on past experience; and there is the factor of present interest and desire.

Attention is obviously a reaction of the individual to the stimulus that gets his attention; and it is in part a motor {249} reaction. The movements that occur in attending to an object are such as to afford a better view of it, or a better hearing of it, or, in general, such as to bring the sense organs to bear on it as efficiently as possible.

We may distinguish two sorts of motor reaction that occur in attention: the general attentive attitude, and the special adjustments of the sense organs. An audience absorbed in a speech or musical performance gives a good picture of the general attentive attitude. You notice that most people look fixedly towards the speaker, as if listening with their eyes, and that many of them lean forward as if it were important to get just as close as possible. All the little restless movements cease, so that you could "hear a pin drop", and at the tensest moments even the breath is checked. The attitude of attention is one of tense immobility, with the whole body oriented towards the object of attention. When the object of attention is something not present but thought of, a somewhat similar rigid attitude is assumed; the body is apt to lean forward, the neck to be held stiff, and the eyes to "stare at vacancy", i.e., to be fixed on some convenient object as a mere resting place, while attention is fixed outside the visual field altogether.

But we spoke of attention as mobile, and it would be strange if its mobility did not show itself in the motor reaction. It does in fact show itself in the sense organ adjustments which amount to exploratory reactions. Attention to an object in the hand is shown by "feeling of it", to a substance in the mouth by tasting movements, to an odor by sniffing movements, to a sound by cocking the head and turning the eyes towards the source of sound. The most instructive of this type of attention-reactions are those of the eyes. The eye is focused on the object that arouses attention, the lens being accommodated for its distance by the action of the little ciliary muscle inside the {250} eyeball; the two eyes are converged upon the object, so that the light from it strikes the fovea or best part of each retina; and the eyes are also turned up, down or sidewise, so as, again, to receive the light from the object upon the fovea.

This last class of eye movements is specially instructive and shows specially well the mobility of attention. Let a bright or moving object appear somewhere in the field of view--immediately the eyes turn towards it with a quick jump, fixate it for a few seconds and then jump elsewhere unless the object is found to be specially significant. Watch the eyes of one who is looking at a picture or scene of any sort, and you will see his eyes jumping hither and thither, as his attention shifts from one part of the scene to another. Ask him to abstain from this jumpy movement and let his eyes "sweep over" the scene, and he will confidently try to follow your instructions, but if you watch his eyes you will find them still jumping. In fact, "sweeping the glance" is a myth. It cannot be done. At least, there is only one case in which it can be done, and that is when there is a moving object to look at. Given an object moving at a moderate speed across the field of view, and the eyes can follow it and keep pace with it pretty accurately. But without the moving object as stimulus, the eyes can only execute the jump movement. There are thus two types of exploratory eye movement: the "jump" in passing from one object to another, and the "pursuit movement" in examining a moving object.

In reading, the eye moves by a series of short jumps from left to right along the first line of print, makes a long jump back to the beginning of the second line and another series of short jumps along that line, and so on. To appreciate the value of this jerky movement, we need to understand that each short jump occupies but a thirtieth to a fiftieth {251} of a second, while the "fixation pauses" between jumps last much longer, with the result that over ninety per cent. of the time spent on a line of print is fixation time, and less than ten per cent, is occupied in jumping from one fixation to the next. Now, it has been found that nothing of any consequence is seen during the eye jumps, and that the real seeing takes place only during the fixations. The jump movement, therefore, is simply a means of passing from one fixation to another with the least possible loss of time.

The eye sees an object distinctly only when at rest with respect to the object. If the object is still, the eye must be still to see it distinctly, and to see its different parts must fixate one after the other, jumping from one part to another. But if the object is in motion, the eye may still be able to see it distinctly by means of the pursuit movement, which is a sort of moving fixation.

Eye movement affords a good picture of the mobility of attention. Ordinarily the eye shifts frequently from one part of the field of view to another. When simply exploring a scene, it shifts about in what seems an indiscriminate way, though really following the principle of deserting each object as soon as it has been examined, and jumping to that other object which next has the advantage on account of movement, brightness, color, definite form, or habit of attention. In reading, however, the eye is governed by a definite interest, and moves consecutively along the series of words, instead of shifting irregularly about the page.

A moving object, or an object that is doing something, or even a complex object that presents a number of parts to be examined in turn, can hold the eye for some time. But it is almost impossible to hold the eye fixed for any length of time on a simple, motionless, unchanging object.

Attention is mobile because it is exploratory; it continually seeks something fresh for examination. In the presence of a complex of sights and sounds and touch stimuli, it tends to shift every second or two from one part of the situation to another. Even if you are lying in bed with your eyes closed, the movement of attention still appears in the rapid succession of thoughts and images, and some shift usually occurs as often as once a second.

A few simple experiments will serve to throw the shifting of attention into clearer relief. Look fixedly at a single letter written on a blank sheet of paper, and notice how one part after another of the letter stands out; notice also that attention does not stick absolutely to the letter, since thoughts obtrude themselves at intervals.

         O O O
          O O
         O O O
          O O
         O O O

Fig. 42.--A dot figure, from Sanford. Look steadily at it.]

Or, make a "dot figure", composed of six or eight or more dots arranged either regularly or irregularly, and look steadily at the collection. Probably you will find that the dots seem to fall into figures and groups, and that the grouping changes frequently. Objectively, of course, the dots are grouped in one way as much as another, so that any particular grouping is your own doing. The objective stimulus, in other words, is capable of arousing several grouping reactions on your part, and does arouse different reactions one after another

Shifting also appears in looking at an {253} "ambiguous figure", drawn so as to represent equally well a solid object in either of two different positions. The transparent cube, showing near and far edges alike, is a good example. Look steadily at such a drawing, and the cube will appear to shift its position from time to time. Numerous such figures can be constructed; the most celebrated is the ambiguous staircase. Look steadily at it, and suddenly you see the under side of a flight of stairs, instead of the upper; and if you keep on looking steadily, it shifts back and forth between these two positions.

Fig. 43.--The ambiguous cube figure.

Fig. 44.--The ambiguous staircase figure.

A still more striking case of shifting goes by the name of "binocular rivalry", and occurs when colors or figures that we cannot combine into a single picture are presented, {254} one to one eye, and the other to the corresponding part of the other retina. Hold red glass close in front of one eye and blue before the other, and look through both at once towards a bright background, and you will see red part of the time and blue part of the time, the two alternating as in the case of ambiguous figures.

Fig. 45.--Another ambiguous figure, which can be seen in three ways.

The stereoscope is a great convenience in applying inconsistent stimuli to the two eyes, and by aid of this instrument a great variety of experiments can be made. It is thus found that, if the field before one eye is a plain color, while the other, of a different color, has any little figure on it, this figure has a great advantage over the rival plain color and stays in sight most of the time. Anything moving in one field has a similar advantage, and a bright field has the advantage over a darker one. Thus the same factors of advantage hold good in binocular rivalry as in native attention generally.

A different kind of shifting appears in what is called "fluctuation of attention". Make a light gray smudge on a white sheet of paper, and place this at such a distance that the gray will be barely distinguishable from the white {255} background. Looking steadily at the smudge, you will find it to disappear and reappear periodically. Or, place your watch at such a distance that its ticking is barely audible, and you will find the sound to go out and come back at intervals. The fluctuation probably represents periodic fatigue and recovery at the brain synapses concerned in observing the faint stimulus.

Shiftings of the fluctuation type, or of the rivalry type either, are not to be regarded as quite the same sort of thing as the ordinary shiftings of attention. The more typical movement of attention is illustrated by the eye movements in examining a scene, or by the sequence of ideas and images in thinking or dreaming. Rivalry and fluctuation differ from this typical shifting of attention in several ways:

(1) The typical movement of attention is quicker than the oscillation in rivalry or fluctuation. In rivalry, each appearance may last for many seconds before giving way to the other, whereas the more typical shift of attention occurs every second or so. In fact, during a rivalry or fluctuation experiment, you may observe thoughts coming and going at the same time, and at a more rapid rate than the changes in the object looked at. Attention does not really hold steady during the whole time that a single appearance of an ambiguous figure persists.

(2) Rivalry shifts are influenced very little, if at all, by the factor of momentary desire or interest, and are very little subject to control.

(3) In rivalry, the color that disappears goes out entirely, and in looking at a dot figure or ambiguous figure you get the same effect, since the grouping or appearance that gives way to another vanishes itself for the time being. But when, in exploring a scene with the eyes, you turn from one object to another, the object left behind simply retires to the background, without disappearing altogether; and, {256} in the same way, when attention shifts from one noise to another, the first noise does not lapse altogether but remains vaguely heard. Or when, in thinking of a number of people, one after another comes to mind, the first one does not go out of mind altogether when attention moves to the next, but remains still vaguely present for a few moments.

Shifting occurs also in reflex action. Let two stimuli be acting at once, the one calling for one reflex and the other for the opposed reflex (as flexion and extension of the same limb), and the result is that only one of these reactions will occur at the same time, the other being completely inhibited; but the inhibited reflex gets its turn shortly, provided the two stimuli continue to act, and, in fact, the two reactions may alternate in a way that reminds us of binocular rivalry or ambiguous figures. Three fundamental laws of reaction here come to light.

(1) The law of selection: of two or more inconsistent responses to the same situation (or complex of stimuli), only one is made at the same time.

(2) The law of advantage: one of the alternative responses has an initial advantage over the others, due to such factors as intensity and change in the stimulus, or to habits of reaction.

(3) The law of shifting: the response that has the initial advantage loses its advantage shortly, and an alternative response is made, provided the situation remains the same.

These three laws hold good of reactions at all levels, from reflex action to rational thinking.

The mobility of attention obeys these same laws; only, attention is livelier and freer in its movements than reflex action or than the shifting in rivalry. Attention is more mobile and less bound to rigid rules.

The mobility of attention is only half the story. When we speak, for instance, of a student as having good powers of attention, we are not thinking of mobility but rather of the opposite.

Eye movement, which we employed before as a picture of the movement of attention, affords also a picture of sustained attention. Remember how the eye moves in reading. Every second it shifts, but still it keeps to the line of print. Just so, attention keeps moving forward in the story we are reading, but sticks to the story. The more absorbed we are in the story, the more rapidly we read. Attention is sustained here, and still it moves. Sustained attention is not glued to one point, by any means, but is simply confined to a given object or theme, within which its motion may be as lively as ever.

What is it, then, that sustains attention? Evidently it is the factor of present desire or interest, already mentioned. It is a reaction-tendency, aroused to activity by some stimulus or other, unable to reach its goal instantly, but persisting in activity for a while and facilitating responses that are in its line, while inhibiting others. Such a tendency facilitates response, i.e., attention, to certain stimuli, and inhibits attention to others, thus causing them to be overlooked and neglected.

For the student, the ideal attention-sustainer is an interest in the matter presented. If, however, he cannot get up any absorbing interest in the subject-matter at once, he may generate the necessary motive force by taking the lesson as a "stunt", as something to be mastered, a spur to his self-assertion. In the old days, fear was often the motive force relied upon in the schoolroom, and the switch hanging {258} behind the efficient teacher's desk was the stimulus to sustained attention. There must be some tendency aroused if attention is to be sustained. The mastery impulse is certainly superior to fear for the purpose, but better than either is a genuine interest in the subject studied.

In order to get up a genuine interest in a subject--an objective or inherent interest--it is usually necessary to penetrate into the subject for some little distance. The subject may not appeal to any of our native impulses, or to any interest that has been previously acquired, and how then are we to hold attention to it long enough to discover its inherent interest? Curiosity will give us a start, but is too easily satisfied to carry us far. Fear of punishment or disapproval, hope of reward or praise, being put on our mettle, or realizing the necessity of this subject for our future success, may keep us going till we find the subject attractive in itself.

So, when the little child is learning to read, the printed characters have so little attractiveness in themselves that he naturally turns away from them after a brief exploration. But, because he is scolded when his mind wanders from those marks, because other children make fun of his blunders, because, when he reads correctly, he feels the glow of success and of applause, he does hold himself to the printed page till he is able to read a little, after which his interest in what he is reading is sufficient, without extraneous motives, to keep his nose between the covers of the story book more, perhaps, than is good for him. The little child, here, is the type of the successful student.

Attention to a subject thus passes through three stages in its development. First comes the instinctive exploratory sort of attention, favored by the native factors of advantage. Next comes the stage of forced attention, driven by {259} extraneous motives, such as fear or self-assertion. Finally arrives the stage of objective interest. In the first and last stages attention is spontaneous, in the middle stage forced. The middle stage is often called that of voluntary attention, since effort has to be exerted to sustain attention, while the first and last stages, being free from effort, may be called involuntary.

Distraction is an important topic for consideration in connection with sustained attention. A distraction is a stimulus that attracts attention away from the thing to which we mean to attend. There are always competing stimuli, and the various factors of advantage, especially desire or interest, determine which stimulus shall get attention at any moment.

In the excited insane condition known as "mania" or the "manic state", the patient is excessively distractible. He commences to tell you something, all interest in what he has to say, but, if you pull out your watch while he is talking, he drops his story in the middle of a sentence and shifts to some remark about the watch. He seems to have no impulse persistent enough to hold his thoughts steady. There are contrary insane conditions in which it is almost impossible to distract the patient from his own inner broodings, so much is he absorbed in his own troubles.

Distraction is a favorite topic for experiment in the laboratory. The subject is put to work adding or typewriting, and works for a time in quiet, after which disturbances are introduced. A bell rings, a phonograph record is played, perhaps a perfect bedlam of noise is let loose; with the curious result that the subject, only momentarily distracted, accomplishes more work rather than less. The distraction has acted as a stimulus to greater effort, and by this effort {260} is overcame. This does not always happen so in real life, but it shows the possibilities of sustained attention.

There are several ways of overcoming a distraction. First, greater energy may be thrown into the task one is trying to perform. The extra effort is apt to show itself in gritting the teeth, reading or speaking aloud, and similar muscular activity which, while entirely unnecessary for executing the task in hand, helps by keeping the main stream of energy directed into the task instead of toward the distracting stimuli. Effort is necessary when the main task is uninteresting, or when the distraction is specially attractive, or even when the distraction is something new and strange and likely to arouse curiosity. But one may grow accustomed or "adapted" to an oft-recurring distraction, so as to sidetrack it without effort; in other words, a habit of inattention to the distracting stimulus may be formed. There is another, quite different way of overcoming a distraction, which works very well where it can be employed, and that is to couple the distraction to the main task, so as to deal with both together. An example is seen in piano playing. The beginner at the piano likes to play with the right band alone, because striking a note with the left hand distracts him from striking the proper note with the right. But, after practice, he couples the two hands, strikes the bass note of a chord with the left hand while his right strikes the other notes of the same chord, and much prefers two-handed to one-handed playing. In short, to overcome a distraction, you either sidetrack it or else couple it to your main task.

The subject of distraction brings to mind the question that is often asked, "Can any one do two things at once?" In this form, the question admits of but one answer, for we {261} are always doing at least two things at once, provided we are doing anything else besides breathing. We have no trouble in breathing and walking at the same time, nor in seeing while breathing and walking, nor even in thinking at the same time. But breathing, walking, and seeing are so automatic as to require no attention. The more important question then, is whether we can do two things at once, when each demands careful attention.

The redoubtable Julius Caesar, of happy memory, is said to have been able to dictate at once to several copyists. Now, Caesar's copyists were not stenographers, but wrote in long-hand, so that he could speak much faster than they could write. What he did, accordingly, was undoubtedly to give the first copyist a start on the first letter he wished to send, then turn to the second and give him a start on the second letter, and so on, getting back to the first in time to keep him busy. Quite an intellectual feat, certainly! But not a feat requiring absolutely simultaneous attention to several different matters. In a small way, any one can do something of the same kind. It is not impossible to add columns of numbers while reciting a familiar poem; you get the poem started and then let it run on automatically for a few words while you add a few numbers, switch back to the poem and then back to the adding, and so on. But in all this there is no doing of two things, attentively, at the same instant of time.

You may be able, however, to combine two acts into a single coördinated act, in the way just described under the head of distraction, and give undivided attention to this compound act.

Similar to the question whether we can attentively perform more than a single act at a time is the question of {262} how many different objects we can attend to at once. The "span of attention" for objects of any given kind is measured by discovering how many such objects can be clearly seen, or heard, or felt, in a single instant of time. Measurement of this "span" is one of the oldest experiments in psychology. Place a number of marbles in a little box, take a single peek into the box and see if you know how many marbles are there. Four or five you can get in a single glance, but with more there you become uncertain.

In the laboratory we have "exposure apparatus" for displaying a card for a fifth of a second or less, just enough time for a single glance. Make a number of dots or strokes on the card and see whether the subject knows the number on sight. He can tell four or five, and beyond that makes many mistakes.

Expose letters not making any word and he can read about four at a glance. But if the letters make familiar words, he can read three or four words at a glance. If the words make a familiar phrase, he gets a phrase of several words, containing as many as twenty letters, at a single glance.

Expose a number of little squares of different colors, and a well-trained subject will report correctly as many as five colors, though he cannot reach this number every time.

Bringing together now what we have learned regarding the higher and more difficult forms of attention, as revealed by sustained attention and work under distraction, by the span of attention and by trying to do two things at once, we find the previously stated three laws of attention further illustrated, and a couple of new laws making their appearance.

(1) The law of selection still holds good in these more {263} difficult performances, since only one attentive response is made at the same instant of time. Automatic activities may be simultaneously going on, but any two attentive responses seem to be inconsistent with each other, so that the making of one excludes the other, in accordance with the general law of selection.

What shall we say, however, of reading four disconnected letters at the same time, or of seeing clearly four colors at the same time? Here, it would seem, several things are separately attended to at once. The several things are similar, and close together, and the responses required are all simple and much alike. Such responses, under such very favorable conditions, are perhaps, then, not inconsistent with each other, so that two, three, or even four such attentive responses may be made at the same time.

(2) The law of advantage holds good, as illustrated by the fact that some distractions are harder to resist than others.

(3) The law of shifting holds good, as illustrated by the constant movement of attention, even when it is "sustained", and by the alternation between two activities when we are trying to carry them both along simultaneously.

(4) The law of sustained attention, or of tendency in attention, is the same old law of tendency that has shown itself repeatedly in earlier chapters. A tendency, when aroused to activity, facilitates responses that are in its line and inhibits others. A tendency is thus a strong factor of advantage, and it limits the shifting of attention.

(5) A new law has come to light, the law of combination, which reads as follows: a single response may be made to two or more stimuli; or, two or more stimuli may arouse a single joint response.

Even though, in accordance with the law of selection, only one attentive response is made at the same time, more than {264} one stimulus may be dealt with by this single attentive response. Groups of four dots are grasped as units, familiar words are grasped as units. Notice that these units are our own units, not external units. Physically, a row of six dots is as much a unit as a row of four, but we grasp the four as a unit in a way that we cannot apply to the six. Physically, six letters are as much a unit when they do not form a word as when they do; but we can make a unitary response to the six in the one case and not in the other. The response is a unit, though aroused by a number of separate stimuli.

The law of combination, from its name, is open to a possible misconception, as if we reached out and grasped and combined the stimuli, whereas ordinarily we do nothing to the stimuli, except to see them and recognize them, or in some such way respond to them. The combination is something that happens in us; it is our response. If the expression were not so cumbersome, we might more accurately name this law that of "unitary response to a plurality of stimuli".

Sometimes, indeed, we do make an actual motor response to two or more stimuli, as when we strike a chord of several notes on the piano. The law of combination still holds good here, since the movements of the two hands are coördinated into a single act, which is thought of as a unit ("striking a chord"), attended to as a unit, and executed as a unit. Such coördinated movements may be called "higher motor units", and we shall find much to say regarding them when we come to the subject of learned reactions. The law of combination, all in all, will be found later to have extreme importance in learned reactions.

Passing now to another side of the study of attention, we shall immediately come across a sixth law to add to our list.

Up to this point, the introspective side of the psychology of attention has not been considered. One of the surest of all introspective observations belongs right here, to the effect that we are more conscious of that to which we are attending than of anything else. Of two stimuli acting at once upon us, we are the more conscious of that one which catches our attention; of two acts that we perform simultaneously, that one is more conscious that is performed attentively.

We need not be entirely unconscious of the act or the stimulus to which we are not attending. We may be dimly conscious of it. There are degrees of consciousness. Suppose, for example, you are looking out of the window while "lost in thought". You are most conscious of the matter of your thoughts, but conscious to a degree of what you see out of the window. Your eyes are focused on some particular object outside, and you are more conscious of this than of other objects seen in indirect vision, though even of these last you are not altogether unconscious. Consciousness shades off from high light to dim background.

The "field of attention" is the maximum or high light of consciousness; it comprises the object under attentive observation, the reaction attentively performed. The "field of consciousness" includes the field of attention and much besides. It includes objects of which we are vaguely aware, desires active but not clearly formulated, feelings of pleasantness or unpleasantness, of tension, excitement, confidence, etc.

Apparently the field of consciousness shades off gradually into the field of unconscious activity. Some physiological processes go on unconsciously, and very habitual movements may be almost or entirely unconscious. The boundary {266} between what is vaguely conscious and what is entirely unconscious is necessarily very vague itself, but the probability is that the field of consciousness is broader than we usually suspect, and that many activities that we ordinarily think of as unconscious, because we do not observe them at the time nor remember them later, lie really near the margin of the field of consciousness, but inside that field. "Unconscious motives", such as spite or pride often seem to be, are probably vaguely conscious rather than unconscious. We shall return to the fascinating topic of the unconscious at the close of the book.

Degree of consciousness does not always tally with intensity of sensation or energy of muscular action. You may be more conscious of a slight but significant sound than of much louder noises occurring at the same time. You may be more conscious of a delicate finger movement than of a strong contraction of big muscles occurring at the same time. Degree of consciousness goes with degree of mental activity. Of all the reactions we are making at the same time--and usually there are several--the most active in a mental way is the most conscious. The slight sound arouses intense mental response because it means something of importance--like the faint cry of the baby upstairs, noticed instead of the loud noises of the street. The delicate finger movement aims at some difficult result, while the big muscles may be doing their accustomed work automatically.

It is not always the most efficient mental process that is most conscious; indeed, practising an act makes it both more efficient and less conscious. It is, rather, the less efficient processes that require attention, because they require mental work to keep them going straight.

Our sixth law of attention, emerging from this introspective study, is naturally of a different style from the remainder of the list, which were objectively observed; yet it {267} is no less certain and perhaps no less significant. It may be called:

(6) The law of degrees of consciousness, and thus stated: An attentive response is conscious to a higher degree than any inattentive response made at the same time. An inattentive response may be dimly conscious or, perhaps, altogether unconscious. The less familiar the response, and the higher it stands in the scale of mental performances, the more attentive it is, and the more conscious.

Attentive observation is more trustworthy than inattentive, and also gives more facts. Attentive movement is more accurate than inattentive, and may be quicker as well. Attentive study gives quicker learning than inattentive, and at the same time fixes the facts more durably.

Shall we say, then, "Do everything attentively"? But that is impossible. We sense so many stimuli at once that we could not possibly attend to all of them. We do several things at once, and cannot give attention to them all. A skilful performance consists of many parts, and we cannot possibly give careful attention to all the parts. Attention is necessarily selective, and the best advice is, not simply to "be attentive", but to attend to the right things.

In observation, the best plan is obviously to decide beforehand exactly what needs to be observed, and then to focus attention on this precise point. That is the principle underlying the remarkably sure and keen observation of the scientist. Reading may be called a kind of observation, since the reader is looking for what the author has to tell; and the rule that holds for other observation holds also for reading. That is to say that the reader finds the most when he knows just what he is looking for. We can learn {268} something here from story-reading, which is the most efficient sort of reading, in the sense that you get the point of the story better than that of more serious reading matter, the reason being that attention is always pressing forward in the story, looking for something very definite. You want to know how the hero gets out of the fix he is in, and you press forward and find out with great certainty and little loss of time. The best readers of serious matter have a similar eagerness to discover what the author has to say; they get the author's question, and press on to find his answer. Such readers are both quick and retentive. The dawdling reader, who simply spends so much time and covers so many pages, in the vague hope that something will stick, does not remember the point because he never got the point, and never got it because he wasn't looking for it.

In skilled movement, or skilled action of any sort, the best rule is to fix attention on the end-result or, if the process is long, on the result that immediately needs to be accomplished. "Keep your eye on the ball" when the end just now to be achieved is hitting the ball. Attention to the details of the process, though necessary in learning a skilled movement, is distracting and confusing after skill has been acquired. The runner does not attend to his legs, but to the goal or, if that is still distant, to the runner just ahead of him.

The chief facts to take account of in attempting to form a conception of the brain action in attention are mobility, persistence in spite of mobility, and focusing.

The mobility of attention must mean that brain activities are in constant flux, with nerve currents continually shooting hither and thither and arousing ever fresh groups of neurones; but sustained attention means that a brain {269} activity (representing the desire or interest or reaction-tendency dominant at the time) may persist and limit the range of the mobile activities, by facilitating some of these and inhibiting others.

The "focusing" of mental activity is more difficult to translate into neural terms. The fact to be translated is that, while several mental activities may go on at once, only one occupies the focus of attention. This must mean that, while several brain activities go on at once, one is superior in some way to the rest. The superiority might lie in greater intensity of neurone action, or in greater extent; that is, one brain activity is bigger in some way than any other occurring at the same time--bigger either because the neurones in it are working more energetically or because it includes a larger number of active neurones.

But why should not two equally big brain activities sometimes occur at the same moment, and attention thus be divided? The only promising hypothesis that has been offered to explain the absence of divided attention is that of "neurone drainage", according to which one or the other of two neurone groups, simultaneously aroused to activity, drains off the energy from the other, so putting a quietus on it. Unfortunately, this hypothesis explains too much, for it would make it impossible for minor brain activities to go on at the same time as the major one, and that would mean that only one thing could be done at a time, and that the field of consciousness was no broader than the field of attention. On the whole, we must admit that we do not know exactly what the focusing of attention can mean in brain terms.

1. Outline the chapter, in the form of a number of "laws", putting under each law the chief facts that belong there.

2. See if you can verify, by watching another person's eyes, the statements made on page 250 regarding eye movements.

3. Choose a spot where there is a good deal going on, stay there for five minutes and jot down the things that attract your attention. Classify the stimuli under the several "factors of advantage".

4. Mention some stimulus to which you have a habit of attention, and one to which you have a habit of inattention.

5. Close the eyes, and direct attention to the field of cutaneous and kinesthetic sensations. Do sensations emerge of which you are ordinarily only dimly conscious? Does shifting occur?

6. Of the several factors of advantage, which would be most effective in catching another person's attention, and which in holding his attention?

7. How does attention, in a blind person, probably differ from that of a seeing person?

8. Doing two things at once. Prepare several columns of one-place numbers, ten digits in a column. Try to add these columns, at the same time reciting a familiar poem, and notice how you manage it, and how accurate your work is.

9. Consider what would be the best way to secure sustained attention to some sort of work from which your mind is apt to wander.

Walter B. Pillsbury gives a full treatment of the subject in his book on Attention, 1908, and a condensed account of the matter in Chapter V of his Essentials of Psychology, 2nd edition, 1920.

Another full treatment is that of Titchener, in his Textbook of Psychology, 1909, pp. 265-302.

On the topic of distraction, see John J. B. Morgan's Overcoming of Distraction and Other Resistances, 1916.

Before leaving the general topic of native traits and passing to the process of learning or acquiring traits, we need to complete our picture of the native mental constitution by adding intelligence to reflex action, instinct, emotion, feeling, sensation and attention. Man is an intelligent animal by nature. The fact that he is the most intelligent of animals is due to his native constitution, as the fact that, among the lower animals, some species are more intelligent than others is due to the native constitution of each species. A rat has more intelligence than a frog, a dog than a rat, a monkey than a dog, and a man than a monkey, because of their native constitutions as members of their respective species.

But the different individuals belonging to the same species are not all equal in intelligence, any more than in size or strength or vitality. Some dogs are more intelligent than others, and the same is notably true of men. Now, are these differences between members of the same species due to heredity or environment? This question we can better approach after considering the methods by which psychologists undertake to measure intelligence; and an analysis of these methods may also serve to indicate what is included under the term "intelligence".

Not far from the year 1900 the school authorities of the city of Paris, desiring to know whether the backwardness of many children in school resulted from inattention, mischievousness and similar difficulties of a moral nature, or from genuine inability to learn, put the problem into the hands of Alfred Binet, a leading psychologist of the day; and within a few years thereafter he and a collaborator brought out the now famous Binet-Simon tests for intelligence. In devising these tests, Binet's plan was to leave school knowledge to one side, and look for information and skill picked up by the child from his elders and playmates in the ordinary experience of life. Further, Binet wisely decided not to seek for any single test for so broad a matter as intelligence, but rather to employ many brief tests and give the child plenty of chances to demonstrate what he had learned and what he could do. These little tests were graded in difficulty from the level of the three-year-old to that of the twelve-year-old, and the general plan was to determine how far up the scale the child could successfully pass the tests.

These were not the first tests in existence by any means, but they were the first attempt at a measure of general intelligence, and they proved extraordinarily useful. They have been added to and revised by other psychologists, notably by Terman in America, who has extended the scale of tests up to the adult level. A few samples from Terman's revision will give an idea of the character of the Binet tests.

From the tests for three-year-olds: Naming familiar objects--the child must name correctly at least three of five common objects that are shown him.

Six-year test: Finding omissions in pictures of faces, from which the nose, or one eye, etc., is left out. Four such pictures are shown, and three correct responses are required to pass the test.

Eight-year test: Tell how wood and coal are alike; and so with three other pairs of familiar things; two out of four correct responses are required to pass the test.

{273}

Twelve-year test: Vocabulary test--rough definitions showing the child's understanding of forty words out of a standard list of one hundred.

The question may be raised, "Why such arbitrary standards-three out of five required here, two out of four there, forty out of a hundred the next time?" The answer is that the tests have been standardized by actual trial on large numbers of children, and so standardized that the average child of a given age can just barely pass the tests of that age.

Intelligence is measured by Binet on a scale of mental age. The average child of, let us say, eight years and six months is said to have a mental age of eight years and six months; and any individual who does just as well as this is said to have this mental age, no matter what his chronological age may be. The average child of this age passes all the tests for eight years and below, and three of the six tests for age nine; or passes an equivalent number of tests from the total series. Usually there is some "scatter" in the child's successes, as he fails in a test here and there below his mental age, and succeeds here and there above his mental age, but the failures below and the successes above balance each other in the average child, so that he comes out with a mental age equal to his chronological age.

[Footnote: The Binet scale, it must be understood, is an instrument of precision, not to be handled except by one who has been thoroughly trained in its use. It looks so simple that any student is apt to say, "Why, I could give those tests!" The point is that he couldn't--not until he knew the tests practically by heart, not till he had standardized his manner of conducting them to agree perfectly with the prescribed manner and till he knew how to score the varying answers given by different children according to the scoring system that goes with the tests, and not till, by experience in handling children in the tests, he was able to secure the child's confidence and get him to do his best, without, however, giving the child any assistance beyond what is prescribed. Many superior persons have looked down on the psychological examiner with his (or her) assortment of little tests, and have said, "Certainly no special training is necessary to give these tests. You simply want to find out whether the child can do these stunts. I can find out as well as you." They miss the point altogether. The question is not whether the child can do these stunts (with an undefined amount of assistance), but whether he does them under carefully prescribed conditions. The child is given two, three or four dozen chances to see how many of them he will accept; and the whole scale has been standardized by try-out on many children of each age, and so adapted that when given according to instructions, it will give a correct measure of the child's mental age. But when given by superior persons in ignorance of its true character, it gives results very wide of the mark. So much by way of caution.]

If a child's mental age is the same as his chronological age, he is just average, neither bright nor dull. If his mental age is much above his chronological, he is bright; if much below, dull. His degree of brightness or dullness can be measured by the number of years his mental age is above or below his chronological age. He is, mentally, so many years advanced or retarded.

Brightness or dullness can also be measured by the intelligence quotient, which is employed so frequently that it is customarily abbreviated to "IQ". This is the mental age divided by the chronological, and is usually expressed in per cent. The IQ of the exactly average child, of any age, is 1, or 100 per cent. The IQ of the bright child is above 100 and of the dull child below 100. About sixty per cent. of all children have an IQ between 90 and 110, twenty per cent, are below 90 and twenty per cent, above 110. The following table gives the distribution in somewhat greater detail:

   IQ below 70,  1%
   IQ    70-79,  5%
   IQ    80-89, 14%
   IQ    90-99, 30%
   IQ  100-109, 30%
   IQ  110-119, 14%
   IQ  120-129,  5%
   IQ over 129,  1%
                ---
                100

For convenience, those with IQ under 70 are sometimes labeled "feeble-minded", and the others, in order, "borderline", "low normal", "average" (from 90 to 110), "superior", "very superior", "exceedingly superior"; but this is arbitrary and really unscientific, for what the facts show is not a separation into classes, but a continuous gradation from one extreme to the other. The lower extreme is near zero, and the upper extreme thus far found is about 180.

While the mental age tells an individual's intellectual level at a given time, the IQ tells how fast he has progressed. An IQ of 125 means that he has picked up knowledge and skill 25 per cent. faster than the average individual--that he has progressed as far in four years as the average child does in five, or as far in eight as the average does in ten, or as far in twelve as the average does in fifteen. The IQ usually remains fairly constant as the child grows older, and thus represents his rate of mental growth. It furnishes a pretty good measure of the individual's intelligence.

Since, however, the Binet tests depend greatly on the use of language, they are not fair to the deaf child, nor to the child with a speech defect, nor to the foreign child. Also, some persons who are clumsy in managing the rather abstract ideas dealt with in the Binet tests show up better in managing concrete objects. For all such cases, performance tests are useful. Language plays little part in a performance test, and concrete objects are used. The "form board" is a good example. Blocks of various simple shapes are to be fitted into corresponding holes in a board; the time of performance is measured, and the errors (consisting in trying to put a block into a differently shaped hole) are also counted. To the normal adult, this task seems too simple {276} to serve as a test for intelligence, but the young child finds it difficult, and the mentally deficient adult goes at it in the same haphazard way as a young child, trying to force the square block into the round hole. He does not pin himself down to the one essential thing, which is to match blocks and holes according to shape.

Another good performance test is the "picture completion". A picture is placed before the child, out of which several square holes have been cut. These cut-out pieces are mounted on little blocks, and there are other similar blocks with more or less irrelevant objects pictured on them. The child must select from the whole collection of little blocks the one that belongs in each hole in the picture. The better his understanding of the picture, the better his selection.

The tests so far described, because they have to be given to each subject individually, require a great deal of time from the trained examiner, and tests are also needed which can be given to a whole group of people at once. For persons who can read printed directions, a group test can easily be conducted, though much preliminary labor is necessary in selecting and standardizing the questions used. Group testing of foreigners, illiterates, and young children is more difficult, but has been accomplished, the directions being conveyed orally or by means of pantomime.

The first extensive use of group intelligence tests was made in the American Army during the Great War. A committee of the American Psychological Association prepared and standardized the tests, and persuaded the Army authorities to let them try them out in the camps. So successful were these tests--when supplemented, in doubtful cases, by individual tests--that they were adopted in the receiving {277} camps; and they proved very useful both in detecting those individuals whose intelligence was too low to enable them to learn the duties of a soldier, and those who, from high intelligence, could profitably be trained for officers.

The "Alpha test", used on recruits who could read, consisted of eight pages of questions, each page presenting a different type of problem for solution. On the first page were rows of circles, squares, etc., to which certain things were to be done in accordance with spoken commands. The subject had to attend carefully to what he was told to do, since he was given each command only once, and some of the commands called for rather complicated reactions. The second page consisted of arithmetical problems, ranging from very simple at the top of the page to more difficult ones below, though none of them went into the more technical parts of arithmetic. One page tested the subject's information on matters of common knowledge; and another called for the selection of the best of three reasons offered for a given fact, as, for example, "Why is copper used for electric wires? Because--it is mined in Montana--it is a good conductor--it is the cheapest metal." Another page presented disarranged sentences (as, "wet rain always is", or "school horses all to go"), to be put straight mentally, and indicated on the paper as true or false.

Many group tests are now in use, and among them some performance tests. In the latter, pictures are often employed; sometimes the subject has to complete the picture by drawing in a missing part, sometimes he has to cancel from the picture a part that is superfluous. He may have to draw a pencil line indicating the shortest path through a maze, or he may have to continue a series of marks which starts off according to a definite plan. The problems set him under each class range from very easy to fairly difficult.

The principal fact discovered by use of standardized intelligence tests is that the tests serve very well the purpose for which they were intended. In expert hands they actually give a fairly reliable measure of the individual's intelligence. They have located the trouble in the case of many a backward school child, whose intelligence was too low to enable him to derive much benefit from the regular school curriculum. His schooling needed to be adjusted to his intelligence so as to prepare him to do what he was constitutionally able to do.

On the other hand, it sometimes happens that a child who is mischievous and inattentive in school, and whose school work is rather poor, tests high in intelligence, the trouble with him being that the work set him is below his mental level and therefore unstimulating. Such children do better when given more advanced work. The intelligence tests are proving of great service in detecting boys and girls of superior intelligence who have been dragging along, forming lazy habits of work, and not preparing for the kind of service that their intelligence should enable them to give.

Some results obtained by the "Alpha test" are given in the following table, and in the diagram which restates the facts of the table in graphic form. The Alpha test included 212 questions in all, and a correct answer to any question netted the subject one point. The maximum score was thus 212 points, a mark which could only be obtained by a combination of perfect accuracy and very rapid work (since only a limited time was allowed for each page of the test). Very seldom does even a very bright individual score over 200 points. The table shows the approximate per cent, of individuals scoring between certain limits; thus, {279} of men drafted into the Army, approximately 8 per cent. scored below 15 points, 12 per cent. scored from 16 to 29 points, etc. Of college freshmen, practically none score below 76 points, 1 per cent. score from 76 to 89 points, etc.

             Per cent. of     Per cent. of
             drafted men      college freshmen
             making these     making these
             Scores           Scores
Scores
0-14 points     3              0

15-29          12              0

30-44          15              0

45-59          16              0

60-74          13              0

75-89          11              1

90-104          9              4

105-119         7              8

120-134         6             14

135-149         4             23

150-164         2             24

165-179         1.3           13

180-194         0.5            7

195-212         0.2            1
              -----          ---
              100            100

The "drafted men", consisting of men between the ages of twenty-one and thirty-one, fairly represent the adult male white population of the country, except in two respects. Many able young men were not included in the draft, having previously volunteered for officers' training camps or for special services. Had they been included, the percentages making the higher scores would have gone up slightly. On the other hand, many men of very low intelligence never reached the receiving camps at all, being inmates of institutions for the feebleminded or excluded from the draft because of known mental deficiency; and, of those who reached {280} the camps, many, being illiterate, did not take the Alpha test. It is for this reason that the graph for drafted men stops rather short at the lower end; to picture fairly the distribution of intelligence, it should taper off to the left, beyond the zero of the Alpha test.

Fig. 46.--Distribution of the scores of drafted men, and also of college freshmen, in the Alpha test. The height of the broken line above the base line is made proportional to the percent of the group that made the score indicated just below along the base line. (Figure text: army median--65, freshman median--150)

College freshmen evidently are, as they should be, a highly selected group in regard to intelligence. The results obtained at different colleges differ somewhat, and the figures here given represent an approximate average of results obtained at several colleges of high standing. The median {281} score for freshmen has varied, at different colleges, from 140 to 160 points.

[Footnote: The "median" is a statistical measure very similar to the average; but, while the average score would be obtained by adding together the scores of all the individuals and dividing the sum by the number of individuals tested, the median is obtained by arranging all the individual scores in order, from the lowest to the highest, and then counting off from either end till the middle individual is reached; his score is the median. (If the number of individuals tested is an even number, there are two middle individuals, and the point midway between them is taken as the median.) Just as many individuals are below the median as above it. The median is often preferred to the average in psychological work, not only because it is more easily computed, but because it is less affected by the eccentric or unusual performances of a few individuals, and therefore more fairly represents the whole population.]

It will be noticed in the graph that none of the freshmen score as low as the median of the drafted men. All of the freshmen, in fact, lie well above the median for the general population. A freshman who scores below 100 points finds it very difficult to keep up in his college work. Sometimes, it must be said, a freshman who scores not much over 100 in the test does very well in his studies, and sometimes one who scores very high in the test has to be dropped for poor scholarship, but this last is probably due to distracting interests.

No such sampling of the adult female population has ever been made as was afforded by the draft, and we are not in a position to compare the average adult man and woman in regard to intelligence. Boys and girls under twelve average almost the same, year by year, according to the Binet tests. In various other tests, calling for quick, accurate work, girls have on the average slightly surpassed boys of the same age, but this may result from the fact that girls mature earlier than boys; they reach adult height earlier, and perhaps also adult intelligence. College women, in the Alpha test, score on the average a few points below college men, but this, on the other hand, may be due to the fact that the Alpha test, being prepared for men, includes a few questions that lie rather outside the usual range of women's interests. On the whole, tests have given very little evidence of any significant difference between the general run of intelligence in the two sexes.

Tests of the Binet or Alpha variety evidently do not cover the whole range of intelligent behavior. They do not test {282} the ability to manage carpenter's or plumber's tools or other concrete things, they do not test the ability to manage people, and they do not reach high enough to test the ability to solve really big problems.