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PSYCHOLOGY

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PSYCHOLOGY

GENERAL AND APPLIED

BY

HUGO MUNSTERBERG

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D. APPLETON AND COMPANY NEW YORK AND LONDON

1920

BP 131

A475*

COPYRIGHT, 1914, BY

D. APPLETON AND COMPANY

Printed in the United States of America

To Herbert Sidney Langpeld0

PREFACE

It can hardly be claimed that a new textbook of psychology is needed because there is lack of old ones. On the contrary, we have a bewildering variety, and America has contributed a large and brilliant share. Yet the plan and aim of the present book are very different from all of them.

One difference is indicated even by its sub-title; it includes the applied psychology as well as the general. Hitherto the textbooks have been confined to the theo- retical study. The time seems ripe for bringing the psychological work into full contact with the practical efforts of civilization. The application of psychological studies to education and law, to industry and commerce, to health and hygiene, to art and science, deserves its place in the psychological curriculum. Thus the last third of this book may be a supplement to any other textbook.

But the book adds to the usual material still another essential part. The psychology of our textbooks is individual psychology; this volume also includes the social psychology. The processes which result from the social contact have traditionally been neglected, because individual psychology had to reach a certain completeness before the scientific interest could turn to social conscious- ness. But our day, which has seen the ripening of applied psychology, has brought us also the rapid growth of social psychology, and its outlines ought to be drawn in any map of the psychological world.

Finally, the traditional psychology is confined to descriptions and explanations. Very justly, such an ex- planatory account of mental life omits an entirely different

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viii PEEFACE

aspect, its inner meaning. But this meaning of the acts of our mind offers, after all, problems of its own. They must be solved; we cannot simply ignore them. This book, therefore, traces them in a special part, called Purposive Psychology. Our causal psychology is and must be a psychology without a soul; the purposive psychology culminates in the understanding of the soul and its freedom.

While the addition of an applied, a social and a pur- posive part makes the material of this book very different from the others, its method, too, deviates in many respects from the customary procedure. I may mention one nega- tive feature : it is not concerned with the structure of the brain and of the sense organs. A book which sketches the outlines of psychology cannot include the details of accessory sciences like the anatomy of the nervous system. In a college course the instructor may easily add such information and show pictures and models.

On the other hand, the book emphasizes the principles, both the biological-physiological and the philosophical. Those who dislike to touch philosophical problems in psychology can easily omit the chapters on the principles of causal psychology and again those on purposive psychology. Yet it is hardly wise to encourage this aver- sion for the wider aspects. Do we not deceive ourselves if we fancy that we can approach the study of mental states with the same naivete with which we can turn to the study of minerals and plants?

HUGO MtlNSTERBERG. Harvard University, May, 1914.

CONTENTS

INTRODUCTION THE AIMS OF PSYCHOLOGY

PAGE

CHAPTER

I. The Interest in Psychology 1

Naive interest in psychology, 1. Scientific interest in psychology, 4.

II. The Realm of Psychology ...... 7

The definitions of psychology, 7. The two standpoints in psychology, 10. Demand for consistency, 14. Causal and purposive psy- chology, 15.

BOOK I

CAUSAL PSYCHOLOGY

PART I. PRINCIPLES OF CAUSAL PSYCHOLOGY

III. Psychological Explanation 21

Psychological laws, 21. The unconscious, 24. The subconscious dispositions, 26. The subconscious operations, 28.

IY. Psychophysical Explanation 34

Connection of mind and brain, 34. Psy- chophysical parallelism, 39.

Y. Scope and Methods op Causal Psychology . 43 The subdivisions of psychology, 43. Self- observation, 47. Indirect observation, 50. Experimental psychology, 52. ix

x CONTENTS

PART II. THE INDIVIDUAL PROCESSES A. THE ELEMENTARY INDIVIDUAL PROCESSES

CHAPTER PAGE

VI. The Nervous System 59

The sense organ-brain-muscle arc, 59. The development of the nervous system, 61. The biological aspect of man, 65.

VII. Stimulation 70

The psychical elements, 70. Optical stimu- lation : The system of light sensations, 72 ; Saturation and brightness, 75; The visual stimuli, 78. Auditory stimulation : The system of sound sensations, 85; The acoustic stimuli, 87. The lower sense stimulations : Taste, 95 ; Smell, 97; Touch, 98; Temperature, 100. In- ternal stimulation : Movement sensations, 101 ; Feeling sensations, 105.

VIII. Association ............ 107

After-effects in the nerve centers, 107. As- sociation by contiguity, 111. Association by similarity, 113. The character of the repro- duction, 116. Conditions of association, 119.

IX. Reaction 122:

The motor process, 122. The sensory ef- fects of the motor processes, 127

X. Inhibition ...... 131

The suppression of mental contents, 131. The central problem of inhibition, 135. The inhibition of actions, 138. The action theory, 139.

B. THE COMPLEX INDIVIDUAL PROCESSES

XI. Perception 145

Unity of perception, 145. The elements of space perception, 147. Space perception and muscle action, 150. Theory of space percep-

CHAPTER

CONTENTS xi

v PAGE

tion, 152. Perception of time, 156. Percep- tion of meaning, 160.

XII. Ideas . . 165

Memory, 165. Imagination, 170. General ideas, 172.

XIII. Activity 176

The impulse feeling, 176. The rivalry of motives, 179. Complex actions, 183. Atten- tion, 187. The thought process, 192.

XIV. Inner States 196

Pleasure and displeasure, 196. The physio- logical basis of simple feelings, 198. The manifoldness of feelings, 201. Emotions, 203. The esthetic attitude, 207. The intellectual attitude, 209.

XV. Personality 213

The unity of the personality, 213. Self- consciousness, 216. The variations of the per- sonality, 221.

PART III. THE SOCIAL GROUP A. ELEMENTARY GROUP PROCESSES

XVI. Individual Differences • • 224

The aim of social psychology, 224. Child- hood and maturity, 227. Sex and race, 231. Character and temperament, 235. Intelli- gence, 238. Abnormal variations, 241.

XVII. Union

The conditions of organization, 246. Volun- tary and involuntary communication, 248. Language, 250. Associations, 251.

XVIII. Submission ■ •

Suggestion and selfassertion, 254. Imita- tion and sympathy, 259. Aggression and self- expression, 262.

246

254

xii CONTENTS

B. THE COMPLEX SOCIAL PROCESSES

CHAPTER PAGE

XIX. Organization 265

The individual and the social mind, 265. Involuntary combinations, 269. Intentional combinations, 273.

Achievement 275

The biological aspect, 275. Material and methods, 277. The types of social achieve- ments, 278.

BOOK II PURPOSIVE PSYCHOLOGY

PART I. PRINCIPLES OF PURPOSIVE PSYCHOLOGY

XXI. Immediate Reality 285

The two psychologies, 285. Causal psy- chology and reality, 288. Scientific recon- struction, 290. Purposive understanding, 293.

XXII. The Soul 297

Purposive acts and causality, 297. Pur- posive acts and time, 301. The connection of purposive acts, 302. The function of the soul, 306.

PART II. THE INDIVIDUAL EXPERIENCES

XXIII. Meaning 310

Meaning in practical life, 310. Problems and methods, 312. The pointing to an oppo- site, 315. The affirmation of sameness, 316.

XXIV. Creation . .'.... 321

Analysis of purposes, 321. The freedom of the will, 323. The creative power, 326.

CONTENTS xiii

PART III. THE SOCIAL EXPERIENCES

CHAPTER PAGE

XXV. Practical Relations 329

Understanding, 329. Interpretation, 330. Social intercourse, 331.

XXVI. Ideal Relations 335

The ideal purposes, 335. The normative acts, 336.

BOOK III

APPLIED PSYCHOLOGY PART I. PRINCIPLES OF APPLIED PSYCHOLOGY

XXVII. The Aim of Practical Psychology .... 341 The present situation of practical psychol- ogy, 341. The limitations of applied psy- chology, 346.

XXVIII. The Psychohistorical Sciences 352

Two types of application, 352. Historical individuals, 356. Historical social events, 359. History and purposive psychology, 363*

PART II. THE PSYCHOTECHNICAL SCIENCES

XXIX. Educational Psychology 365

The educational purposes, 365. The im- parting of knowledge, 369. The development of abilities, 375. The arousing of feelings, 380. The work of the pupils, 3S2. The se- lection of studies, 386. Adjustment to indi- vidual differences, 389.

Legal Psychology 395

The report of the witness, 395. Memory and suggestibility of the witness, 398. The discovery of hidden ideas, 402. The court and the criminal, 406. Prevention of crime, 409.

XIV

CHAPTER

XXXI.

XXXII.

XXXIII.

CONTENTS

PAGE 4.1 Q

Economic Psychology • • •

Psyehotechnies of commerce and industry, 413. The selection of the industrial worker, 415. The adjustment by experimental meth- ods, 418. The apprentice, 421. The technic, 423. Monotony and fatigue, 425. The inter- ests of commerce, 428.

Medical Psychology • *°J

The practical standpoint, 435. Diagnosis of physical disturbances, 437. Diagnosis of mental disturbances, 438. The effect of drugs, 443. Psychotherapy, 443. Prevention of dis- ease, 448.

4.KO Cultural Psychology . * ~* *

The outlying fields of psyehotechnies, 452. Life enjoyment, 454. The fine arts, 455. Music and poetry, 460. The work of the sci- entist, 462. The work of the historian and of the philologist, 466. The work of the psy- chologist, 469.

PSYCHOLOGY

INTRODUCTION. THE AIMS OF PSYCHOLOGY

CHAPTER I

THE INTEREST IN PSYCHOLOGY

Naive Interest in Psychology. — Long before we turned to any scientific psychology, we all were interested in the traits of mental life. To be sure, we watched our material surroundings and were captivated by the happenings of outer nature, before we became aware of the processes in our inner life. But, after all, everybody noticed early whether his memory worked well or badly, how his atten- tion sometimes failed him, how he was able or unable to think out a problem, how fear or hope, and joy or anger, arose in him. He may have been startled by the wonders of his dreams or by the play of his imagination; he may have thought about the limits of his personal talents or about the special gifts of his mind; he may have felt con- flicts between his resolutions and his will. In short, the naive curiosity which turned first to toys and tools, to stones and plants, later turned to memory ideas and fancies of the imagination, to feelings and excitements, to acts of desire and of volition, to talent and intelligence. They cannot be found without: the attention must turn inward to observe them. But at the same time we knew and

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2 PSYCHOLOGY

watched the inner life of the other people around us. We became aware of the varied behavior of men and followed their expression, we tried to understand their peculiar ways and became interested in the display of emotions of those with whom we were in contact. This interest in the behavior of other beings extends to dog and horse and bird.

All such naive observing of our own mental life and of that of our friends satisfies the natural desire for knowl- edge, even if the knowledge is not useful for any practical ends. Yet the practical life drives us steadily toward such observation, too. "We do not want merely to take notice of the curious fact that something which we did remember has slipped from our memory, or that the solution of a, problem suddenly rushes to our mind, or that our atten- tion wanders away during a lecture, or that our liking was stronger than our will. We want to understand still more how much we can trust our memory and our attention and our will, and how we can train our mind or how we can suppress an unwelcome emotion. Above all, we want to look into our neighbor's mind for our practical purposes. How will he behave? His friendliness or his unkindness, his carefulness or his negligence, his good or his bad mem- ory, his humor or his character, may be matters of deep concern to us. We try to foresee how another's mind will work just as we try to foresee how the physical instruments and the chemical substances will help or hinder us.

At first all this remains unconnected, and does not shape itself into any general idea of mind and mind's action. But it easily leads further from mere curiosity to an ear- nest interest. The haphazard knowledge of human be- havior becomes broader, we notice regularities which occur in our mental life, we get a clearer insight into its limita- tions, and we may be led to a common sense theory about the nature of that inner being. We begin to think about the relation of the mind to the body, of freedom and re-

THE INTEKEST IN PSYCHOLOGY 3

sponsibility, of the inheritance of mental qualities, of the life of the mind after death. In the same way our obser- vation of mental life in the interest of practical purposes becomes deeper and wider. The manifold purposes of civi- lization demand this from us. We cannot bring up chil- dren or teach them in classrooms without carefully watch- ing their mental qualities and without trying to foresee how their minds will work in new situations. "We cannot deal with criminals in the courtroom without trying to analyze the motives which impel them. Nor can we be in politics without thinking about the ideas and impulses, the character and the abilities of the public men. We cannot be interested in industrial problems and social questions without giving attention to the mind of the workingman, to his fatigue and to his feelings, to the strain on his attention and to the satisfaction of his desires.

Theoretical interest and practical demands alike lead us in this way at first to a naive, and then to a deliberate, watching of mental life, and by this to the gate of psy- chology. We need only to make the observation more painstaking and careful, more extended and systematic, and we are in the midst of psychology. Of course as soon as we aim toward such deliberate study of the mind, we shall apply more reliable methods than a mere occasional watching of events in our inner life or in the behavior of our neighbors. The botanist, when he examines the plants, can no longer be satisfied with the way in which the friend of nature strolls through the woods and the meadows, pick- ing the flowers which he likes along the path; he seeks definite kinds of plants, dissects them and studies them under his microscope. The psychologist, too, will make himself independent of mere chance, will collect his data from the widest fields of human experience, will produce mental processes at will in order to examine them, will pro- voke all kinds of mental behavior in man and animal, will compare the mental characteristics in adult and child, in

4 PSYCHOLOGY

man and woman, in normal and diseased persons, in dif- ferent races and under different conditions of life. He will repeat and repeat his observations, will disentangle the complex inner states and will seek the elements from which they are composed, and he, too, will use subtle instruments and carefully adjusted apparatus to discover the real facts. But with all this refinement of method and with the expan- sion of the outlook, the original interest does not change its character, but only its strength and seriousness.

Scientific Interest in Psychology. — The motives which may lead us to the systematic study of psychology are as manifold as the naive interests. First of all, we want to understand the working of the mind, the laws which con- trol its processes, the conditions under which it works, the effects which it produces ; we want to understand the inner ties between our mental states, their meaning, the elements which enter into them. This theoretical science will branch out into special sciences which deal with child psychology or pathological psychology or animal psychology or the psychology of individual differences. Moreover the study cannot be confined to single individuals. Their mental life is combined in social action. If we are to understand mental life, we must follow up the working together of human minds from the simplest contact in a friendly talk to the firmest connections in a life of mutual devotion, from the narrowest circle of the family to the widest circle of the civilized nations. The behavior of the social group and the laws of the social mind and the meaning of the social impulses thus fall no less into the compass of psycho- logical interest.

But, as on the level of simple commonsense, so now on the higher level of science, we cannot remain merely theoretical. The practical demands take control of our endeavors. This is not meant in a trivial sense of mere selfish usefulness. Those practical motives with which we may approach the study of psychology are of service to

THE INTEREST IN PSYCHOLOGY 5

the highest tasks of cultured society. The aims of educa- tion and justice, of health and social reform, of industrial enterprise and esthetic achievement, make it daily more necessary to understand the mental factor which enters into the social practice. The engineer must recognize that the mind of the workingman is no less important for the final industrial outcome than the machines. The lawyer cannot confine his interest to the legal problem; he must understand the working of the minds of all who figure in the court, the defendant and the plaintiff, the witness and the jury. The teacher of our modern days knows that an understanding of the mind of the pupils is worthy of the same scholarly effort which is devoted to the content of instruction. The physician is aware that his drugs and his remedies must be supplemented by carefully adjusted in- fluences on the mind of the patient.

The application of psychological knowledge, however, may not be limited to the practical tasks to be fulfilled. We may apply psychology for the understanding of the life around us and of the life which has passed away. With the interest of the historian we may try to analyze the psychological processes of the events of earlier times. The personalities of the heroes and the movements of the masses, the leaders in politics and in war, in religion and in art and in every unfolding of civilization may be brought nearer to our understanding by the application of psy- chology. The great wars and revolutions, the growth of nations and their decay, the development of religions and arts, the changes in the language and customs, all may be explained with the help of psychological knowledge.

We desire to know and to understand the working of the mind with the theoretical interest with which we study the stones and the stars. We feel the practical interest which makes us master the mental reality to use it as a tool for the purposes of civilization. Yet these are not the only motives for such a study. The interests which

6 PSYCHOLOGY

lead toward the pursuit of scholarly psychology may arise from a still deeper source. We want to understand the problems of inner life and of human behavior, because we feel, at first vaguely, that they are intimately connected with the ultimate questions of our life reality. To under- stand the science of our mind then no longer means to acquire some little specialists knowledge, as if we were to learn a chance chapter of natural science or history, but it means insight into the last meaning of our total exist- ence: what are we, and whence do we come? Is our will free in its decisions, or is it dependent upon the actions of the brain? Is our mind really controlling our body, or are our mental processes only accompanying the currents in the nervous system? And such questions lead at once to those of freedom and responsibility, and further on to the deepest problems of duty and morality, and ultimately of religion. Or again we may turn to psychology under the pressure of other philosophical doubts. We seek truth and beauty and morality in the belief that these ideals have a lasting value of their own; must not our loyal belief be undermined by the understanding that such thoughts of ideals are merely processes in individual minds, and thus dependent upon the psychological laws? How can these ideals be valid for us personally, how can they be binding for mankind, if they are nothing but the passing states of our mind, like memories and dreams? The deepest con- cerns of our soul are here involved.

CHAPTER II THE REALM OF PSYCHOLOGY

The Definitions of Psychology.— We have discussed the reasons why men may turn to psychology, but we have not as yet stated what psychology really is. We have gone on without any exact definition ; we have so far left every- thing in the vague and indefinite form in which common- sense takes hold of it. We have spoken of inner life or of mental states or of human behavior, of observing our inner experience, of understanding personalities, of describing and explaining the processes of the mind, and we have used some other similarly general terms without even asking whether they characterize correctly the aims of the psy- chologist. We might just as well have spoken of the soul or of consciousness, or, to use the more scholarly term, of psychical phenomena. No one of such phrases was pro- posed as a definition to mark out clearly the work which the student of psychology has to take up.

Usually textbooks of psychology begin with a precise definition. We have abstained from that, because there is some danger involved in such a starting point. All astron- omers agree as to what astronomy can be and ought to be; but the psychologists disagree as to the aims of psychology. Only where a consensus of opinion exists can it be right to begin at once with a definite statement of what the par- ticular science is called to undertake. Where different views are possible we have hardly a right to go to the work with a more or less arbitrary decision that one defini-

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8 PSYCHOLOGY

tion and not another is to be accepted. To discover what psychology really is, ought to be the goal of a penetrating inquiry. Various possibilities ought to be considered. The neglect of this demand has too often led to a regrettable one-sidedness. It may even be that the inner life de- mands different kinds of scientific treatment, which may be equally justified and which may equally fall into the com- pass of that which the vagueness of commonsense would call psychology. Then we should have no right to say that, because one kind of psychology is valuable, therefore no other exists. There may be two or more standpoints pos- sible in psychology, and a general definition ought to be wide enough to include them. Yes, it may be said that to reach a clear understanding as to the true meaning of psy- chology is a more difficult task than the solution of any special psychological problem. And it must be frankly confessed that, while modern psychology has made rapid progress in the mastery of the special facts, it has pro- gressed only slowly toward this fundamental problem of psychology, what its aim ought to be.

This may seem to some a slow way of approach. They are anxious to come to the actual facts of mental life and to study the realities of conscious experience instead of en- tering into cumbersome discussions about the principles and underlying purposes of psychology. They do not want abstract theories, which seem to them a wrangling about words, but are longing for a knowledge of concrete proc- esses and their laws. But such a desire for a hasty ap- proach to the details is ill advised; its hope is illusory. The uncritical rush toward the mental states cannot bring us nearer to them. We must know first what kind of facts belong to our study, and what way of approach is de- manded by it. And if we do not settle these preliminary questions patiently, we cannot wonder if later we find confusion among the so-called facts.

The objects of psychology cannot be collected like flow-

THE REALM OF PSYCHOLOGY 9

ers, which we pick, and butterflies, which we catch, and which we can bring home and show to others. Memory ideas and imaginative acts, feelings and emotions, volitions and judgments are not facts which can be picked or caught. And if we speak of them, describe them to others, and make their meaning clear, or explain them, we must have somehow settled for ourselves those problems of theory. We cannot take hold of any mental facts without seeing them through some kind of a theory, and, if we really aim toward a consistent view of mental life, we have no right to be satisfied with the superficialities of commonsense or with the dogmatic statements of an arbi- trary definition : we must really examine what it means to> speak of psychological facts, and how psychology is to approach them.

As to certain aims, to be sure, all psychologists agree. Here, above all, belongs their decision to abstain from any judgment of value. If the psychologist approaches mental life, he has no interest in asking whether the mental states are valuable or not. He does not care whether the will impulses in the mind are good or bad, moral or im- moral, whether the imaginings of the mind are beautiful or ugly, whether the thoughts in the mind are wise or foolish, whether the emotions of the mind are holy or sinful. The dissecting botanist is interested in the ugliest weed as much as in the beautiful flower, the chemist cares for the con- stitution of the deadly poison as much as for that of the helpful drug. In the same way the psychologist is surely interested in the analysis of the criminal act as much as in that of the heroic deed, in the babbling of the insane mind as much as in the reasoning of the thinker, in the silliest • play of the infant as much as in the highest crea- tive processes of the artistic mind. He remains the neutral observer who understands and explains the mental events without forming a judgment on them. As soon as he begins to evaluate them he oversteps the boundaries of his

10 PSYCHOLOGY

realm and is trespassing on the fields of logic, ethics and esthetics.

But so long as we only agree that the value aspect of mental life is not accessible to the psychologist, we have not settled anything as to his material. "We may begin here, too, with a negative claim: the psychologist is not concerned with the outer physical objects. The processes and laws of bodies as such are never the material for a psychological study. Yet with this we are already approaching debatable ground. Some might doubt the correctness of this sweeping statement, and limit it to the inorganic world and the vegetable kingdom. They would say that, if we approach the bodies of the animals and above all the bodies of the human organisms, we have a part of the physical world before us which is of greatest importance for the psychologist. But there is no real contradiction. Nobody can doubt that the mental life which the psychologist studies is most intimately connected with the functions of the body, of the nervous system, of the brain. But while it is so firmly connected, and while the body and its functions are thus indeed of deepest im- port for the psychologist, the body is not itself the real object of his study. The growth of the flowers is intimately dependent upon the soil and the water and the light, and yet water and light and soil are not the objects of the botanist's study. The mental life may be dependent upon the nervous system and the brain, but it does not consist of such physical processes.

The Two Standpoints in Psychology. — The elements which we have gathered so far in order to define the aims of psychology are two. We have said that the psycholo- gist is interested only in the inner experiences as against the outer physical world, and that he has to do with them in a theoretical way, abstaining from all judgments of value, from all liking and disliking, praising and blam- ing. But this is certainly still insufficient for a positive

THE EEALM OF PSYCHOLOGY 11

account of his actual work, because the chief question re- mains: what is inner experience, what is our inner per- sonal life? The difficulty lies in the fact that we can take account of ourselves in several ways and the inner experience may thus appear as something very different, from different standpoints. The frequent failure to dis- criminate them is more than anything else responsible for the confusion and the shortcomings in the field of psy- chology. We can take two fundamental attitudes toward the inner experience, and both are important and signifi- cant; we have no right to prefer the one to the exclusion of the other, or, worst of all, to mix the two in a hap- hazard way. Those two attitudes do not start with schol- arly psychology. They prevail in our ordinary life and are intertwined in our daily intercourse. "We may per- haps suggest the difference at first in saying that we can try to explain mental life and that we can try to under- stand mental life.

If someone asks us a question, our aim is to understand what he has in mind. We try to enter into his thought and to understand his feeling about it, in order to take an attitude toward the question in answering yes or no. If we succeed, we feel sure that we have grasped everything which is in the questioner's mind. His whole inner experi- ence has become clear to us and is completely under- stood. Yet exactly the same mental process of the ques- tioner might awake in us an entirely different interest. Instead of considering the meaning, we might ask our- selves what causes these thoughts and feelings. How did those ideas enter the mind? Are they perhaps effects of some earlier experience? How do those questions arise in consciousness, and from what elements are they composed ? Then we look on the other man 's mind as a kind of mental mechanism, made up of a variety of mental states, the appearance and disappearance of which demand some kind of explanation. We may even explain them by brain

12 PSYCHOLOGY

processes of which the questioner himself does not know anything, or by after-effects of earlier impressions which he may have forgotten.

These two standpoints present themselves in every bit of experience. If a man commits a crime, we may be interested in understanding the motives and aims in his mind, and, if we are to judge his deed, we certainly must try to think ourselves into his mind, in order to understand his action from the inside. His emotions and his volition, his crime, everything is to be understood as the expression of his personality. Only through this do we enter into his self. Yet we might study the same criminal from an en- tirely different point of view ; we might ask ourselves from what causes this criminal deed arose in this man. How far are his education, his life habits, his surroundings, his state of health responsible for the development of these impulses ? How far did the fatigue of his brain, or the in- fluence of alcohol, or a disease produce the abnormal im- pulse ? What causes interfered with the mental resistance of his will? From what source did the ideas or the mem- ories and the hopes or fears arise, and how did they come to result in that criminal deed?

In the most trivial conversations or in the most moment- ous situations of life the mind with which we are dealing may in this way be to us either a self into whose purposes we enter, or a bundle of mental states which are linked to- gether. In the same act of experience we may change be- tween the two standpoints. The crying child may awaken our sympathy, and we naturally try to understand his pain, or his sorrow. But at the next moment we think how to distract his attention, that is, we think how to cause in his mind a new process by which the displeasure will become inhibited. To do this the child's mind must be looked on as a set of connected processes in which the effects which will result can be determined beforehand.

Yet this twofold way of looking into the neighbor's

THE EEALM OF PSYCHOLOGY 13

mind shows itself no less when we think of our own mental life. We go through the world and mingle among men, each one always feeling himself as an individual person- ality whose feelings and ideas are his real self. Our love and hate, our likes and dislikes, our agreeing and disagree- ing, our thinking of this and of that, are the acts which stand for our personal life. We live in those feelings and emotions and thoughts; we ourselves are those inner activ- ities. And yet we may consider this same inner life as if we were spectators looking on at that procession of inner events, observing the happenings in our own consciousness. Then we give our attention to the structure of our mem- ories and imaginative ideas, perceptions and thoughts, and even our feelings and emotions and volitions then lie before us like objects of which we become aware. Anyone who begins self observation is forced to take just such an atti- tude toward his inner life. He watches himself, looks out for every bit of sensation, of feeling, which he finds in his mind, in order to describe them, and if possible to explain them. A greater contrast can hardly be imagined : on the one side the stream of life in which our will and feeling and thought are to us meaning and expression of our self, and on the other side the neutral taking account of the processes in our mind as if they were a spectacle which we are objectively watching.

Surely the first standpoint is the more natural one. If you and I talk with each other, I do not only take you as such a subject whom I am to understand, but I feel my- self as a subject who agrees and disagrees, who likes and dislikes what you say, and who wants his own opinion to be understood. It is quite improbable that I have reasons to watch my mental states as objects, while we are engaged in our conversation. But if I afterward begin to think about it, I may very well call back those ideas and emo- tions of mine and make them pass before my inner eye as mere mental happenings which come and go like the clouds

14 PSYCHOLOGY

and the sunshine and the landscape outside, and I may analyze them and observe their elements, their structure, their connections and their effects. It is a somewhat arti- ficial method : it is artificial like all analysis and dissection. It is more natural to drink the water than to analyze it in the laboratory into its chemical elements. But if we want to understand what we can expect from the water, we must determine its constitution and examine its properties. It is indeed a kind of scientific, naturalistic attitude toward our inner life, when we begin to treat it like a series of objects. But as soon as we want to foresee what effects are to be expected and what causes are at work and how the parts hang together, we cannot help choosing this artificial standpoint.

Demand for Consistency. — The psychologist has no right to indulge in any mixing of the two modes of ap- proach. No doubt, it is always easier to be inconsistent, and the temptation to such inconsistency is great here. As long as the psychologist gives account of the perceptions and the memories, the colors and the tones, the smells and the noises, it appears so much more convenient to describe them as various contents in the mind and to analyze them and then to turn to their explanation. On the other hand, if he has to give account of feelings and volitions and emo- tions, of character and temperament and judgment, it seems so much easier to take the other standpoint and to speak of their meaning and to interpret their purposes. But if we do so we can never reach a consistent and unified account of mental life, and that must after all remain the goal which the psychologist cannot give up. As long as he is to describe and to explain, he cannot acknowledge that there is anything in the mind which does not allow such description and explanation. He must feel like the nat- uralist, who takes it for granted that everything in the universe is subordinated to natural laws. Correspondingly, if we are to interpret mental life and to understand it

THE EEALM OF PSYCHOLOGY 15

in its meaning, then we must do justice to such a demand for every function of our mind. Our own personal life and that of our friends and our foes then comes in question only as an expression of meaning, and everything has to be looked on from that point of view.

In medieval times the astronomers tried to explain some movements of the stars by their natural laws, and some by the fact that the angels were moving the stars. We know to-day that no consistent view of the universe can be gained, if we mix two such different accounts. Either we interpret the processes of nature religiously as an ex- pression of God and his angels, or we explain them through causal laws. Either viewpoint will yield us a unified aspect of the world, but we have no right to combine the laws and the angels in one scientific picture. The psychol- ogist who makes us understand inner life by interpreting the meaning and following up the inner purposes, gives us indeed a perfectly unified view of man 's mind ; and so does the other psychologist who treats mental life as a mechanism which is to be described and to be explained as a causal system. In other words, we must acknowledge a true psychology as complete only if it allows room for two different aspects of personal experience, each of which must be consistently carried through. Both kinds of psychology are justified, if they are carried through with this con- sistency. To recognize the difference means to do justice to both sides. Life needs both ; science cannot ignore them. A complete psychology must deal with the whole mental life as a system of mental processes to be explained, and must deal in another part with the whole mental life as an expression of personality to be understood in its meaning. The two parts must supplement each other.

Causal and Purposive Psychology. — It means very little what name we give to the two aspects of psychical experi- ence, but it means extremely much to keep them cleanly separated and to recognize distinctly the principles which

16 PSYCHOLOGY

control them. "We might call the one aspect objective and the other subjective. Sometimes the first has also been called a psychology of mental states and the other a psy- chology of the self. Again a quite characteristic choice of titles is to call the first the psychology of the content of consciousness and the other the psychology of meaning. We might also speak of explanatory psychology as against interpretative psychology. Yet we prefer the designation which points most directly to the deepest character of the contrast, and shall call the one the causal psychology, the other the purposive psychology.

To understand mental life as a system of causes and effects is indeed the most significant aim of the one kind of study ; and to understand it in its meanings, and that is, in its purpose, is the fundamental condition for the other kind. Everything else, the special principles and the spe- cial methods and the special conceptions, follows from this parting of the ways. Every further discussion ought there- fore to refer to the one aspect or to the other. Hence our introduction to the total study of psychology has here reached its end, because from now on we must separate the two groups of inquiries, until they finally reach a point where they come together again. That meeting point is reached in applied psychology which speaks of the prac- tical application of mental facts in the service of our hu- man purposes. The selection of those purposes is a matter of purposive psychology, the mental effects to be used a matter of causal psychology. They are thus joined in that practical part which comes nearest to real life. But, until we reach it, we must be loyal to the chosen one-sidedness with which we follow mental life at first only on the one, and then only on the other side.

The programme for this book is thus clear and evident. We shall speak first of the causal aspect of the mental life, then of the purposive aspect and finally of the prac- tical aspect. Both in the causal and in the purposive

THE KEALM OF PSYCHOLOGY 17

psychology we shall discuss first the general principles and methods, then the individual processes, and finally the so- cial processes. It is necessary indeed to keep this plan con- stantly before our mind. Then only every detail can be understood in its right proportion. Otherwise it would be necessary to put before every paragraph of the causal psychology a danger signal which would warn the student not to take this account as the whole truth, but to remem- ber that the purposive aspect of the same mental act is no less true and no less significant. But we trust that this is not needed. We shall resolve the personality into the ele- mentary bits of psychical atoms and shall bring every will act into a closed system of causes and effects. But in the purposive part we shall show with the same con- sistency the true inner unity of the self and the ultimate freedom of the responsible personality. Those two ac- counts do not exclude each other; they supplement each other, they support each other, they demand each other. The last part of the purposive psychology will bring us to a height from which this inner harmony of the two aspects becomes clear. Then every feeling of contradiction will disappear, and we shall be forced to see that causality and freedom, complexity and unity, natural laws and ideals do not interfere with one another, but can be combined in an ultimate view of pulsating reality.

One of the household instruments of our psychological laboratories is the well-known stereoscope, into which two fiat pictures of a landscape are put. The left eye sees an ordinary photograph of a landscape from the left, the right eye the same landscape taken from the right, and either gives the incomplete impression of a flat surface. But as soon as both pictures are seen with the two eyes together, the two one-sided, flat impressions disappear and instead of them one lifelike vista of the scene is perceived with its depth and plastic fullness. We too have to draw at first the one, and then the other picture of man's ex-

18 PSYCHOLOGY

perience, each taken from a special standpoint, each re- maining one-sided, flat and lifeless. But we shall see, if both are grasped together and combined in a higher unity of understanding, that they blend into one plastic view of personality, with the true depth and fullness of real life.

BOOK I. CAUSAL PSYCHOLOGY

PAET I. PKINCIPLES OF CAUSAL PSYCHOLOGY

CHAPTER III

PSYCHOLOGICAL EXPLANATION

Psychological Laws. — The aim. of the causal psycholo- gist is the explanation of the mental processes. How is true explanation possible? The physicist who seeks expla- nations for the occurrences in nature tries to find the proc- esses which regularly precede other processes in experience. From the regularities which he observes he develops the physical laws and reaches through that the first stage of explanation. He knows the law that, if an electric cur- rent is closed, a certain magnetic phenomenon happens, and, if the electric current is broken, the magnetic phenomenon stops. The law allows it to be determined beforehand whether the magnetic power of the iron will appear or not. There seems to be no difficulty for the psychologist in observing such regularities also among the processes of the mind. We notice often that after one process in con- sciousness another process occurs. The taste of candy brings with it a certain feeling of pleasure; the taste of cod liver oil brings just as regularly a feeling of dis- pleasure. Moreover the feeling of pleasure, as soon as it has become a process in consciousness, awakes another process, namely the will to keep that sensation. The un- pleasant feeling stirs up the will to get rid of the im- pression. Such regular connections can be found a thou- sand times in our daily life, and, if we are interested in

21

22 PSYCHOLOGY

watching them in subtler detail, we can observe them under exact conditions.

No doubt, if we proceed with such observations, we can secure a large number of psychological laws. To mention one which we may use as a typical illustration, we may think of a law which has been known as long as psycholo- gists have studied the human mind, a law formulated by the first great psychologist, Aristotle: the law of associa- tion. If we ever experience two things together, the ideas of the two become linked in such a way that whenever the one idea is brought to our consciousness again the other idea arises too. Everyone has observed that. We have met a man and we have heard his name, and that visual idea of his face and that acoustical idea of his name were tied together; the law of association makes it necessary that, if we meet the man again, his name comes to our mind, or if we hear the name we remember how he looks. From such a loose, vague form the psychological observation can easily be carried to very exact connections, which can be verified only by careful studies. We shall find in the course of our work many such psychological laws which characterize the regular behavior of our perceptions and memories, our feelings and volitions. They are the con- densed expressions of frequently observed uniformities in the succession of psychical contents. But can they really furnish us a true explanation, and are they sufficient for the causal understanding of our mind?

The first fundamental difficulty with an explanation of mental life through such psychological laws lies in the evident disconnectedness and incompleteness of the ma- terial in consciousness. This shows itself in a twofold form, on the one side in our perceptions, on the other side in the ideas, volitions and higher mental processes. In- deed, how could we hope to explain by any observed regu- larities in the mental content the appearance of the per- ceptive impressions. I hear at this moment the ringing of

PSYCHOLOGICAL EXPLANATION 23

bells, that is, the tone sensation arises in my consciousness. If I were to rely on strictly psychological explanation, I should have to seek in my own consciousness for causes which effected the appearance of this sound impression. But nothing in my mind suggested to me the coming of this sound. I did not think of bells before, which might have produced in my mind the tone sensations. My mind was filled with entirely different contents, when suddenly these tone sensations of bells broke in. Nothing which preceded in my consciousness seems to offer the least foot- hold for the explanation of these tone sensations. But the same is true, of course, of every visual impression which comes to my mind or of every touch, of every word which is spoken to me and of every printed line which I read. Everything enters into my consciousness as a new content for which I cannot possibly seek the causes in the preced- ing contents of consciousness, and for which, therefore, any explanation through strict psychological laws seems illog- ical.

But the other aspect of the incompleteness is no less striking: complex ideas, words, impulses, emotions, thoughts arise constantly in our consciousness without any preceding contents which could really explain their ap- pearance. We try to think of a name, and, while we are in the midst of entirely different engagements, the name suddenly pops into our head. We were occupied with a problem, and, after we were no longer thinking of it, the solution appeared over the horizon of our consciousness. A melody arises in our mind, a fancy of imagination appears, without any noticeable cause, a mood takes control of us, we do not know why. But we can go much further. Let us think of the case of ordinary speaking. In common conversation the words come to our mind, while we are speaking them; we are generally not aware of any causes in our consciousness which determine the selection of the particular words. We hear the question and we give the

24 PSYCHOLOGY

answer offhand before we discover in our consciousness any ideas which may lead to the reply. It is as if just the con- necting links of thought are left out, or, rather, are hidden from our conscious awareness.

This fundamental difficulty has led to two types of theories, both of which seek to explain the coming and going of the conscious contents by agencies and processes which are not in consciousness. They leave the sphere of selfobservation in order to supply a connected chain of causes and effects. The one puts the responsibility on psychical processes which lie outside of consciousness : it is a theory of the unconscious mind or of the subconscious. The other seeks the explanation not through psychical causes at all, but turns to the brain processes of the or- ganism, explaining the changes in the mental life indirectly by changes in the nervous system. We must examine the right and wrong, the value and the limits of both schemes of explanation. The unconscious has the first right to be considered, as it has the advantage of remaining in the world of the psychical.

The Unconscious. — Mental processes which are not con- tained in a consciousness are usually called unconscious. But this word is often carelessly used for processes which do not really lie outside of consciousness. Especially in the study of abnormal mental life we frequently use the term unconscious, where we actually mean that the content of an experience and the act of experience itself are entirely forgotten. The somnambulist who awakes in the morning and finds that he wrote a letter during the night, of which he no longer knows anything, is said to have written it unconsciously. But we have no reason to believe that dur- ing the act of writing he was not fully aware of his activ- ity. He saw the letter paper as if he were in a normal waking state. The abnormal happening consisted rather in the fact that this conscious experience left no memory traces in his mind. As we are accustomed to remember

PSYCHOLOGICAL EXPLANATION 25

what was in our consciousness, everything which is entirely extinguished appears to us as if it never had been in our consciousness. We find the same abnormal processes in certain mental diseases or in hypnotic states and in all such cases we have no right to relegate to the unconscious that which has slipped from consciousness and which cannot be brought back.

Again we often say that something was not done con- sciously where we really mean that it was not done with a full harmonious use of all mental energies. The man who is poisoned by a drug or who is in the delirium of fever or in a state of drunkenness or in the midst of an attack of mental disease may behave without selfcontrol and without the regulation by the idea of his own self. Hence he may be considered not responsible for his actions. We may even say that he has acted without selfconscious- ness, but we have no right to say that he was unconscious. The content of his consciousness was chaotic, but his ideas and emotions and volitions, however disorderly, passed on just as much in consciousness as if he were in normal health.

We are here interested only in those mental processes which are really not in consciousness at all, and only these are covered by our term. Yet it is doubtful whether the word unconscious would be the most significant. It too easily suggests anything which is not conscious and that means that the whole physical universe could be called un- conscious too. If we want to separate the unconscious stones on the street from the unconscious mental states in ourselves, we shall have to call these psychical processes subconscious. As the iceberg in the ocean shows only its smallest part above the surface of the water while far the largest part is below, a small part of our mental contents can be found above the surface of consciousness, while most of them remain below, subconscious.

This theory is widespread and popular, because it fits

26 PSYCHOLOGY

temptingly into any purpose of explanation. But if we approach its detail, we must recognize that it does not fulfill its promises and is thoroughly unsatisfactory. The pur- pose is to explain the appearance of the contents of con- sciousness. Those who want to reach this end through the hypothesis of the subconscious believe that they find all the necessary requisites in two assumptions. First they imagine that all our experiences sink into the subconscious when they disappear from consciousness. There they are stored up and lie unused until they, are brought to con- sciousness again. Something reminds me of a street which I passed years ago and of a talk which I had on that street corner. The picture of the houses, the phrases of our talk, come back to me. In order to explain that, I am ex- pected to believe that those sights and those* words were lying somewhere at the bottom of my mind. I never thought of them during the years which have passed ; thus they surely were not in consciousness. Yet how could I bring them back, if they had not lasted in some subcon- scious form. The mere lying in the subconscious, however, is not enough. Something must have selected them now and must have pushed them at this moment from the sub- conscious over the threshold into consciousness. There must be some activity at work or at least some interplay of the ideas ; in short, it is not enough to believe that rem- nants of old experiences are kept below consciousness, but the theory must demand secondly that all the time activ- ities and processes go on in the subconscious, just as in our conscious mind. Those subconscious ideas must pro- duce new thoughts, must start impulses to action, must select the words which we are to speak and must look out for everything which is to be done by us, and which is not proceeding in the light of our consciousness. "We may examine these two sides of the theory independently.

The Subconscious Dispositions. — The first claim is the existence of those mental memory traces. All our school

PSYCHOLOGICAL EXPLANATION 27

knowledge which we can call back, everything which we have seen or heard, tasted or smelt, must linger somewhere in that obscure region. Such an assumption is from the start utterly fantastic. In consciousness ideas interfere with one another, feelings inhibit one another; we cannot be happy and miserable at the same time. But in the para- dise of the subconscious the lion and the lamb are to lie down together. The millions of impressions and joys and pains and feelings exist subconsciously together without destroying one another. Ultimately such a hopeless theory is nothing but a crude materialism. The mental ideas are treated as if they were little balls or cubes which can be piled up, and this means that the ideas are imagined to be like physical things which last. Our inner experience demands a very different view. The conscious states are processes which take place, and when the process is ended it remains no more than the tunes of the piano remain in the piano case or the athletic movement in the muscles. We can think the same idea always anew, just as we can play the same melody on the piano or perform the same athletic feat. But we cannot imagine that the tones are hidden in the strings of the piano and the muscle move- ments kept in store in the limbs.

Hence it is at least an improvement, if it is claimed that not the ideas themselves remain in the subconscious, but only dispositions for the appearance of the mental proc- esses. The mind somehow holds traces of all the French words and historical dates which we learned, but these traces are not real syllables and sounds but only slum- bering dispositions out of which through the activity of the mind new copies of the old ideas can be generated. Can this really help us? If the appearance of a conscious process is dependent upon a subconscious disposition, how are we then to explain our perceptions of the outer world? I hear the bells ringing. The sounds enter my conscious- ness. Must I suppose that I have a subconscious disposi-

28 PSYCHOLOGY

tion for these bell sounds, and even for this new melody of the bells which I have never heard before. Of course, then I must have such a disposition for everything on earth which can enter into the sphere of my senses. I must have a disposition for the smell of the chemical substance which some chemist may produce to-morrow in his laboratory. All those dispositions resulting from my little personal ex- periences are then insignificant compared with the trillions for all which may possibly become the object of my sense perceptions.

But as soon as we take refuge in such an unlimited hypothesis, it becomes entirely useless. If there is in our mind a disposition for everything imaginable, it can no longer serve as an explanation for the particular idea which comes to our mind. Then we must have the dis- positions not only for the French words which we learned, but also for the Chinese words which someone may teach us later. Yet no one would accept such a gigantic appa- ratus for the explaining of our sensations. It would seem so much more natural that I hear the bells because the sound waves of the bells reach my ear and stimulate my ear nerve and finally my brain, and that my brain excite- ment is the real cause for my hearing the sounds. We are practically relying on such a theory all the time. We do not feel surprised that even the newest color and taste and smell awake impressions in our consciousness, because they have somehow stimulated and excited our eye and brain. We do not demand a special psychological disposition be- sides. At any moment the perceptions of our senses can arise in our consciousness without any subconscious mental dispositions, simply through the excitation of our brain. Then is it not illogical to require such mental forerunners in the case of the memory ideas, instead of seeking here too the causes in a brain process, as in the case of the perceptions ?

The Subconscious Operations. — The other function of

PSYCHOLOGICAL EXPLANATION 29

the subconscious was that of the selective activity, of awak- ing and stirring up, of inhibiting and suppressing, of link- ing the ideas and connecting the thoughts in order to pro- duce those results which finally appear in consciousness. We know that many a problem is solved in our mind with- out our following the process step by step in consciousness. We form our decisions, we shape our plans, we get our inspirations in processes of which we know consciously only the beginning and the end, but all the necessary inter- play of ideas and all the linking of motives which evidently lie between must have gone on in the subconscious. Hence the theory insists in the interest of explanation that exactly the same mental processes which go on in full self-conscious attention can proceed also in the subconscious underworld. As soon as this is granted, it seems as if all difficulties were removed. The processes below consciousness offer them- selves the more conveniently as no one can know them from direct observation and anything can be ascribed to them which seems desirable for a neat explanation. The most complicated mental operations can easily be attached to such an unconscious mind. Just here, however, we are working under a complete illusion, which we must dispel.

In the interest of explanation we postulate that the same mental operations can go on subconsciously which we know from our conscious experience. But we do so before we ask the decisive question, namely, whether even those con- scious operations are really able to produce the mental ef- fects. It may be that we are unable to explain any mental results by those processes which proceed in consciousness. In that case it would evidently be absurd to explain them by the same processes below consciousness. And just this is indeed the case.

The ideas which follow one another in consciousness may appear in their order thousands of times; and yet the mere fact that they occur again and again does not link them to real causes and effects. They follow one another,

30 PSYCHOLOGY

but no causal necessity binds them together. Take once more the case of the association of ideas. The flower I see by the roadside brings to my mind its botanical name which I learned years ago, and if someone mentions to me the name of the flower, that brings to my consciousness the visual image of the flower, as I saw it before. I rely on that power of my memory, just as I rely on the laws of electricity which make the lamp burn when I turn the switch. Certainly my memory may not render the service at a particular time ; I may have forgotten the name or the picture of the flower may have faded away or I may con- fuse it with a similar plant. But this does not interfere with the working of the association law, any more than the laws of electricity are to be given up because my lamp may be burnt out or the contact of the switch may have become defective. Yet there remains a fundamental dif- ference between any such psychological connection and a physical one.

The physicist sees before him the goal of bringing all the processes in nature ultimately to mere mechanical move- ments of atoms. This alone gives a definite meaning to his view of the world. The mere observation of regularities is only the starting point for him. What has happened a hundred times may be different the hundred and first time. He has a right to predict the event for the hundred and first time only if he can recognize the necessity of the process ; and this is reached only if he can bring it down to mechanical movements of the smallest particles. Under the pressure of such a demand he develops his physical theories of ether waves and so on, and splits what he calls atoms at one stage into still smaller fragments like the electrons, but he can never rest until he sees somehow the connection between the mere observed regularity in nature and those necessary mechanical movements. The natural scientist may be in many fields of physics or chemistry still very far from this ideal, but it remains the guiding

PSYCHOLOGICAL EXPLANATION 31

star. He takes it for granted that if he knew the whole truth every change in the outer world could be explained by a mere change of position of the smallest parts. No theories, not even the new ones of the dynamic type, have really ' altered these scientific assumptions, as long as the theories really aimed toward scientific explanation and not to a mere purposive interpretation of nature. On this background the scientist has a right to claim that all his laws are meant as expressions of causal necessity.

The psychologist has nothing to offer which is similar. He cannot speak of such necessity in the connection of psychical facts in consciousness. This is not because psy- chology is still too incomplete and too far from its goal, but because this cannot possibly be the goal of psychology. It lies in the nature of the psychical objects that, however much regularity we may find in their behavior, they can newer be directly linked by causal necessity. We may* observe that the flower brings us its name or that the name brings the picture of the flower, but that mental impression of the flower and that mental idea of the name are simply two events which follow each other, while we have not the slightest insight into a mental mechanism which could be supposed to link them. The whole play of connection in the physical world is conceivable, because every bit of those physical objects remains and changes only its place. The candle may disappear when it burns down, but every atom of it can still be traced in the atmo- sphere. Of the mental objects the opposite is true. The single mental experience is an act which is going on but which does not last, which cannot be found again any- where in the mental universe. We may have a thousand times new ideas of the same object, but the same idea cannot come back a second time. The same hope, the same anger, the same desire, the same decision cannot be brought to consciousness once more. If we feel and will with the same intent, we must go through the performance

32 PSYCHOLOGY

anew; we cannot revive the withered will of yesterday, and, where nothing lasts, we cannot conceive a really neces- sary connection.

This is not accidental; it cannot be otherwise. This whole splitting of our experiences into physical things and into men- tal things is artificial and is not suggested by immediate ex- perience. We do not find the flower in the field and beside that our perception of the flower in our mind. The flower which we pick there is neither that complex of atoms of which the physicist speaks nor that content of consciousness of which the psychologist speaks. It is both in one, and it is in the interest of explaining the world that we divide that impression into two parts, the physical and the mental object. We call physical the object in so far as it can be grasped in ever new experiences; it is a physical object in so far as everyone can look at it, and as we ourselves can return to it ever anew. On the other hand, we call the object mental in so far as it is given only in the one act of our personal awareness. This then in- volves that the physical object lasts and that its parts can never disappear from the universe, and that the psychical object can never exist beyond that one act of immediate awareness and that it can never reappear. The physical objects, accordingly, change only their positions and their movements can be traced through their necessary paths, because each particle lasts. In consciousness no mental object can be followed up, because it can never last; it has given itself out in the act in which it appears in consciousness. Hence it would be meaningless to seek a true causal connection between two succeeding mental objects, however often we may observe their succession.

But if we must acknowledge that the psychical objects which we know in consciousness cannot furnish us with any understanding of causal connection, it is evident that the subconscious mental objects would not do it either. We wanted to introduce the hypothesis that there are sub- conscious ideas exclusively for the purpose of furnishing a causal explanation for the mental interplay. The as-

PSYCHOLOGICAL EXPLANATION 33

sumption was that those subconscious mental states might then produce the same effects as the conscious states. But as we see now that the conscious states themselves are unfit for a real explanation of causes and effects, it would be utterly useless to duplicate them in the subconscious. Even if such subconscious ideas and feelings and volitions ex- isted, they could not contribute anything to the explana- tion: they would again simply follow one another without our understanding why they come and go. Such a hy- pothesis would be entirely useless. We must acknowledge that there is no causal necessity which directly links the changes in the world of mental objects. We know such necessity only in the physical world.

Such a conclusion must not be misunderstood. It would be absurd to misinterpret it as if it were meant to say that there cannot be necessity in our inner life. On the con- trary, all our thinking and feeling and doing are bound together by ties of inner necessity. If we think logically, the premises of our thoughts bind us in forming our conclusions. Our pledge binds our will in its actions. But this inner necessity which gives real meaning to our whole life and in which our duties and obligations lie, refers to the purposive aspect of our inner experience. If we take our thoughts and wills in their meaning, then, of course, they are firmly linked together. As soon as we come to the discussion of the purposive psychology, we shall see that everything there is controlled by this inner necessity. But here we are in the midst of the discussion of causal psychology in which the ideas and volitions are not looked on as purposes which we interpret, but as objects which we find in consciousness and which we want to describe and to explain. And only for this onesided objective aspect the last word must be that there is no direct causal connection possible and that it cannot be introduced by the construction of a subconscious mental machinery.

CHAPTER IV PSYCHOPHYSICAL EXPLANATION

Connection of Mind and Brain. — ¥e have seen that a real insight into the necessary connections of mental states cannot be gained and can never be hoped for from mental processes alone, whether conscious or subconscious. Only when we have recognized this fundamental difficulty in the efforts for psychological explanation can we un- derstand the way which modern psychology has taken so successfully. It starts from the commonsense experience that our light and sound impressions depend upon the light and sound in the surrounding physical world. We find a succession of tones in our consciousness, because someone plays the piano. But everyone knows too that the mere existence of the physical tones or of the colored lights is in itself not sufficient to awake the sound or the red or the green in our consciousness. Those processes in the outer world, the vibrations of the string in the piano, or the light vibrations of the painting, must reach our sense organs, our ear or eye. If the eyelid is closed, the colors do not produce color sensations.

Scientific observations, however, easily lead beyond this matter of course knowledge. The scientist knows that it is not enough for the light rays to reach the eye, but that the nerve which connects the eye with the brain must be intact too. If it is cut or destroyed by disease, the light which falls into the eye cannot awake the light sen- sations in consciousness. Moreover even if the nerve is undisturbed, it is essential that those brain parts to which

34

PSYCHOPHYSICAL EXPLANATION 35

the nerve leads be in working order. If by a hemorrhage in the rear part of the brain the so-called optical centers are made ineffective, the patient becomes blind. Hence the true connection between the physical and the mental event cannot be established between the light sensation and the light ray; it exists rather between light sensation and the brain process which is produced through the action of the eye under the stimulation of the light. Taste and smell, pressure of weight and contact and temperature must stimulate the sense organs first and then the nerve and finally the brain for sweet or sour, touch or warmth to be felt. Even if the physical process occurs in our own body, if a muscle is swollen or a tooth is revolting, the ache cannot be felt unless the nerve can conduct the irri- tation to the brain.

But it seems no less a matter of course that mind and body are connected wherever an action is performed. I have the will to grasp for the book before me and obedient- ly my arm performs the movement. The muscles contract, the whole physical apparatus comes into motion through the preceding mental process of volition. The same holds true where no special will act arouses the muscles. If a thought is in my mind and it discharges itself in appro- priate words, those words are first of all movements of lips and tongue and vocal chords and chest, physical proc- esses which have followed the mental experience. The ideas and feelings may also be the starting points for other bodily changes. They may make a man blush as large groups of blood-vessels become dilated, or he may become pale because the blood-vessels are contracted, or he may cry because the tear gland is working, or his muscles may tremble, or his skin may perspire; his whole organism may resound with physical excitement which some words may have stirred up. The observations of the scientist here too link the changes which occur in the skin and the muscles and the glands and the blood-vessels with

36 PSYCHOLOGY

the activities of the brain. The bodily effects of the inner states do not take place, if the nerves which lead from the brain to these peripheral organs of the body are de- stroyed. If we press the movement nerve of the upper arm until it becomes inactive, our. will is unable to move the fingers. But the nerve is again only the transmitter; the real beginning of the process lies in the brain. If the breaking of a blood-vessel has destroyed a certain part of the brain, the patient is paralyzed, that is, his mental will can no longer move his arm or his leg.

Yet this group of facts seems very different from the first group, the perceptions. There we found that a brain excitement is the condition under which our sensations of color or sound or taste Or pain arise in consciousness : an immediate co- incidence of brain action and conscious experience. Here we notice only that some kind of brain activity has to start our will actions or our emotional responses, but we have in that no sign that the will or the emotion itself is accompanied by a brain process. It may be that the will or the feeling or the thoughts go on as psychical events in consciousness, without any parallel action in the brain and that they only end with playing somewhat on a brain center which realizes the activity in the nerves and muscles.

But the observation of effects is at this point naturally sup- plemented by theoretical reasoning. Let us look at the situa- tion from the standpoint of the natural scientist. We find that muscles are contracted, that glands are producing secretions, that the blood circulation of the body is changed. These are evidently physical processes which the scientist must explain by the same principles by which he explains every other event in the physical universe. He takes it for granted that every movement of mole- cules is the effect of physical causes. If the chain of physical causes and effects were interrupted anywhere, and an atom changed its direction of movement without a foregoing physical cause, the event would be to him a miracle, a mystery, a de- struction of natural science. He knows that not all causes are known to him and that especially in the world of the living organisms many processes are still unexplained to-day, but he can

PSYCHOPHYSICAL EXPLANATION 37

never give up the assumption that a fuller knowledge would be able to explain them. This is the real foundation of modern science; it is the ideal which guides every effort of the scientist and he calls scientific truth that which brings him nearer to this ideal. He must go far beyond mere observations in order to fulfill this demand of thought. But he can never satisfy him- self with the easy solution that at this or at that point an exception is to be admitted and an effect is to be recognized without a preceding physical cause. Where he does not dis- cover the cause, he acknowledges an unsolved problem.

From such a strictly naturalistic point of view the brain process which starts the movement of our fingers or our lips cannot possibly be without foregoing physical causes. The scientist cannot call it an explanation, if he simply refers this brain excitement to the intruding of a mental will or a mental idea. In the closed system of mechanical causes the power of a mental idea to change the brain excitements would be as much of a miracle as if our idea changed the course of the moon. The true physical causes, accordingly, must be a brain process which coincides with those emotions or ideas or volitions. Only then can the great postulate of modern science, the conservation of physical energy, be satisfied by the actions in the organism. The scientific theory thus leads to the conclusion that all the mental states which seem to produce actions of the body are them- selves accompanied by brain excitements. Hence the two large groups of facts which we considered, the stimulations of the sense organs and the movements of the body, thus after all lead to the same interpretation : in both cases the mental states, the sensation or the volition, need as a counterpart a certain brain occurrence.

We may turn to a third group of facts. If the tempera- ture of the blood is raised in fever, the mental processes become confused: if hashish is smoked, the mind wanders to paradise. A cup of tea may make us sociable, a few glasses of wine may give us a new mental optimism and exuberance, a dose of bromide may annihilate the irrita- tion of our mind. If we inhale ether, or if arteries in our

38 PSYCHOLOGY

neck are pressed so that the brain is insufficiently sup- plied with blood, the whole content of consciousness fades away. A blow on the head may wipe out the memory of the preceding hours ; a tumor in the brain may completely change the personality; a disease in certain convolutions in the brain brings with it the loss of the power of speech ; inhibition in the growth of the brain involves on the mental side feeblemindedness and idiocy. A pathological degen- eration of certain groups of brain cells is accompanied by demented states.

We might point to still a fourth group of facts which seems to indicate the intimate relation between the brain and the mental processes. The comparative anatomist shows us that the development of the central nervous system in the kingdom of animals goes parallel with the development of the mental functions. Any special func- tion of the mind may in certain animal groups have reached an unusual height, and then we see certain parts of the brain correspondingly developed. The dog has a keener sense of smell than man : the part of the brain which is in direct connection with the nerves of the nose is much bulkier in the dog's brain than in the human organism. The physiologist adds to these comparative observations his experimental results. He can demonstrate that electric stimulations of definite spots on the surface of a dog's brain produce movements of barking and whining, or movements of the front legs or of the tail. On the other hand the dog becomes unable to fulfill the mental impulses if certain definite parts of his brain are destroyed. Physiologists may show, from the monkey down to the pigeon, to the frog, to the ant, to the worm, how the be- havior of animals is changed as soon as certain groups of nervous elements are extirpated. Of course the animal can- not furnish us with selfobservations. The dog may bark or whine : and yet be a mere physical machine, without consciousness. We are therefore on safer ground, if we

PSYCHOPHYSICAL EXPLANATION 39

confine ourselves at first to the study of human beings, where both the physical outside event and the psychical inner event are observable and are the objects of com- munications. Even the diseased mind or the child 's mind furnishes us with such selfobservational material. The patient can tell us what abnormal emotions oppress his mind, and the child can report to us what he sees and hears.

Psychophysical Parallelism. — We have shown that man's perceptions and memories, volitions and impulses, occur together with brain excitements. This, however, is cer- tainly not a proof that every mental event is correlated with nervous processes. There may be some act of atten- tion, some subtle feeling, some sudden decision, some flight of imagination, which is independent of any brain action. Here is the point where we must return to our previous argument. We saw, when we discussed the possible psychological explanations, that the appearance of a mental content can never be explained by any foregoing mental state. It lies in the nature of the psychical objects that they cannot be linked directly as causes and effects. Yet we acknowledged that the chief aim of objective psychology is to understand the coming and going of the mental states as necessary. One way to gain such an ultimate explana- tion of all mental events is evidently open. The psycholo- gist has only to generalize what he has found out about the impressions and volitions and the effects of drugs and of brain diseases. He has to go forward to the general postulate that every single mental state be understood as the accompaniment of a special brain process. This is exactly the assumption upon which the scientific causal psychology of to-day depends.

It would be very superficial to deny that such an as- sumption goes beyond what is at present the result of actual observation. It is ultimately a postulate. But every science begins with postulates and only those statements

40 PSYCHOLOGY

which fulfill them have the dignity of truth in the midst of that scientific realm. The astronomer knows that he has not understood a movement of the stars until he has found the causes : he presupposes that no star moves simply by magic power and that nowhere in the astronomic universe the chain of causality is broken. In the same way the psychologist who aims toward explanation of psychical states assumes that every mental state is an accompani- ment of a physical brain process. Only when such a frame- work of theory is built up by a general postulate can those observations of the laboratory, of the clinic, and of daily life, find their right setting. We may still be unable to point to the special brain process which lies at the bot- tom of a particular mental state : and yet, if the assump- tion is accepted, we know beforehand that there is no shadow of an idea, no fringe of a feeling, no suggestion of a desire which does not correspond to definite processes in the brain. The details may and must be material for diverging opinions, but the conflict of such hypothetic theories has nothing to do with the certainties of the un- derlying conviction that, if we knew the whole truth, we should recognize every single mental happening as parallel to a physical process in the nervous system.

It is indeed evident that such an assumption is perfectly sufficient to fulfill our demand. If every mental element is somehow bound together with a definite process in a particular brain part, the physical interplay of the brain processes can now be used to explain the coming and going of these mental states. We saw that the physical world to which the brain and all its millions of nerve cells belong is conceived as controlled by causality. One brain process must lead to the next brain process. If the first is accom- panied by one mental state, the second by another mental state, we can explain indirectly why the one psychical event is succeeded by the other. If hearing the name of our friend brings back to our mind the memory image of

PSYCHOPHYSICAL EXPLANATION 41

his face, no causal necessity binds that word impression and this face impression in our mind. But if that word impression is linked with one brain excitement and that face impression with another, and if we can show that by physical laws the first brain state must be followed by the other brain state, we explain indirectly why the hearing of the name must stir up the seeing of the face.

Of course the explanation must not be sought in a wrong direction. Such a theory does not in the least explain to us why certain brain excitements are accompanied by the sensations of blue or red or sour or salt. But that is not the aim of our explanatory theory. The brain process is not to figure as the cause of the sensation, nor the sensa- tion as the cause of the brain process. The various ele- ments from which our content of consciousness is built up are ultimate facts for the objective psychologist. Sour is sour and salt is salt : the difference between those two men- tal states is something which must be accepted and can never be explained by the brain processes. The excite- ment in the nervous system and the content in the con- sciousness are entirely incomparable, and it would not con- tribute anything to our understanding, if we called the one the cause of the other.

The real aim of the theory is entirely different. We are to explain why these sensations or feelings or volitions arise and disappear in a certain order in spite of the fact that no direct connections exist among them. We do not want to explain that a sensation a or a sensation o exists, but we want to explain and must explain why the sensation a is followed by the sensation o. We do that in showing that sensation a is always present when the brain process A occurs, and that sensation b is always present when the brain process B is going on. Between A and B is a true causal connection. If A precedes, B must necessarily fol- low, and this brings us to an indirect understanding of why sensation a is necessarily succeeded by sensation &.

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As soon as we recognize clearly the real aim of such a theory, it becomes insignificant to us what kind of a meta- phor we use to present it to popular imagination. A favorite term for it is "psychophysical parallelism." The comparison with two parallel lines suggests indeed very well that every change on the psychical side must corre- spond to a change on the physical. Yet we must not forget that this relation is not reversible. Most of the brain proc- esses are not accompanied by psychical states at all. If we call those processes in the nervous system which have their psychical eccompaniment "psychophysical proc- esses," we certainly have no right to consider the psycho- physical processes an uninterrupted chain. Purely physi- cal processes lie between them. Of the two parallel lines which the metaphor suggests, only one, the physical, is con- tinuous, while the other would have to be drawn as a broken line, which often exists only in single dots.

The theoretical discussion has to end with this general postulate of parallelism. How it can be fulfilled, which mental states are to be correlated to which brain proc- esses, and which laws control them is not to be deduced from theory, but from the detailed study of facts. The further elaboration of the psychophysical system thus be- longs to the special part. But the whole special part has to be built up on this foundation. It would be an illusion to fancy that any observations could alter the postulate with which we start. It is the assumption by which causal psychology is possible at all. Every observed fact must be reconstructed until it can be inclosed within the general frame of the psychophysical theory.

CHAPTER V

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY

The Subdivisions of Psychology.— Wherever mental life exists, it must be possible to take the objective point of view toward it and to consider it as a content of an indi- vidual consciousness. As such, it is material for the de- scription and explanation. Hence the realm of causal psychology is as wide as that of mental life. Where the furthest boundary of this realm lies may seem debatable. There is only one test for the existence of consciousness, namely, our subjective, practical acknowledgment. If someone acknowledges the reality of inner attitudes in the spider, but not in the jellyfish, we have no objective method to prove that the mental life begins at another stage. Not a few feel inclined to extend the realm even further down and to acknowledge mental life in the re- actions of certain plants when they turn toward the light or respond to contact. Very little depends upon such shift- ing of the lower limit'; we certainly all agree that from the insects upward to the leaders of mankind we have a world of mental life in which many different degrees of men- tal development and mental complexity can be found. A real comparison with the lower forms of mental life does not lie in our compass. We shall emphasize the bio- logical aspect and the continuity of the development, but the interest in man's mind is our predominant issue.

If we are to draw one decisive frontier line between two large groups in human psychology, it ought to be between the mental life of the individuals and that of the social

43

44: PSYCHOLOGY

groups. Of course, there is no mental process in the social group which is not contained in individual minds. The inspirations and impulses and ideas of a nation are, as material for causal psychology, only contents of conscious- ness in millions of individual persons. And yet the psychologist has good reasons to acknowledge the significant difference. The circle of those who are mentally combined in society may be large or small, may be a state or merely a family: in any case the combination of such individual cerebral systems is far more than a mere summation of the single members. New forms of psychophysical life and new results arise from the mutual influence. Here really a new kind of psychological experiences is found and new groups of psychological interests are touched.

We shall accordingly divide the causal psychology into individual and social psychology. At one point the two fields overlap. The large group of interesting facts which refer to the individual differences of men may just as well be treated in the one as in the other department. If we study individual psychology, we are led from the simple states to those most complex formations which constitute the personal individuality. The end point of individual psychology is therefore the observation of the individuals in their differences. But this is exactly the starting point for the social psychologist. Society might exist through the combination of individuals who are all alike. But the society which experience really shows us receives its mani- foldness and its complexity above all from the great va- riety of persons who enter into it. Society is a com- bination of unlike individuals, and to consider the in- dividual as a member of society means first of all to char- acterize him in his difference from the other members. For this reason we shall often point to personal differences in the discussion of individual psychology, but the real study of personal variations will be the introductory chap- ter of our social psychology. The same double function is

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 45

characteristic of child psychology and abnormal psychol- ogy. We shall refer to the mental facts of childhood and of disease in discussing the mind of the individual, but we shall consider them chiefly when we deal with the hu- man differences in social psychology.

All the other usual groupings of psychological facts refer to other aspects. The discrimination, for instance, of edu- cational psychology, legal psychology, medical psychology, industrial psychology, refers to the standpoint of the prac- tical psychologist, which will interest us in the last part of the book. On the other hand, if we speak of experi- mental psychology, physiological psychology, comparative psychology and so on, we do not characterize different groups of material, but different methods by which this material is to be mastered.

To be sure the term physiological psychology can mean not only psychology as studied by physiological methods, but also psychology as an account of mental states in their relation to physiological brain processes. To us this is not a special part of causal psychology, inasmuch as we have convinced ourselves that we cannot have psychological explanation at all, if we do not consider every psychical process as part of the psycho- cerebral correlation. We may have to deal with individual or with social psychology, with animal or with human psychol- ogy, with child psychology or with abnormal psychology: in every case we deal with physiological psychology, even if we often abstract from the physiological aspect.

A more dangerous characterization of psychology is pro- posed by the too frequently used term functional psychology. The word is so easily misleading, because it has at least two entirely different meanings. The difference becomes clear through the contrast to structural psychology. The structure of the mind and the functions of the mind are related to each other as the anatomy of a bodily organ is related to its physiology. The one has a static, the other a dynamic, character. Structural psychology describes that which can be found in conscious- ness at a given instant, and functional psychology shows how

46 PSYCHOLOGY

successive mental states are parts of a process which leads to cer- tain ends. The one takes a cross-section of the stream, and the other follows the stream itself.

If we interpret the meaning1 of structural and functional psychology in this way, it is clear that they belong intimately together. The functional aspect is then not in the least contra- dictory to the structural. They supplement each other, and while we discuss the function, we never forget that it is described in constant reference to the structure. Both are essential parts of causal psychology. But the term functional is just as often used with an entirely different meaning. The function is then no longer a series of describable objective states analogous to the function of a bodily organ. But it is the mental act itself in its purposiveness, as it is experienced in the attitude of the self. Functional psychology is then entirely removed from the world of describable objects and understood as an account of those functions in the personality which point beyond them- selves and are felt as deeds of the subject. In short, it is the psychology which we call purposive. If the word functional is used in this sense, it does indeed stand in contrast to struc- tural psychology and the latter term is then usually expanded so far that it covers the whole ground of causal psychology, in- cluding the structural account of mental functions.

In order to evade the difficulties of this double meaning, we shall avoid this too popular phrase altogether. It has greatly hindered the mutual understanding in modern psychology. This, however, in no way means that we shall neglect either of the two different accounts of functional psychology. As far as it is the same - as our purposive psychology we shall present its claims in full detail, as soon as we have ended the discussion of causal psychology. On the other hand as far as it means the dynamic aspect in the midst of causal psychology, we shall certainly do the fullest justice to it as it is only the natural consequence of the theory of psychophysical parallelism which we have ac- cepted. If the mental states are understood as accompaniments of brain processes, they are completely linked with the bodily life of the organism and through it with the whole psycho- physical development. This whole psychocerebral process will appear to us as the central part of that complex biological func-

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 47

tion by which the individual adjusts himself usefully to his sur- roundings. The psychophysical process thus enters into the sys- tem of organic reactions, which can never be understood if they are not related to their useful effects. Hence we are everywhere obliged to emphasize the functional aspect in the midst of causal psychology, and any effort to confine the work to a mere struc- tural account would leave out the most important and the most interesting feature.

Self observation. — If we were* to divide the whole realm of causal psychology from the point of view of the various methods, the fundamental division ought to lie be- tween the psychology based on self observation and the psychology based on the observation of others. The di- vision line must not be misunderstood. The material which the psychologist secures by the method of selfobserva- tion is certainly not confined to that which he finds in his own personal consciousness. All the mental experiences which fellow-workers observe in themselves and report to him count for him just as much as if he had observed them in his own mind. As soon as we are in the midst of psychological work, we cannot go back to philosophical doubts concerning the reality of the fellow 's mind ; we take it for granted that he can observe his content of conscious- ness as well as we observe our own. If somebody else describes to me his afterimages or his headache, I accept it as material gained by the introspective method just as if I myself observed the colors or the ache. The essential point is not whether I or someone else experiences it, but whether the observer and the observed are the same person, or not. If the child simply cries and laughs, he experiences the feelings, but I observe them ; the case is therefore not one of selfobservation. And if the melancholic patient shows to me that he is brooding on sad ideas, again I am the observer and he is the observed. If we call the psycho- logical observation which is not introspective an indirect observation, every study of the mental life of animals or of

48 PSYCHOLOGY

infants or of seriously diseased persons will be mostly in- direct. Moreover we may carry on indirect observations on any one of our neighbors who on another occasion may furnish us with direct observational results. The one easily shades off into the other. The child may describe his inner experiences, and we gain through this introspective ac- counts; and yet we may at the same time observe the child's behavior and draw indirect conclusions as to his inner states, which may be very different from his own reports.

Selfobservation or introspection is certainly the funda- mental method. Yet we cannot deny that it is surrounded with serious difficulties. They can be found in various directions. The method of introspection has often been de- nounced because it is an activity which goes on in the same mind in which the processes occur which are to be observed. As all activities in our mind influence one an- other, it is to be feared that this effort to observe the inner changes often destroys its object. There is an element of truth in this. If a poem has filled our mind with a subtle, delicate feeling tone, and suddenly our scientific effort of selfobservation breaks in so as to fixate those shades of feel- ing, the chances are great that the whole affection may evaporate, because it was disturbed by the entirely dif- ferent mental setting.

If we are depressed or angry or enthusiastic for men or events, we are hardly able to turn our introspective attention on these inner excitements, and if we force our will to introspecting, the enthusiasm or the anger will be inhibited. But we can well combine the will to observe with the undisturbed experience of a perceptive impres- sion or of a memory image or of imaginative experiences or even of a thought. Moreover the emotional and volitional excitement which does not allow a neutral spectator on the fence of our consciousness may be brought back by a later act of memory, and we may observe and analyze by intro-

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 49

spection to-day the emotional excitement of yesterday. Above all the ability to live through a mental experience in its original freshness and yet to take inner snapshots of it may be strongly developed by training. Anyone interested in psychological analysis can acquire a certain skill in com- bining the attitude of observing with the practical life at- titudes, just as we can learn to perform two different movements with the two hands without mutual interference.

Even if our selfobservation is careful and backed by knowledge of the bodily processes, it is evident that it must be confined to those chance experiences which the stream of life bears to our shore. Every individual ex- perience is narrowly limited, and if we observe only what the accidents of the day bring into our sphere, our ma- terial will be scanty and insufficient for a systematic study of mental possibilities. Many selfobservers may bring to- gether the outcome of their introspection; yet the results must be haphazard as long as they are confined to that which presents itself to them by chance. Worst of all, these results must be extremely vague and rough. Really careful and subtle discrimination is hardly possible, and the comparison of the effects of different conditions can- not be expected, if the conditions themselves are not under control. Unaided selfobservation, therefore, appeared a satisfactory method in the history of human thought, only as long as psychology was essentially a speculation about the human soul. The vague general impressions which the thinker received from the working of his will or emotion or memory were sufficient as starting points for the soul philosophy which did not have to be a science of experience.

But since the psychologist has turned into the new path, and like the naturalist aims toward the goal of scientific description and explanation, the merely occasional glances at his own mental life can no longer satisfy the student of the mind. He must on the one side supplement the self-

50 PSYCHOLOGY

observation by the observation of others whose mental ex- periences are different from his own, and on the other side he must bring selfobservation itself under carefully controlled conditions and make it independent of the hap- hazard events of the day. But however desirable such ex- pansion of method is, and however necessary for every serious study, it certainly cannot mean a disregard of the introspective method. Those observations of others always need interpretation in the light of selfobservation, and all those exact and subtle means for the analysis of our own mental life remain, after all, only refinements of self- observation. Even the work of the psychological labora- tory, in which the experiment controls the mental ex- perience, is in no way opposed to selfobservation: on the contrary, it is only a better and more systematic selfob- servation, adjusted to the higher scientific demands.

Indirect Observation. — We may turn first to the efforts to extend the observation beyond our own mental life. Introspection is direct observation. Therefore we must now ask: how does the psychologist supplement it by in- direct observation? We presuppose at first that this in- direct study proceeds under the natural conditions of life without artificial interference. The characteristic feature then is that the observer and the observed are no longer the same person. It is clear that no one will turn to the stranger whom he must observe from without in order to find that which he can find in himself. Yet we saw from the start that the effort to observe, especially subtle or strong emotions, may interfere with the mental states themselves. Hence we naturally turn to the watching of fellow-men if we want to trace the undisturbed develop- ment, and particularly the expression, of feelings and emo- tions, impulses, and volitions.

But the chief value lies in the study of those cases in which the mental life is different from our own. The study of the mental abnormities, for instance, may be treated not

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 51

as a department with special objects, but as a scientific method needed to discover the subtler interplay of the nor- mal mental functions. The diseased mind is composed of the same elements as the normal mind : only their propor- tion is changed. There is too much or too little of one or another mental feature. To observe the distorted mind therefore helps us in the understanding of the normal har- mony and proportion, as a caricature may help us to rec- ognize the proper interrelations between the features of the face. The study of the abnormal is in this case not controlled by the interest in the traits of the disturbed mind, but in their value for the analysis of the normal mind. In the same way child psychology may serve as a method. We compare the consciousness of the adult with the simpler and simpler forms in the mind of children ; we may trace the ideas of space and time and number, or the ideas of one's own personality or the ideas of fellow- beings and similar highly complex structures in our mind down to the elementary forms in youth, in childhood and in infancy, and understand their composition through the comparison. The study of different species or of different races, of different ages or of different pathological varia- tions is indirect in so far as the observer is not the ob- served, but it brings at least the organism into the field of direct observation. We can go still a step further and gather mental material from individuals who do not come into contact with us at all.

We have this in the case of statistical results, which, especially in the form of the so-called moral statistics re- ferring to occupations and vocations, crimes and sui- cides, marriages and divorces, education and religion, and many other results of psychical motives in the national body, are important for the study of social psychology. Another line of study is opened if we turn to the archives of history. The records of the past, with their accounts of unusual minds, heroes or artists, martyrs or criminals,

52 PSYCHOLOGY

all speak of mental structures and mental functions which are sufficiently different from the routine mind to attract the interest of the psychologist.

This again must be supplemented by the study of the objective products of minds: it may be the work of indi- viduals, such as an artistic or scholarly or religious or political creation ; it may be the achievement of the masses, such as languages or laws or customs or policies or religions. They all reflect light on the mental mechanism which brought them into existence. "We can study the dif- ferences of minds in studying the differences between the works of architecture which old India or Egypt or Assyria or Greece or Rome have left to posterity ; and the changes of the historic languages can be understood as the prod- ucts of simple psychophysiological processes, which repeat themselves in millions of individuals. We might even take a last step and acknowledge that the poet also furnishes us with material which allows observation of mental proc- esses. The persons of his epic and dramatic works are not real, and he himself is not a causal psychologist, as he creates minds, but does not describe and explain them. But if we usually call a great poet like Shakespeare a great psychologist, we mean that his imagination has created individuals whose mental acts are so lifelike and internally true that the psychologist can substitute them in his studies for real personalities.

Experimental Psychology. — Thus direct and indirect observation combined can bring an abundance of material from the marketplaces of life to the workroom of the psychologist ; and yet of this indirect study it may be said, as we had to say about the direct introspection, that true thoroughness and exactitude cannot be reached as long as everything is left to the chance offerings of nature. The chemist and the physicist do not leave it to the current of natural events to bring up the phenomena which de- serve scientific interest. They build their laboratories ar^

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 53

produce there artificially conditions under which the ob- servations can be repeated in ever-new forms and under complete control of the factors which enter into the event. The experiment of the naturalist is indeed nothing but the observation of the physical or chemical processes under conditions which are artificially introduced for the pur- poses of the observation. The psychologist too can hope for a perfection of direct and indirect observation only if he introduces experimental methods. In the persistent effort to make use of the experiment for the study of causal psychology lies the most characteristic feature of the psychology of the last decades.

This was the decidedly new turn on account of which modern psychology is not seldom called the new psychol- ogy, in striking contrast to the preceding two thousand years of psychological interest. In the past the study of the mind, in spite of its essentially philosophical char- acter, did not lack elements of empirical observation, but the observations were confined to mental life under nat- ural conditions. With the middle of the nineteenth cen- tury the observation under artificial conditions begins. The psychologists themselves were not the leaders in the new method. The physiologists who studied the functions of the eye and ear and of the muscles were led to experi- ments which threw light on mental facts and gave the strongest impulse toward an independent interest in men- tal experiments. Suggestions came also from other neigh- boring sciences. Physicists examined experimentally the relations between the strength of the physical impressions and the inner sensations. Even the astronomers found reasons to experiment with regard to mental functions, as it was observed that the correct observation of the stars depended upon mental conditions, which varied among dif- ferent observers. It became necessary to measure the rapidity with which the individual mind reacted on the astronomical stimulus, and that led to general experiments

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on the quickness of mental processes. Not a few psycho- logical experiments were carried on in this way before the psychologists began to establish special laboratories for their own purposes. The first institute, which was to be the mother institute of most psychological laboratories the world over, was founded in Leipzig in 1879. It was de- voted exclusively to selfobservation under artificial condi- tions, and it naturally began with such simple experiments as those which had been carried on in the neighboring fields before. The development was an unusually quick one; the movement spread to all countries, Germany and the United States leading in this new interest. America has at present more than half a hundred psychological laboratories.

The internal development, however, was still more rapid. In its early days it seemed a matter of course that only elementary processes would be accessible to experimental methods. The borderland regions between mind and body, the sensations and perceptions, space and time problems, the simplest association and reaction questions were the natural field, while the higher mental activities seemed beyond reach. But, as soon as the psychologists had their own keys, many new doors could be opened. The experi- mental method was soon successfully brought to the study of memory and of attention, later of feelings and emo- tions, of thoughts and esthetic states and volitions. Cer- tainly the experiment under laboratory conditions is as yet net equally developed in all regions of mental life, and is so far better adjusted to the problems of perception and memory than to those of emotion and will. Yet it can be said that there is no group of mental processes which has not been made accessible to the experimental method.

But the triumph of the laboratory is not confined to the rich development of methods for exact selfobservation. Its aid is no less significant in the regions of indirect ob- servation. The old animal psychology consisted of ahec-

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 55

dotes of dogs and horses, hunting stories and onesided interest in the mental life of ants and bees ; the experiment transformed it into an exact science which traces every mental function through the whole kingdom of animals. Child psychology was not in the same degree dependent upon experimental methods, as the opportunities for steady observation under natural conditions were more favorable, and much excellent detail had been observed by parents and teachers before the experiment aided the study. More- over it is evident that the hygienic interests of the child set rather narrow limits to persistent experimentation. Yet here too the experiment has been applied with full success from the reactions of the infant in its first minutes of life to the complex mental processes of the adolescent. In the same way the laboratory method has shed new light on the disturbances of the diseased mind, and still more on those abnormities which lie in the borderland between health and illness. Moreover in the sphere of mental abnormity the experiment has taken still another form. The aim is not only to carry on experimental studies with the ab- normal mind, for instance, research on the abnormal memory or intelligence or feeling, but to produce by ex- periment abnormal mental states in otherwise normal men. The typical case is that of hypnotism. The hypnotic ex- periment is certainly an effective means for the discovery of many psychological facts which cannot be studied under normal conditions.

The whole science of psychical life is thus revolutionized by the methods of experiment, and throughout has been victorious in this sign. But its strength ought not to be misinterpreted. We have emphasized before that the experiment does not stand in contrast to selfobservation and is by no means superseding it, but only aiding it. We have to add now that it is no less misleading, if it is brought into contrast with the qualitative analysis of mental states and is glorified as a scheme to perform a quantitative measurement of the conscious experience. On

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the, surface it looks indeed as if the laboratory work were measuring mental states as such. If we look deeper, we recog- nize that this is an illusion. All which we measure are physical quantities, and all the figures which enter into our laboratory report refer ultimately to physical conditions of mental experi- ence. The mental experience itself remains only a qualitative manifoldness. The mental states are alike, or are different, but one never contains a number of others. A physical ten-candle- power light contains ten times the light of one candle, but the psychical light impression of the strong light does not contain so and so many times the light impressions of the weaker. The strong and the faint impression are different, but we cannot find the one in the other. All physical measurements are based on the counting of units. The ten-foot distance contains ten times one foot. But in the world of impressions or other mental states neither the contents themselves nor their differences from one another can be put together and summed up.

If we call two mental states equal, the term must not be used in the mathematical sense. It means only that we do not discriminate qualitative differences. If we were to apply arith- metic to the mental relations themselves, we should be entirely misled. If we start with a red sensation and go through all shades of red orange to orange and so on by smallest steps to yellow and green and blue and violet and purple, we can count the number of just noticeable differences, and this number would be much larger for the distances from red to purple through- out the rainbow colors than from red to green; and yet psycho- logically red and purple are very similar, and show a very small difference, while red and green are very different. The knowl- edge of ten pages of text is not ten times the knowledge of one page; the memory image of two men is not twice the memory image of one man; we cannot have the same anger or the same volition three times. We have no right to believe that exact psychology has made the mental life itself measurable. The exactitude refers to the discrimination of qualitative differences on the mental side and careful measurement of the causes and effects on the physical side. This is not a weakness of present day psychology which the future may overcome, but it is one of the deepest characteristics of the psychical material itsel£

SCOPE AND METHODS OF CAUSAL PSYCHOLOGY 57

•

Only one further methodological aspect must be men- tioned. All the methods of direct and indirect observa- tion under natural and under experimental conditions re- ferred to the mental states and their relation to preced- ing or following physical events. We have not yet spoken about the ways by which the correlation between the men- tal event and the accompanying parallel brain process is determined. Such methods can hardly be called psycho- logical, however important the results of such work may be for the theoretical explanation of the psychologist. In the foreground here are the methods of anatomy, of physi- ology and of pathology. The anatomist traces the connec- tions between particular brain parts and the sense organs or the muscles, and in this way can throw light on the psychophysical functions of those nervous centers. The contribution of the anatomist becomes especially impor- tant through comparative anatomy. If certain mental abilities are characteristic of some animals, while they are rudimentary in others, the anatomist can find out whether a particular region of the central nervous system is highly developed in the one and undeveloped in the other group.

But the more direct aid to this side problem comes from the physiologist, who studies directly how far the artificial stimulation of a certain brain region produces in the animal an expression of mental activity and how far the artificial destruction of the same central region results in an interference with that particular form of mental be- havior. And finally the pathologist gathers the material which the dissection of the diseased brain after the death of the patient exhibits. If certain mental functions had become defective during lifetime and the autopsy now shows a degeneration of special brain tracts, the pathologist links the mental and the physical disturbances. In the middle of the last century the discovery of characteristic lesions of the brain in cases of speech defects gave to

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psychology an impulse in this direction which led to a long series of most important researches. These pathological observations, on the other hand, were constantly supple- mented by the physiological experiments and aided by the rapid progress of comparative anatomy. In this way the theory of psychocerebral parallelism found its fullest de- velopment in the same few decades in which experimental psychology was unfolding. The results of both are com- bined in the system of modern causal psychology.

PAET II. THE INDIVIDUAL PEOCESSES A. THE ELEMENTARY INDIVIDUAL PROCESSES

CHAPTER VI

THE NERVOUS SYSTEM

The Sense Organ-Brain-Muscle Arc. — If every feeling, every idea, every will act, every emotion must be con- sidered as an accompaniment of brain processes, we must try first of all to understand these organic processes them- selves, before we connect them with psychical experiences. We may look on the brain, accordingly, with the eyes of the physiologist, who seeks to reduce everything to physi- cal and chemical changes in the cells of the body and who, from his standpoint, cannot be aware of any accom- panying mental states. What are the character and the significance of the brain processes, seen from his view- point? Are they to him numberless chance activities in the cells of the brain, or can he unify them and illuminate the manifoldness by a simple principle? Let us compare the situation with the physiologist's interest in some other bodily organ. The heart is performing its complicated contractions, the stomach is producing its gland secre- tions. Does the physiologist ever feel satisfied with simply recording those physical and chemical facts ? He certainly goes far beyond such a mere description of cell activity; he asks how far this heart contraction or stomach secre-

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tion is useful for the purpose of our organism. Through this problem of usefulness, the physical-chemical mechan- ism is brought into an entirely new light. It leads to a true explanation of the organ and its development.

As soon as the biologist can show that a part of the organism is useful for its conservation, he can apply all the principles which the modern doctrine of evolution re- gards as vehicles for the advance of the race. He would be unable to explain a bodily apparatus which is unneces- sary for the selfpreservation of the race. But if it can be shown that a particular variation of the body is helpful to the individual or its descendants in the struggle for physical existence, he understands that it gave to the or- ganism a more favorable chance to survive and to transmit its traits to the next generation. To be sure, the biologist of to-day considers the process of race evolution not so simple as it appeared somfc decades ago in the high tide of Darwinism. Many new difficulties and many necessary side principles have to be acknowledged ; and yet the fun- damental principles stand. If we aim toward a causal ex- planation of the forms of animal life and not toward a purposive interpretation of the plans of nature, we must recognize in the usefulness of the organ the condition for its development.

But if this is the case, the biologist cannot consider the heart or the stomach as isolated organs. The contractions of the heart would be entirely useless, if there were no arteries and no veins connected with it and no lungs for the chemism of the blood ; and the pepsin secretion of the stomach would be useless, if the whole system of the di- gestive apparatus from the mouth cavity downward were not connected with it. As soon as such a group of organs is understood as a unity, their combined action indeed ap- pears indispensable for the individual and therefore ex- plainable from the standpoint of evolutionary biology.

The brain of the frog as well as the brain of man would

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likewise be superfluous and useless, if it were considered as an isolated apparatus. But everything is changed when the brain is understood as the complicated central mechan- ism of a much larger system. The brain is in direct con- nection with the outer surface of the body and with the sense organs on it. The eyes, the ears, the nose, the skin are linked by hundreds of thousands of nerve fibers with the sensory parts of the brain. At the same time the muscles which contract the peripheral organs of the body are connected with the motor parts of the brain, and in the brain itself the sensory and the motor parts are com- pletely interrelated by millionfold paths. Hence the brain can work like a central switchboard through which the ex- citement of the sensory system, beginning with the stimula- tion of the sense organs, is transmitted to the motor system, where it ends with the contraction of muscles. The nerves which lead from the surface of the body to the brain are the centripetal part, and the nerves which lead from the brain to the muscles are the centrifugal part of one arc of which the brain is the central part. If this arc is considered as a whole, its unified function be- comes evident. The sense organs are stimulated by the surrounding world, and the muscles produce the changes in the surrounding world. The arc from sense organ through the brain to the muscle is the apparatus by which the organism can adjust its actions in the outer world to the conditions of the surroundings.

The Development of the Nervous System. — We said that the biologist is able to explain such systems, in case that their physiological functions are useful to the or- ganism. As soon as this arc from sense organ through the brain to the muscle is considered as such a mechanism by which the movements are adjusted to the surroundings, its usefulness is evident. An organism which had sense organs and brain and could receive inner excitements from the lights and sounds and odors and pressures of the world

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could not survive if no nerves connected the brain with the muscles ; and on the other hand a brain connected with the motor apparatus would be entirely useless if it were not influenced by the excitements of the sense organs. In both cases alike the organism would be helpless. But as soon as the motor action is a response to the sensory stimuli, the conservation of the individual can be secured. It can escape the dangers, can withdraw from the injurious contact, can approach and grasp the nourishing substance, can attack the enemy and follow the prey.

If we look over the whole world of animals, we find that at every stage of development this useful correlation be- tween sense organ and motor response is effective. It is just this usefulness of adjustment, this fitness of expres- sion and impression which leads the naturalist instinctively to a psychological interpretation of animal behavior. The actions are so usefully adapted to the surroundings and so clearly serve the interests of the individual and its descend- ants that we always feel tempted to see in them the work- ing of a selecting intelligence, or at least a conscious regu- lation by sensations and feelings and will impulses. The amoeba which we watch under the microscope in a drop of water responds to the stimuli of the surroundings in a perfectly useful way. If a dangerous stimulus comes in contact with its surface, its contractile substance forms a ball and by that reduces the chance of contact to the min- imum; if nourishing matter touches the same surface, it reacts by expanding and bringing its body as much as possible into contact with it. The monocellular being acts there as if it hated the one and loved the other, and as if liking or disliking had led to considerations and finally to will impulses. These useful reactions are so com- pletely adjusted to the narrow needs of those lowest beings that we have no right to say that they are less perfect than the more complicated reactions of the higher or- ganisms which because of their greater differentiation need

THE NERVOUS SYSTEM 63

a much richer system of responsive movements for the struggle of life. The infusor is no less well adapted to the helpful and injurious conditions in his drop of water than the frog to those in his pond or the man of civiliza- tion to those in his metropolis.

But the biologist may stick consistently to his purely physical-chemical view, in spite of the apparent expres- sion of intelligence. After a meal millions of cells in our organism perform the work of transforming the food into substances which are needed by the body and distributing them to the various organs of the body with the greatest possible adjustment to the needs. A host of intelligent chemists could not work out in years the details of the processes which our abdominal organs carry out in a few hours. And yet the physiologist does not refer them to any abdominal soul, or to any planning intelligence: he starts with the conviction that all these useful perform- ances result from merely physiological cell activities. The usefulness and apparently intelligent fitness of the motor reactions in the infusor and the frog and the man do not, therefore, demand the reference to intelligence either, as long as we remain loyal to the physiologist's stand- point. On the contrary, it is this usefulness, as we saw, which becomes the vehicle for a biological explanation.

In the lowest forms the whole surface may still receive all the stimuli which are essential, and the whole body may still contract and expand. Then differentiation leads to an increased sensitiveness of particular regions to special outside excitements, that is, it leads to the forma- tion of sense organs. Correspondingly, special parts of the bodily substance acquire ability for isolated contraction; that is, they become muscles. As soon as sense organs and muscles are developing, the transmission of the excite- ment from the one to the other must become localized too. Special paths of least resistance form themselves; they are the nerves. The next step is a more complex interrelation

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between the various organs of stimulation and the various muscles. One sense stimulus must be able to produce the contraction of many muscles, or many sense stimuli must be able to cooperate toward the contraction of one particu- lar muscle. This is possible only when the nerves form a network. Such an interconnection allows the cooperation of many parts, but the responses are still the reactions to the immediate stimuli.

As soon as evolution has reached a stage of higher com- plexity, the animal would be unable to protect itself against dangers and to secure its food and its safety, if a further variation were not developed by natural selection. The movements must not only be adapted to the impres- sions of the moment, but also to the earlier ones. The action then becomes a response to the present experiences together with the preceding ones. All that is necessary for this great further step is that certain parts of that network of nerves which intermediates between surface and muscle acquire a new trait. They must become able to sum up excitements; the first impression must leave a certain after-effect which unites with the later excitements in the control of the resulting reactions. The animal can now adjust its movements to objects which are not im- mediately in the sphere of its senses, but which previously were connected with the present surroundings. Those parts of the nervous system which especially regulate the cooperation of peripheral functions and stir up the after- effects of preceding stimuli become anatomically distinct nervous centers.

As soon as we reach the higher animals, this system of centers is developed to a high complexity. Protected by the skull and the vertebrae, the clusters of central organs are grouped as brain and spinal cord. Sensory nerves lead to them from the higher sense organs and from every part of the skin, and motor nerves lead from the central nervous system to every muscle. The interrelations be-

THE NERVOUS SYSTEM 65

tween the various regions in spinal cord and brain become richer and richer from fish to reptiles and amphibians, to birds and mammals. The immediate arcs between the sen- sory and motor centers become more and more subordinated to the superstructure, the cerebral hemispheres, which reach their fullest development in the higher mammals. Only through their centers the most complex correlations of the lower centers can be secured. The situation becomes still more complex by the fact that not only the surface but also the inner organs send their messages to the brain, and that the centrifugal impulses do not go merely to the outer muscles, but also to the glands and blood vessels and inner organs. But even where this nervous differentiation has reached its greatest manifoldness, we find as its only function this perfectly useful adjustment of the reaction to the physical-chemical conditions of the surroundings, and as it remains useful at every stage, the intermediating brain action appears entirely explainable.

The Biological Aspect of Man. — Fundamentally no new principle sets in when nature proceeds from the highest animals to the human beings. Three features are especially characteristic of the new step. They have long been prepared in the reactions of the animals. First man develops the tool. It is a condition for an extreme advance in achievement, and yet the change is exactly in the direc- tion in which the development from the infusor to the monkey went on. It is a new means for reacting usefully on the surrounding world. It is simply an extension of that arc from sense organ through brain to muscle. Our eye is sharpened by the telescope and the microscope, our ear receives messages by long distance telephone, our brain is stimulated by cable and newspaper from every place on the globe, our brain connections are disburdened by our libraries, the motor impulses of our brain can produce dynamite explosions, and better than by our muscles we can swim by our steamers, can run by our locomotives,

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can fly by our aeroplanes. This enrichment of the reac- tion apparatus shows one fundamental advantage, on which our whole technical civilization is based : the new additions to the biological arc are detachable. They are not de- stroyed by the death of the individual. In the whole com- plexity which they have reached during the lifetime of the organism they can be handed over to the descendants. The work of the generations can be cumulated in them. But the role of the central nervous system remains un- changed ; from a biological point of view the brain which receives the stimuli from the remotest corners of the earth and which can produce effects that may last through thou- sands of years, remains the automatic transmitter between the centripetal and the centrifugal excitements.

Secondly, one of the motor products is especially sig- nificant, the air waves which the vocal cords produce as means of communication. The language of man is pre- ceded by the sounds which the animals produce, just as the technic of man is preceded by the nest of the bird and even by the house of the snail. The biologist has no difficulty in understanding the development of this ap- paratus which functions by producing sounds as they at- tract or warn or threaten other animals in a most useful way. Its further differentiation in the rise of man remains entirely open to such a biological explanation. Every step forward had its distinct advantage for the preservation of the social group in the struggle for existence. The sound which the one ejects and the other receives as ear stimulus becomes a substitute for the objects of the surroundings. The more the language becomes differentiated, the larger is the circle of things which one individual can bring into the sphere of others by words just as if they were present to sense. Moreover not only the things, but their mutual relations are replaced by sounds and the man who hears the spoken language is thus stimulated by a much larger part of the world than ever could reach him through actual

THE NERVOUS SYSTEM 67

sense contact. Any relations past and future can now become the stimuli which lead the brain to action, and the sound is replaced by the signs of the written or printed words. Each speaking individual lives in a world which is incomparably richer than that in which the individuals on the biologically lower stage moved, but it is again merely a new advance in the same direction of evolution. Besides the development of tool and language, and in very close dependence upon them, we find, thirdly, the spread of all forms of cooperation. Animal life anticipates this method of adjustment to external conditions, especially in the joint work of the family. But only with man does the great economic exchange set in. It is again only an enrichment of the functions of the physiological arc. At the stage of the human differentiation the single in- dividual is no longer able to receive all the sensory stimuli, to produce all the motor reactions and to make all the con- nections between the sensory and the motor systems which would be needed for his personal protection. A social dif- ferentiation begins by which the one produces reactions useful not only to himself but to many others, and is in exchange relieved by the reactions which others perform for him. From this new principle the market arises, the vocations and professions develop, life becomes more and more complicated ; and yet every individual activity in the service of such cooperation still remains the most use- ful possible reaction of the organism to the total set of con- ditions. The development reaches its climax in those ac- tions which, seen from an inner point of view, appear di- rectly opposed to the principle of selfpreservation, namely the altruistic actions. The moral life is the unselfish life : actions are performed which serve not the actor but an- other individual. Yet, from a biological viewpoint the situation appears different. Each individual's preserva- tion is first of all bound up with the welfare of the whole group to which he belongs. A group of mutually helpful

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organisms will survive, while a group of individuals which fight one another must be weak and without chances.

Hence the biologist, however one-sided his standpoint must be, is perfectly justified in claiming that the whole system of human brain processes is biologically useful and therefore explainable through merely physical causes like all t the other functions of the organism. The diffi- culties which he finds in his way, the unsolved detailed problems of inheritance, of growth and so on refer to the function of the blood-vessels or of the digestive tract as much as to that of the nervous system. But he does not need any mental interference in the latter more than in that of the former. He can take it for granted that even the wisest word and the noblest action may be consistently understood as a physical- chemical effect of strictly physi- ological causes. If all the atomistic dispositions of the brain and all the influences on the brain with all their after-effects were known, the acquaintance with the present sense stimuli would be sufficient to determine what motor response would go on in the individual. It is no counter- argument that the stimuli may be very similar, and yet the effects extremely different. In a telegram which we receive the change of a single letter may change all the reactions of greatest joy into those of deepest distress. But that is not surprising, as all the earlier experiences of the brain have created a setting in which the one or the other optical word sign moves entirely different physiological levers. A minimum dose of arsenic may also appear extremely simi- lar to a dose of sugar ; and yet as soon as it is swallowed, it affects millions of cells in the organism by its destructive power.

We now have the foundations for a truly psychophysical system. We have recognized that the causal aspect of mental life requires us to treat all the mental elements as accompaniments of brain processes, and all their connec- tions as results of physiologically necessary causal proc-

THE NERVOUS SYSTEM 69

esses. This would be a hopeless undertaking, if it were by principle impossible to explain all the brain actions in human life from mere physical causes. But now we have seen that as parts of the arc between sense organ and muscle they are under all circumstances useful in their normal functioning and therefore physically explainable. The task before us is to understand the psychical elements and their coming and going as parallel to this closed chain of physical events. Every psychical element and every psychical law must accordingly be understood as related to some part or some process in the biological arc, either to its centripetal or its central or its centrifugal segment. This biological view of psychophysical action, which is in- dispensable for causal psychology, must control the study of every single feature. The usefulness of the processes is the condition for their development.

CHAPTER VII STIMULATION

The Psychical Elements. — The chain of processes from the stimulation of the sense organ to the movement of the muscles, which has appeared to us so far as a merely physi- cal activity of the nervous system, must now be illuminated by the mental events which accompany it. We naturally begin with those which form the initial part in this life process of organic adjustment. No impulse to adapted action is possible unless as a starting point the outer world impresses the brain. Physiologically, our question would be only : what external processes have the power to stimu- late the central nervous system ? We should then trace the impressions which the light rays and the sounds and the temperatures and the pressures and the odors may exert on the brain elements when they are transmitted through sense organs. But for us the problem is now a psychophysi- cal one : what mental contents accompany the brain proc- esses that result from such external stimulation? As soon as this psychological side is emphasized, the analysis of the mental impressions must be the starting point. We find in ourselves experiences which correspond to the stimula- tions from without. We must resolve these inner states. We ask accordingly which elements we can discriminate when we see and hear and touch the world around us.

Only one way is open to us. We must turn our attention to the impressions which we receive and try to discriminate in them all noticeable differences. If we taste some ice cream, we may feel the impression as a unit, but if we

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begin to analyze that perceptive material, we easily dis- criminate the coldness from the sweetness and the mere touch impression from either. And if we are aiding this selfobservation by experiment, our separation of elements may go still further. Experimenting does not necessarily require the use of instruments. "We perform an experi- ment if we observe the taste of ice cream while we close the passages of our nose. Then we find that, under these artificial conditions, the sweet loses its chocolate flavor. That is, we discover that the impression which appeared to be a mere taste also contained elements of smell. We have accordingly no elementary content before us when we ex- perience the impression of chocolate ice cream, because we can resolve it into simpler factors, into the taste sensation of sweet and the smell sensation of flavor and the tempera- ture sensation of cold and the tactual sensation of smooth- ness; and if we went on experimentally, we should be able to show that even this impression of smoothness can be re- solved into still simpler elements. To enumerate all the mental indivisible parts which can be discovered in our outer impressions demands an introspection with all the aids which the laboratory can furnish. The apparently simple stimuli like pressure on the skin or contact often demand the most complicated experimental investigations to discover the mental elements in their perception.

If the elements of our perceptions are called sensations,. the list of our sensations is long, and yet rather short com- pared with the multitude of objects which we perceive. On the one hand the same elements may be combined in numberless forms, just as the few letters of the alphabet are combined into the works of Shakespeare. On the other hand the technical devices of civilization may transform the stimuli of outer things to bring them into the limited compass of our sensations. To protect ourselves we must react to the dangerous bacilli of diphtheria and tuber- culosis and we must discriminate the tenth of a degree of

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blood temperature and the smallest poisonous addition to our food. Our naked senses are not sufficient. We cannot see the dangerous tubercle bacillus as we see the danger- ous snake, nor can we discriminate by our senses a tenth of a degree of temperature or smell or taste a milligram of arsenic. All this is done by those detachable appendages to our senses. We see by the microscope, we measure with the thermometer, we examine the chemical reactions. Biologically, the sensory apparatus is by these technical methods wonderfully enriched. The circle of objects which stimulates our psychophysical system and becomes the starting point for reactions, is gigantically expanded, but the number of psychophysical elements is not increased by this change. No attachment to the eye can bring to the brain any visual elements which are not contained in the natural impressions without the technical help. On the contrary, the devices of technic may easily lead to a neglect of sense discriminations by which the number of sensation differences becomes decreased. We civilized men may be less aware of difference of temperature sensations than the primitive people since we do not give attention to them and rely on the visual impressions which the ther- mometer furnishes. We must now study the different groups of sensations, and may begin with the most com- plex, the sensations of light.

a. OPTICAL STIMULATION

The System of Light Sensations. — Looking out into the street we see objects near and far, to the right and to the left, large and small, and in all possible forms. Moreover we see the objects changing their forms and positions. We see a man walking, that is, his passing through different places in succeeding times, as directly as we see the color of his red necktie. But when it comes to enumerating the elements, we recognize that all the space traits involve re-

STIMULATION 73

lations and are not elementary as that red color impression is. If we seek the visual elements, we are not interested whether the objects are round or triangular and in what rhythm they succeeded one another. We consider simply the elementary material out of which the mental impressions are formed. In doing so we single out a side of the actual experience which never exists alone. Even the shortest light impression has a time value for us, and the smallest color point has a space value. But we want to abstract at first from these aspects as much as we disregard the fact that the color has an element of pleasantness or unpleas- antness for us, or that it forces itself on our attention.

The classification which lies nearest is that which sep- arates the colors from the colorless light sensations. To gain a quick survey of both regions, we may group all the colorless sensations in one series from white through the light grays and dark grays down to black. We may pro- ceed similarly with the colors. In the rainbow series of the spectrum we recognize at once the red, orange, yellow, blue, green, violet. But if a long spectrum is carefully ex- amined and we study the smallest differences of neighbor- ing spots which we can discriminate, the well-trained eye distinguishes between the extreme red and the extreme vio- let about one hundred and fifty small steps. There are all the greenish yellows and yellowish greens, and bluish greens and greenish blues, and so on. If this were all, we should have between red and violet one long series of many colors, just as we had between white and black one long series of grays, in both cases each sensation most similar to its neighbor and separated by a just perceivable difference.

But the two cases, after all, are not alike. If we go from white to black, we feel that every point between them, every gray, has a certain similarity to both, and the fur- ther we go away from white and the more we approach the black, the less our gray appears whitish and the more blackish. If we pass from red to violet, the experience is

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quite different. At first we come from red through orange red to orange yellow, to golden yellow, to yellow, and have along the whole way the distinct impression of a decreas- ing similarity to the red and an increasing similarity to the yellow. The yellow itself no longer reminds us of the red. As soon as we pass the yellow, we come into a series in which each color tone has similarity to both yellow and green, changing toward greenishness the further we re- move from yellow. At green again a fundamental change appears. Each following color becomes less greenish and more bluish until we reach blue. And now the turn comes for the last time. Toward the end of the spectrum the colors become less and less bluish and more and more red- dish. If we add the various hues of purple to the violet, we can pass directly from the blue through violet without any break to the red sensation with which the spectrum began. In the white gray black series we had only two end points, black and white. Everything between them is character- ized by similarity to both. But we see that in the color series we have four such points of reference, red, yellow, green and blue, and every possible color impression gets its color value through its similarity to two of these four points.

How ought we to interpret this color series. If we look at a series of uniform colored papers, a greenish blue or a reddish blue, that is violet, or a reddish yellow, that is orange, appear to us, each taken by itself, just as simple as a yellow or a blue or a green. If we emphasize this fact, we should have to say that these one hundred and fifty color sensations are all independent ultimate elements. This is often maintained. But after all this ignores the significant fact from which we started, namely that if we pass along through the spectrum series, we can feel every hue between red and yellow as being related to those two end points, and the same of the colors between yellow and green, and green and blue, and blue and red. What else

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does this similarity to the two colors mean but that under the favorable conditions of such an experiment we become aware of the reddishness and yellowishness in the orange, which we are accustomed to ignore, if we look at the orange alone. There is some real reddishness and some real bluish- ness in the violet sensation.

To be sure, those two elements in it are not mixed like salt and pepper. At every physical violet point both the red and the blue are found. But we are not speaking here of physical stimuli ; we are speaking of the mental content and, if two mental contents become mixed, we cannot expect anything but a new mental content in which the two ele- ments which enter lose their independent character, fuse into a unit, and yet give to the new product similarity to both of the two. We have a right, accordingly, to say that all those one hundred and fifty color differences result from 'the combination of the mental elements red, yellow, green and blue. The achromatic series then de- mands the same interpretation. Every gray is a mix- ing and blending of the white sensation and the Mack sensation.

Saturation and Brightness. — A glance at the world teaches us that these pure spectral colors and the series of grays are only a small part of our impressions. Hardly any colored objects in a room show those rich and saturated colors which the spectrum presents. Our blotting paper may be green, but it is a dull and unsaturated green in which the greenishness does not appear with that im- pressiveness in which it stood out in the spectrum ; and the brown oak furniture is colored, and yet its color has found no place in that rainbow series. Nor did we have there any pink or olive or salmon or lilac color in our series of a hundred and fifty hues. Yet here too we quickly discover a simple systematic order, if we study what results when the pure color sensations are mixing and fusing with color- less sensations. As white and black are blending in gray,

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white and red are blending in pink, and white and violet in lilac, and black and yellow in brown.

Here, "too, the question of simplicity arises. The pink in itself appears an entirely simple, unified impression. But if we look over that whole long series from pure red to pure white, each step a little less reddish, and a little more whitish, then we recognize that every pink contains a red- dish and a whitish element. Every single colorless sensa- tion from white through gray to black can fuse with every single color sensation and can be mixed with it in any pro- portion. Our blotting paper green is green fusing with a rather dark gray, and the blotting papers vary between a rather saturated green with little gray in it to an almost grayish paper with very little green in it. If we were seeking a graphic symbol, we could think of every one of the one hundred and fifty hues as the apex of a triangle of which the base is a line from white to black', containing all the different shades of gray which we can discern. In these triangles every point of the base can be connected by a straight line with the apex, and each of these lines would represent the series of different mixtures between the color sensation and a particular gray sensation, that is, the color of the apex in all degrees of saturation. We are ac- customed to call those which lie on the whitish side of the triangle the tints and , those on the blackish side of the triangle the shades.

Everyone of these triangles would contain, accordingly, several hundred different combinations of the hue with all kinds of gray in all proportions. On the other hand evi- dently no combination in one triangle could reappear in any of the other triangles. The psychologists, therefore, recognize thirty to forty thousand different color impres- sions. Yet it is clear that as everyone of those hues was a blending of the four colors, red, yellow, green, blue, and every gray a blending of the two impressions, white and black, and °very tint and shade a blending of one of the

STIMULATION 77

colors with one of the grays, this bewildering manifoldness can be brought down to a system of combinations of six light sensations. In order to determine a particular color impression, we must indicate which of the six impressions are present and with what intensity they enter into the combination.

This whole system of light impressions can be looked on from another point of view. We spoke of the colorless series as one which leads from white through gray to black, and we treated those two end points as two qualities like red and blue. But in ordinary life we are inclined to take a different point of view. The black is darkness to us, the absence of light sensations, and the series from black through gray to white presents an increasing brightness. If the sun shines on white paper and then we close the shutters of the windows, the white becomes gray, and the more we exclude the light the more blackish it becomes; and yet it is more natural to say, not that black is mixed in, but that it becomes darker and darker. We all have a certain difficulty in watching our real light sensations, be- cause we attach the names of the objects to the light and believe that the sensation is still present as long as we know that the object is before us. We call a blackboard black, even if the sun shines on it so fully that we see practically a rather light gray ; and we call our paper white in spite of a deep shadow on it by which we actually see a dark gray. But if we emancipate ourselves from this thought of the objects, we recognize that under all circumstances the series from white to black means the series from greatest brightness to deepest darkness.

As soon as we study this brightness aspect of our light impressions, the world of colors appears to us also bright and dark. The yellow is brighter than the blue, and the blue tints and shades can go through any degree of bright- ness. If the sun breaks through the clouds, every color in our room becomes brighter, and if twilight falls, every

78 PSYCHOLOGY

color becomes darker. We can easily determine the degree of brightness by comparing the color with various grays. A color patch on the background of a blackish gray may appear bright, on the background of a whitish gray it may appear dark, and in changing the gray we can find the gray background on which it appears neither brighter nor darker, but equally bright. We can thus refer the brightness of every color impression to an objective scale of gray sensa- tions. From this point of view we must be able to arrange the color sensations also according to the different degrees of brightness. It is evident that this is not a really new element in our impressions, but Only a new angle of com- parison suggested by particular interests.

The Visual Stimuli. — Our next question must be how these visual sensations which we have mustered are re- lated to the visual stimuli of the surroundings. The world is visible in so far as it sends out or reflects ether waves of a particular length. The long ether waves which carry the wireless messages stand in no relation to vision. But if they become as short as 690 millionths of a millimeter, they produce in our nervous system an excitement which is ac- companied by the sensation of red, and if the waves be- come shorter and shorter, the psychocerebral processes pass through those one hundred and fifty hues to violet, where the rays are only 390 millionths of a millimeter long. If the ether waves become still shorter, they cannot reach the optical centers and are invisible, in spite of their chemical effects. While the color hue corresponds to the length of the wave, the saturation corresponds to the simplicity of the waves. The more complex the wave becomes, that is, the more wave rhythms are combined in the light rays, the more uncolored light sensation is added to the color. When all possible rays of the sunlight are mixed, the pure white and gray result. The brightness, finally, depends upon the intensity of the light, that is the height of the wave.

As to the correlation between the brightness and the in-

STIMULATION 79

tensity of the light rays, one fact stands in the foreground. The just perceivable difference between two sensation brightnesses does not depend upon the absolute but upon the relative difference of the light intensities. The same amount of candle-power which makes a gray just noticeably lighter, when added to a weak light, would not produce any brightening, if it were added to a stronger light. The five times stronger illumination demands a five times greater addition in order to produce on the psychical side the same just noticeable difference. The addition which is needed must stand in the relation of 1 to 120. The light of a wax candle throws clear shadows in a dark room; that is, we see distinctly the light difference between the fields on which its light falls and those which remain with- out. But as soon as the sunlight floods into the room, those candle shadows become invisible. Yet the absolute difference between the places which are lighted by the candle and the not lighted neighboring places remains the same. We do not notice this difference now, because the much stronger sunlight has added to both so much light intensity that the relation between them is entirely changed. For the same reasons we do not see the stars by daylight.

This observation that the brightness of our light sensa- tions shows equal differences when the compared stimuli are in equal relations has an especial significance, because this principle can be found in all other sense regions too. It surely holds for tones and noises, for pressure sensations and movement sensations, and probably for taste sensa- tions. Everywhere we find thai the equal difference of the intensity of sensations depends upon equal relations of the corresponding stimuli. But the significance of this law lies most of all in its historical importance. It was the germ from which modern experimental psychology developed. Based on observations of Weber and systematically de- veloped by Fechner in the middle of the last century, it

80 PSYCHOLOGY

appeared as the first case in which psychical experiences could be brought into a definite relation to exactly meas- urable physical facts. The vista of a psychology similar to the measuring natural sciences was opened by this dis- covery. As it was the first law which connected the psychi- cal and the physical facts in the terms of exact measure- ment, historical respect has even left to it the somewhat pompous name of the psychophysical law.

The apparently simple relation between sensations and physical stimuli indicates only the typical conditions. It is true we can produce all color sensations by changing the wave lengths, all degrees of saturation by changing the mixture of waves, and all degrees of brightness by chang- ing the height of the waves. But this does not exclude changes occurring in all three directions under still other conditions. The following facts are especially noteworthy : First, we may go from a saturated color to mere gray not only by mixing it with other colors, but by decreasing its intensity. All colors appear gray in twilight. Or we may get gray by mixing only two lights of particular wave lengths, the so-called complementary colors, like yellow and blue or purplish-red and blue-green. Moreover we may see gray, if we have pure light of one length only, if it is far aside from the point which we fixate.

On the other hand we may produce a special color hue, if light rays of that particular wave length do not stimu- late our nervous system at all, but if lights of greater and less length are mixed. We can see orange by being stimu- lated by simple waves, but we can also see it under the in- fluence of red and yellow together. Furthermore, we may see a color in spite of the complete mixture of all rays, if the field is surrounded by color. It is the effect of color contrast. A little piece of gray paper appears blue on a yellow ground, yellow on a blue ground, red on a bluish- green ground and bluish-green on a red ground. And we may see a color, too, if the complementary color preceded :

STIMULATION 81

the color after-image. If we look at the purplish sinking sun, and then at a white wall, we see greenish balls on the white ground. The relations between the physical light rays and the psychocerebral sensations of light are thus after all very complicated. In order to understand them, we are obliged to give attention to the apparatus which intermediates between the rays of the outer world and the brain processes with their sensations. t

The Eye. — If we consider the construction of the human eye, we must not forget that the evident biological aim of this instru- ment is not only to bring to the brain notice of the light changes in the outer world in general, but to separate the light stimula- tions from hundreds of thousands of points in the outer world. The brain must adjust itself to the distribution of colors and lights in the whole space around us and in everyone of those smallest spots we must be able to recognize all the changes of quality, intensity and mixture of light. We are not engaged here in the analysis of space perception, but in order to under- stand the structure of the eye, this function of the separation of the messages from many single points cannot be disregarded. Thus the task of the eye cannot be fulfilled by having only one apparatus which is sensitive lo the changes of light rays, but re- quires hundreds of thousands of such end organs. They are of two types, the so called rods and cones. The shorter, the cones, are bottle-shaped; the longer, the rods, are straight, standing so near together that a half million of them form the cup-like retina which is the background of the eye. The cones alone fill the center, the fixation point, the region of sharpest seeing, while the rods increase in number with the distance from the center.

Each of these hundreds of thousands of rods and cones is in connection with a nerve fiber, and all these turn toward one exit, leaving the retina in one big cable at the nasal side of the eye. These two cables from the right and left eye exchange half their fibers on the way to the brain. Those which come from the right side of the right retina go together with those from the right side of the left retina toward the right sidp of the brain.

82 PSYCHOLOGY

and correspondingly those from the two left sides of the retinas to the left side of the brain. After passing several middle sta- tions, they finally reach the rear part of the brain, the occipital lobes of the hemisphere. If a hemorrhage destroys these occi- pital parts on the right side of the brain, the right halves of both eyes become blind.

The retina is kept functioning by a network of blood-vessels, the choroid. In order that the light rays may reach every part of this 'system of nerve end organs, this hollow cup, the retina and choroid, is filled with a gelatinous substance through which the light passes. In order to regulate the amount of light and thus to protect the sensitive end organs against overstimulation, the front is covered by a shutter with an opening, the pupil. This shutter, the iris, which according to its pigment looks green or brown, and if pigment is lacking looks blue, can contract or dilate. In full sunlight the pupil is so small that it admits only the twentieth part of the light which would pass in if the pupil were as wide as it is in twilight. This whole system is covered by a tough membrane, the white sclerotic. Its front part is again translucent to light; this is the cornea.

Yet these parts would be insufficient to produce an image, that is to secure the stimulation of one rod or cone only by one light point in the outer world. The rays of light which come from one light point would flood through the pupil and reach hundreds of thousands of rods and cones. In addition a lens is needed by which the rays diverging from one light point of the outer world will converge toward one point in the retina. Such a lens is fixed in the front part of the eye, immediately behind the iris. If it were a rigid lens like that of the photographer, a sharp image could be secured only from objects which lie at a particular distance from the eye. The photographer brings his lens nearer to or further from the photographic plate, if he wants sharp images of objects at different distances. In the eye the lens does not change its dis- tance from the retina, but its curvature. The refracting power of the lens is in this way increased when the objects come nearer. All blurring can thus be avoided.

The simplest proof that the rods and cones are really the visual elements by which the ether waves are transformed into

STIMULATION 83

the nerve excitements, lies in the fact that the region where the fibers turn into the cable of the optical nerve, and where no rods and cones exist, is blind. The anatomical difference of struc- ture suggests that cones and rods have different functions. Only the cones serve both for the seeing of colors and of colorless light, while the rods respond to colored light and to mixed light alike by an excitement which leads to colorless sensations. On the other hand the rods are, in the eye adapted to darkness, able to react on very faint light, which is too weak to stir up the cones. Hence in late twilight we no longer discriminate by the fixation point/ which contains cones only. For these reasons it also follows that the peripheral regions of the retina lack all color vision. A colored object moved out far from the fixa- tion point must throw its lights on regions almost without cones; it appears simply gray. Between the central regions, however,, in which all colors are visible and the peripheral ones, where no color is seen, we find a zone of the retina in which red and green are lacking, but yellow and blue are effective. It is well known that "about two per cent, of all men possess a retina which func- tions also in its central part like this. They are colorblind. They cannot recognize red and green, and everything seems to them composed of yellow, blue, white and black.

If we are to account for this difference between the central region where all colors are seen and the middle zone in which blue and yellow alone are visible, we cannot refer to any ana- tomical differences like those between cones and rods. There must be differences in the cones themselves, but these differences are not visible under the microscope. We are therefore confined to theories about their chemical constitution. We must consider it probable that the cones contain various chemical substances, each of which responds to ether waves of a certain length. The cones in the middle zone, for instance, perhaps contain only two such substances, one of which becomes excited by relatively long waves, producing in the brain the excite- ment which is accompanied by the yellow sensation, the other excited by relatively short waves, producing the blue sensation.

But the facts would then at once suggest a further develop- ment of the theory. We know that blue and yellow mixed give

84 PSYCHOLOGY

gray. We might expect therefore that these two substances are only differentiations of the substance in the rods, so that, when both substances are excited at the same time, the same process results which arises in the rods from every kind of light waves. In the cones of the central region the chemical substances may have become still further differentiated. Substances which respond to ether waves from the red and the green part of the spectrum are developed, but if all four substances are working together, again we get the excitation which leads to the color- less gray sensation. A number of such chemical theories have been proposed. We cannot discuss their, merits and their shortcomings here. They must be measured by the suc- cess with which they explain the facts of color mixing, of color after-images, of color contrasts, of adaptation to color and so on.

The biological import of all these details of optical stimula- tion is evident. It is essential for the individual that he adjust his actions to the objects of his surroundings, not only with re- gard to the manifoldness of their forms, which colorless vision would impress on him, but also with regard to their richness of coloring. Yet it would be bewildering if everything which en- tered his sphere stimulated his brain with equal completeness. His reactions must be focused, and therefore his vision too must be most differentiated in the center of the field. The outlying objects must form only a general background, indicating where changes are going on. For this purpose it is advantageous to the psychocerebral mechanism if the side parts of the retina are widely expanded, but attuned only to colorless impressions. It is no less useful for the individual that neighboring fields pro- duce contrast effects, as by this the objects stand out from one another. Through the mechanism for color adaptation, the brain becomes independent of chance illumination, and can thus adjust itself correctly to the world of things whatever colored light may fall on it. By the working of the psychophysical law the mind can recognize the objects of the surroundings more easily. If it did not hold, every cloud before the sun would change the face of the things around us. Differences which we should notice in strong light would be swept away by the weaker illumination.

STIMULATION 85

b. AUDITORY STIMULATION

The System of Sound Sensations. — As in the case 'of vision, the study of the psychophysical processes in the world of sound, too, may be approached directly from the side of consciousness. The biologist would simply ask on what sounds of the outer world the organism reacts, judg- ing from the outer behavior the cerebral effectiveness of the stimuli. The psychologist analyzes the inner experience first and then correlates it to the physical and physiological processes. The world of sounds to which the human mind adjusts itself evidently differs from that of the animals much more than the world of human vision from that on which animals react. Man and beast alike must regulate their actions with reference to the visible things around them, and it is only an incidental feature for most men that a fragment of that visible world consists of writing and printing, that is of symbols for actual things. The hear- ing of man, on the other hand, is rather little concerned with the sounds and noises which the things themselves produce and which are essential for the animal. The sounds which most often control the reactions of man are the sounds of speech which merely point to objects.

Among men, however, it seems almost as if the audible world of the psychologist is of a particular order, inasmuch as he is accustomed to give even to this most important part in the realm of sound, to speech, no more attention than to the noises of the surrounding things, and instead to con- centrate all his interests on the tones of music. Yet this is not by chance. The tones can easily be brought into clear and definite series like the color sensations; nothing simi- lar can be hoped for the host of noises. A simple grouping such as we found for the colorless light sensations is im- possible for the toneless sound sensations. Moreover the only promising approach to a better understanding of the noises comes through the study of the tones, and the psy-

86 PSYCHOLOGY

chologist is therefore justified in studying the system of tone sensations first of all.

Yet it would be onesided to think of tones only in refer- ence to music. The demand for a biological interpretation must warn us against this. The musical use of tones evi- dently has no significance for the conservation of life. The ability to listen to a symphony does not help in the strug- gle for existence. Music is the only art which makes use of a material that has no bearing on our practical work. In the development of the animal race nature cannot have built up the psychophysical mechanism of tone hearing in order that man may hear the richness of sounds from musical instruments. The tones as elements of music are thus a psychophysical by-product, but there are tone ele- ments in most of the noises, and the vowels of our language are tone combinations, while only the consonants are true noises.

If we try to bring order into the tones, we recognize easily three different directions in which the impressions may vary. A singing voice sounds, different from a whistle or from a violin, and these different from a trumpet or from a piano or from a bell or from a flute or from an organ pipe. This variation is technically called timbre. Every timbre, on the other hand, can be varied in the direction of lower and higher tones. If we pass over the keys of the piano from the left to the right, the specific piano timbre remains unchanged, but the tones pass from low to high. The low tone sensations appear massive, full, heavy, and we are readily inclined to perceive them as expansive, while the high tones appear thin, agile, light. The variation in this direction is called pitch. Finally each tone may change from strong to faint, from fortissimo to pianissimo.

This threefold character of the change naturally sug- gests a comparison with the three dimensions of the visual sensations. If we consider only the psychological aspect, it would seem most natural to treat the differences of

STIMULATION 8?

timbre as the really fundamental differences of tones and to compare them, accordingly, with the variety of colors. The orchestra is a rainbow of sounds. The multitude of instrumental differences is as primary as the multitude of colors. The brightness difference from the darkest gray to the lightest then subjectively corresponds to the pitch dif- ference from the lowest tone to the highest, and the strength of the fully saturated color, decreasing to the point where the color tone disappears, corresponds to the transition from the strong tone to the feeble. In practical life we work with such classifications. If we hear a single tone, we do not give our attention to its particular pitch. Very few persons, indeed, have the ability to recognize absolute pitch. But we do say it is a bell that rings or the sound of a voice or a trumpet tone or a whistle. The psychologist, however, prefers a less natural grouping of the three factors. He considers the pitch as fundamental, and com- pares the changes of pitch with the changes of color. In doing so he is influenced essentially not by the inner ex- perience, but by the relation of the tones to the physical stimuli.

The Auditory Stimuli. — How can we correlate this three-dimensional system of tones to the sound excitement of the outer world? The normal sources of sound are air waves. The audible limits are about 20 vibrations for the lowest tones, about 50,000 for the highest. The tones of the piano, to be sure, lie within the much narrower limits of 30 and about 4,000. The just discriminable differ- ences of pitch are smallest in the middle regions of musi- cal hearing. An increase of one-fifth of a vibration can there be discriminated by a well-trained ear. In the region of the highest tones differences of several hundred vibra- tions are needed to make two neighboring tones distin- guishable. Nearly 10,000 steps may be discriminated be- tween the lowest and the highest tones by a good ear. This long scale of tones of different pitch is evidently not the

88 PSYCHOLOGY

scale of music. In the auditory pitch series, every tone finds a place when it shows a difference from its neighbor: in the musical pitch series only a limited number of spe- cially selected tone sensations are accepted. The physical principle of this selection is the simple arithmetical rela- tion of the tone waves. The octave is characterized by the relation of 1 to 2, the duodecim 1 to 3, the double octave 1 to 4, the fifth 2 to 3, the third 4 to 5, the fourth 3 to 4, and so on.

This description of the tones used in music is evidently physi- cal and not psychological. How can we select the musically valuable tones from the audible multitude by psychical features? Of course, we might refer to the pleasure which results from their sounding together, but this is an effect produced by the musical tones, not a characterization of the tones themselves. Here the conception of fusion offers itself. We saw that red and blue fuse in the violet, red and yellow in the orange, blue and green in the blue-green, with the result that each of the entering colors loses to some degree its independence and so blends with the other color that it is difficult to recognize the elements in the combination. Only by comparing them with the independent colors is their presence in the mixture felt.

The tones of different pitch show a very different tendency to fuse with one another when they are together in our mind. Most of the audible tones interfere with one another or remain entirely separated, but others more or less fuse. The highest de- gree of fusion characterizes the octave. If an untrained observer hears two tones in the relation of 1 to 2, he is generally unable to recognize them as two tones at all. The two tones blend com- pletely into one. Next to it comes the double octave, then the fifth, then the third, with much smaller tendency to fusion, the fourth and the sixth. This fusion is strictly a mental experience, and it is indeed a sufficient condition for choosing a limited number of tones out of the tone series of audible sensations. Instruments like the organ or the piano are so built that no other tones but those which subjectively can be brought into combinations of fusion, and which physically show the simplest

STIMULATION 8^

relations in the number of vibrations, can be produced. In the string instruments the whole scale of audible tones can be played, but the fingers which shorten the strings by pressing them down at definite points secure vibrations in those exact relations. The singer creates that same effect by exact contrac- tions of the muscles in the larynx. While the tones in the simplest relations fuse, tones which show only a small difference in the number of vibrations cannot sound together without a disturbing interference. If a tone of 500 vibrations is given together with one of 503, we hear three times in the second a swelling and sinking which is felt as an interruption; the so called beats. If their number increases, they give to the tones something rough ; the beautiful smoothness of the tones is gone.

The strength of the tone sensations corresponds to the amplitude of the air waves. The psychophysical law, which we found valid for light intensities, holds for tone intensities, too : the just perceivable differences of the sen- sations depend upon equal relations of the stimuli. A chorus of forty voices may need the adding of ten singers in order that the sound appear stronger. But for four voices, it is enough to have a fifth man, and a mighty chorus of four hundred would need one hundred more for the difference to be felt.

The relation of timbre to the physical waves is more complicated. That which gives character to our musical in- struments cannot be, like the pitch and strength of the tone, connected with the length or height of the single waves. It always depends upon the combination of different waves. We saw that musical intervals exist between physical tones which stand in simple arithmetical relations. Musical in- struments are 'physical structures which never produce one physical tone alone, but always a combination of several such tones in simple arithmetical relations. The essential condition is only that these additional tones which have two times, three times, four times, five times and so on, more vibrations than the lowest tone be much weaker than

90 PSYCHOLOGY

this tone with the smallest number of vibrations. If it were otherwise, if we should hear, for instance, a tone of one hundred vibrations and with equal strength that of two hundred, three hundred and four hundred, we should really perceive a manifoldness of tones, however much they might fuse. It would be a musical chord. But if the tone of one hundred vibrations is strong, while those others are weak, our immediate impression is not that of a manifold- ness of tones combined in a chord, but that of one tone in a particular timbre. The mental effect of these weaker vibrations is not the impression of coordinated tones, but only that well-known shading of the lowest tone which gives the instrumental character.

The best approach to these overtones is through the use of resonators, hollow bodies, which, when they are held before the ear, reenforce a particular overtone so much that it stands out from the combination which forms the timbre. Yet as soon as the tone is strengthened it is no longer the natural instrumental tone. As long as we leave the ele- ments in their natural intensities, we may recognize the parts, but this does not destroy the timbre character of the lowest element of the combination. Subjectively, the sig- nificant flavor of an instrumental tone remains, even if we discriminate elements in it, and thus the whole must be acknowledged as a psychological unit, while it is physically a complex combination. It is this complexity of the outer stimulus which makes the psychologist usually unwilling to accept the timbre as a basis for the classification of tones, and leads him to prefer the pitch.

When we speak of combinations of tones, either in chords or in timbre, it would, of course, be* a misunder- standing to fancy that the combined tones remain inde- pendent air waves. If the sound of a chord comes to us, we do not have some air particles which move in one rhythm and others in a second and again others in a third, but each air particle moves under the influence of all the vibrating

STIMULATION 91

bodies. The waves are combined, as the circles on a pond are combined when two stones are thrown into it. In the cases of the overtones, the sounding string itself combines the various movements. The complexity of such a com- bination becomes evident, if we think that we can hear a whole symphony through the telephone. The one vibrating telephone diaphragm must vibrate in such a complex rhythm that we can recognize all the various instruments in the orchestra. A combination of tones means, therefore, not a mere summation of simple regular waves, but the formation of complex waves. The characteristic feature is that, as lorfg as we have to do with musical tone combina- tions, the resulting wave, however complex, remains a periodical one; that is, it repeats after a certain time ex- actly the same form, and the length of that time is given by the vibration of the deepest tone which enters. If the tones of one hundred, two hundred, three hundred and four hundred vibrations are combined in any relative intensity as chord or as timbre, the resulting wave repeats itself after every hundredth of a second. As soon as we no longer have to do with musical tone combinations, that is, if the vibrations which enter into the combi- nation do not stand in a simple arithmetical rela- tion, the physical product is an unperiodical air vibra- tion, and this is the external condition of most of the noises.

All the continuous noises, all roaring and rumbling, rustling and hissing, buzzing and whispering, howling and rasping, consist of such unperiodical air waves. Only the sudden noises, the clicks and snaps and cracks, correspond to single, explosion-like air movements. Many of the noises by which the world tortures us are combinations of such continuous noise elements with successive sudden noise shocks. Not a few noises contain strong tone elements. If a piece of wood falls to the floor, we hear it as a noise only, but it is quite possible to cut a series of pieces of

92 PSYCHOLOGY

wood so that, if one after another is thrown to the floor, a distinct melody of tones results.

The Ear — In the case of vision, when we had discussed the light sensations and the related external stimuli, we turned to the sense organ in order to understand the transition from the ether waves to the psychocerebral excitements. We must now raise the same question concerning the sound sensations and the physical sounds. How are they connected by the actions of the ear? The problem which is to be solved is clear. There must be an apparatus by which the various sound waves pro- duce various nervous excitements. If we take it for granted that the central processes for the different tones are 'excitements of locally different brain units, we must suppose that every tone of a special pitch reaches a special end organ in the ear and that its excitement is carried in a special nerve fiber to a special cell in the brain. As we saw that we could discriminate ten thousand steps of pitch, ten thousand end organs would have to exist, each of which could pick up the waves of a particular rhythm.

If this were realized, there would be no mechanical difficulty in the second demand which we must raise; namely, that these ten thousand end organs resolve the complex periodic waves into their elements, that i% into all those simple tones which were combined in a chord or in a timbre. We saw that how- ever many simple waves may be superadded, they form together a periodic wave as long as the elements stand in simple arith- metical relations. But the physicist also knows the reverse. Every periodic wave, however complex, can be understood as a combination of elementary waves which stand in simple rela- tions. Theoretically, any chord or timbre wave can be resolved, accordingly, into a number of pure tones. The ear must have the analytic power to resolve the complex wave into these elements.

The prevalent view is that all these tasks are fulfilled in the ear by sympathetic vibration. If we sing a tone in a room in which a piano is standing, the one piano string which gives the same tone responds by vibrating, while all the other strings remain at rest. Each vibrating body answers in this way to the waves of the surrounding medium, if they correspond to its

STIMULATION 93

own rhythm. If we had a harp of ten thousand strings, each one a little longer and heavier than the preceding, the longest moving in twenty vibrations in the second, the shortest in fifty thousand, every air vibration in the limits of hearing would start the movement of one of these wires. Just such a harp is contained in our inner ear. It is not actually a system of isolated wires, but a continuous, long, narrow membrane. Yet this membrane is held at its longer sides at such a tension that it can work mechanically as if thousands of parallel strips were stretched beside one another. The longest is about half a milli- meter, the shortest about the twelfth part.

This suspended membrane must be reached by the sound waves. It is contained in a bone cavity which is formed like a snail shell, a spiral of two and one-half revolutions. The membrane divides this spiral tube into a lower and an upper passageway, which are connected with each other at the top. The whole cavity is filled with liquid. Each of the tubes contains at the bottom a little membranous window. If the one is pushed inward, the water in the whole system must be pressed and must push the other window outward. If the first, the so-called oval window, is brought into vibration, the whole liquid content must take up the rhythm and force itself in waves against the long- stretched membrane, in which the sympathetic vibration of the corresponding string results. The oval window receives its rhythmic movements from a stirrup-formed bone, and this is fastened to other small bones, the hammer and anvil, which lie on the inside of the ear drum.

The air movement, which reaches the ear from without, pro- duces the vibration of the drum membrane, this transmits its movement to those three bones, and the stirrup drums its rhythm on the oval window, which pushes the liquid of the spiral cavity and reaches through it those fibers in the stretched membrane which respond sympathetically to the particular number of vibra- tions. Each of these fibers is in connection with a special nerve, and they all are joined in the big cable of the acoustic nerve, which leads to the brain and which carries each special fiber to a particular brain cell. The excitement of this brain cell is accompanied by the tone sensation of the special pitch. The com- plex wave of the chord or the timbre is in this way resolved into

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i

its components. In the case of the noises the excitement is not confined to single strings in the membrane, but whole large parts of the membrane are pushed at the same time, and produce that vague effect in which the single tones are no longer heard.

This whole theory has been attacked at its foundations re- cently, because it offers difficulties in the explanation of some subtle effects. It seems, especially, not to account well for the difference tones, which the well-trained ear can easily find. Their pitch corresponds to a number of vibrations which is the difference between two objectively given sounds, a low humming tone which is musically of importance. The opponents of the theory that our hearing depends upon the principle of sym- pathetic vibration are rather inclined to think that the rhythm and complexity of the waves may be carried through the nerves themselves and may produce different qualities of excitements in the same brain center. The various tones would correspond then not to the vibrations of different brain cells, but to the various kinds of function in the same brain unit. There are many prac- tical difficulties in the way of such an idea. We know, for in- stance, the not infrequent pathological cases in which certain parts of the pitch scale are lacking. We can easily understand that the lowest or the highest or some middle part of the long, stretched membrane might be defective, and this corresponds to anatomical observations, but no other theory can give an account of such disturbances.

Yet the more important argument is theoretical, and it throws light on the whole situation of psychophysical theories. This whole correlation between the mental and the anatomical physio- logical facts is not an object of discovery, but one of organiza- tion. A theory does not fulfill its purpose, if it simply explains a particular group of facts and does not adjust itself to the causal understanding of the totality of mental processes. The mere demand for psychophysical parallelism would, of course, be just as well satisfied if different tones corresponded to dif- ferent excitements in the same cell, as if they corresponded to the action of locally separated cells. Just as the diaphragm of the telephone can swing with so many variations that a whole orchestra can be heard through the vibrations of the one plate, any one brain cell too may receive a whole symphony. If the

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perception of tones alone were involved, the one theory might serve as well as the other.

But if we stand before the final decision, we must look much further. These tones enter into memory processes. "We can reproduce a melody in our mind, and we shall soon see that this memory depends upon processes of association and that these associations can easily be understood, if they are explained by the action of nerve fibers which connect the locally different cells, but cannot be understood by a succession of different ex- citements. The theory of the harp in our ear will thus have to be accepted, unless the association processes too can be put upon an entirely new basis.

c. THE LOWES. SENSE STIMULATIONS

Taste. — Taste, smell and touch are grouped as lower senses, compared with sight and hearing, since the world with which they bring us in contact is that of our bodily interests only. Our intellect gets no stimulus through tongue, nose and skin which is comparable to that of words which we read or hear, and even our esthetic satisfaction from odors and tastes can hardly be compared with the enjoyment of true beauty through the visual and audible arts. The flavors of the meal are pleasant, but not beauti- ful. Yet this lower type of service is surely not unim- portant. The attractive taste and smell of the food, the disagreeable smell of that which is impure and poisonous, are strong hygienic regulations of our behavior. It is true that this psychophysical apparatus does not work perfectly. There are poisonous gases which do not smell, and a few poisonous chemicals which taste sweet, and even the alco- holic beverages, pleasant to the taste and smell of not a few, must be classed among the dangerous chemical substances. But on the whole, taste and smell tempt us and warn us in our biological interests, the one adjusted to the solids and liquids, the other to the gases which enter our organism.

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The number of distinct elementary taste sensations is certainly very small. The endless variety of perceptions which we may gain by eating and drinking results from the manif oldness of combinations, and in these combinations the smell sensations show much greater richness of differ- ences than those of taste; and superadded are the tactual impressions, the temperature sensations and not least the impressions of our reaction movements in the mouth cavity. If our psychological analysis, especially when aided by exact experimental conditions, singles out the taste ele- ments, sweet, salt, sour and bitter remain the ultimate factors. Each of these four sensations can pass through various intensities. The claim that there is a special alka- line and metallic taste probably accredits to taste something which is a blending of taste and smell. The opposite claim that even sour and salt are not real tastes, but that they receive their characteristic content from combinations of taste with tactual and other sensations, seems not tenable either. It is true that salt brings an element of burning, and sour an element of contraction. But they can be recognized as effects of the tastes, not as parts of them, just as the pleasantness or unpleasantness is not itself a real part of the taste. The oily or soft or pricking effect of taste substances must also be separated from the real taste itself. The four taste qualities show a certain inner rela- tion not quite dissimilar to that of the four color sensa- tions. Especially if they- are in moderate strength, they blend with one another and fuse in different degrees, and within certain limits they can neutralize one another. Sweet and salt, salt and bitter, sour and salt, sweet and bitter, diminish each other, if they are given in weak solutions. Moreover, similar to light, the taste sensation fades away when the stimulus continues. We become adapted ; a weak bitter taste cannot last long. The experi- ment proves that the adaptation to one taste may strengthen some of the other tastes.

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The physical stimulus which leads to the psychocerebral ex- citation of taste sensations is liquid substance; that is, any solid material must partially be dissolved by the saliva of the mouth in order to excite the end organs of the gustatory nerve. It does not seem possible to give a definite chemical characteriza- tion of those stimuli which produce the four tastes. Roughly speaking, the sensation of salt corresponds to those substances which the chemist calls salt, the sweet to the sugar, the sour to the acids, but these names themselves are evidently used in chemistry on the basis of the taste impressions, neglecting the not rare exceptions in which an acid or a salt may appear taste- less or sweet. The sense organs are taste buds which lie in fungiform, foliated and circumvallate papillae. The nerve end- ings in those papillae may all respond only to one single kind of stimulus or to two or to three, to sugar, acid and salt alike; that is, taste bulbs of different function may be combined in a single papilla. The tip of the tongue, the edges of the middle part and the root are the chief taste regions, but it must be added that this is true only of the adult, as children have fully devel- oped taste sense all over the tongue and also in other parts of the mouth cavity. The prevalence of certain taste papillae in special regions is not without influence on characteristic motions of the face in tasting sweet or bitter substances, and these mo- tions again become so intimately related to the significant feeling tones of the tastes that we can trace the effects in many emo- tional expressions of the face.

Smell. — As the small number of elementary colors con- trasts with the multitude of elementary tones, the quartette of tastes contrasts with the host of smell sensations. Yet while the thousands of tone sensations form one continu- ous series in which each stands between two others from which it is just perceptibly different, the smell sensations of man appear rather chaotic. They are, anyhow, probably scanty compared with those of some animals. The dis- crimination of smells by the dog can hardly be understood from the olfactory experience of man, whose erect position makes it biologically less important to depend upon scent.

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Nevertheless it is quite possible to form certain groups of the smell sensations of man. All kinds of flower fragrance have a certain similarity, and the odors of tea or vanilla would fall into the same group. They are quite different, for instance, from the odor of the various kinds of fruit or wine, and both again are widely separated from the nau- seous odors of decaying matter. Usually nine large groups are acknowledged, and each of them can be further sub- divided.

If odors are combined, they can sometimes produce an entirely new impression in which the elements can hardly be recognized. More often a balancing effect re- sults ; one smell neutralizes the other, at least for a short time. The most characteristic feature of the situation is the quick adaptation to smell. We cannot keep an unin- terrupted smell impression beyond a few minutes. As soon as we become adapted to a strong smell, similar smells are lost also, while others remain unchanged. The stimulus is always vaporous. A direct correlation between the sensa- tion and the atomistic constitution of the odorous sub- stances has not yet been reached. The end organs of the nerve lie in the highest part of the cavity of the nose. They are long thin cells, clustered together in a narrow region, somewhat aside from the chief respiratory passageway. They can be reached, of course, not only by particles of the air which we inspire, but also from the rear side from near the root of the tongue. If the professional tea taster wants to discriminate the various aromas he gargles the tea in order that the vapor may enter the nose cavity from behind.

Touch. — The impressions of the so-called fifth sense have long been divided by psychophysiologists into pure touch sensations, temperature sensations, and pain sensa- tions. Compared with the richness of tactual impressions which the skin furnishes, it seems surprising that the analysis shows after all only one single quality of sensation

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in various degrees of intensity. We know how in extreme cases of blind deaf mntes the tactual sensations may become the vehicle to bring the highest civilization to their minds ; but we have only the one sensation, pressure, which begins with a slight feeling of contact and increases steadily. The manifoldness of apparently simple impressions results first from the spatial variations. The pressure upon a large area gives a different tactual feeling from pressure on a small spot without any conscious reference to the space. Moreover the contact at the forehead feels different from the contact at the finger; but the tactual quality may be the same, just as a color sensation is the same whether it comes from above or below. Secondly we receive many complex impressions as if they were tactual sensations of a specific kind. The smooth and the rough, the wet^ and the dry and the greasy give us significant touch sensations ; and yet we can easily become aware that they are nut new tactual elements, but combinations. The interrupting of the tactual sensations, the combining with the temperature sensations, the feeling of resistance, and so on are responsi- ble for their mental structure. We have no independent touch sensations either when we discriminate light and heavy bodies ; we perceive their differences not only by the intensity of the pressure on the skin, but by the pressure of the deeper inner organs and by the muscular effort of

lifting.

A well-known phenomenon is the quick adaptation to> tactual impressions. We are not aware of our clothes or of the chair on which we sit. The chief impression is always felt where two neighboring regions are under rather differ- ent pressures. The sense organs for touch are spread over the whole body, but they are distinct, isolated nerve ap- paratus. No touch sensation can be produced between these instruments in the skin, if the stimulus is sufficiently small and the pressure not so strong as to stimulate the neighbor- ing regions. In those parts of the skin where hairs can be*

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iound, and this refers by far to the greater part of the body's surface, an end apparatus for tactual impressions is near the root of every single hair. But also in those regions of the skin where there is no hair, the little end organs are distinctly isolated. On an average about two hundred may be found to the square inch, but they are unevenly dis- tributed according to the biological needs of the different organs.

Temperature. — While the tactual sensations show greater simplicity than the popular view would acknowl- edge, the temperature sensations are of more kinds than is Tisually supposed. We speak of one temperature sense which, as the mercury of a thermometer goes up and down, reacts with different intensities of temperature sensation. The psychologist, on the other hand, must separate the cold .sensation and the warm sensation as fundamentally differ- ent, and has good reason to consider the hot sensation also as an impression qualitatively different from the warm and the burning pain. The introspection corresponds here to ihe physiological discovery that cold and warm sensations result from the action of entirely separate sense organs. Just as the tactual end organs are small isolated instru- ments, the end organs for cold and the end organs for warmth are distributed over the whole skin, about seventy cold spots on the average to the inch, and irregularly be- tween them a much smaller number of warm spots.

If we move a cold pointed pencil slowly over a sensitive region, we feel the cold sensations flashing up from time -to time, and between these points no sensitiveness for cold at all. Yet the temperature limits below which the cold and above which the warm sensations arise are not constant; they are shifting with the temperature of the whole skin in that region. The most surprising fact, however, is that the cold spots, which do not respond to luke-warm tempera- ture at all, awake a distinct cold sensation as soon as they are stimulated by a hot temperature. If a broad object

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of about fifty degrees Celsius touches the skin, the effect, accordingly, must be that it reaches many cold and many warm spots. The warm spots react with intense warm sen- sations and the cold spots with cold sensations. This irri- tating mixture of warmth and cold gives an apparently uni- fied impression of new character, that of heat.

The skin is finally the bearer of a fourth kind of end in- struments, which are densely distributed over the whole body, the end organs for cutaneous pain sensations; they are more frequent than either touch or temperature organs. If a sharply localized stimulus like a needle point reaches such a spot, a thin little thrill can be felt distinctly dif- ferent from a mere tactual sensation, and if the stimulus is more severe, a really piercing pain results. They easily fuse with pressure sensations and are characterized, by a tendency not to fade and to produce long after-effects. We shall have to return to the discussion of pain when we speak of internal stimulations, but it ought to be empha- sized from the start that the pain sensation in itself is in- dependent of the unpleasant feeling which is constantly at- tached to it. In common language we are inclined to call a pain a feeling, as a pain which we get from being cut or burned is always strongly accentuated by this feeling re- action, while a color or a smell or a tone may be pleasant or unpleasant or indifferent. Yet the mere regularity of the connection does not change the character of the sensation. As we separate the tone sensations from their pleasantness or a foul smell sensation from its unpleasantness, we ought to consider the pain sensation, too, at first strictly as a sensation, and abstract from the subjective element of our disliking it.

d. INTERNAL STIMULATION

Movement Sensations. — The sensory functions of the organism appeared to us as the first part of the processes in the sense organ-brain-muscle arc; they start the com-

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plex brain excitements which ultimately result in motor impulses to action. But these actions cannot really serve all biological needs of the individual, if the sensory impressions on which they are based are con- fined to that which goes on outside the body. The sensorial stimulations which come from within the body must in- fluence the central and centrifugal processes as much as the messages from without. A fatigue sensation in our muscles, a hunger sensation in our stomach, a pain sensa- tion in our head, may influence the central arc processes still more than colors or sounds. In principle there can be no difference between the excitements which are carried to the sensorial centers when the sense organ lies in the skin or when the sense organ lies in the joints or between the muscles or when the nerve itself becomes irritated. Those internal stimulations cannot show the abundant manifoldness of the world of sight and sound, nor do they offer an equal sharpness and distinctness of quality and of local difference. Moreover the difficulty which they pre- sent to a subtle study of the relations between the mental states and the physical stimuli is naturally much greater. Yet we must survey at least some specimens of these groups. The psychologically most important stimulation from within is that which results from the movements of the body. Whenever we are acting, we receive impressions from our moving members. We may mostly ignore them, just as we usually disregard sensations of our skin. But as soon as we turn our attention to our walking or lifting or writing or speaking, we become well aware of the mani- foldness of impressions which result from the activities. Even movements like those in respiration or convergence of the eyeballs may become noticeable. The importance of these sensations for the structure of mental life is funda- mental. We shall find sensations of this group prominent when we come to the analysis of space and time perception, of attention and emotion and, above all, of the conscious-

STIMULATION 10a

ness of the self and the will. Yet these sensations them- selves offer rather little to the observer.

We may discriminate two qualitatively different elements, the movement sensation and the tension sensation. The movement sensation, which is related to the real change of position, may result from passive as well as from active movements. Its intensity varies very slightly; it even seems doubtful whether we have a right to speak at all of different intensities of the movement sensation. The ex- perience of weaker or stronger bodily movement is very complex: tension sensations and tactual impressions are combined there with the muscle sensations, and the muscle sensation itself usually becomes expanded over larger fields and lengthened in time when the move- ment grows. But a muscle sensation does not change its quality or intensity by being spread out in space and time, just as a color sensation is not changed by filling a greater area and a longer interval.

The sense organs which are stimulated by the movements are probably twofold. There are sensitive end organs in the joints. As every movement of our legs or arms or fingers involves rota- tions on the bones of the joints, these end organs must be af- fected by the muscle contractions. When we bend our limbs ourselves or when they are passively bent without our muscle contraction, the angle at which a change is just noticeable re- mains the same in both cases. This suggests indeed that the elbow or the knee or the wrist are the sources of the sensation. This is still more directly proved by the fact that the discrimina- tion of active movements is greatly hindered when a galvanic current through the joint decreases the sensitiveness of these joint sense organs. Yet we are aware of our movements also in parts of the body where no joints exist. We notice the motions of our tongue and lips and cheeks and eyeballs. Moreover, even in passive joint movements pressure and tension on the muscles themselves are unavoidable. Probably not only the joints but the muscles too contain internal sense organs ; they are stimulated

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"by the pressure which the contracting muscles exert on them. In any case the sensation is caused by the movement itself and not by the position of the muscles. It is certainly wrong to inter- pret the movement impression as a perception of successive posi- tions. On the contrary we become aware of the position by the perception of movement. The mere position of the limbs in complete rest gives no characteristic sensation.

The tension sensation is very similar to the movement sensa- tion, and yet can be distinguished. Here we may speak of dif- ferent intensities, corresponding to the increasing physical ten- sion. It is the tension sensation which informs us most directly whether the weights we lift are light or heavy, distinct from the movement sensation which tells us whether we lift the weights through a long or a short distance. If we try to move our limbs and are prevented, the pulling or pushing is again signaled to us by the tension sensation. The decrease of this tension is felt as a relaxation. The chief sense organs are here probably in the tendons by which the muscles are attached to the bones. Both the tension and the movement sensations resemble the contact sensations of the skin. Sensory nerves in the muscles are also the sources of the sensations of fatigue. It is an after-effect of long or strong muscle contraction. The