Classics in the History of Psychology

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Christopher D. Green
York University, Toronto, Ontario

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On the Witness Stand:
Essays on Psychology and Crime

Hugo Münsterberg (1908/1925)


If a girl blushes when a boy's name is mentioned in the family sitting-room, we feel sure, even if she protests, that he is not quite indifferent to her young heart. If she opens a letter and grows pale while reading it, she may assure us that the event is unimportant; we know better. If she talks with you and every word makes you believe that her entire interest belongs to you and your remarks, it is enough for you to see that her fingers are playing nervously with her fan, and that her breathing has become deep and vehement and her eyes restless since a certain guest has entered the room; you know she is hardly listening to you and waits only for him to approach her. And if he does not come, -- she may be masterful in simulation and the artificial smile may never leave the lips, yet you will hear her disappointment in the timbre of her voice, you may see it even in the width of the pupil of her eye. Yes, the hidden feeling betrays itself often [p. 114] against the will of the best comedian in life. It may be easy to suppress intentionally the conspicuous movements by which we usually accentuate the emotions. It is not necessary to become wild with anger and to collapse in sorrow, we may even inhibit laughter and tears, and a New Englander will never behave like a Southern Italian. But the lips and hands and arms and legs, which are under our control, are never the only witnesses to the drama which goes on inside -- if they keep silent, others will speak. The poets know it well. Through the dramatic literature of all ages is repeated the motive of the unintentional expression of emotions. The ghastly memory of a gruesome past seems locked up in the hero's mind; and yet when he is brought back to the place of his deed, it comes to light in his paleness and trembling, in the empty glaring of his eyes and the breaking of his voice. There is hardly a tragedy of Shakespeare in which the involuntary signs of secret excitement do not play their rôle. And the comedies of all time vary the same motive with regard to the lighter sins of love and social entanglement. The helpless stammering of the excited [p. 115] lover betrays everything which his deliberate words are to deny.

But the signs which made Hamlet sure that his mother had committed murder have not been overlooked by those who are on the track of the criminal in our practical life. The suspected man who pales before the victim while he pretends not to know him, or who weeps at hearing the story of the crimes which he disavows, is half condemned in the eyes of the prosecutor. When the conspiracy against Dreyfus sought to manufacture evidence against him, they made much of the fact that he trembled and was thus hardly able to write when they dictated to him a letter in which phrases of the discovered treasonable manuscript occurred. Much of that which the police and the delinquents call the third degree consists of these bodily signs of a guilty conscience; to make the accused break down from his own inner emotion is the triumph of such maladministration of law.

It seems that even some of the superstitions of barbaric times which claimed to discover the guilty by all kinds of miracles sometimes contained a certain truth of this kind. They depended on apparently [p. 116] mysterious signs which in reality sometimes belonged to the bodily effects of emotion. Evidently primitive life sharpens the observation of such symptoms. One-of the most adventurous "gunmen" of the West told me that when he was attacked by mobs he behaved as if he were constantly spitting; he went through such motions because it always discourages the crowd when they see that their adversary does not fear them, and they would know that a man who is afraid cannot spit -- the emotion of fear dries up the mouth and throat.

Of course, everyone knows how uncertain and unsafe such crude police methods must be. There cannot be justice if we base our judgment on the detective's claim that a man blushed or trembled or was breathing heavily. It would hardly be better than those superstitious decisions of early times. There are too many who believe that they see what they expect to see, and very different emotions may express themselves with very similar symptoms. The door is open for every arbitrariness if such superficial observations were to count seriously for acquittal or for conviction. [p. 117] But that provokes the natural question: cannot science help us out? Cannot science determine with exacitude [sic] and safety that which is vague in the mere chance judgment of police officers? More than that: cannot science make visible that which is too faint and weak to be noticed by the ordinary observer? The bystander watches the expressions of the strong overwhelming emotions--but can science, can experimental psychology, not bring to light the traces of the whole interplay of feelings, the light and passing ones as well as the strong, and the most hidden suggestions of consciousness as well as heavy emotional storms?

The question is indeed pressing, as the idea of the psychological expert in court cannot be withdrawn from public discussion. The mental life, -- perception and memory, attention and thought, feeling and will -- plays too important a rôle in court procedure to reject the advice of those who devote their work to the study of these functions. And especially the progress of modern psychology has been too rapid in recent years to ignore it still with that condescension which was in order [p. 118] at the time when psychologists indulged in speculation and psychological laboratories were unknown. To-day the psychologist operates with the methods of exact science, and the method which is here demanded seems entirely in harmony with his endeavours. The problem is whether he can record objectively the passing symptoms and whether he can get hold of expressions too faint to be perceptible to our senses. But just that the laboratory psychologist is aiming at constantly and successfully. Whether he measures the time of mental acts or analyses the complex ideas, whether he studies the senses or the volitions, he is always engaged in connecting the vague inner impression with an outer measurable fact which can be recorded, and in throwing full light on that which escapes notice in ordinary life.

In the region of feelings and emotions the experimental methods of psychology have been certainly not less successful than in other fields of inner life. To confine ourselves to that special problem which interested us from the point of view of law: the psychologist can indeed register [p. 119] the symptoms of inner excitement and, more than that, can show the effects of feelings and emotions of which the mere practical observation does not give us any trace. Yet even the subtlest detective work of the psychological instruments refers only to the same bodily functions which make us visibly blush in shame, pale and tremble in fear, shiver in horror, weep in grief, perspire in anxiety, dance in joy, grow hot and clench the fist in anger. Everywhere the blood vessels contract or dilate, the heart beat changes, the glands increase or decrease their activity, the muscles work irregularly: but the instruments allow us to become aware of almost microscopic changes. We may, perhaps, point to a variety of lines along which such inquiry may move.

To begin with a very simple group of processes, we may start with our ordinary movements is of the arm: does feeling influence them? I can give my reply from a little diary of mine. I kept it years ago. It was not the regulation diary -- there was no sentimentality in it, but mostly figures. Its purpose was to record the results of about twenty experiments which took about half an hour's time. [p. 120] I had the material for these little experiments always in my pocket and repeated them three or four times a day throughout several months. I fell to experimenting whenever daily life brought me into a characteristic mental state, such as emotion or interest or fatigue or anything important to the psychologist. One of these twenty experiments was the following: I attached to the bottom of my waistcoat a small instrument which allowed me to slide along an edge between thumb and fore-finger of the right hand, both outwards and inwards. Now I had trained myself to measure off in this way from memory distances of four and eight inches. Under normal conditions my hand passed through these distances with exactitude [sic] while the eyes were closed; the apparatus registered carefully whether I made the distance too long or too short. The results of many hundreds of these measurements went into my diary together with a description of the mood in which I was.

When I came to figure up the results after half a year's records I found a definite relation between my feelings and my arm movements. My diary indicated essentially three fundamental pairs of [p. 121] feeling in the course of time. There was pleasure and displeasure, there was excitement and depression, and there was gravity and hilarity. The figures showed that in the state of excitement both the outward and inward movements became too long, and in the state of depression both became too short; in the state of pleasure the outward movements became too long, the inward movements too short; in the state of displeasure the opposite -- the outward movements too short and the inward movements too long. In the case of gravity or hilarity no constant change in the length of the movement resulted, but the rhythm and rapidity of the action was influenced by them.

Here were, for the first time, three distinct sets of feelings separated and recognised through three distinct ways of bodily behaviour. After the publication of my figures, others came from other starting points to such division of our feelings into three groups, while some believe that there are only two sets. Still others hold, and I should not disagree, that pleasure and displeasure alone are the fundamental feelings; that a colour or a sound is agreeable seems primary, that it is exciting [p. 122] or soothing is secondary. On the other hand the number of those secondary feelings seems to me to-day still larger than it did at that time; I am inclined to accept man more simple feelings and find for everyone characteristic expressions of movement. All this becomes important as soon as the psychologist begins to explain the feelings and asks how far the sensations themselves enter as parts into the feelings.

But what concerns us here is the fact that the pleasurable and the unpleasurable mood betray themselves in opposite movement -- impulses of which we are unaware. I had meant in those hundreds of cases to make exactly the same outward and inward movements and yet the experiments disclosed the illusion. Of course, we all know how in joy the outward movements are reinforced; the boy swings his cap and the whole body stretches itself, while in anger the opposite impulses prevail -- the contraction of the fist becomes typical. The experiments show that these various impulses are at work when we do not know and do not show it: we must bring the man before a registering apparatus to find out from [p. 123] his motions without his knowledge whether sunshine or general cloudiness prevails in his mind.

But the unintentional movements may become symptoms of feelings in still a different way. The thing which awakes our feeling starts our actions towards the interesting object. All muscle reading or thought reading works by means of such a principle. The ouija-board of the spiritualists is a familiar instrument for the indication of such impulses, and if we want a careful registering of the unnoticeable movement, we may use an automatograph -- a plate which lies on metal balls and thus follows every impulse of the hand which lies flat on it; the plate has an attachment by which the slightest movements are registered on a slowly moving surface. If the arm is held in a loop which hangs from the ceiling, the hand will still more easily follow the weakest impulse without our knowledge. Ask your subject to think attentively of a special letter in the alphabet and then spread twenty-five cards with the letters in a half-circle about him; his arm on the automatograph will quickly show the faint impulse towards the letter of which he thought, although he remains entirely [p. 123] unaware of it. And if a witness or a criminal in front of a row of a dozen men claims that he does not know any one of them, he will point on the automatograph, nevertheless, towards the man whom he really knows and whose face brings him thus into emotional excitement. Still easier may be the graphic record, it is not necessary to Show a definite direction but simply a sudden reaction. The hand may lie on a rubber bulb or on a capsule covered with very elastic rubber and the slightest movement of the fingers will press the air in the capsule which, through a rubber tube, is conducted to a little bulb that pushes a lever and the lever registers its up and down motions. The accused may believe himself to be motionless, and yet when he hears the dangerous name of the place of his crime or of an accomplice, his unintentional muscle contraction will be registered. It is only a question of technique thus to take exact record of the faintest trembling when a little cap is attached to the finger.

The emotional interest may betray itself in an interesting way even through movements which are ordinarily not consciously guided like those of our [p. 125] hands and fingers; I am thinking of the eye movements. I found that our eyes may go their own way without our knowledge. My subject, for instance, looks straight forward; I show him a card with a printed word which is indifferent to him. We have agreed beforehand that after seeing and reading the card he is to close his eyes, to turn his head somewhat sidewards, and then to open his eyes again. The experiment shows that if he does perform these acts, his eyes, after the sideward movement of his head, look in the same direction in which his head points. I repeat this several times; always with the same result. Now I take a card with a word which, I know, is emotionally important to my subject from an earlier experience. The result is suddenly changed: he reads it, closes his eyes, turns his head, opens his eyes again, and, without his knowledge, his eyes have not followed his head but are still turned towards the exciting word -- the feeling interest has been betrayed by the unintentional backward rotation of the eye-balls. I may show in this way to the suspected man one indifferent thing after another; his eyes will follow his head. Then I show an object which was [p. 126] instrumental in the crime or which was present at the place of the deed or which belonged to the victim and, if he recognises it, his eyes will stick to it while his head is moving and after. Yes, the police know from old experience that not only do the eyes want to be back at the exciting scene, but the whole man is magnetically drawn to the spot where the crime was committed. Dostojewski shows us how the murderer, almost against his own will, returns to the place of his emotion and thus runs upon his doom.

We are still speaking, of course, of movements and yet of an entirely different process if we consider the breathing. Our inspirations and expirations can be registered in finest detail and a variety of elegant methods are available. Perhaps the simplest "pneumograph" consists of a tube made of spiral wire and covered with rubber, to be attached by ribbons to the chest. Every respiratory movement lengthens and shortens the tube, and this presses a part of the air contained into a little capsule, the cover of which follows the changing pressure of the air and moves a registering lever, usually a large straw which enlarges the movements [p. 127] of the cover. The end of the straw but touches the smoked surface of a slowly revolving drum; it thus writes in the thin layer of smoke a wave line which shows the subtlest features of the breathing. It is a simple task to measure every element of such a curve, every change in the length, in the height, in the angle, in the regularity of the wave; and that means every change in the rapidity, rhythm, distribution, pauses and strength of the breathing. As soon as such delicate methods of registration are applied, the intimate relation between feeling and breath becomes evident. Pleasure, for instance, makes the respiration weaker and quicker; displeasure, stronger and slower; excitement makes it stronger and quicker; acquiescence, weaker and slower. But such generalisations cannot do any justice to the manifoldness of changes that may occur: every ripple on the interests of the mind reflects itself in the changes of the pneumographic wave -- it may be an agreeable or disagreeable smell or taste, it may be exciting or depressing news from without or a fancy from within.

The same holds true for the heart beat, measured [p. 128] by the blood wave in the arteries; such a pulse writer is called a sphygmograph. It may be attached, for instance, to the wrist; a delicate lever presses against the wall of the blood vessel just where the finger of the physician would feel the pulse. The lever is attached again to the thin rubber which covers an air chamber, and the changing pressure of air is again transmitted to a long straw which writes an enlarged record of the movement on the revolving drum, rotating regularly by means of clockwork. Here again the height and length and form of every pulse beat may have its own physiognomy. When we write pulse and breathing together on the same drum, we see at once that even every ordinary inspiration changes the pulse; while we inhale we have a pulse different from the we exhale. Far more influential are the feelings. Again it is only an insufficient abstraction if we generalise and say: pleasure heightens and retards the pulse, displeasure weakens and accelerates it, or excitement makes the pulse stronger and quicker, acquiescence weaker and slower. But there is still another way open to observe the changes in our blood [p. 129] vessels. We may examine the quantity of blood, for instance, which streams to a limb, by means of the so-called plethysmograph. The arm is held by a large tube filled with water; a rubber ring closes the tube. The change of blood supply which makes the arm swell changes the pressure which the water exerts against the air, which is again conducted through a rubber tube to a recording lever; every emotional excitement speaks in the blood supply of every limb. All these instruments of registration have belonged for decades to the household equipment of every physiological laboratory; it was therefore a sad spectacle when recently scores of American papers told their readers that I had invented the sphygmograph and automatograph and plethysmograph this summer -- they might just as well have added that I invented the telegraph last spring. To recent years belongs only the application of these instruments for the study of feelings and emotions.

But we may go still further and point to expressions of emotions which are entirely beyond human senses. If we put our hands on two copper plates and make the weak galvanic current of a [p. 130] battery run through the plates and our body, we can, with the help of a delicate galvanometer, measure the slightest variations of the resistance to the current. Experiment shows that such changes occur, indeed, if our brain is excited; any emotional disturbance influences the resistance: it seems that the activity of the sweat-glands in the skin is under the nervous influence of our feelings, and the functioning of these glands alters the electrical conditions. A word we hear may excite us and at once the needle of the galvanometer becomes restless: there is no more uncanny betrayal of our inmost mind. Or we may point to the curious facts of the knee jerk. A little hammer falls always from the same height on the tendon of the knee, and every time the leg makes a jerking reflex movement, the angle of which can be registered. Experiment shows again that this angle changes with the emotional excitement of the mind; evidently the brain sends impulses down to the lower part of the spinal cord where the knee reflex is produced, and the emotion inhibits those messages and changes the whole function. Even the temperature of the body seems to be influenced [p. 131] by excitement; the experienced physician knows how the emotion of the patient can change his feverish state, and experiment seems to indicate similar changes for the normal state.

There is thus really no doubt that experimental psychology can furnish amply everything which the court demands: it can register objectively the symptoms of the emotions and make the observation thus independent of chance judgment, and, moreover, it can trace emotions through involuntary movements, breathing, pulse, and so on, where ordinary observation fails entirely. And yet, it seems to me that a great reluctance and even a certain scepticism as to the practical application of these methods is still in order. Firstly, the studies in this field of the bodily registration of emotion are still in their beginnings and so far many difficulties are not overcome; there are still contradictions in the results of various scholars. Especially we know too little yet about the evident individual differences to make, for instance, a breathing and pulse curve to-day a basis for a legal condemnation or acquittal. The facts themselves are so complicated that much further work [p. 132] must be done before we can disentangle the practical situations.

Secondly, experiment gives us so far not sufficient hold for the discrimination of the guilty conscience and the emotional excitement of the innocent. The innocent man, especially the nervous man, may grow as much excited on the witness stand as the criminal when the victim and the means of the crime are mentioned; his fear that he may be condemned unjustly may influence his muscles, glands and blood vessels as strongly as if he were guilty. Experimental psychology cannot wish to imitate with its subtle methods the injustice of barbarous police methods. The real use of the experimental emotion-method is therefore so far probably confined to those cases in which it is to be found out whether a suspected person knows anything about a certain place or man or thing. Thus if a new name, for instance, is brought in, the method is reliable; the innocent, who never heard the name before, will not be more excited if he hears that one among a dozen others; the criminal, who knows the name as that of a witness of the crime, will show the emotional [p. 133] symptoms. And yet, it may be rash to propose narrow limits for the practical use, as the rapid progress of experimental crimino-psychology may solve to-morrow those difficulties which seem still to stand in the way to-day.