Reactions and Perceptions
James McKeen Cattell
ONE of the many contributions which make James's "Principles " the foundation of modern psychology is the emphasis placed on the relation of movements to mental life. We are told that physiologically considered the whole neural mechanism is a machine for converting stimuli into reactions, and one of the most original applications of the fact that objects excite bodily changes by preorganized mechanism is made in the explanation of the emotions, I venture to take this occasion to propose a thesis, which in certain aspects is analogous to the James theory of the emotions. This thesis is that perceptions are distinguished from images by the greater prominence of the conative or motor elements.
Hume begins the first book of the " Treatise" with the familiar words : "Ail the perceptions of the human mind resolve themselves into two distinct kinds, which I shall call impressions and ideas. The difference betwixt these consists in the degrees of force and liveliness with which they strike upon the mind, and make their way into our thought or
( 572) consciousness." Now it is apparently possible to make a further analysis to the effect that the superior force and liveliness of the impression as compared with the idea, or of the perception as compared with the image, is due in part to the greater prevalence and definiteness of the motor elements.
It is not intended to argue that the larger motor element is the only criterion of perceptions. They probably have a " local sign," dependent on the part of the brain concerned ; but it is likely that motor centres give the most significant differentia. A perception may, as a rule. be more intense, definite, and complete than an image, as the result of more intense, definite, and complete stimulation in the case of the afferent currents from the sense organs. These currents are also likely to produce more decided invasions of the train of ideas, and the usually more sudden appearance is doubtless one of the factors giving a perception its superior vividness.
When, however, following the path blazed by James and cleared by Dewey and Münsterberg, we approach the subject from the side of the sensorimotor arc, it appears that the way we react is as much a part of the psychophysical process as the kind of stimulation, and the motor elements are as integral a part of the perception as the strictly sensory elements. The stimuli pouring into the central nervous system from the extra-bodily world do not arrive in order that we may perceive them or may
( 573) write a system of psychology about them. but in order that we may react to them. In our daily life we must continually avoid obstacles and dangers, must continually get what we need or want. Our relations with the material world are primarily of this kind ; in the case of the lower animals they are almost exclusively of this kind. If a light is presented, my eyes turn toward it ; if some one speaks to me, I am ready to answer. The response is due to the mechanism of the nervous system as organized at birth and reorganized by experience. The organism that failed to react in this way could not survive, and natural selection accounts no worse for the increasing complexity of our reaction than for the increasing complexity of the organism.
In the case of images and ideas, the motor element is not absent, but it is less prominent. They are less likely to be followed by definite movements, which again give rise to new afferent currents with their accompanying perceptions. If some one speaks to me, I am in the habit of answering ; if I imagine the voice, I do not answer audibly if at all. The light I see is not necessarily more faint than the light I imagine, but there is a difference in vividness or liveliness, which can very well be attributed to the more customary need to react and to the greater prominence of the motor element. The nervous system is so organized that we react to objects, and the perceptions thus have superior vividness and reality, which enable us under ordi-
( 574) -nary circumstances to distinguish perceptions from images. Our reactions as a rule work and are useful, giving rise to new perceptions and new reactions, which also work, and thus the material world becomes real for us.
When a cat sees or smells a mouse, it jumps to seize it, and the mouse runs to its hole. The motor discharge in the cerebral centres of the cat is as much a part of the perception of the mouse or of the mouse situation as are the incoming currents. The incoming currents and the pre-existing structure of the centres cause the discharge, and the perception, in my opinion, usually follows the discharge in time. This time order I pointed out more than twenty years ago in the case of the reaction-time. Here the stimulus does not cause a perception which causes a movement, but the stimulus and the pre-arranged brain connections cause the movement, and the process is subsequently given in consciousness as awareness of the kind of stimulus and the kind of movement.
The anthropomorphic cat. if it catches the mouse, has a series of agreeable experiences, which are convincing proof of the existence of a real mouse and of a physical and, for it, rational world. When the mouse situation again occurs, the eat has a lively and vivid perception of a real mouse. But while the cat is waiting for the mouse to turn up, it may have memories and images. It does not jump at these, because its nervous system is not made
( 575) that way. It is the incoming currents that arouse the suitable responses. Centrally excited processes do not and can not excite the same responses. for in this case the animal would not survive. It is only a mad cat that may jump at an imaginary mouse, and for it the jumped-at mouse becomes real. It should, of course, be remembered that inhibitions are as integral parts of the motor processes as discharges. The cat waiting for the mouse to come within reach is all muscular tension, which is part of the vivid perception of the approaching mouse. It appears indeed that consciousness is related to inhibition in a peculiarly intimate fashion.
The character and validity of our perceptions are prescribed by the motor responses no less than by the incoming currents. Thus the visual world is one in which we can do things rather than one in which we simply see objects. As I go forward to shake hands with a friend and approach from distance of six feet to three, the image on the retina becomes twice as large, but there is no change in the apparent size of the man. A table has a rectangular top, from whatever point of view I look at it. I know that in the retinal image two of the angles are acute and two are obtuse, but I hesitate and make a geometrical construction before I know which is which. Most people would not suspect that if the arm is held at full length, the tip of the little finger will more than cover the sun. We have this year made in our laboratory some experiments
( 576) which measure the extreme extent of our inability to compare the sizes of retinal images as such. Incidentally I may remark that the indifference of the actual retinal images seems to account for the ordinary optical illusions. A slight clue, such as arrested movements of the eyes or possible perspective, may readily distort size or direction.
Experiments of my own, which I described several years ago, give a somewhat striking demonstration of the extent to which perceptions are shaped by the requirements of motor response. Curiously enough, it had not been remarked that in the vision of daily life objects are presented to the eye one after another, but are perceived side by side. As I look about the room. first one object and then another falls on the area of distinct vision, but I see the objects, not one after another at the same place, but side by side in the spatial arrangement in which I should find them, and covering a field in which it would be impossible for me to see simultaneously.
The results are similar if the eyes are still and the objects are moved over the retina. If I look through a window one centimetre square, and be-hind it three centimetre squares separated by centimetre spaces are passed, I do not see one square after the other. but the three squares side by side, somewhat crowded together and blurred, but two or three times as large as the window through which they are seen. If in this way first red is
( 577) exhibited and then green. we do not see first red and then green, but red, white, and green, side by side and covering a field several times as large as the retinal image. We perceive as a spatial continuum what is a time series in the physical world, in the incoming currents and in the brain centres.
In these cases each perceives the same physical stimulus in his own way. He may see the green above the red, or conversely ; the green within the red, or conversely ; bars of red and green arranged vertically or horizontally. etc. The first time that a stimulus is presented to an observer. he ordinarily has only a vague perception. The same stimulus after several trials gives a clear perception, which thereafter tends to remain the same for the same observer, though likely to be very different for different observers. When the actual physical stimulus is explained to observers, some of them see it as before, others quite differently. All of which shows that the attitude of the observer is as integral, a part of perceptions as the incoming nervous cur rents, and that perceptions are prescribed by reactions.
It is sight and kinaesthetic sensations which, in the main. give us our spatial and material world. In sight, the movements of the eyes, head, and body are of extreme importance. We have with. these senses immediate and constant reactions to stimuli. hearing is less objective, owing to the loss of movable ears. but it is still rather intimately
( 578) connected with movement, especially on the side of time correspondence. Smell, taste, and organic sensations have decreasing objectivity. The re-actions occur mainly within the body, and as we have the same body always with us, we regard it as part of ourselves rather than of the material world. This is especially true of the body known by kinesthetic and organic sensations ; the seen body, which alters its relation to the visual world, is more likely to be regarded as part of it.
Kinaesthetic perceptions and images have a peculiar position. We can form an image of a light or sound, but we cannot directly produce an objective light or sound ; we can, however, directly produce movements. It may not be clear in a given case whether we have an image of a movement or have actually produced a movement or a partially inhibited impulse to make the movement. It appears to me that in so far as my thoughts are in sensory terms, they are mainly in the form of motor speech. I am inclined to believe that the articulation or the impulse to articulate actually takes place, and that it is not a matter of images at all, but of this I am not sure. Now the difficulty of discriminating between kinaesthetic perceptions and images seems, to a slight degree at least, to support the view that it is the motor element which distinguishes sights and sounds from visual and auditory images.
Pleasures and pains are sui generis like colors and
( 579) sounds. They probably have the teleological significance usually attributed to them ; in any case,
they tend, as a rule, to accompany, respectively, those performances that are beneficial or harmful to the organism or to the race. They seem to accompany both incoming and outgoing currents, and they are very vivid and real, but are not objectified. This seems, in part at least, to be accounted for by the fact that the senses which give us most knowledge of the physical world give us the least pleasure-pain, and conversely. The organic sensations give us no knowledge of the extra-bodily world and but little of what happens within the body, but the hedonic elements are constant may be intense. Images of pleasures and pains are lacking or obscure, and this holds also — at least in my own case — for organic sensations, smells, and tastes. It seems that the sensori-motor arcs beginning and ending in the physical world give reality to our perception of objects, and the arcs beginning and ending within the body give reality to ourselves.
In the case of the emotions the cerebral commotion, as James has so brilliantly argued, is probably chiefly due to the excitation of bodily changes id) the object and the discharges to the brain from the bodily excitation. It is not an essential part of the theory that the emotion should be correlated only with the afferent currents ; indeed, the theory is apparently strengthened if we assume that feel-
( 580) -ings and emotions are associated with those cerebral conditions which discharge into the viscera, etc., as well as with the conditions excited by afferent currents from the inner body. In Dewey's words, the emotional excitement represents the tension of stimulus and response. It appears to me that the incoming currents and the discharges which lead to definite muscular reactions give reality to the perceptions, and the incoming currents and the discharges to the inner organs with the vaguer muscular contractions give rise to the emotions. Then the purposive movements cause new stimuli and new reactions which add further vividness and reality to our perception of objects, and the commotion within the body gives rise to new excitations and to new discharges by which the emotion is heightened.
The theory does not require us to draw a definite line between perceptions and images. It is indeed confirmed by cases in which they are confused, for this occurs when the motor reactions are confused — when they are inhibited or are excessive. In sleep, in reverie, in some forms of hypnotism, intoxication, and insanity, the motor reactions are lacking or indefinite. In these cases there are dreams, visions. and hallucinations. We do not respond to the objects of the real world, and the distinctions between objects and ideas, between perceptions and imaginings, are obscured or obliterated. As a man falls asleep, he becomes passive,
( 581) he does not look or listen, and gradually his imagery becomes visions and dreams. In slight delirium or opium intoxication, if the patient arouses himself and responds to the environment the visions disappear, but return as soon as he relapses into inaction. I made a long while ago some experiments with hashish. Under the influence of this drug the subject may relapse into a passive condition in which time becomes endlessly long, space endlessly extended, and curious hallucinations occur. But if he gets up and walks about, looks and listens. the hallucinations practically disappear. In hypnotism the subject becomes passive, he can be made cataleptic, his movements are suggested to him instead of being normal responses to the environment. Artificial passivity is a prominent factor in the trances of the mystics and of the eastern yoga. In melancholia the failure of adequate motor responses precedes the hallucinations.
On the other hand, objects and images are equally likely to be confused when the motor reactions are excessive or unnatural. It is when the girl passes the churchyard at night, starting at every sight and sound, that she sees the tomb-stone as a ghost. In mania and in some phases of hysteria and delirium, the movements are uncontrolled and there are delusions and hallucinations.. In the dancing mania and other psychological epidemics, in the ramp-meeting revivals and the rest, the excessive and irrelevant movements may be
( 582) regarded as the cause rather than as the effect of the mental disintegration. Rhythmic movements are in a way extra-natural, not representing normal response to stimuli ; they are a common method of producing ecstasy and abnormal Mental states with hallucinations and the like. In savage rites and religious manias we have these in a crude form. In dancing and in singing, in music and in poetry, in oratory and in the intoned church service, we have them in more refined fashion ; and we may regard the rhythmic motor impulses as one of the causes of the slight intoxication, the heightened emotional sensibility and loss of reality of the material world which then occur. I have myself lost self-consciousness with extraordinary completeness when playing football. Every muscle of the body is in action or in a state of unstable equilibrium, and the consciousness of a distinction between one's self and the rest of the world completely disappears. Something of the same kind to a lesser degree still occurs when I play tennis or swim in the sea.
It may further be noted that in many of the cases cited above we have first excessive or unnatural motor discharge, followed by lack of response. Typical but extreme cases are the epileptic fit — a violent explosion followed by coma — or mania followed by dementia. In intoxication the first symptom is the weakening of normal inhibition, the loosened tongue, the taking of one
( 583) more glass, etc. This is followed by disintegration of the normal reflexes --- staggering, thick speech, double vision. Finally coma supervenes.
It is of course possible that in all these eases the mental changes may not be due to the motor disturbances, but that they have a common cause. Fatigue, fasting, abnormal blood supply, a cerebral poison or emotional excitement may be regarded as the cause both of the excessive or lacking motor responses and of the mental disorganization, But. while it is not necessary to exclude other factors, the motor theory seems to be a simple and adequate explanation. It accounts for these disturbances but does not depend on. them for its verification.
We cannot separate images from perceptions. Images are revivals of past sensations, and perceptions are mainly supplied by conditions of the central nervous system. Images and perceptions are equally the result of brain changes, which are them-selves part of the world's material system. But the brain changes which are excited from within are less likely to result in motor discharges than those which form parts of sensori-motor area. This is necessary if the organism is to survive and prosper. The more pronounced motor elements of the sensori-motor arcs are represented by superior vividness in perceptions as compared with images, This appears to be at least one of the factors enabling us to construct the world in which we live, and the statement appears to be a step, however small, in
( 584) the direction of passing from metaphysics to science, from epistemology to psychology, from theory of knowledge to knowledge of facts.
It is a discovery of natural science that each of us remains within his own
experience. This experience is, however, such that it leads us to live in the
world of common sense and perhaps later in the world of natural science. I do
not see why epistemology or metaphysics should want to come in here as something
super-psychological or meta-scientific. We can as a logical entertainment
construct queer worlds ; but none of these is the world in which we live. We can
fancy a world of Arthurian knights, or of Arabian nights, or of metaphysical
twilight, but those who should act as though they lived in such worlds would
find themselves in those parts of the real world known as prisons or insane
asylums. So long as the world of common sense and natural science continues to
honor the drafts that we draw on it, we have satisfactory evidence of its
solvency. This, I trust, is sound pragmatism,