An Introduction to Comparative Psychology

Chapter 9: Synthesis and Correlation

C. Lloyd Morgan

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IN the foregoing chapter we submitted impressions to analysis, and we found that the ultimate psychological results of that analysis were sensations. We saw that these included sensations of the special senses, sensations of pain and general sensibility, and motor-sensations, any or all of which may carry with them an emotional tone pleasureable or the reverse. And, furthermore, we saw that the sensations might in physiological analysis be further decomposed into impulses,-the sensation purple, for example, being due to a combination of such physiological impulses. I have used such phrases as " the combination of physiological impulses to give rise to a sensation " to avoid pedantry and circumlocution. But it may be noted that such phrases are, in strictness, open to a very serious criticism. Physiological impulses are waves of molecular change of some sort-, and are physical in their nature; while sensations are elements in consciousness, and psychical in their nature. No combination of physical impulses can give rise, it may be said, to a psychical or conscious condition, for there, is no community of nature, and no thinkable continuity, between physical states and consciousness. With this criticism I am heartily in agreement. What I should say, in strictness, is, that the physiological conditions which are the concomitants of sensations are due to the combination of physiological impulses, the concomitants of which are infra-consciods, or do not rise above the threshold of consciousness. But such sentences as this are rather cumbrous ! While, therefore, I

(145) heartily agree with the spirit of the criticism, I shall for the sake of brevity and clearness use the less accurate phraseology.

We have now to see how the sensation-elements are combined synthetically to form impressions as we know them; how they enter into correlation with each other; and how they call up through association representations of similar sensation-elements. It must be remembered that the web of consciousness, even in sense-experience, is wonderfully complex, with a complexity which beggars description. All that we can do in this chapter is to consider some of the more important of the correlations and to indicate the manner in which sensations enter into synthetic union.

When we look at such an object as a cubical brick lying on a table at a distance of three or four feet from us, we obtain a definite impression. We are, however, using two eyes. On the retina of each eye there is an image of the brick; but the grouped impulses from the two retinas are factors in a single impression. Moreover, the two images are not quite alike, for the two eyes look out on the brick from slightly different positions, and a little experimenting will show that what is seen with the left eye is not quite the same aspect of the brick as that which is seen with the right eye. But not only do the different groups of impulses from the two eyes conspire to give rise to a single impression, they also give, or aid in giving, to the impression the specific quality of solidity or spatial depth. This may be experimentally shown with the aid of the stereoscope. By means of this instrument two different flat pictures, taken from slightly divergent points of view, are seen at the same time, the one with the left eye, the other with the right. The effect is a wonderfully perfect illusion that the objects have solidity, and that they stand out in space of three dimensions. Even if the pictures are only momentarily

(146) illuminated by the electric flash, the illusion of solidity is still conveyed. It would seem, then, that the synthetic combination of the impulses generated by two different retinal images, gives to the visual impression its element of solidity or depth. Now the question arises, have we in this synthesis a combination of physiological impulses; or a combination of sensations ? In other words, is the dissociation point of the depth element of a visual impression within the conscious region, or is it infra-conscious ? For me, if I can trust my powers of introspection, it is infra-conscious. Psychologically I cannot analyse the element of solidity in a given impression. I know perfectly well that it results from the synthetic combination of two retinal images. But it is for me a sensation which, though it results from a physiological synthesis, resists all my efforts after psychological dissociation. Others, however, affirm that it is possible by close analysis of visual impressions to distinguish between the two retinal images. For them the dissociation-point is within the conscious region. In any case the important point to notice. is that the combination, however and wherever occurring (and it may physiologically occur in the lower brain-centres), does not merely produce a composite, and hence more or less blurred impression, but a clear-cut and definite impression, with a new quality, that of outness, distance, and solidity. If it be asked why the synthetic combination gives rise to this new quality in the psychical product, we must reply that we do not know. We know practically nothing concerning the ultimate " whys " of consciousness, though we know a little concerning the proximate " whys" and the "hows." We do not know why ray.- of a certain vibration frequency give the sensation red, while rays of another vibration frequency give the sensation green. We do not know why, when there are combined upon the retina the rays which give the sensation red with the rays which give the sensation green, we get a quite new sensation

(147) different from both, which we call yellow. So, for pscyhology, visual distance and solidity, the third dimensional space element, appears to be an ultimate element. We may explain, or attempt to explain, physiologically how it is generated, but why it takes this form we cannot say.

There are, however, other factors, which aid in giving to visual impressions their quality of distance, and to space, as presented to the eye, its element of depth. If we hold a pencil on our forefinger, about ten inches from our face, and 'focus our eyes alternately on this and on some distant object, we shall become aware, by the exercise of a little introspective attention, that there are present psychical elements other than those belonging to the visual sensations as such. These elements are sensations associated with certain movements of the eyes, or parts of the eyes, during the process of focussing. Physiology shows that these movements are of two kinds. First, there are movements of greater or less convergence of the two eyes, so as to make the image fall on the most sensitive area of the retina ; and secondly, there are movements of accommodation within the eye by which, through a change in the curvature of the hinder surface of the lens, the image is rendered more clearly defined. It is probably impossible psychologically to distinguish between these two, though physiologically they are quite distinct. Moreover, these motor-sensations are seldom rendered focal except for purposes of psychological analysis. They are normally marginal, and are only dragged to the light of focal consciousness to satisfy the demands of scientific analysis. But I have written so far in vain if I have not made it clear that the influence of the subconscious margin, in determining our states of consciousness, is of extreme importance, and needs constant recognition.

When we see, then, a focal object set in a visual field, there are, apart from and in addition to visual sensations (that is to say, sense-data supplied by the retinas), motor-

(148) sensations (that is to say, sense-data due to movements of or in the eyes). And these latter, in correlation with the binocular factor, aid in giving to our impressions of sight their visual depth. They aid also in giving to objects their solidity. For when we take in the form or figure of any object, our eyes wander over its several parts with varying convergence and accommodation for distance. And it must be remembered that as, during our waking hours, we look hither and thither, and comprise now this, now that, and now the other object in our glance, we proceed by successive gradations, the motor impulses forming a continuous series associated with constantly changing adjustments. This continuity of the motor series is probably not a little helpful in giving rapidity and exactness to our visual localization.

It appears, therefore, that the depth element in visual impressions, as given through the combined impulses from two retinas, is correlated with motor-sensations of convergence and adjustment. We have now to see that the extension element, as given in the grouped impulses from each retina, is likewise correlated with other motor-sensations. To this end, let us begin by noting what takes place when we observe a moving object in the field of vision., We are watching, we will suppose, a game of billiards. Again and again our eyes follow. the balls in their movements across the table. We are at most but dimly subconscious of our own motor-sensations as our eyes follow the movements of the billiard balls. It is the object itself as moving on which in each case attention is fixed. The ball is in the focus of vision, and as it moves the surrounding margin is gradually changing. Often two balls are moving at once. We fix our attention on one of them, and follow it with our eyes; but we are aware of the movements of the other as changes in the margin of vision; and we can leap with our eyes from one ball to the other with almost infallible accuracy. We can, if we like, while white and red are moving, fix our eyes

(150) on "spot," which is at rest. When the- movements are entirely in the margin of the visual field, our eyes are still; there are no motor-sensations, but we have to exercise some control to prevent our eyes going off after one bay or the other, so strong is the tendency of our eyes to follow the moving object. So far as vision is concerned, therefore, movements are gradual changes in the relation of the focus to the margin, or relative changes within the margin, or both. And these changes are usually correlated-with motor-sensations due to the movements of the eyes.

Now let us take a visual scene in which there is no movement. The game of billiards is over; the players have departed; only the psychologist remains. He fixes his eye on the red, and makes it focal in a marginal setting of the table with white and "spot" and a cue leaning at one corner. This catches his attention and away fly his eyes to render it focal. The whole scene shifts, and assumes new relations to a new focus. There has been no movement in the external factors of the scene, but there has been a complete rearrangement of the scene for consciousness; there is a new focus to a different margin. In that margin the large picture on the further wall catches his attention. it is a fair work of art with its focal point or centre of grouping sufficiently well defined. Our psychologist cannot, however, grasp the full work of the picture at a single glance. His eye wanders over it to embrace in succession the various details. He successively focusses all the essential features and each successive focussing gives a new psychological impression, a new focus with a new -margin. Then he returns to the centre of grouping, and begins to take in the full effect of the work of art as a whole. He grasps the, general effect as a complex impression. For in any visual field there is a focal impression to which the rest of the field is marginal ; and within the complex, impression there is a centre of grouping to which the rest of the impression is

(150) relatively marginal. If, as we look at a picture, there is an subsidiary detail which catches the attention as not yet mastered, away go the eyes to this point to make it for thee moment focal, and only when we feel that we have got its value for the total effect do we return again to the centre of grouping. In looking, therefore, at an unchanging scene there is abundant employment of eye movements, and we seem amply justified in saying that the relation of the focus to the margin (that is, the extension element) in any given visual scene is closely correlated with the eye movements necessary to bring any desired part of the margin into focus, The Visual field is given in direct visual experience as extended and, when sensations of accommodation are added to the other motor-sensations, as having depth. There is not only a focus but a margin, And the relation of the one to the other is correlated with and suggestive of motor. sensations due to movements of and in the eyes.

Both the visual impressions and the correlated motor sensations are presentative, they take their origin in impulses due to excitations of the afferent nerves. The visual field is, however, partly thrown into three-dimensional form through suggestion and association. The relative intensities, shading, shadows, the appearance due to haze, the relative blurring of objects in the margin, all these are suggestive of the distance element. As visual impulses they are, of course, presentative ; but it is their suggestive or representative force that gives them value in this respect. The painter has to rely on such suggestions for giving the distance element or depth to his picture. But when we look at the picture, We feel that the depth, admirably as it may be represented, is suggested and not actually presented.

In the case of touch, as with vision, the extension which is given in tactile experience is closely correlated with motorsensations. Suppose that we are feeling for an object in the dark, and that our wrist is brought into contact with it or,

(151) with another object. There is not only a sensation of touch, but the impression is localized as originating at the wrist. Under such circumstances we at once move the hand and arm in such a way as to bring the fingers to bear upon the object; and the localization of the touch is correlated with the motor- sensations thus arising. Or suppose there is some source of irritation, say, at the back of the neck. At once the hand is carried to the spot to ascertain the nature of the irritant and to remove it. And here again the localization of the spot where the stimulus is applied is correlated with motor-sensations due to the movement of the hand to the spot. The correlation is by no means perfect in the absence of sight. If we get some one to press gently with the point of a pencil on our thigh or calf or upper arm, and then, with shut eyes, try and place our finger on -the exact spot we shall probably miss it by an inch or so. Practice, however, rapidly and to a considerable degree improves the accuracy of the correlation and associated localization.

And not only is there a correlation between touch-sensations and appropriate motor-sensations, there is a close correlation between tactual and visual impressions. A friend has left on my table a fossil for identification. No sooner do my eyes fall upon it than my hand is reached forth to pick it up. Such association of visual and tactual experience is a very frequent and constant one from our earliest days, The child is repeatedly stretching out its hands, and we may observe how often the eyes follow the hands in their movements. In 'the first months of life there is ample opportunity for the establishment of close relationship between movements of the hands and fingers and movements of the eyes, and of both with changes in the visual field. When the child begins to crawl and move about, there is further opportunity for the establishment of correlations between these more extended movements and visual

(152) distance. Distance deepens to tactual experience, and new and most valuable correlations are formed between these new acquisitions and previous visual experience. And as the months go by there is a constant and progressive correlation of visual and tactual experience.

The exact mode of the establishment of this correlation is unfortunately left to conjecture. We have no recollection, or scarcely any recollection, of all that occurs in the building up of our psychical experience during the first two years of life. The probabilities are, however, that the psychical correlations are founded upon physiological co-ordinations which are inherited. This is a somewhat important point which needs a little explanation. By saying that the psychical correlations are founded upon physiological coordinations which are inherited, I mean that in the individual development the latter are prior to the former, the physiological co-ordinations to the psychological correlations. Consciousness, if I may so say, does not come into possession of a dead organism and then begin to pull the strings and make it work and live. Nor does consciousness bring with it any inherited knowledge of the world and what it is, of the body and how it works, or of the relation of one to the other. It is very doubtful whether conscious experience is or can be inherited. For sonic time consciousness is but a spectator, and, could he but remember, probably a dazed and confused spectator, of the physiological and organic reflexes of the body with a part of which it is closely if not inseparably associated. It is only gradually that consciousness begins to have sonic power of guidance and control over the organic mechanism At first the organism is merely a marvellous physiological automaton, the nature and mode of working of which the nascent consciousness has to learn by experience.

A strong stimulus in a marginal part of the retina probably causes in the young child an organic reflex, by

(153) which those muscles are called into play which are fitted to turn the eyes, so as to make this stimulus focal. The co-ordinated movements of the eyes, their convergence and accommodation are almost certainly physiological, and due perhaps to infra-conscious impulses carried inwards by afferent nerves to the lower brain centres. But this organic reflex, though not in the first instance the result of conscious experience, is nevertheless accompanied by consciousness, and thus contributes to the upbuilding of experience. There is no conscious guidance in the initial stages, but conscious data are being provided for such guidance in the future. The stimulus of a bright object may also initiate, probably as a further organic reflex, the stretching forth of the hand towards it, while the contact of the object with the palm certainly gives rise to a grasping reflex. These reflexes, too, though not due to conscious guidance, are nevertheless accompanied by consciousness; and associations are thus established between the results of visual experience, and the results of motor and tactual experience.

How the psychical data afforded to the infant by the early use of its sense-organs, and by the motor-sensations which .accompany inherited reflexes, are organised into a consciousness which embraces them all in a complex unity, we can but conjecture. It is not difficult, indeed, to build up a conjectural psychical baby, but it is equally easy to show how conjectural that psychical baby is. Of this however we may be tolerably sure, that it is through the grouping of the diverse data[1] and the correlation of the testimony

(154) of the senses that the process is somehow effected. Consciousness is essentially a synthetic unity, and perhaps in this synthesis we may see a subjective aspect of that universal synthetic tendency which we discern in diverse forms throughout the objective world of nature, -- a synthetic tendency which is seen alike in the genesis of a raindrop, of a crystal, and of the solar system ; in the exquisite structure of the frustule of a diatom, in the form and brilliancy of a humming-bird, and in the silken gold of a maiden's hair. Many thinkers are unable to conceive how the synthesis of consciousness can be effected in the absence of a supernatural ego which effects the synthesis. For them the ego or individual personality is not the product of, but the supernatural producer of, the synthesis. But we are not wont to regard the genesis of a complex crystal as due to any individual act of supernatural synthesis, but rather as the outcome of a tendency which permeates inorganic mature. And in like manner we may regard the selective synthesis which gives rise to consciousness a's due to a tendency which permeates the whole realm of psychical existence.

We are here however approaching a philosophical question which we cannot now discuss. It is sufficient in this place to note that the consciousness of the infant involves the extensive correlation of psychical data. What we call the extension and externality or outness of objects involves such correlation. The mere reception of stimuli on an extended surface does not suffice to give rise to the perception of extension. The difference between high and

(155) low musical tones is probably due to the stimulation of different parts of an extended surface, but they carry with them no extension element in consciousness. There is here no correlation, such as there is between visual and tactual extension. But though such organized correlation may be regarded as essential to the selective synthesis of consciousness, yet, I must repeat, the exact mode of its development and the stages of correlation are, and are likely to remain, conjectural.

Let us now summarize the correlations which we have briefly considered as contributing to the synthesis of our visual experience. There is, first of all, a correlation of the testimony of the two retinas, and here the correlation is probably infra-conscious; secondly, and concurrently, there is the correlation of visual sensations proper with the motor-sensations of accommodation; thirdly, there is a correlation of the changes which occur in the retinal field with the motor-sensations which arise from the movements of the eyes in their sockets. Co-ordinate and concurrent with this organization of a visual field through the correlation of retinal sensations with motor-sensations, is the organization of a tactual field through the correlation of sensations of touch with those motor-sensations which are subservient to tactual experience. And throughout all the stages of the organization of these two fields there are cross correlations, by which the experience gained in the visual field is brought into relation with experience gained in the tactual field. So that for normally constituted individuals experience is never gained separately in the visual field, and it! the tactual field; but through constant correlations, the one with the other, the two fields coalesce in a common field of practical experience. Even so we have not nearly exhausted the many modes of correlation which enter into the fabric of our common work-a-day consciousness. There is an auditory field, an olfactory field, and a field of temperature. There is too a

(156) motor field, in which the movements of-the limbs, head, and body as a whole are correlated. All of these, though of distinctly subordinate importance, are more or less definitely correlated with the fields of vision and of touch, and contribute to the orderly complexity of practical experience; and all are knit into an harmonious whole by that synthetic activity, in the absence of which there would be no states of consciousness at all. 

And this complex process of correlation, the result of a natural and-inherent synthetic activity, involves both presentative and representative elements. In the visual impression itself there is a synthesis of presentative impulses, and on this there rapidly follows a further synthesis, -involving suggested representative elements. For the original presentative impulses, and the sensations to which they give rise, form nuclei, around which representative element rapidly cluster and combine to form synthetic products of yet greater complexity. Let us steadily bear in mind that states of consciousness as we know them are wonderfully complex, with focal and marginal constituents, and with presentative and representative elements. We may i n our analysis disentangle some of the strands of the many-hued, yet harmonious, tapestry of consciousness; but let us not forget that, as we know it in practical experience, the tapestry itself is a synthetic unity of marvellous and exquisitely intricate workmanship.


  1. We have some evidence concerning the correlation of newly acquired data in the case of those who have received sight as the result of a surgical operation. A world hitherto interpreted mainly through touch has to be interpreted anew for vision. It is said that to such individuals objects seem to be in contact with, or in close proximity to, the eyes; and that solid bodies, such as the cube or sphere, are taken to be flat surfaces. Even the human face seems to be a flat plane. One must be careful not to build too much on abnormal cases. The apparatus for convergence and accomodation so long unused, could scarcely be expected to supply normal data to -consciousness. The requisite stimuli for organic responses having been so long withheld, the apparatus for physiological response might well for some time he out of gear, and would thus supply data different from those which the healthy infant receives.

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