Philosophy

In this chapter we shall consider the question of images. As the reader doubtless knows, one of the battle-cries of behaviourism is “death to images”. We cannot discuss this question without a good deal of previous clearing of the ground.

What are “images” as conceived by their supporters? Let us take this question first in the sense of trying to know some of the phenomena intended, and only afterwards in the sense of seeking a formal definition.

In the ordinary sense, we have visual images if we shut our eyes and call up pictures of scenery or faces we have known; we have auditory images when we recall a tune without actually humming it; we have tactual images when we look at a nice piece of fur and think how pleasant it would be to stroke it. We may ignore other kinds of images, and concentrate upon these, visual, auditory, and tactual. There is no doubt that we have such experiences as I have suggested by the above words; the only question is as to how these experiences ought to be described. Then we have another set of experiences, namely dreams, which feel like sensations at the moment, but do not have the same kind of relation to the external world as sensations have. Dreams, also, indubitably occur, and again it is a question of analysis whether we are to say that they contain “images” or not.

The behaviourist does not admit images, but he equally does not admit sensations and perceptions. Although he does not say so quite definitely, he may be taken to maintain that there is nothing but matter in motion. We cannot, therefore, tackle the question of images by contrasting them with sensations or perceptions, unless we have first clearly proved the existence of these latter and defined their characteristics. Now it will be remembered that in Chapter V we attempted a behaviourist definition of perception, and decided that its most essential feature was “sensitivity”. That is to say, if a person always has a reaction of a certain kind B when he has a certain spatial relation to an object of a certain kind A, but not otherwise, then we say that the person is “sensitive” to A. In order to obtain from this a definition of “perception”, it is necessary to take account of the law of association; but for the moment we will ignore this complication, and say that a person “perceives” any feature of his environment, or of his own body, to which he is sensitive. Now, however, as a result of the discussion in Chapter XVI, we can include in his reaction, not only what others can observe, but also what he alone can observe. This enlarges the known sphere of perception, practically if not theoretically. But it leaves unchanged the fact that the essence of perception is a causal relation to a feature of the environment which, except in astronomy, is approximately contemporaneous with the perception, though always at least slightly earlier, owing to the time taken by light and sound to travel and the interval occupied in transmitting a current along the nerves.

Let us now contrast with this what happens when you sit still with your eyes shut, calling up pictures of places you have seen abroad, and perhaps ultimately falling asleep. Dr. Watson, if I understand him aright, maintains that either there is actual stimulation of the retina, or your pictures are mere word-pictures, the words being represented by small actual movements such as would, if magnified and prolonged, lead to actual pronunciation of the words. Now if you are in the dark with your eyes shut, there is no stimulation of the retina from without. It may be that, by association, the eye can be affected through stimuli to other senses; we have already had an example in the fact that the pupil can be taught to contract at a loud noise if this had been frequently experienced along with a bright light. We cannot, therefore, dismiss the idea that a stimulus to one sense may, as a result of past events, have an effect upon the organs of another sense. “Images” might be definable as effects produced in this way. It may be that, when you see a picture of Napoleon, there is an effect upon your aural nerves analogous to that of having the word “Napoleon” pronounced in your presence, and that that is why, when you see the picture, the word “Napoleon” comes into your head. And similarly, when you shut your eyes and call up pictures of foreign scenes, you may actually pronounce, completely or incipiently, the word “Italy”, and this may, through association, stimulate the optic nerve in a way more or less similar to that in which some actual place in Italy stimulated it on some former occasion. Thence association alone may carry you along through a series of journeys, until at last, when you fall asleep, you think you are actually making them at the moment. All this is quite possible, but so far as I know there is no reason to hold that it is more than possible, apart from an a priori theory excluding every other explanation.

What I think is clearly untenable is the view, sometimes urged by Dr. Watson, that when we are, as we think, seeing imaginary pictures with the eyes shut, we are really only using such words as would describe them. It seems to me as certain as anything can be that, when I visualise, something is happening which is connected with the sense of sight. For example, I can call up quite clear mental pictures of the house in which I lived as a child; if I am asked a question as to the furniture of any of the rooms in that house, I can answer it by first calling up an image and then looking to see what the answer is, just as I should look to see in an actual room. It is quite clear to me that the picture comes first and that words after; moreover, the words need not come at all. I cannot tell what is happening in my retina or optic nerve at these moments of visualisation, but I am quite sure that something is happening which has a connection with the sense of sight that it does not have with other senses. And I can say the same of aural and tactual images. If this belief were inconsistent with anything else that seems to me equally certain, I might be induced to abandon it. But so far as I can see, there is no such inconsistency.

It will be remembered that we decided in favour of perceptions as events distinct from those which they perceive, and only causally connected with them. There is, therefore, no reason why association should not work in this region as well as in the region of muscles and glands; in other words, there is no reason to deny what used to be called “association of ideas”, in spite of the fact that bodily changes can also be associated. If a physical basis is wanted, it can be assumed to exist in the brain. The state of the brain which causes us to hear the word “Napoleon” may become associated with the state of brain which causes us to see a picture of Napoleon, and thus the word and the picture will call each other up. The association may be in the sense-organs or nerves, but may equally well be in the brain. So far as I know, there is no conclusive evidence either way, nor even that the association is not purely “mental.”

When we try to find a definition of the difference between a sensation and an image, it is natural to look first for intrinsic differences. But intrinsic differences between ordinary sensations and ordinary images, for example as to “liveliness”, are found to be subject to exceptions, and therefore unsuitable for purposes of definition. Thus we are brought to differences as to causes and effects.

It is obvious that, in an ordinary case, you perceive a table because (in some sense) the table is there. That is to say, there is a causal chain leading backwards from your perception to something outside your body. This alone, however, is hardly sufficient as a criterion. Suppose you smell peat smoke and think of Ireland, your thought can equally be traced to a cause outside your body. The only real difference is that the outside cause (peat smoke) would not have had the effect (images of Ireland) upon every normal person, but only upon such as had smelt peat smoke in Ireland, and not all of them. That is to say, the normal cerebral apparatus does not cause the given stimulus to produce the given effect except where certain previous experiences have occurred. This is a very vital distinction. Part of what occurs in us under the influence of a stimulus from without depends upon past experience; part does not. The former part includes images, the latter consists of pure sensations. This, however, as we shall see later, is inadequate as a definition.

Mental occurrences which depend upon past experience are called “mnemic” occurrences, following Semon. Images are thus to be included among mnemic occurrences, at least so far as human experience goes. This, however, does not suffice to define them, since there are others, e.g. recollections. What further defines them is their similarity to sensations. This only applies strictly to simple images; complex ones may occur without a prototype, though all their parts will have prototypes among sensations. Such, at least, is Hume’s principle, and on the whole it seems to be true. It must not, however, be pressed beyond a point. As a rule, an image is more or less vague, and has a number of similar sensations as its prototypes. This does not prevent the connection with sensation in general, but makes it a connection with a number of sensations, not with one only.

It happens that, when a complex of sensations has occurred at some time in a person’s experience, the recurrence of part of the whole tends to produce images of the remaining parts or some of them. This is association, and has much to do with memory.

It is common to speak of images as “centrally excited”, as opposed to sensations, which are excited by a stimulus to some sense organ. In essence this is quite correct, but there is need of some caution in interpreting the phrase. Sensations also have proximate causes in the brain; images also may be due to some excitement of a sense-organ, when they are roused by a sensation through association. But in such cases there is nothing to explain their occurrence except the past experience and its effect on the brain. They will not be aroused by the same stimulus in a person with similar sense-organs but different past experience. The connection with past experience is clearly known; it is, however, an explanatory hypothesis, not directly verifiable in the present state of knowledge, to suppose that this connection works through an effect of the past experience on the brain. This hypothesis must be regarded as doubtful, but it will save circumlocution to adopt it. I shall therefore not repeat, on each occasion, that we cannot feel sure it is true. In general, where the causal connection with past experience is obvious, we call an occurrence “mnemic”, without implying this or that hypothesis as to the explanation of mnemic phenomena.

It is perhaps worth while to ask how we know that images are like the sensations which are their prototypes. The difficulty of this question arises as follows. Suppose you call up an image of the Brooklyn Bridge, and you are convinced that it is like what you see when you look at Brooklyn Bridge. It would seem natural to say that you know the likeness because you remember Brooklyn Bridge. But remembering is often held to involve, as an essential element, the occurrence of an image which is regarded as referring to a prototype. Unless you can remember without images, it is difficult to see how you can be sure that images resemble prototypes. I think that in fact you cannot be sure, unless you can find some indirect means of comparison. You might, for example, have photographs of Brooklyn Bridge taken from a given place on two different days, and find them indistinguishable, showing that Brooklyn Bridge has not changed in the interval. You might see Brooklyn Bridge on the first of these days, remember it on the second, and immediately afterwards look at it. In looking at it, you might find every detail coming to you with a feeling of expectedness, or you might find some details coming with a feeling of surprise. In this case you would say that your image had been wrong as regards the details which were surprising. Or, again, you might make a picture of Brooklyn Bridge on paper, from memory, and then compare it with the original or a photograph. Or you might content yourself by writing down a description of it in words, and verifying its accuracy by direct observation. Innumerable methods of this kind can be devised by which you can test the likeness of an image to its prototype. The result is that there is often a great likeness, though seldom complete accuracy. The belief in the likeness of an image to its prototype is, of course, not generated in this way, but only tested. The belief exists prior to evidence as to its correctness, like most of our beliefs. I shall have more to say on this subject in the next chapter, which will be concerned with memory. But I think enough has been said to show that it is not unreasonable to regard images as having a greater or less degree of resemblance to their prototypes. To claim more is hardly justifiable.

We can now reach a definite conclusion about perception, sensation, and images. Let us imagine a number of people placed, as far as possible, in the same environment; we will suppose that they sit successively in a certain chair in a dark room, in full view of illuminated pictures of two eminent politicians of opposite parties whose names are written underneath them. We will suppose that all of them have normal eyesight. Their reactions will be partly similar, partly different. If any of these observers are babies too young to have learnt to focus, they will not see sharp outlines, but a mere blurr, not from an optical defect, but from a lack of cerebral control over muscles. In this respect, experience has an effect even upon what must count as pure sensation. But this difference is really analogous to the difference between having one’s eyes open and having them shut; the difference is in the sense-organ, although it may be due to a difference in the brain. We will therefore assume that all the spectators know how to adjust the eyes so as to see as well as possible, and all try to see. We shall then say that, if the spectators differ as widely as is possible for normal human beings, what is common to the reactions of all of them is sensation, provided it is connected with the sense of sight, or, more correctly, provided it has that quality which we observe to be common and peculiar to visual objects. But probably all of them, if they are over three months old, will have tactile images while they see the pictures. And if they are more than about a year old, they will interpret them as pictures, which represent three-dimensional objects; before that age, they may see them as coloured patterns, not as representations of faces. Most animals, though not all, are incapable of interpreting pictures as representations. But in an adult human being this interpretation is not deliberate; it has become automatic. It is, I think, mainly a question of tactile images: the images you have in looking at a picture are not those appropriate to a smooth flat surface, but those appropriate to the object represented. If the object represented is a large one, there will also be images of movement—walking round the object, or climbing up it, or what not. All these are obviously a product of experience, and therefore do not count as part of the sensation. This influence of experience is still more obvious when it comes to reading the names of the politicians, considering whether they are good likenesses, and feeling what a fine fellow one of them looks and what unmitigated villainy is stamped upon the features of the other. None of this counts as sensation, yet it is part of a man’s spontaneous reaction to an outside stimulus.

It is evidently difficult to avoid a certain artificiality in distinguishing between the effects of experience and the rest in a man’s reaction to a stimulus. Perhaps we could tackle the matter in a slightly different way. We can distinguish stimuli of different sorts: to the eye, the ear, the nose, the palate, etc. We can also distinguish elements of different sorts in the reaction: visual elements, auditory elements, etc. The latter are defined, not by the stimulus, but by their intrinsic quality. A visual sensation and a visual image have a common quality which neither shares with an auditory sensation or an auditory image. We may then say: a visual image is an occurrence having the visual quality but not due to a stimulus to the eye, i.e. not having as a direct causal antecedent the incidence of light-waves upon the retina. Similarly an auditory image will be an occurrence having the auditory quality but not due to sound-waves reaching the ear, and so on for the other senses. This means a complete abandonment of the attempt to distinguish psychologically between sensations and images; the distinction becomes solely one as to physical antecedents. It is true that we can and do arrive at the distinction without scientific physics, because we find that certain elements in our integral reactions have the correlations that make us regard them as corresponding to something external while others do not—correlations both with the experience of others and with our own past and future experiences. But when we refine upon this common-sense distinction and try to make it precise, it becomes the distinction in terms of physics as stated just now.

We might therefore conclude that an image is an occurrence having the quality associated with stimulation by some sense-organ, but not due to such stimulation. In human beings, images seem to depend upon past experience, but perhaps in more instinctive animals they are partly due to innate cerebral mechanisms. In any case dependence upon experience is not the mark by which they are to be defined. This shows how intimate is the dependence of traditional psychology upon physics, and how difficult it is to make psychology into an autonomous science.

There is, however, still a further refinement necessary. Whatever is included under our present definition is an image, but some things not included are also images. The sight of an object may bring with it a visual image of some other object frequently associated with it. This latter is called an image, not a sensation, because, though also visual, it is not appropriate to the stimulus in a certain sense: it would not appear in a photograph of the scene, or in a photograph of the retina. Thus we are forced to say: the sensation element in the reaction to a stimulus is that part which enables you to draw inferences as to the nature of the extra-cerebral event (if any) which was the stimulus;9 the rest is images. Fortunately, images and sensations usually differ in intrinsic quality; this makes it possible to get an approximate idea of the external world by using the usual intrinsic differences, and to correct it afterwards by means of the strict causal definition. But evidently the matter is difficult and complicated, depending upon physics and physiology, not upon pure psychology. This is the main thing to be realised about images.

The above discussion has suggested a definition of the word “image”. We might have called an event an “image” when it is recognisably of the same kind as a “percept”, but does not have the stimulus which it would have if it were a percept. But if this definition is to be made satisfactory, it will be necessary to substitute a different word in place of “percept”. For example, in the percept of a visible object it would be usual to include certain associated tactual elements, but these must, from our point of view, count as images. It will be better to say, therefore, that an “image” is an occurrence recognisably visual (or auditory, etc., as the case may be), but not caused by a stimulus which is of the nature of light (or sound etc., as the case may be), or at any rate only indirectly so caused as a result of association. With this definition, I do not myself feel any doubt as to the existence of images. It is clear that they constitute most of the material of dreams and day-dreams, that they are utilised by composers in making music, that we employ them when we get out of a familiar room in the dark (though here the rats in mazes make a different explanation possible), and that they account for the shock of surprise we have when we take salt thinking it is sugar or (as happened to me recently) vinegar thinking it is coffee. The question of the causation of images—i.e. whether it is in the brain or in other parts of the body—is not one which it is necessary to our purposes to decide, which is fortunate, since, so far as I know, there is not at present any adequate evidence on the point. But the existence of images and their resemblance to perception is important, as we shall see in the next chapter.

Images come in various ways, and play various parts. There are those that come as accretions to a case of sensation, which are not recognised as images except by the psychologist; these form, for example, the tactual quality of things we only see, and the visual quality of things we only touch. I think dreams belong, in part, to this class of images: some dreams result from misinterpreting some ordinary stimulus, and in these cases the images are those suggested by a sensation, but suggested more uncritically than if we were awake. Then there are images which are not attached to a present reality, but to one which we locate in the past; these are present in memory, not necessarily always, but sometimes. Then there are images not attached to reality at all so far as our feeling about them goes: images which merely float into our heads in reverie or in passionate desire. And finally there are images which are called up voluntarily, for example, in considering how to decorate a room. This last kind has its importance, but I shall say nothing more about it at present, since we cannot profitably discuss it until we have decided what we are to mean by the word “voluntary”. The first kind, which comes as an accretion to sensation, and gives to our feeling of objects a certain rotundity and full-bloodedness which the stimulus alone would hardly warrant, has been considered already. Therefore what remains for the present is the use of images in memory and imagination; and of these two I shall begin with memory.