Philosophy

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. 9 I.e. the immediate stimulus, not the “physical object”. 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.