It will be observed that we are not attempting at present to say what constitutes perception, but only what kind of behaviour on the part of a person whom we are observing will justify us in saying that he has perceived this or that feature of his environment. I suggest that we are justified in saying that a man “perceives” such a feature if, throughout some such period as a day, there is some bodily act which he performs whenever that feature is present, but not at any other time. This condition is clearly sufficient, but not necessary—that is to say, there may be perception even when it is not fulfilled. A man’s reaction may change through conditioning, even in so short a period as a day. Again, there may be a reaction, but one which is too slight to be observable; in this case the criterion of perception is theoretically satisfied, but not practically, since no one can know that it is. We often have evidence later on that something was perceived, although at the moment there was no discoverable reaction. I have frequently known children repeat afterwards some remark which, at the time, they seemed not to have heard. This sort of case affords another kind of evidence of perception, namely, the evidence afforded by a delayed response. Some people will sit silent and impassive in a company of talkers, giving no evidence that they are listening; yet they may go home and write down the conversation verbatim in their journals. These are the typical writers of memoirs. More remarkable still, I know one man—a man of genius, it is true—who talks incessantly, who yet, after meeting a total stranger, knows exactly what the stranger would have said if he had been given the chance. How this is managed, I do not know; but such a man is rightly called “perceptive”.
Obviously, in dealing with human beings old enough to talk, words afford the best evidence of perception. A man’s verbal responses to perceptive situations do not change much after the first few years of life. If you see a kingfisher, and at the same moment your companion says “there’s a kingfisher”, that is pretty conclusive evidence that he saw it. But, as this case illustrates, our evidence that some one else has perceived something always depends upon our own perceptions. And our own perceptions are known to us in a different way from that in which the perceptions of others are known to us. This is one of the weak spots in the attempt at a philosophy from the objective standpoint. Such a philosophy really assumes knowledge as a going concern, and takes for granted the world which a man derives from his own perceptions. We cannot tackle all our philosophical problems by the objective method, but it is worth while to proceed with it as far as it will take us. This whole question of perception will have to be attacked afresh from a different angle, and we shall then find reason to regard the behaviouristic standpoint as inadequate, though valid so far as it goes. We have still, however, a long road to go before we shall be driven to consider the subjective standpoint; more particularly, we have to define “knowledge” and “inference” behaviouristically, and then, making a new start, to consider what modern physics makes of “matter”. But for the moment there are still some things to be said about perception from the objective standpoint.
It will be seen that, according to our criterion of perception, an object perceived need not be in contact with the percipient’s body. The sun, moon, and stars are perceived according to the above criterion. In order, however, that an object not in contact with the body should be perceived, there are physical as well as physiological conditions to be fulfilled. There must be some physical process which takes place at the surface of the body when the object in question is suitably situated, but not otherwise; and there must be sense-organs capable of being affected by such a process. There are, as we know from physics, many processes which fulfil the necessary physical conditions, but fail to affect us through the inadequacy of our sense-organs. Waves of a certain sort make sound, but waves of exactly the same sort become inaudible if they are too short. Waves of a certain sort make light, but if they are too long or too short they are invisible. The waves used in wireless are of the same sort as those that make light, but are too long. There is no reason a priori why we should not be aware of wireless messages through our senses, without the need of instruments. X-rays are also of the same sort as those that make light, but in this case they are too short to be seen. They might render the objects from which they come visible, if we had a different sort of eye. We are not sensitive to magnetism, unless it is enormously powerful; but if we had more iron in our bodies, we might have no need of the mariner’s compass. Our senses are a haphazard selection of those that the nature of physical processes renders possible; one may suppose that they have resulted from chance variation and the struggle for existence.
It is important to observe that our perceptions are very largely concerned with form or shape or structure. This is the point emphasised by what is called “Gestaltpsychologie”, or psychology of form. Reading is a case in point. Whether we read black letters on white paper or white letters on a blackboard is a matter which we hardly notice; it is the forms of the letters that affect us, not their colour or their size (so long as they remain legible). In this matter, the sense of sight is pre-eminent, although blind men (and others to a less degree) can acquire a good knowledge of form by the sense of touch.
Another point of importance about our perceptions is that they give us, within limits, a knowledge of temporal sequence. If you say to a man “Brutus killed Cæsar”, and then “Cæsar killed Brutus”, the difference between the two statements is likely to be perceived by him if he is listening; in the one case he will say “of course”, in the other “nonsense”, which is evidence of his having different perceptions in the two cases, according to our definition. Further, if you ask him what the difference is, he can tell you that it is a difference in the order of the words. Thus time-order within a short period of time is clearly perceptible.
The objective method, which we have been applying in this chapter, is the only possible one in studying the perceptions of animals or of infants before they can talk. Many animals too low in the scale of evolution to have eyes are yet sensitive to light, in the sense that they move towards it or move away from it. Such animals, according to our criterion, perceive light, though there is no reason to suppose that they perceive colour or visual form or anything beyond the bare presence of light. We can perceive the bare presence of light when our eyes are shut; perhaps one may imagine their sensitiveness to be more or less analogous in its limitations.
It is not to be supposed, in any case, that “perceiving” an object involves knowing what it is like. That is quite another matter. We shall see later that certain inferences, of a highly abstract character, can be drawn from our perceptions to the objects perceived; but these inferences are at once difficult and not quite certain. The idea that perception, in itself, reveals the character of objects, is a fond delusion, and one, moreover, which it is very necessary to overcome if our philosophy is to be anything more than a pleasant fairy-tale.
[CHAPTER VI]
MEMORY OBJECTIVELY REGARDED
We are concerned in these chapters with what we can know about other men by merely observing their behaviour. In this chapter, I propose to consider everything that would commonly be called “memory”, in so far as it can be made a matter of external observation. And perhaps it may be as well, at this point, to state my own view of the question of “behaviourism”. This philosophy, of which the chief protagonist is Dr. John B. Watson, holds that everything that can be known about man is discoverable by the method of external observation, i.e. that none of our knowledge depends, essentially and necessarily, upon data in which the observer and the observed are the same person. I do not fundamentally agree with this view, but I think it contains much more truth than most people suppose, and I regard it as desirable to develop the behaviourist method to the fullest possible extent. I believe that the knowledge to be obtained by this method, so long as we take physics for granted, is self-contained, and need not, at any point, appeal to data derived from introspection, i.e. from observations which a man can make upon himself but not upon any one else. Nevertheless, I hold that there are such observations and that there is knowledge which depends upon introspection. What is more, I hold that data of this kind are required for a critical exposition of physics, which behaviourism takes for granted. I shall, therefore, after setting forth the behaviourist view of man, proceed to a scrutiny of our knowledge of physics, returning thence to man, but now as viewed from within. Then, finally, I shall attempt to draw conclusions as to what we know of the universe in general.
The word “memory” or “remembering” is commonly used in a number of different senses, which it is important to distinguish. More especially, there is a broad sense, in which the word applies to the power of repeating any habitual act previously learnt, and a narrow sense, in which it applies only to recollection of past events. It is in the broad sense that people speak of a dog remembering his master or his name, and that Sir Francis Darwin spoke of memory in plants. Samuel Butler used to attribute the sort of behaviour that would usually be called instinctive to memory of ancestral experience, and evidently he was using the word “memory” in its widest possible sense. Bergson, on the contrary, dismisses “habit-memory” as not true memory at all. True memory, for him, is confined to the recollection of a past occurrence, which, he maintains, cannot be a habit, since the event remembered only occurred once. The behaviourist maintains that this contention is mistaken, and that all memory consists in the retention of a habit. For him, therefore, memory is not something requiring special study, but is merged into the study of habit. Dr. Watson says: “The behaviourist never uses the term ‘memory’. He believes that it has no place in an objective psychology.” He proceeds to give instances, beginning with a white rat in a maze. On the first occasion, he says, it took this rat forty minutes to get out of the maze, but after thirty-five trials he learnt to get out in six seconds, without taking any wrong turnings. He was then kept away from the maze for six months, and on being put in it again he got out in two minutes, with six mistakes. He was just as good as he had been before at the twentieth trial. We have here a measure of the extent to which the habit of the maze had been retained. A similar experiment with a monkey showed even more retentiveness. He was put into a problem box which at first took him twenty minutes to open, but at the twentieth trial he opened it in two seconds. He was then kept away from it for six months, and on being put back in it he opened it in four seconds.