Illusions: A Psychological Study

by James Sully

Illusions of Perspective: A. Definite Localization.

In order to understand these errors of mnemonic perspective, we shall have to inquire more closely than we have yet done into the circumstances which customarily determine our idea of the degree of propinquity or of remoteness of a past event. And first of all, we will take the case of a complete act of recollection when the mind is able to travel back along an uninterrupted series of experiences to a definitely apprehended point. Here there would seem, at first sight, to be no room for error, since this movement of retrospective imagination may be said to involve a direct measurement of the distance, just as a sweep of the eye over the ground between a spectator and an object affords a direct measurement of the intervening space.

Modern science, however, tells us that this mode of measurement is by no means the simple and accurate process which it at first seems to be. In point of fact, there is something like a constant error in all such retrospective measurement. Vierordt has proved experimentally, by making a person try to reproduce the varying time-intervals between the strokes of the pendulum of a metronome, that when the interval is a very small one, we uniformly tend to exaggerate it in retrospection; when a large one, to regard it, on the contrary, as less than it actually was.[117]

A mere act of reflection will convince any one that when he tries to conceive a very small interval, say a quarter of a second, he is likely to make it too great. On the other hand, when we try to conceive a year, we do not fully grasp the whole extent of the duration. This is proved by the fact that merely by spending more time over the attempt, and so recalling a larger number of the details of the period, we very considerably enlarge our first estimate of the duration. And this leads to great discrepancies in the appreciation of the relative magnitudes of past sections of time. Thus, as Wundt observes, though in retrospect both a month and a year seem too short, the latter is relatively much more shortened than the former.[118]

The cause of this constant error in the mode of reproducing durations seems to be connected with the very nature of the reproductive act. It must be borne in mind that this act is itself, like the experience which it represents, a mental process, occupying time, and that consequently it may very possibly reflect its time-character on the resulting judgment. Thus, since it certainly takes more than a quarter of a second to pass in imagination from one impression to another, it may be that we tend to confound this duration with that which we try to represent. Similarly, the fact that in the act of reproductive imagination we under-estimate a longer interval between two impressions, say those of the slow beats of a colliery engine, may be accounted for by the supposition that the imagination tends to pass from the one impression to the succeeding one too rapidly.[119]

The gross misappreciation of duration of long periods of time, while it may illustrate the principle just touched on, clearly involves the effect of other and more powerful influences. A mere glance at what is in our mind when we recall such a period as a month or a year, shows that there is no clear concrete representation at all. Time, it has been often said, is known only so far as filled with concrete contents or conscious experiences, and a perfect imagination of any particular period of past time would involve a retracing of all the successive experiences which have gone to make up this section of our life. This, I need not say, never happens, both because, on the one hand, memory does not allow of a complete reproduction of any segment of our experience, and because, on the other hand, such an imaginative reproduction, even if possible, would clearly occupy as much time as the experience itself.[120]

When I call up an image of the year just closing, what really happens is a rapid movement of imagination over a series of prominent events, among which the succession of seasons probably occupies the foremost place, serving, as I have remarked, as a framework for my retrospective picture. Each of the events which I thus run over is really a long succession of shorter experiences, which, however, I do not separately represent to myself. My imaginative reproduction of such a period is thus essentially a greatly abbreviated and symbolic mode of representation. It by no means corresponds to the visual imagination of a large magnitude, say that of the length of sea horizon visible at any one moment, which is complete in an instant, and quite independent of a successive imagination of its parts or details. It is essentially a very fragmentary and defective numerical idea, in which, moreover, the real quantitative value of the units is altogether lost sight of.

Now, it seems to follow from this that there is something illusory in all our recallings of long periods of the past. It is by no means strictly correct to say that memory ever reinstates the past. It is more true to say that we see the past in retrospect as greatly foreshortened. Yet even this is hardly an accurate account of what takes place, since, when we look at an object foreshortened in perspective, we see enough to enable us imaginatively to reconstruct the actual size of the object, whereas in the case of time-perspective no such reconstruction is even indirectly possible.

It is to be added that this constant error in time-reproduction is greater in the case of remote periods than of near ones of the same length. Thus, the retrospective estimate of a duration far removed from the present, say the length of time passed at a particular school, is much more superficial and fragmentary than that of a recent corresponding period. So that the time-vista of the past is seen to answer pretty closely to a visible perspective in which the amount of apparent error due to foreshortening increases with the distance.

In practice, however, this defect in the imagination of duration leads to no error. Although, as a concrete image answering to some definite succession of experiences a year is a gross misrepresentation, as a general concept implying a collection of a certain number of similar successions of experience it is sufficiently exact. That is to say, though we cannot imagine the absolute duration of any such cycle of experience, we can, by the simple device of conceiving certain durations as multiples of others, perfectly well compare different periods of times, and so appreciate their relative magnitudes.