(G) Mental Association and the Memory-Continuum (cont.)
When in retrospect we note that a particular presentation X has had a place in the field of consciousness, while a series of objects A B C D
have succeeded each other, then we may be said in observing this relation of the two to perceive the duration of X. And it is in this way that we do subjectively estimate longer periods of time. But first, it is evident that we cannot apply this method to indefinitely short periods without passing beyond the region of distinct presentation; and, since the knowledge of duration implies a relation between distinguishable presentation A B C D and X, the case is one in which the hypothesis of sub-consciousness can hardly help any but those who confound the fact of time with the knowledge of it. Secondly, if we are to compare different durations at all, it is not enough that one of them should last out a series A B C D, and another series L M N O; we also want some sort of common measure oft hose series. Locke was awake to this point though he expresses himself vaguely (Essay, ii. 14, §§ 9-12). He speaks of our ideas succeeding each other "at certain distances not much unlike the images in the inside of a lantern turned round by the heat of a candle," and "guesses" that "this appearance of their in train varies not very much in a waking man." Now what is this "distance" that separates A from B, B from C, and so on, and what means have we of knowing that it is tolerably constant in waking life? It is probably that the residuum of which we have called a temporal sign; or, in other words, it is the movement of attention from A to B. But we must endeavour here to get a more exact notion of this movement. Everybody knows what it is to be distracted by a rapid succession of varied impressions, and equally what it is to be wearied by the slow and monotonous recurrence of the same impressions. Now these "feelings" of distraction and tedium owe their characteristic qualities to movements of attention. In the first, attention is kept incessantly on the move: before it is accommodated to A, it is disturbed by the suddenness, intensity, or novelty of B; in the second, it is kept all but stationary by the repeated presentation of the same impression. Such excess and defect of surprises make one realize a fact which in ordinary life is so obscure as to escape notice. But recent experiments have set this fact in a more striking light, and made clear what Locke had dimly before his mind in talking of a certain distance between the presentations of a waking man. In estimating very short periods of time, of a second or less, indicated say by the beats of a metronome, it is found that there is a certain period for which shorter periods are on the whole overestimated, and longer periods underestimated. This we may perhaps take to be evidence of the time occupied in accommodating or fixing attention. Whether the "point of indifference" is determined by the rate of usual bodily movement, as Spencer asserts and Wundt conjectures, or conversely, is a question we need not discuss just now. But, though the fixation of attention does of course really occupy time, it is probably not in the first instance perceived as time, i.e., as continuous "protensity," to use a term of Hamiltons, but as intensity. Thus, if this supposition be true, there is an elements in our concrete time-perceptions which has no place in our abstract conception of time. In time conceived as physical there is no trace of intensity; in time psychically experienced duration is primarily an intensive magnitude, witness the comparison of times when we are "bored" with others when we are amused. It must have struck every one as strange who has reflected upon it that a period of time which seems long in retrospect such as an eventful excursion should have appeared short in passing; while a period, on the contrary, which in memory has dwindled to a wretched span seemed everlasting till it was gone. But, if we consider that in retrospect length of time is represented primarily and chiefly by impressions that have survived, we have an explanation of one-half; and in the intensity of the movements of attention we shall perhaps find an explanation of the other. What tells in retrospect is the series a b c d e, &c.; what tells in the present is the intervening t1t2t3, &c., or rather the original accommodation of which these temporal signs are the residuum. For, as we have seen elsewhere, the intensity of a presentation does not persist, so that in memory the residuum of the most intense feeling of tedium may only be so many ts in a memory-continuum whose surviving members are few and uninteresting. But in the actual experience, say, of a wearisome sermon, when the expectation of release is monotonous dribble of platitudes, the one impressive fact is the hearers impatience. On the other hand, so long as we are entertained, attention is never involuntary, and there is no continually deferred expectation. Just as we are said to walk with least effort when out pace accords with the rate of swing of our legs regarded as pendulums, so in pastimes impressions succeed each other at the rate at which attention can be most easily accommodated, and are such that we attend willingly. We are absorbed in the present without being unwillingly confined to it; not only is there no motive for retrospect or expectation, but there is no feeling that the present endures. Each impression lasts as long as it is interesting, but doe not continue to monopolize the focus of consciousness till attention to it is fatiguing, because uninteresting. In such facts, then, we seem to have proof that our perception of duration rests ultimately upon quasi-motor objects of varying intensity, the duration of which we do not directly experience as duration at all. They do endure and their intensity is a function of their duration; but the intensity is all that we directly perceive. In other words, it is here contended that what Locke called an instant or moment "the time of one idea in our minds without the succession of another, wherein therefore we perceived no succession at all" is psychologically not "a part in duration" in that sense in which, as he says, "we cannot conceive any duration without succession" (Essay, ii, 16, 12).
How do we know that the distance between our ideas cannot vary beyond certain bounds? This is not altogether a psychological question; but we are perhaps entitled to note some interesting facts bearing upon it which may also serve to connect the perceptions of duration and succession. If we make a Savarts wheel with a single tooth revolve slowly, say in three-quarters of a second, it will be found that in the long-run we estimate this interval correctly, -- slight overestimates and slight underestimates occurring indifferently. If we next place a second tooth opposite the first, letting the wheel revolve as before, so as to divide the three-quarters of a second into two intervals, we shall on the average overestimate it, and must increase the whole period to reach a new point of indifference. With two other teeth at right angles to the first two, the three-quarters of a second will appear longer still, and the time cease to overestimate it. If we next employ, say six teeth, 60º apart, the wheel revolving as at first, we shall detect ourselves attending to the alternate strokes, say to the first, third, and fifth, or perhaps to the third and the sixth; in this way, though we continue to overestimate the total period, we can note the number and regularity of the subdivisions. If these, however, be yet further increased, we can no longer reproduce them, though still aware that the whole period is divided into parts. But b y the time we have introduced about fifteen equidistant teeth, although there is physically an alternation of noise and silence as before, we perceive only a continuous hum, which steadily changes in quality as the number of teeth is further increased. Facts like these not only show that we estimate duration primarily by the effects of attention, but also make it probable that such estimate is fairly constant, since it is always approximately the same physical interval that becomes blurred. Further, we see that, where the distance between successive presentations is too short for a separate fixation of attention upon each, we proceed to take them in groups. This procedure is facilitated by differences in the quality and intensity of the objects as well as by differences in the intervals between them; hence among other things the aesthetic properties of modulation and rhythm.
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