§ 3. Perception of Lapse of Time. — The immediate experience of timetransience is probably universal in all conscious life. Some rudimentary form of it probably exists even at the level of the sensation-reflex. But in the case of the higher animals, the facts require us to assume much more than this. Their actions are intelligently adjusted so as to occur at the right moment. To explain this, we need more than the immediate experience of timetransience. We must assume that a succession of different experiences, or the duration of the same experience, produces a cumulative effect varying with the lapse of time. We have seen that the earlier stages of any process having continuity of interest leave behind them a cumulative disposition which modifies succeeding stages of the total experience. We must now add that this cumulative effect varies in its nature with the amount of time which the process has taken. In this way we can explain why an animal or a human being in preparing for action should be able to wait for the right moment, having no means of determining the right moment except lapse of time. What measures the lapse of time is the cumulative effect of the process of attending. When we are listening to a sound, our experience is different at the end of one minute from what it is at the end of two minutes, although the sound itself may not have altered in quality. This experience is unique in kind, and it certainly does not consist in having the parts of the sound-sensation as they successively occur, spread out before us in a sort of durationline or durationblock. The same explanation applies to what is called empty time. In music, the several notes are separated by temporal intervals. To keep time is to measure these intervals correctly. But it is difficult to say by what means we can measure them, except by the process of expectant attention itself. Certainly it is by no ideal reproduction of a series of events. Of course, empty time is only relatively empty; what is absent from it is the special kind of experience which marks its beginning and end. There are always other experiences going on, especially of a motor and organic kind.

The immediate estimate of lapse of time is most accurate for small intervals.* It appears to become progressively less precise as the intervals become larger. If we go for a walk and ask ourselves at any moment how long we have been walking, we can say immediately without any explicit process of calculation that we have been about halfanhour or about an hour. The limits of error are indeed very wide, but undoubtedly there seems to be some power of estimating lapse of time, even for these comparatively long periods. It is not quite a fair test to try this experiment without previous practice; a man may be able to estimate lapse of time with a fair amount of accuracy, and yet not have established an accurate relation between his subjective estimate and time as measured by the clock. With practice it is found that a person can tell with a tolerable approach to accuracy and without express calculation when an hour, or two hours, or halfanhour has elapsed.

It should be noted that continuity of interest has varying degrees. We may pass from occupation to occupation, and so have a series of distinct mental processes each having its own special interest. But from another point of view they may all have a certain unity and continuity with each other. We may successively read a book, go for a walk, and eat our dinner. Each of these processes has its own special interest relatively disconnected from the others. But they have unity of interest, as parts of our personal lifehistory. Hence they may collectively contribute to determine our immediate estimate of lapse of time.

* Many experiments have been made to determine more precisely the conditions on which it depends: but the results obtained are so ambiguous and conflicting, that I have not thought it advisable to trouble the student with them.

The part played by attention in determining this immediate estimate is illustrated by the fact that conditions affecting attention affect it also. When we are bored by monotony, or when we are distracted by a too great variety and rapidity of experiences, the duration of time is so to speak magnified. We say that it "passes very slowly." When attention is very in tensely and disagreeably aroused, as in moments of acute danger, minutes may appear as hours. On the other hand, when attention passes easily from object to object, and is agreeably absorbed by each in turn, time passes rapidly. After an entertaining conversation, we may be astonished to find that the hands of the clock have travelled over so much space. This contrast only holds good for the immediate estimate of lapse of time due to the cumulative effect of past process. When we ideally recall a period of time, and estimate it by the number and variety of the events which have taken place in it, the period which has been agreeably spent is apt to appear relatively longer, and the period in which we have been bored, shorter. In ideal retrospect, periods which appeared interminable while they were passing, shrink as it were; whereas periods that seemed on their actual occurrence to pass rapidly are correspondingly expanded when we review them in the form of a train of ideas.