DURATION (ML. duratio. from Lat. durare, to last). or PET:SIsTENCE IN TIME. The simplest temporal determination of mental processes. It may be assumed that every simple conscious proc ess and every state of consciousness has a nor mal duration. varying with variation of circum stances, but still capable of numerical statement. The ascertainment of this normal duration is of importance to an exact psychology. and a good deal of work has accordingly been done upon it. Unfortunately, the complication of factors is so great, even in the most favorable case--that of sensation—that the results so far obtained must be taken with reserve. Suppose, e.g. that we try to determine the duration of pressure sensation by applying an intermittent stimulation at It chosen point of the cutaneous surface, and not ing the rapidity at which the stimuli may fol low each other without giving rise to a single emit humus pressure. If we mark the point at which the stimuli are still just sufficient ly separated to give a rough, thrilling percep tion. we shall say that the shin can discrim inate pressures of of a seeond's duration and under. If, on the other band, we demand that the pressure sensations be full and clear, we shall put their duration as high as 72 ,1 or 2, of a second. And these two values will vary. further, with the intensity of the applied stimuli. In the sphere of vision, the duration of sensation depends partly upon the intensity of stimulus, partly upon the char acter of the visual interval which separates the given sensations. kiilpe estimates it, omitting the negative after - image (q.v.) at of a second. Temperature sensations last, on the average. about half a second. The times re quired for the cognition of tone, vary con siderably with practice. Maximal practice pre supposed, they lie, apparently, between one and two vibrations, and thus decrease with increase of the pitch-number of the stimulus. Thus, a tone of 64 vibrations must he sounded for 4 of a second, while a tone, of 1ST vibrations can lie cognized in of a second. There is, however, a point upon the scale at which the duration of stimulus necessary to the cognition of a tonal quality sinks to an absolute minimum. This point lies at the (I of :1168 vibrations in the second, which eon be heard if the tone sound only for of a second. For the duration of a pulse or wave of attention, see .ArrENTIoN.) No investigation of affective durations has as yet been undertaken.
Psychologists have also made a study of dura tion as such—i.e. of our capacity to perceive and to compare empty time-intervals. two electric sparks, seen in daylight, are clearly differentiated if the time between them amount to of a second; the snaps of two sparks are heard as separate. under favorable conditions, if the interval be as small as of a second. When the impressions belong to two different sense • I toile]] - hearing, touch - sight, sight-hearing), the just noticeable interval varies with the order in which they come (touch-hearing or hearing-touch), and With the direction of at tention; the values most frequently obtained fall within the limits and of a second. It
need hardly be said that the judgment in these cases is a judgment simply of the separateness of the two sensations, and that the attention is directed upon the stimuli themselves and not upon the length of the time-interval between theta.
Our appreciation of the relative duration of short intervals—i.e. our judgment as to whether a given interval is longer or shorter than all other—is somewhat astonishingly accurate. For psychological purposes, interval: fall into three groups: Ill 'Short' times, ranging from the just noticeable duration to about 0.5 or 0.6 of a second; (2) 'moderate' times, extending from this latter value to :3 or 4 seconds: and (3) 'large' times, from • seconds upward. In the ease of (1) our temporal estimation is direct ; the impressions \Odell limit the intervals (sharp sounds) are all in consciousness together; we do not compare the intervals, but judge simply of the rapidity or rate of succession of the limiting stimuli. Our judgment is therefore strongly influenced by the quality, intensity, and dura tion of these limiting impressions, as well as by their rhythmieal form, by the direction of at tention. etc. With maximal practice and under favorable conditions, an interval of 0.3 second may be discriminated front an immediately fol lowing interval of 0 303 second. In the case of (2) and (:3), the temporal estimation is indi rect. Large times are judged predominantly in terms not of tittle, but, of its contents: the greater the number of ideas, perceptions, or feelings in the interval, the longer is the interval estimated to be Moderate tittles seem to furnish the ma terial of true temporal comparison. The first limiting impression of the tirst interval is just disappearing from consciousness as the first im pression of the second interval enters. The former impression is then reproduced; a definite direction is given to the strain of attention, and the closing impression of the second interval is 'expected' at a moment corresponding, to that at Nvhieli the first interval closed. The basis of judgment is thus given by strain and other or ganic sensations, With their feel ing:.
The work ,,() far accomplished upon the course of temporal discrimination is ineomplete, and the laws upon which it rests demand further con firmation. It appears. however, that there is constancy of the relative differential sensitivity I see D!SCRIMINATION. over a certain range of short and moderate times; that short interval, are overestimated and longer intervals underestimated: and that this error of estima tion has the zero value at an interval of 0.5 or 0.6 second (indifference point of temporal dis crimination) .
Consult: Ktilpe. Ilittlincs of Psychology (Lon don. 1895) : Wundt, cumhilge r physio/o gischen Psychologif- (Leipzig. IS9:3I :\letunann, in Philosophische Studien, viii. ( Leipzig, l803) : Weyer. in Philosophisebc Studies, ix. (Leipzig, 1894).