6. The attribute of the auditory sense which most of all adapts it to the more accurate apprehension of the temporal relations in external processes, is the exceedingly short persistence of its sensations after the external stimulation; so that any temporal succession of sounds is reproduced with almost perfect fidelity in the corresponding succession of sensations. In close connection with this we have certain psychological properties of temporal auditory ideas.
In the first place, they differ from temporal ideas of touch in that often only the extremities of the single intervals that go to make up the total idea, are marked by sensations. In such a case the relations of such intervals to one another are estimated essentially by the apparently empty or heterogeneously filled intervals that lie between the limiting sensations.
This is especially noticeable in the case of rhythmical auditory ideas. There are in general two possible forms of such ideas: continuous or only rarely interrupted successions of relatively lasting sensations, and discontinuous successions of strokes, in which only the extremities of the rhythmical periods are marked by external sounds. For a discontinuous succession of entirely uniform sounds the temporal attributes of the ideas are in general more apparent than for lasting impressions, since in the former case the influences of the tonal qualities are entirely wanting. We may confine our consideration to discontinuous series, because the principles that apply here hold for continuous successions also. In fact, the rhythmical division in the latter case, as may be easily observed, is made by means of certain single accents which are either given in the external impression or abitrarily applied to it. [p. 149]
7. A series of regular strokes made in this way as the simplest form of temporal auditory ideas, is distinguished from the simplest form of temporal touch-ideas, described above (p. 147), mainly by the absence of all objective sensational content in the intervals.
The external impressions here do nothing but divide the separate intervals from one another. Still, the intervals of such a series are not entirely empty, but are filled by subjective affective and sensational contents which correspond fully to those observed in tactual ideas. Most emphatic of all are the affective contents of the intervals. These feelings in their successive periods of gradually rising and suddenly satisfied expectation, are the same as in the course of a rhythmical tactual movement.
Even the sensational substratum for these feeling is not entirely absent; it is merely more variable. Sometimes it is nothing but the sensations of tension of the tympanum in their various intensifies. Then again it is the accompanying sensations of tension from other organs, or finally other sensations of movement in cases where an involuntary rhythmical movement is connected with the auditory series. But on account of the changeable character and generally small intensity of these motor sensations, the affective processes in auditory ideas 'are very much more clearly perceptible.
It follows from the conditions described that the influence of the subjective elements on the character of time-ideas is the easiest to demonstrate. First of all, this shows itself in the effect which different rates of the sensations have on the formation of temporal ideas. It is found that there is a certain medium rate of about 0.2 sec. which is most favorable for the union of a number of successive auditory impressions. Now, it is easy to observe that this is the rate at which the above mentioned subjective sensations and feelings are most emphatic in their alternation. If the rate is [p. 150] made much slower, the strain of expectation is too great and passes into an unpleasurable feeling which becomes more and more unendurable. If, on the contrary, the rate is accelerated, the rapid alternation of feelings becomes fatiguing. Thus, in both directions limits are approached where the synthesis of the impressions into a rhythmical time-idea is no longer possible. The upper limit is about one second, the lower about 0.1 sec.
8. Then again, this influence of the course of our sensations and feelings upon our apprehension of temporal intervals, shows itself just as clearly ill the changes that our idea of such an interval undergoes when the conditions of its apprehension are varied without changing its objective length. Thus, it has been observed that in general a period divided into intervals is estimated as longer than one not so divided. We have here a phenomenon analogous to that observed in the illusion with interrupted lines (p. 125). The overestimation is generally much greater for temporal intervals. This is obviously due to the fact that the oft repeated alternation in sensations and feelings in an interval of time have a much greater influence than the interruption of the movement through points of division in the case of the similar spacial illusion. Furthermore, if in a long series of regular beats single impressions are emphasized by their greater intensity, or by some qualitative peculiarity, the uniform result is overestimation of the intervals preceding and following the emphasized impression, in comparison with the other intervals of the same series. If, however, a certain rhythm is produced successively with weak and then with strong beats, the rate appears slower in the first case than in the second.