Harvard Psychological Studies Part 11

_ST=CT=_ 3.0 SECS.

Subject _R_, 100. Subject _P_, 105.

L E S d L E S d SSS 32 56 12 + 20 SSS 16 67 22 - 9 WWW 11 53 36 - 25 WWW 19 72 14 + 5 SSW 6 27 67 - 61 SSW 17 56 32 - 15 WWS 57 36 7 + 50 WWS 37 61 7 + 30 WSS 10 45 45 - 35 WSS 9 69 27 - 18 SWW 3 31 66 - 63 SWW 3 64 33 - 25

By the above table the absolute intensity of the stimulus is clearly shown to be an important factor in determining the constant error of judgment, since in both cases the change from _SSS_ to _WWW_ changed the sign of the constant error, although in opposite directions. But the effect of the relative intensity is more obscure. To discover more readily whether the introduction of a stronger or weaker stimulation promises a definite effect upon the estimation of the interval which precedes or follows it, the results are so arranged in Table IX. that reading downward in any pair shows the effect of a decrease in the intensity of (1) the first, (2) the second, (3) the third, and (4) all three stimulations.

TABLE IX.

Subject _R._ Subject _P._

(1) _SSS_ + 20 - 6 _WSS_ - 35 - 55 - 18 - 12

_SWW_ - 63 - 25 _WWW_ - 25 - 38 + 5 + 30

(2) _SSW_ - 61 - 15 _SWW_ - 63 - 2 - 25 + 10

_WSS_ - 35 - 18 _WWS_ + 50 + 85 + 30 - 48

(3) _SSS_ + 20 - 6 _SSW_ - 61 - 81 - 15 - 7

_WWS_ + 50 + 30 _WWW_ - 25 - 75 + 5 - 25

(4) _SSS_ + 20 - 6 _WWW_ - 15 - 35 + 5 + 11

There seems at first sight to be no uniformity about these results.

Decreasing the first stimulation in the first case increases, in the second case diminishes, the comparative length of the first interval.

We get a similar result in the decreasing of the second stimulation.

In the case of the third stimulation only does the decrease produce a uniform result. If, however, we neglect the first pair of (3), we observe that in the other cases the effect of a _difference_ between the two stimulations is to lengthen the interval which they limit. The fact that both subjects make the same exception is, however, striking and suggestive of doubt. These results were obtained in the first year's work, and to test their validity the experiment was repeated at the beginning of the present year on three subjects, fifty series being taken from each, with the results given in Table X.

TABLE X.

_ST_ = 3.0 secs. = _CT_.

Subject _Mm._ Subject _A._ Subject _D._

S E L d S E L d S E L d SSS 24 13 13 - 11 7 30 13 + 6 10 31 9 - 1 WSS 33 9 8 - 25 20 24 6 - 14 17 27 6 - 11 SSW 19 15 16 - 3 23 16 11 - 12 10 31 9* - 1 WWW 19 12 19 0 13 26 11 - 2 1 40 9 + 8 SWW 18 30 2 - 16 23 21 6* - 17 7 38 5 - 2 WWS 13 16 21 + 8 12 30 8 - 4 15 25 10 - 5

*Transcriber's Note: Original "16" changed to "6", "19" to "9".

a.n.a.lysis of this table shows that in every case a difference between the intensities of the first and second taps lengthens the first interval in comparative estimation. In the case of subject _Mm_ a difference in the intensities of the second and third taps lengthens the second interval subjectively. But in the cases of the other two subjects the difference shortens the interval in varying degrees.

The intensity difference established for the purposes of these experiments was not great, being less than that established for the work on the first two subjects, and therefore the fact that these results are less decided than those of the first work was not unexpected. The results are, however, very clear, and show that the lengthening effect of a difference in intensity of the stimulations limiting an interval has its general application only to the first interval, being sometimes reversed in the second. From the combined results we find, further, that a uniform change in the intensity of three stimulations is capable of reversing the direction of the constant error, an intensity change in a given direction changing the error from positive to negative for some subjects, and from negative to positive for others.

III. INTERPRETATION OF RESULTS.

We may say provisionally that the _change_ from a tactual stimulation of one kind to a tactual stimulation of another kind tends to lengthen subjectively the interval which the two limit. If we apply the same generalization to the other sensorial realms, we discover that it agrees with the general results obtained by Meumann[15] in investigating the effects of intensity changes upon auditory time, and also with the results obtained by Schumann[16] in investigations with stimulations addressed alternately to one ear and to the other.

Meumann reports also that the change from stimulation of one sense to stimulation of another subjectively lengthens the corresponding interval.

[15] _op. cit._ (II.), S. 289-297.

[16] _op. cit._, S. 67.

What, then, are the factors, introduced by the change, which produce this lengthening effect? The results of introspection on the part of some of the subjects of our experiments furnish the clue which may enable us to construct a working hypothesis.

Many of the subjects visualize a time line in the form of a curve. In each case of this kind the introduction of a change, either in intensity or location, if large enough to produce an effect on the time estimation, produced a distortion on the part of the curve corresponding to the interval affected. All of the subjects employed in the experiments of Group 2 were distinctly conscious of the change in attention from one point to another, as the two were stimulated successively, and three of them, _Hy_, _Hs_ and _P_, thought of something pa.s.sing from one point to the other, the representation being described as partly muscular and partly visual. Subjects _Mr_ and _B_ visualized the two hands, and consciously transferred the attention from one part of the visual image to the other. Subject _Mr_ had a constant tendency to make eye movements in the direction of the change. Subject _P_ detected these eye movements a few times, but subject _B_ was never conscious of anything of the kind.

All of the subjects except _R_ were conscious of more or less of a _strain_, which varied during the intervals, and was by some felt to be largely a tension of the chest and other muscles, while others felt it rather indefinitely as a 'strain of attention.' The characteristics of this tension feeling were almost always different in the second interval from those in the first, the tension being usually felt to be more _constant_ in the second interval. In experiments of the third group a higher degree of tension was felt in awaiting a light tap than in awaiting a heavy one.

Evidently, in all these cases, the effect of a _difference_ between two stimulations was to introduce certain changes in sensation _during_ the interval which they limited, owing to the fact that the subject expected the difference to occur. Thus in the third group of experiments there were, very likely, in all cases changes from sensations of high tension to sensations of lower, or vice versa. It is probable that, in the experiments of the second group, there were also changes in muscular sensations, partly those of eye muscles, partly of chest and arm muscles, introduced by the change of attention from one point to another. At any rate, it is certain that there were certain sensation changes produced during the intervals by changes of locality.

If, then, we a.s.sume that the introduction of additional sensation change into an interval lengthens it, we are led to the conclusion that psychological time (as distinguished from metaphysical, mathematical, or transcendental time) is perceived simply as the quantum of change in the sensation content. That this is a true conclusion is seemingly supported by the fact that when we wish to make our estimate correspond as closely as possible with external measurements, we exclude from the content, to the best of our ability, the general complex of external sensations, which vary with extreme irregularity; and confine the attention to the more uniformly varying bodily sensations. We perhaps go even further, and inhibit certain bodily sensations, corresponding to activity of the more peripherally located muscles, that the attention may be confined to certain others.

But attention to a dermal stimulation is precisely the condition which would tend to some extent to prevent this inhibition. For this reason we might well expect to find the error in estimation more variable, the 'constant error' in general greater, and the specific effects of variations which would affect the peripheral muscles, more marked in 'tactual' time than in either 'auditory' or 'optical' time. Certainly all these factors appear surprisingly large in these experiments.

It is not possible to ascertain to how great an extent subject _Sh_ inhibited the more external sensations, but certainly if he succeeded to an unusual degree in so doing, that fact would explain the absence of effect of stimulation difference in his case.

Explanation has still to be offered for the variable effect of intensity difference upon the _second_ interval. According to all subjects except _Sn_, there is a radical difference in att.i.tude in the two intervals. In the first interval the subject is merely observant, but in the second he is more or less reproductive. That is, he measures off a length which seems equal to the standard, and if the stimulation does not come at that point he is prepared to judge the interval as 'longer,' even before the third stimulation is given. In cases, then, where the judgment with equal intensities would be 'longer,' we might expect that the actual strengthening or weakening of the final tap would make no difference, and that it would make very little difference in other cases. But even here the expectation of the intensity is an important factor in determining tension changes, although naturally much less so than in the first interval. So we should still expect the lengthening of the second interval.

We must remember, however, that, as we noticed in discussing the experiments of Group 2, there is complicated with the lengthening effect of a change the _bare constant error_, which appears even when the three stimulations are similar in all respects except temporal location. Compare _WWW_ with _SSS_, and we find that with all five subjects the constant error is decidedly changed, being even reversed in direction with three of the subjects.

Now, what determines the direction of the constant error, where there is no pause between the intervals? Three subjects reported that at times there seemed to be a slight loss of time after the second stimulation, owing to the readjustment called for by the change of att.i.tude referred to above, so that the second interval was begun, not really at the second stimulation, but a certain period after it. This fact, if we a.s.sume it to be such, and also a.s.sume that it is present to a certain degree in all observations of this kind, explains the apparent overestimation of the first interval. Opposed to the factor of _loss of time_ there is the factor of _perspective_, by which an interval, or part of an interval, seems less in quant.i.ty as it recedes into the past. The joint effect of these two factors determines the constant error in any case where no pause is introduced between _ST_ and _CT_. It is then perfectly obvious that, as the perspective factor is decreased by diminishing the intervals compared, the constant error must receive positive increments, _i.e._, become algebraically greater; which corresponds exactly with the results obtained by Vierordt, Kollert, Estel, and Gla.s.s, that under ordinary conditions long standard intervals are comparatively underestimated, and short ones overestimated.

On the other hand, if with a given interval we vary the loss of time, we also vary the constant error. We have seen that a change in the intensity of the stimulations, although the relative intensity of the three remains constant, produces this variation of the constant error; and the individual differences of subjects with regard to sensibility, power of attention and inhibition, and preferences for certain intensities, lead us to the conclusion that for certain subjects certain intensities of stimulation make the transition from the receptive att.i.tude to the reproductive easiest, and, therefore, most rapid.

Now finally, as regards the apparent failure of the change in _SSW_ to lengthen the second interval, for which we are seeking to account; the comparatively great loss of time occurring where the change of att.i.tude would naturally be most difficult (that is, where it is complicated with a change of attention from a strong stimulation to the higher key of a weak stimulation) is sufficient to explain why with most subjects the lengthening effect upon the second interval is more than neutralized. The individual differences mentioned in the preceding paragraph as affecting the relation of the two factors determining the constant error, enter here of course to modify the judgments and cause disagreement among the results for different subjects.

Briefly stated, the most important points upon which this discussion hinges are thus the following: We have shown--

1. That the introduction of either a local difference or a difference of intensity in the tactual stimulations limiting an interval has, in general, the effect of causing the interval to appear longer than it otherwise would appear.

2. That the apparent exceptions to the above rule are, (_a_) that the _increase_ of the local difference in the first interval, the stimulated areas remaining unchanged, produces a slight _decrease_ in the subjective lengthening of the interval, and (_b_) that in certain cases a difference in intensity of the stimulations limiting the second interval apparently causes the interval to seem shorter than it otherwise would.

3. That the 'constant error' of time judgment is dependent upon the intensity of the stimulations employed, although the three stimulations limiting the two intervals remain of equal intensity.

To harmonize these results we have found it necessary to a.s.sume:

1. That the length of a time interval is perceived as the amount of change in the sensation-complex corresponding to that interval.

2. That the so-called 'constant error' of time estimation is determined by two mutually opposing factors, of which the first is the _loss of time_ occasioned by the change of att.i.tude at the division between the two intervals, and the second is the diminishing effect of _perspective_.

It is evident, however, that this last a.s.sumption applies only to the conditions under which the results were obtained, namely, the comparison of two intervals marked off by three brief stimulations.