Harvard Psychological Studies Part 10

[14] _op. cit._ (II.), S. 284.

2. The second group of experiments introduced the factor of a difference between the stimulation marking the end of an interval and that marking the beginning, in the form of a change in locality stimulated, from one finger to the other, either on the same hand or on the other hand. Two cla.s.ses of series were given, in one of which the change was introduced in the standard interval, and in the other cla.s.s in the compared interval.

In the first of these experiments, which are typical of the whole group, both of the subject's hands were employed, and a tapping instrument was arranged above the middle finger of each, as above the one hand in the preceding experiment, the distance between middle fingers being fifteen inches. The taps were given either two on the right hand and the third on the left, or one on the right and the second and third on the left, the two orders being designated as _RRL_ and _RLL_ respectively. The subject was always informed of the order in which the stimulations were to be given, so that any element of surprise which might arise from it was eliminated. Occasionally, however, through a lapse of memory, the subject expected the wrong order, in which case the disturbance caused by surprise was usually so great as to prevent any estimation.

The two types of series were taken under as similar conditions as possible, four (or in some cases five) tests being taken from each series alternately. Other conditions were the same as in the preceding work. The results for the six subjects employed are given in Table IV.

TABLE IV.

_ST_= 5.0 SECS. TWO HANDS. 15 INCHES.

Subject. Average RT. No. of Series.

RRL. RLL.* (Table II.) _Hs._ 4.92 6.55 (5.26) 50 _Sh._ 5.29 5.28 (5.34) 50 _Mr._ 5.02 6.23 (5.25) 60 _Mn._ 5.71 6.71 (6.19) 24 _A._ 5.34 5.89 (5.75) 28 _Sn._ 5.62 6.43 (5.47) 60

*Transcriber's Note: Original "RRL"

From Table IV. it is apparent at a glance that the new condition involved introduces a marked change in the time judgment. Comparison with Table II. shows that in the cases of all except _Sh_ and _Sn_ the variation _RRL_ shortens the standard subjectively, and that _RLL_ lengthens it; that is, a local change tends to lengthen the interval in which it occurs. In the case of _Sh_ neither introduces any change of consequence, while in the case of _Sn_ both values are higher than we might expect, although the difference between them is in conformity with the rest of the results shown in the table.

Another set of experiments was made on subject _Mr_, using taps on the middle finger of the left hand and a spot on the forearm fifteen inches from it; giving in one case two taps on the finger and the third on the arm, and in the other one tap on the finger and the second and third on the arm; designating the orders as _FFA_ and _FAA_ respectively. Sixty series were taken, and the values found for the average _ET_ were 4.52 secs, for _FFA_ and 6.24 secs, for _FAA_, _ST_ being 5.0 secs. This shows 0.5 sec. more difference than the experiment with two hands.

Next, experiments were made on two subjects, with conditions the same as in the work corresponding to Table IV., except that the distance between the fingers stimulated was only five inches. The results of this work are given in Table V.

TABLE V.

_ST_= 5.0 SECS. TWO HANDS. 5 INCHES.

Subject RRL. RLL. No. of Series.

_Sh._ 5.32 5.32 60 _Hs._ 4.40 6.80 60

It will be noticed that _Hs_ shows a slightly wider divergence than before, while _Sh_ pursues the even tenor of his way as usual.

Series were next obtained by employing the first and second fingers on one hand in exactly the same way as the middle fingers of the two hands were previously employed, the orders of stimulation being 1, 1, 2, and 1, 2, 2. The results of sixty series on Subject _Hs_ give the values of average _ET_ as 4.8 secs. for 1, 1, 2, and 6.23 sees, for 1, 2, 2, _ST_ being 5.0 secs., showing less divergence than in the preceding work.

These experiments were all made during the first year's work. They show that in most cases a change in the locality stimulated influences the estimation of the time interval, but since the details of that influence do not appear so definitely as might be desired, the ground was gone over again in a little different way at the beginning of the present year.

A somewhat more serviceable instrument for time measurements was employed, consisting of a disc provided with four rows of sockets in which pegs were inserted at appropriate angular intervals, so that their contact with fixed levers during the revolution of the disc closed an electric circuit at predetermined time intervals. The disc was rotated at a uniform speed by an electric motor.

Experiments were made by stimulation of the following localities: (1) First and third fingers of right hand; (2) first and second fingers of right hand; (3) first fingers of both hands, close together, but just escaping contact; (4) first fingers of both hands, fifteen inches apart; (5) first fingers of both hands, thirty inches apart; (6) two positions on middle finger of right hand, on same transverse line.

A standard of two seconds was adopted as being easier for the subject and more expeditious, and since qualitative and not quant.i.tative results were desired, only one _CT_ was used in each case, thus permitting the investigation to cover in a number of weeks ground which would otherwise have required a much longer period. The subjects were, however, only informed that the objective variations were very small, and not that they were in most cases zero. Tests of the two types complementary to each other (_e.g._, _RRL_ and _RRL_) were in each case taken alternately in groups of five, as in previous work.

TABLE VI.

_ST_= 2.0 SECS.

_Subject W._

(1) CT=2.0 (3) CT=2.2 (5) CT=2.0 113 133 RRL RLL RRL RLL S 3 3 9 20 5 21 E 18 19 25 16 18 14 L 24 28 16 14 17 15

_Subject P._

(1) CT=2.0 (3)CT={1.6 (5) CT={1.6 {2.4 {2.4 113 133 RRL(1.6) RLL(2.4) RRL(1.6) RLL(2.4) S 2 16 12 16 15 10 E 38 32 32 21 26 19 L 10 2 6 15 14 21

_Subject B._

(1) CT=2.0 (2) CT=2.0 (6) CT=2.0 113 133 112 122 aab abb S 4 21 5 20 7 6 E 23 19 22 24 40 38 L 23 10 23 6 3 6

_Subject Hy._

(1) CT=2.0 (2) CT=2.4 (1a) CT=2.0 113 133 112 122 113 133 S 12 46 17 40 17 31 E 9 2 14 8 9 7 L 29 2 19 2 14 2

In the series designated as (1a) the conditions were the same as in (1), except that the subject abstracted as much as possible from the tactual nature of the stimulations and the position of the fingers. This was undertaken upon the suggestion of the subject that it would be possible to perform the abstraction, and was not repeated on any other subject.

The results are given in Table VI., where the numerals in the headings indicate the localities and changes of stimulation, in accordance with the preceding scheme, and _'S'_, _'E'_ and _'L'_ designate the number of judgments of _shorter_, _equal_ and _longer_ respectively.

It will be observed that in several cases a _CT_ was introduced in one cla.s.s which was different from the _CT_ used in the other cla.s.ses with the same subject. This was not entirely arbitrary. It was found with subject _W_, for example, that the use of _CT_ = 2.0 in (3) produced judgments of shorter almost entirely in both types. Therefore a _CT_ was found, by trial, which produced a diversity of judgments. The comparison of the different cla.s.ses is not so obvious under these conditions as it otherwise would be, but is still possible.

The comparison gives results which at first appear quite irregular.

These are shown in Table VII. below, where the headings (1)--(3), etc., indicate the cla.s.ses compared, and in the lines beneath them '+' indicates that the interval under consideration is estimated as relatively greater (more overestimated or less underestimated) in the second of the two cla.s.ses than in the first,--indicating the opposite effect. Results for the first interval are given in the line denoted 'first,' and for the second interval in the line denoted 'second.'

Thus, the plus sign under (1)--(3) in the first line for subject _P_ indicates that the variation _RLL_ caused the first interval to be overestimated to a greater extent than did the variation 133.

TABLE VII.

SUBJECT _P._ SUBJECT _W._ SUBJECT _B._ SUBJECT _Hy._ (1)--(3) (3)--(4) (1)--(3) (3)--(5) (2)--(1) (6)--(2) (2)--(1) First. + - + - - + - Sec. + + - + + + +

The comparisons of (6) and (2), and (1) and (3) confirm the provisional deduction from Table IV., that the introduction of a _local change_ in an interval _lengthens_ it subjectively, but the comparisons of (3) and (5), (3) and (4), and (2) and (1) show apparently that while the _amount_ of the local change influences the lengthening of the interval, it does not vary directly with this latter in all cases, but inversely in the first interval and directly in the second. This is in itself sufficient to demonstrate that the chief factors of the influence of locality-change upon the time interval are connected with the spatial localization of the areas stimulated, but a further consideration strengthens the conclusion and disposes of the apparent anomaly. It will be noticed that in general the decrease in the comparative length of the first interval produced by increasing the spatial change is less than the increase in the comparative length of the second interval produced by a corresponding change. In other words, the disparity between the results for the two types of test is greater, the greater the spatial distance introduced.

The results seem to point to the existence of two distinct factors in the so-called 'constant error' in these cases: first, what we may call the _bare constant error_, or simply the constant error, which appears when the conditions of stimulation are objectively the same as regards both intervals, and which we must suppose to be present in all other cases; and second, the particular lengthening effect which a change in locality produces upon the interval in which it occurs. These two factors may work in conjunction or in opposition, according to conditions. The bare constant error does not remain exactly the same at all times for any individual and is probably less regular in tactual time than in auditory or in optical time, according to the irregularity actually found and for reasons which will be a.s.signed later.

3. The third group of experiments introduced the factor of variation in intensity of stimulation. By the introduction of a loop in the circuit, containing a rheostat, two strengths of current and consequently of stimulus intensity were obtained, either of which could be employed as desired. One intensity, designated as _W_, was just strong enough to be perceived distinctly. The other intensity, designated as _S_, was somewhat stronger than the intensity used in the preceding work.

In the first instance, sixty series were taken from Subject _B_, with the conditions the same as in the experiments of Group 1, except that two types of series were taken; the first two stimulations being strong and the third one weak in the first type (_SSW_), and the order being reversed in the second type (_WSS_). The results gave values of _ET_ of 5.27 secs. for _SSW_ and 5.9 secs. for _WSS_.

In order to get comprehensive qualitative results as rapidly as possible, a three-second standard was adopted in the succeeding work and only one compared interval, also three seconds, was given, although the subject was ignorant of that fact--the method being thus similar to that adopted later for the final experiments of Group 2, described above. Six types of tests were given, the order of stimulation in the different types being _SSS, WWW, SSW, WWS, SWW_ and _WSS_, the subject always knowing which order to expect. For each of the six types one hundred tests were made on one subject and one hundred and five on another, in sets of five tests of each type, the sets being taken in varied order, so that possible contrast effect should be avoided. The results were practically the same, however, in whatever order the sets were taken, no contrast effect being discernible.

The total number of judgments of _CT_, longer, equal, and shorter, is given in Table VIII. The experiments on each subject consumed a number of experiment hours, scattered through several weeks, but the relative proportions of judgments on different days was in both cases similar to the total proportions.

TABLE VIII.