Harvard Psychological Studies, Volume 2

by Unknown

Observer	Twelve Letters	Three Letters	One Letter.
A	+.012 sec.	-.029 sec.	-.010 sec.
G	-.022 sec.	+.004 sec.	-.004 sec.
Sh	+.028 sec.	-.079 sec.	-.057 sec.
St	-.050 sec.	-.036 sec.
Bo	+.029 sec.	-.015 sec.	-.022 sec.

The method of right and wrong cases was used in the next group of experiments, to secure the same conditions of making the judgment in each of the three cases used above. Selecting a letter near the middle of each series, I asked the observer, in each of these cases, just as in that of the single letter, to say whether the click was before, on, or after the letter. I worked out, in successive experiments by successive adjustments, from the position of apparent simultaneity of click and letter, in both directions, to a point where in 75% of the cases the click seemed to come before; and also to one where it seemed to come after, in 75% of the cases. So also I worked in both ways, by successive adjustments, from regions of clear discrimination of time-difference and direction, to points where the time-relation was uncertain or wrong in 75% of the trials. By averaging the just perceptible and the just not perceptible, in each case, the thresholds were obtained for "click first" and "click last." The time between these thresholds I call the "range." It is really a measure of James's "specious present" and of Stern's "Präsenzzeit." (An admirable presentation of similar results by Wilhelm Peters[114] has appeared since this work was done.) The best means of comparing these results, for our present purposes, and also of bringing them into relation with the complication-results already obtained, is to take the mean point between these thresholds, and state its position, in time, relative to the time of the visual stimulus (letter) just before or after which the click came. This mean point is called the "Threshold Mean" in the following tables. In Table IV, for example, "After Letter .026 sec." means that the mean point between the thresholds, "click first" and "click last" falls twenty-six sigmas after the time of the exposure of the letter. These results are readily comparable with those of Peters. By dividing the "range" by two, and adding the "threshold mean" to one half, and subtracting it from the other, one has the total interval between "click first" and "click last" and its place with reference to the time of the visual stimulus.

TABLE IV

Obs.		Twelve Letters		Three Letters		One Letter
A	Threshold Mean	After Letter	.026 sec.	On Letter		After Letter	.020 sec.
	Range		.093 sec.		.041 sec.		.062 sec.
G	Threshold Mean	Before Letter	.015 sec.	Before Letter	.020 sec.	After Letter	.062 sec.
	Range		.072 sec.		.083 sec.		.304 sec.
Sh	Threshold Mean	Before Letter	.003 sec.	After Letter	.027 sec.	After Letter	.003 sec.
	Range		.172 sec.		.111 sec.		.241 sec.

It must be distinctly understood that these "threshold means" are not displacements, and that the two cannot be compared as if they were statements of the same facts. These means indicate the centre of gravity of the "click first" "click last" interval with respect to the visual stimulus. Changes in this centre of gravity may reasonably be expected to approximate a variation inverse to that of the displacements of the auditory stimulus. For example, any change in the conditions which would tend to increase a negative displacement would tend also to put the centre of gravity of the "click first" "click last" interval after the visual stimulus, or, if it were already after, to increase its time after. So also the positive displacement and the position of the threshold mean before the visual stimulus may be considered similar indications. For a click given at the time of the threshold mean of a given observer, in connection with the same visual stimulus, would certainly be judged by that observer as simultaneous with the visual stimulus. If, then, this mean is before the visual stimulus, the sound will be displaced positively, i. e., coördinated with a visual stimulus coming later. If the mean is after the visual stimulus, the sound will be displaced negatively, i. e., coördinated with a visual stimulus coming earlier. The position of the mean of the thresholds indicates a tendency toward the displacement of the auditory impression in the opposite direction.

In Table III, three out of five observers, A, Sh, and Bo, show a change from a negative displacement in the series of three to a positive displacement in the series of twelve. If this were the effect of the series, the same should show in the series of three as compared with the single letter. Such a change is manifest in the results of Bo. It is, however, very slight. The others increase the negative displacement from the single letter to three letters. In Table IV, of the same three observers represented, Sh changes the threshold mean from after in the three-letter series to before in the twelve-letter series, and A changes from after in one letter to on in three letters. These changes correspond to changes from negative to positive displacements for increase of series and introduction of series. G shows the same change from one letter to three, in both tables. These changes, in 55% of the cases offered for comparison in the two tables, indicate a decrease of negative displacement and an introduction of positive displacement as the effect of the visual series. The visual element is made more focal in expectant attention as it is more isolated, and so the tendency toward negative displacement and increasing negative displacement as the serial character of the visual impressions is stripped off. But there are strong counteractive tendencies, which control the 45% of comparisons not mentioned above, where the increasing series shows increasing negative displacement.

In the series all the observers adopted the method which has been outlined above, that of letting the click pick out the letter, or letting the letter announce itself. One said "the letter hits the sound." After this sorting-out of the letter, they resorted to the system of tests and counter-tests, in succeeding trials, to correct the first impression. One can readily understand, then, that when they were taken off the series altogether, an entirely different kind of adjustment had to be made. G did not succeed in making this new adjustment very well, as is shown by his exceptionally large range under one letter. He could not get the two impressions to come together. In attending to either one, he could not get the other in relation to it. There was something in the visual series which enabled him to get the visual impression in line with the auditory, and when this was absent the same kind of work could not be done.

St had also a peculiar method, which was directly dependent upon the serial character of the visual stimuli and impressions. He allowed the series of clicks and the series of visual impressions to establish themselves as a complex rhythm. Each series was rhythmic independently. The two got connection by means of the click appearing as an "after-strike," as on the piano, to a member of the visual series. The letter "flashes out" for him as that of which the click was the "after-strike." The click was thus between two letters. But there was no amount of before or after about it. It was a general quality of the whole complex which was taken to mean such and such a position of click in the series. What he thus translated into temporal judgments, were qualitative aspects of the rhythmic experience, to which he usually attached no temporal meaning whatever. Learning how so to translate them into temporal terms was a definite process of training for him. Under these circumstances, he of course had an entirely new lesson to learn when the visual series was taken away. In fact, it might be, he would now find no visual impression to which the click could be an after-strike, and so he would be entirely without material to translate into temporal terms.

Under these circumstances it is not surprising to find G and St exceptions to the majority of the observers in this experiment. This makes more probable the effect of the series, inferred above for the other observers,—namely, series decreases negative displacement.