The purpose of this investigation was to determine by the method of constant stimuli the effect (1) of instructions, and (2) of time intervals between the standard and the comparison stimuli, upon the distribution of judgments when equal weights are used for successive comparison.
Experiment I
The general procedure of this experiment as well as of the one following (Experiment II) was similar to that of Arons and Irwin. Ten cylindrical hardrubber weights of 100 g. each, arranged in pairs on a revolving table, were used as stimuli. The rhythm of lifting was controlled by means of a metronome set at 92 per minute.
The experiment consisted of three series. In Series I, the observers were instructed simply to judge the second weight of each pair with respect to the first, using the categories, lighter, equal and heavier. In Series II, they were further instructed that the difference between the standard and the comparison stimuli was much increased, while in Series III, they were told that all the stimuli were of equal weight.
Results:
1. Of the six observers who took part in the experiment, five showed a tendency to over-estimate, and one a tendency to under-estimate, the second of the Pair throuvhotit the three series.
2. The observers who had previous training in lifted weight experiments gave in the initial part of the experiment a greater number of differential judgments than the untrained observers, but this difference disappeared with the progress of the experiment.
3. There was also a tendency for the majority of observers not to give the same category of judgment twice in succession. Thus, the judgment of “lighter” was usually followed by the judgment of “heavier,” and
vice versa. Only one observer gave judgments of equality, frequently in succession.
4. The effect of instruction was very conspicuous. The number of differential judgments obtained in Series II far exceeded that in Series I and III, the latter of which yielded more equality judgments than the other categories.
Experiment II
This experiment was divided into three parts. In Part I the time interval between the first and the second stimuli was 1.30 sec., in Part II, 1.95 sec. and in Part III, 3.25 sec.
Results:
1. Only four out of twenty-nine observers who participated in Part I underestimated the second stimulus, while the remaining twenty-five over-estimated it.
2. Although there were great individual differences, on the whole the number of “heavier” judgments as compared with the number of “equal” as well as of “lighter” judgments tended to increase with the increase in the length of time intervals between the first and the second stimuli.
3. There were eases, however, where observers who made negative time errors (or positive time errors) with shorter time intervals committed positive time errors (or negative time errors) with longer time intervals.
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