明るさ継時比較における先行挿入刺激の抑制効果について (II)

抄録

From the results in our first report, it is presumed that an extra-stimulus (e), which is presented preceding the two comparative stimuli (N and V), has two different inhibitory effects upon the successive comparison of brightness, in addition to the so-called assimilation-contrast effect. In this second report, further analyses were made to test the existence of these two effects of e more in detail. (Regarding procedure and condions, see the first report).
The main results were as follows:
1) When e (physically equivalent to N in brightness) was presented immediately following N and the inhibitory after-effect of e upon the excitation of N was eliminated, the tendency for the negative time-error disappeared at shorter time-intervals between N and V. And, in reverse, the time-error shifted noticeably toward a positive direction, i.e., V was underestimated. But when the time-interval was made longer, underestimation of N occurred in the same way as when e was presented immediately preceding N, though its magnitude was relatively small (Exp. V, see Fig. 3).
2) According to obserbers' introsections, e was seen a little darker than N there, especially at shorter intervals. But the comparative judgement between N and V was not so difficult at shorter intervals, even if e was interpolated between them. On the other hand, the fusing proccess had advanced between images of N and e at longer intervals. And he was forced to take a strong analytical attitude to separate images of N and e, to compare N with V directly.
3) These tendencies mentioned above were still noticed, when the brightness of e was made phenomenally equivalent to that of N, to eliminate more perfectly the assimilation effect occurrable between them (Exp. VI, see Fig. 4).
4) When two light-spots, placed by side in a horizontal line, were presented twice and a spatial grouping was produced in place of a temporal grouping between the two preceding stimuli, the tendency for the negative time-error disappeared again and the error shifted slightly toward a positive direction at shorter time-intervals. However, at longer time-intervals the error shifted toward a negative direction. Moreover, the image of the first stimulus-figure had become vague rather rapidly in spite of impressiveness on its appearance (Exp. III, see Fig. 1).
5) The above-mentioned tendencies were still noticed when the brightness of the stimulus-figure in the experimental series was made phenomenally equivalent to that in the control series (where a light-spot was presented twice in succession) to eliminate the central tendency occurrable between these two series (Exp. IV, see Fig. 2).
6) In addition, it was verified that the shift of time-error toward a negative direction seen at longer intervals by presenting e befor N, was never due to that e, in place of N, was compared with V, or that the level of N was assimilated to that of e (Exp. I, II).
From these results in the first report and the second one, it is concluded that the after-effect of e which inhibits the perceptual excitation of N certainly exists; but that underestimation of N seen at longer intervals throughout these experiments is rather commonly caused by the inhibitory effect, perhaps similiar to the Kohler-Restorff effect, which has progressed in the field of memory trace with the passage of time.