1954 年 25 巻 3 号 p. 195-206
In a previous report (this Journal, 1953, 23, 239-245), the author investigated the temporal factors of figural after-effects. The present study is concerned with the spatial factors of figural after-effects. The experimental variables were the diameter of the I-circle, the diameter of the T-circle, the distance between the centers of the I- and T-circles, and the width of the outline of the I-circle. The effects of the“differential experiment” method were also examined.
Experimental conditions and procedure-The black outline circles on the sheets of white paper were used for the I- and T-figures (See Fig. 1). Immediately after each 15 second inspection of the I-figure, one of the T-sheets each of which consisted of a T-circle of the constant size and a comparison-circle of varied size was shown. These figures were presented at the distance of 3 meters from the subject. The brightness value of the the object surface was 2 millilamberts. The amount of apparent growth or shrinkage (over-estimation or under-estimation) of the size of the T-circle (as measured by its diameter) was determined by the method of complete series.
The effect of diameter of the I-circle - In the first place, the author investigated the effect of diameter of the I-circle. The diameter of the I-circle was varied from 0.5cm to 12cm, while the diameter of the T-circle was fixed to 2cm or 4cm. The results show that the T-circle grows when it is larger than the I-circle and it shrinks when it is same as or smaller than the I-circle. The amount of shrinkage, in general, is greater than the amount of growth. The maximal growth occurs when the diameter ratio of the I-circle to the T-circle is 1:2, and the maximal shrinkage is obtained when this ratio is 2:1. These rules hold irrespectively of the size of the T-circle (Table 1, 2 ; Fig. 2, 3, 4). These facts suggest that the relative size of the I-circle with respect to the T-circle is a fundamental parameter of figural after-effects.
The effect of diameter of the T-circle - The effect of diameter of the T-circles was studied next. The diameter of the T-circle was varied from 2cm to 8cm, and correspondingly the diameter of the I-circle was varied from 3 cm to 12cm in such a way that its relative size was kept always 1.5 times the size of the T-circle. The results indicate that, as the diameter of the T-circle increases, the amount of after -effect increases proportionally, While its relative amount was from 9 to 10 percent of the size of T-circle. (Table 3, Fig. 5). We may conclude from these results that the relative amount of after-effect is the essential measure of figural after-effects, and that it is determined directly as a function of the relative size of the I-circle. This conclusion is in line with that of the Ogasawara's study of the illusion of the concentric circles (this Journal, 1952, 22, 224-234)
Retinal size vs. apparent size - Which is the determining parameter of the after-effect, the retinal size or the apparent size of the I-cirele? To answer this question, the author performed some experiments in which the I-figures were presented at the distance of 1.5 meters from the subject, and the T-figures at 3 meters. The results show that the growth-effect is caused only by the I-circle smaller than the T-circle in visual angle (Table 4 ; Fig. 6, 7). This fact suggests that the retinal size determined figural after-effects. However, the results as to the points of the maximal after-effects are not consistent. Some support the retinal size (Fig. 6), and the others the apparent size (Table 4, Fig. 7).
The effect of distance between the centers of I- and T-circles - The after-effects were measured when the I-circles were placed eccentrically with the T-circles (Fig. 8). The diameter of the I-circle was fixed to 6cm and that of T-circle to 4cm, and the distance between their centers was varied from 0cm to 5cm.