This is a continuation of the previous study (The Japanese Journal of Psychology, 1967, Vol. 38) on the figure-effect in the third dimension of visual space. The purpose of this study is to examine the effect of a light stimulus figure upon the various positions in the depth direction of space.
The figure-effect was measured by the light threshold method: a small light point (the test light) was presented in front of the stimulus figure, and the light threshold value
t of the point was measured (Fig. 1, 5 and 8). Other experimental procedures were virtually the same as those in the previous report.
In view of the results of the previous study, three experiments were designed to clarify the following points.
1. In experiment I, whether the gradual elevation of the threshold with increase of the depth distance from the stimulus figure can be seen in the different stimulus figure from that of previous study.
2. In experiment II, how the threshold values would change depending on the distance from the stimulus figure in frontal planes parallel to the plane containing the figure.
The light stimuli used in experiment I and II were line figures and the test light was presented at positions lateral-frontal to the figure.
3. In experiment III, what aspects of threshold values can be seen in the frontal space within a contour figure. Large and small figures of circular contour were used as light stimuli. The threshold value was measured on the front space at each of the three positions p
0, p
1, p
2 inside a circle as shown in Fig. 8.
The results of these experiments were as follows:
1. The gradual elevation of the threshold value
t in proportion to the increase of the depth distance from the stimulus figure was not observed in the lateral-frontal space of the line stimulus (Fig. 2, 3 and 4).
2. The threshold values in the frontal parallel planes displayed a falling logarismic curve as the distance from the figure was increased (Fig. 6, 7).
3. In the central axis (p
0) of the circle, the threshold value elevated slightly as shown in Fig. 9, 10, but at places near the contour (p
1, p
2), an elevation was seen clearly as shown in Fig. 11, 12.
From these results, it was concluded that the figure-effects in the depth, i.e., in the third dimension, of visual space were present not only in the light stimulus of two parallel lines used in the previous study, but also in other kinds of light stimulus, and the appearance of the elevation of the threshold value depended on stimulus configuration. The other finding was that the figure-effect presented a different feature in the depth dimension from that in the frontal parallel plane of visual space. But at present, it cannot easily be concluded that the figure-effect in the depth differs from that in the frontal parallel plane in terms of its function. It is supposed that the examination of the mechanism of the two effects is needed in the future.
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