1990 年 8 巻 2 号 p. 57-59
The number of filling lines and their spacing in the Oppel-Kundt figure were varied so that various modes of grouping could be generated by contour-proximity. The magnitude of illusion, that is, the overestimation of a filled extent relative to an un filled extent, was measured by the method of graded series. The results demonstrated that the illusion was strongly influenced by the number of groups of lines rather than simply by the number of lines themselves. It was also found that inhomogeneous spacing which caused ambiguous grouping had only little influence on the illusion. Our previous findings suggested that the retinal separation between adjacent contours was not important for determining the illusion. The present results support this conclusion by implying that the illusion is likely to originate at higher functional levels generating size constancy, figural segregation and the like.