同心円図形錯視に関する条件吟味

Abstract

The “assimilation-contrast” phenomenon accompanying the illusion of concentric circles may briefly be described as follows: With the increase in size of the outer circle, the perceived size of inner circle increases gradually to a certain maximum, beyond which it decreases and even gives negative illusion.The fact that the maximum illusion is given when the ratio of the outer circle to the inner circle is 3/2 is what we are concerned with in this study. We consider that this ratio should be given a functional significance in theoretical considerations of the illusion.We have carried out experiments with a series of modified figures: various part or parts of the original double circles pattern (Stimulus Figures A-I), those accompanied with additional lines (J, M, N), two pairs of parallel straight lines of equal length (K, L, O), and those with different lengths (P).Results can be itemized as follows:1) Figures with inner and outer arcs (A-E) have phenomenal characteristics distinct from those of the original pattern.2) Such a distinction also holds in the case of figures having inner arcs and outer circles (F).3) Dimensional differences of the size and distance in the figures may be of little significance in consideration of functional relations. It follows that two (physical) circles are not always necessary to characterize the illusion of concentric circles (I).4) In the case of figures having inner circles and outer arcs, the arcs are of such significance as. to play the role of circles.5) In perceiving the figures with additional lines (J), the illusion is the maxima when the ratio reaches the value, which is given in the case of full circles.6) The difference between pairs of arcs and pairs of lines is not merely of geometrical nature but supposedly of functional or configurational one.7) In the perception of figures having pairs of straight lines with distances corresponding to those in original circles, the ratio for the maximum illusion changes gradually from 3.5/2 through 3/2 to 2.5/2 as the length of lines increases. This fact means that the distance is not the exclusive factor for determining the illusion and also that the length has some special functional meaning in the case of part figures such as arcs and lines.These results, as a whole, present us the problem of how to consider illusion in terms of configurational factors. However, in explaning functionally the above mentioned phenomena, the concept of Figur itself can not always be a positive factor, for it could not be concluded from above experiments that the space between inner lines in P figure is easier to be perceived as Zusammengefasste than the space between inner arcs in J figure.