THE EFFECT OF HUE AND BRIGHTNESS ON THE SIZE-ILLUSION OF CONCENTRIC CIRCLES

Abstract

In only a few of the many studies made on geometrical, optical illusions has the effect of hue been investigated. Benussi was the first to do so and he found in his study of the Z6llner illusion that hue had little effect on the illusion and that brightness had a differential effect when the figure was drawn in two colors which differed in brightness. When the vertical lines were of one color and the transverse lines of another, the illusion increased as the brightness-difference between the transverse lines and the background increased, and decreased as the brightness-differ. ence between the vertical lines and the background increased.1 If these results are corroborated by other experimenters and with other illusions, they will give us an explanation of the illusions of this type. In particular, they will decide the issue between the physiological theory of neural induction and the Gestalt theory that similarity is a decisive factor in phonemonal grouping. The size-illusion of concentric circles (see Fig. 1), described by Delboeuf in 1893,2 was selected for investigation because it has been used in recent years in numerous studies-particularly in Japan.3 The inner circle of B in Fig. 1 appears larger than Circle A which is physically the same in size; and the outer circle of B appears small than Circle C which again is physically the same in size.