Abstract
Achromatic patterns appear to be colored in some cases (e.g., Benham's disk, Benham, 1895; Skinner's illusion, Skinner, 1932). Recently we found that an achromatic grid pattern consisting of black borders and white tiles, thus a pattern like a negative-positive reversal of Hermann Grid illusion, induces illusory colorization ("Yagoto Illusion," awarded in the 8th Illusion Contest in Japan). We can observe that white squares surrounded by black borders were colored with various vague colors. Since Yagoto Illusion does not require rotation of a figure (Benham's disk) or inspection through a pinhole (Skinner's illusion), the colorization may be mediated by novel mechanisms of color vision. In the present study, we conducted two experiments to examine the characteristics of Yagoto Illusion. In these experiments, we presented two grid patterns side-by-side, one of which was a chromatic grid pattern (black borders and vaguely colored whitish tiles) as a sample and the other was an achromatic grid pattern (blackish borders and whitish tiles) as a test. Participants reported subjective strength of colorization of the test stimulus in comparison to the sample stimulus. In Experiment 1, we manipulated the size of tiles and the width of border, and found that the smaller tiles as well as the thinner borders resulted in the stronger illusory colorization. In Experiment 2, we manipulated the brightness of the achromatic tiles and borders. The results demonstrated that the darker borders led to the stronger colorization. Furthermore, contrarily to the previous reports of illusory colorization wherein the higher black-white contrast induced the stronger colorization (e.g., Packer & Williams, 2003), the stronger colorization was observed for the darker tiles (i.e., weaker contrast) in Yagoto Illusion. Thus, some types of illusory colorization would be more effective for the low contrast stimulus.
Meeting abstract presented at VSS 2017