Perceived Strength of Edge, Depth and Brightness of the Kanizsa Illusion as a Function of the Color Contrast between Figures and Background

The Kanizsa illusion1 (Kanizsa, 1955), one of typical subtypes of the illusory contour, is a particularly intriguing phenomenon for considering the dynamics of our visual object perception (Fig.1). It has been stimulating interests of many researchers in this field for the last several decades. As Kanizsa (1955) originally discussed, this illusion is characterized by three distinct phenomenal properties; illusory edge, apparent depth and apparent brightness. This multi-dimensional property has been undoubtedly the most fascinating feature of the Kanizsa illusion. At the same time, it has been the cause of a divergent discussion on the nature of this illusion, giving rise to various theories that try to explain its generating mechanism. Roughly, these theories fall into two categories: One category emphasizes visual organizational processing such as a figure-ground segmentation (e.g., Gregory, 1972; Bradley & Dumais, 1975; Rock & Anson, 1979); the other regards it as a special case of the simultaneous brightness contrast (e.g., Brigner & Gallagher, 1974; Frisby & Clatworthy, 1975). Then, such categorical distinctions invite the question: Is the Kanizsa illusion essentially a figural illusion or a brightness illusion?