The multiple determination of illusory contours: 1. A review.

Four theories of illusory-contour perception are reviewed--brightness contrast (simultaneous contrast, assimilation, and dissimilation), depth/completion, partial activation of neural feature analyzers, and the diffuse-sharp dichotomy. It is concluded that the processes and mechanisms involved in illusory-contour perception most likely depend upon the stimulus elements used in the illusory-contour display.