Illusory contours induced by isoluminant chromatic patterns.

An illusory-contour was induced by abutting colored gratings embedded in the white field under isoluminance condition. The present study specified the stimulus conditions that invoked the just-perceptible illusory contours for the isoluminant chromatic patterns. The results showed that the purity difference between the colored lines and the white field required for the illusory-contour perception gave a function closely resembling in shape the function obtained for saturation discrimination. Increasing the width of lines reduced threshold for the perception of illusory contours, while the line spacing had no significant effect. The dependence of the illusory-contour perception upon saturation could be accounted for by considering the extraction of the edge and colour information by means of the opponent-color processes observed for the cells in the retina and LGN. On the other hand, the effects of the spatial parameters met the response properties observed for the cells in the visual cortex. It is suggested that the perception of illusory contour may result from hierarchical organization from the retina to cortex in the visual system.