THE INFLUENCE OF ILLUSORY CONTOURS ON THE DETECTION OF LUMINANCE INCREMENTS AND DECREMENTS

The experiment of Dresp and Bonnet [(1991) Vision Research, 31, 1813-1 817] was replicated and extended to include measurements of both lumin ance increment and decrement detection across high luminance illusory contours. The results reveal that illusory contours can influence the detectability of both luminance decrements and increments and, in addi tion, that the magnitude and even the direction of the effect which il lusory contours produce on visual thresholds may vary considerably acr oss individual observers. Finally, in contrast to the monophasic patte rn of threshold variation across low luminance illusory contours, the pattern across high luminance contours is oscillatory.