Set and Subjective Contour

The perception of contours usually results from the presence of sharp local gradients in luminance or wavelength. This volume is, as you know, oriented toward an understanding of the set of stimulus arrays in which lines or edges appear to the observer despite the absence of such physical stimulus variations. These illusory demarcations have been called subjective contours, to distinguish them from objective contours, which are percepts associated with measurable physical modulations in the stimulus.