COLOR-SELECTIVE TILT AFTEREFFECTS WITH SUBJECTIVE CONTOURS

Displays yielding edges visible at sites where the visual stimulus was homogeneous (subjective contours) as well as with edges defined by spatial discontinuities in luminance (real contours) were used to induce the tilt aftereffect [in humans]. Under monoptic conditions, the aftereffect was larger when the inspection and test edges were shown in the same colored light than when they were shown in different colored lights. Under dichoptic conditions (display of inspection edges to 1 eye and test edges to the other eye), the aftereffect was reduced in size and it was no longer selective to the color relationship between the inspection and test stimuli. Similar results were obtained with subjective and real contours. Subjective contours have been treated as products of cognitive and inferential operations, whereas neural edge detectors have been implicated in the perception of real contours. The data suggest the need for caution in attributing the perception of real and subjective contours to fundamentally different processes.