Contour-Contingent Color Aftereffects: Retinal Area Specificity

Abstract

Once an area of the retina was adapted to colored gratings, the aftereffect colors were judged to be most saturated when the test grating approximately coincided with the adapted area, less so as the overlap was reduced. The colors disappeared when the grating was moved just off the area and reappeared when the grating was moved very near it. In brief, the McCollough effect is highly area specific. McCollough demonstrated a color aftereffect specific to the orientation of gratings of light and dark bars (1965). The aftereffect was built up by alternating a vertical grating of black stripes on one color with a horizontal grating on another color. Negative color aftereffects were seen on test gratings of black and white stripes, in a retinal orientation like that of the adaptation gratings. The question in the present paper is whether the aftereffect is area specific. That is, does adapting a small area of the retina to colored gratings produce a color aftereffect that can be elicited by a small test grating placed almost anywhere on the retina, or must the grating fall on the originally exposed area? A nonlocalized aftereffect might reflect a learning process (an association between edge orientation and color) or, alternatively, an adaptation process involving cells with very large receptive fields. A localized aftereffect, on the other hand, might suggest that the effect depends on cells with small receptive fields -and would be consistent with the findings on many other sensory aftereffects. Two classes of area-specific (localized) aftereffects may be distinguished. One class requires that the adaptation, or inducing, stimulus remain quite fixed on the retina. The afterimage is the typical case: a sharp afterimage is seen only when the inducing stimulus is not smeared