McCollough Effect

CORE DEFINITION

First reported by Celeste McCollough, the McCollough effect is a contingent color aftereffect: after alternating exposure to red-and-black horizontal and green-and-black vertical gratings, a neutral black-and-white grid appears tinted in orientation-specific complementary colors. Unlike ordinary retinal afterimages that fade within seconds, it is a learned adaptation that persists for hours, days, or even months and survives changes in gaze, distance, and eye position. Because it depends on pattern orientation rather than simple photoreceptor fatigue, researchers treat it as evidence that adaptation occurs in cortical visual circuits.