Complementary afterimages and the unequal adapting effects of steady and flickering light*

Prolonged exposure to flickering chromatic light of moderate intensity produce a much weaker complementary afterimage than that produced by exposure to stead light of the same average intesity. This difference in adapting effectiveness was investigated by determining theretinal illuminance of the study adapting field required to produce an afterimage equal to that produced by the flickering adapting field. In a variety of conditions, the greater effectiveness of the steady adapting field was confirmed; in several instances a steady field having an average retinal illuminance of only 0.05 times that of the flickering field gave rise to an equally saturated afterimage. The results are taken as evidence that complementary afterimages produced by extended moderate intensity exposure are primarily a consequence of neural adaption.