Evidence of complementary afterimages in the pigeon.

Key pecking of pigeons was reinforced on a variable-interval schedule when ambient illumination came from a green light, but not when it came from a red, yellow, or white light. The different hues were randomly presented for periods of 30 sec each, with the restriction that white never followed red. After discriminative control was established, the pigeons were tested with the same procedure used during training, except that white sometimes followed red. Significantly more responses were made during white-following-red than during white following either green or yellow. These findings indicate that, in changing from red to white, complementary afterimages can be induced in pigeons for a brief period of time. By providing behavioral evidence for afterimages in the pigeon, this technique may be useful to research in comparative neurophysiology, animal discrimination learning, and theories of color vision.