ADAPTIVE ORTHOGONALIZATION OF OPPONENT-COLOR SIGNALS

This paper concerns the processing of the outputs of the two opponent- color mechanisms in the human visual system. We present experimental e vidence that opponent-color signals interact after joint modulation ev en though they are essentially independent under neutral steady adapta tion and after exclusive modulation of each mechanism. In addition, pr olonged modulation linearizes the response function of each mechanism. The changes in interaction serve to orthogonalize opponent signals wi th respect to the adapting modulation, and the changes in response fun ctions serve to equalize the relative frequencies of different levels of response to the adapting modulation. Adaptive orthogonalization red uces sensitivity to the adapting color direction, improves sensitivity to the orthogonal direction, and predicts shifts in color appearance. Response equalization enhances effective contrast and explains the di fference between the effects of adaptation to uniform versus temporall y or spatially modulated stimuli.