The dual role of chromatic backgrounds in color perception

Abstract

This investigation explores the color appearance changes resulting from a continuously presented adapting field. In every experiment, an incremental mixture of red and green monochromatic lights was superimposed on top of a steady red background field. On each experimental trial the intensities of the red background and the red increment were fixed: the subject adjusted the intensity of the green light so that the incremental mixture appeared a "pure" (neither slightly reddish nor greenish) yellow. In one experiment, the increment was a steadily viewed thin annulus seen on a larger background: in another experiment the increment was identical to the background in size and retinal location but was presented as a brief ( 150 msec) flash: in the final experiment the increment was a briefly flashed thin annulus seen on a larger background.For any fixed, relatively dim background level the intensities of the red and green increments were approximately in constant ratio over a nearly 2 log unit range of test intensities. However, with more intense adapting fields the green light to red light incremental intensity ratio decreased as the test intensity was increased, with the ratio asymptoting at high test levels to an adaptation-intensity dependent value.The empirical observations reject both von Kries' Coefficient Law and the notion that only spatial (and or temporal) transients contribute to color signals. The results are consistent with a "two-process" theory where the adapting field is assumed both to contribute directly to the chromatic signal and simultaneously to alter the amplitudes (but not shapes) of the spectral sensitivity functions associated with the three receptor-types of color vision.