SIMULTANEOUS LUMINANCE CONTRAST WITH CHROMATIC COLORS

The variations in the color of a test field of constant luminance duri ng changes in the luminance of a contiguous inducing field was measure d psychophysically. The fields had the same hue (red, green, or blue). The colors induced in the test field could be specified by the streng th of a chromatic quality, and by the strength of the opponent qualiti es luminous/black. The psychophysical relationship between the two kin ds of perceptive variables and test and inducing luminance followed di stinctly different functions. The luminous/black variable varied linea rly with contrast over a large range, as previously found for achromat ic colors. The contrast gain of the luminous/black variable for the re d and green colors was the same as for achromatic colors. The gain for the blue colors was twice the gain for the other colors. The chromati c variables were primarily related to the local luminance. For a given test luminance they were maximal near zero contrast. They followed th e same function as the white component of achromatic colors. It is sug gested that the luminous/black variable is related to spectrally broad band cells with a strong center/surround antagonism, while the chromat ic variables and white are related to cells that lack a spectrally bro adband surround in their receptive field.