Response pooling between chromatic and luminance systems.

Two experiments were designed to examine interactions of the responses of the chromatic and luminance systems to suprathreshold stimuli. We measured simple reaction times (RT) to eight photometrically matched (1 cd/m2) wavelengths between 448 and 658 nm. These chromatic test stimuli were incrementally presented on either a spatially coextensive 1.2 or a larger 2 degrees steady white background. Sectors of the outer annulus region (between 1.2 and 2 degrees) could be removed to allow systematic variation of the extent of the spatial contour between test and background fields. When the white background was spatially coincident with the test field, RTs showed trichromatic saturation-like wavelength dependence, with a maximum RT at 572 nm. As white sectors were added to the annulus (introducing spatial transients between test and background fields), RTs became less and less wavelength-dependent, and were nearly wavelength-independent when a full annulus was used. The data were analysed in terms of a two-system RT model for processing chromaticity and luminance.