Stochastic independence of color-vision mechanisms confirmed by a subthreshold summation paradigm

Integration of differing chromaticities in early and midlevel spatial vision

Using Glass patterns composed of isoluminant dots we have investigated the segregation and integration of chromatic information by the visual system. By measuring pattern detection when the chromaticities of the two elements forming a dot pair are varied (intradipole variation), we characterize integration at an early level of spatial processing. By measuring pattern detection for dot pairs where the within-pair chromaticity is the same but the among-pair chromaticities are varied (interdipole variation) we characterize integration and segregation for a more global, midlevel, spatial processing mechanism. Using isoluminant patterns in which all dots have the same chromaticity, we find that (i) detection thresholds are similar to those for luminance-defined dots, and (ii) an equivalent-contrast metric approximately equates thresholds for various chromaticities, including those along both the cardinal and the intermediate axes of an opponent-color space. When intradipole chromaticity is varied we observe that (i) the ability of visual mechanisms to extract oriented dot pairs decreases with increasing chromaticity differences, and (ii) average bandwidths are similar for cardinal and intermediate directions. For pattern detection with interdipole chromatic variation the visual system does not segregate noise dot pairs from correlated dot pairs on the basis of chromatic differences alone, and appears to integrate oriented dot pairs of differing chromaticities in forming a global percept, even for large color differences. Isoluminant Glass patterns with translational and concentric correlations give similar results. The results are compared with those obtained for contrast variation in luminance-defined Glass Patterns and are discussed in terms of current multistage models of color processing by the visual system.