Color appearance of spatial pattern: the role of increments and decrements

In a number of recent adaptational studies evidence for a different processing of incremental and decremental cone signals has been reported. The present study examined whether such asymmetries occur in spatial pattern as well. Subjects set color matches between a uniform, 2 degrees matching box and bars within squarewave patterns. The squarewaves varied in spatial frequency, color direction, and contrast. For all three cone signals the asymmetric matches showed clear evidence for increment-decrement asymmetries: Although both incremental and decremental matches scaled roughly linearly with pattern contrast, in general, the scalings for the two types of color signals differed. This difference in scaling increased with spatial frequency, thus leading to an increase in the size of the increment-decrement asymmetry with spatial frequency. The matches were well described by means of two-stage models, consisting of a color transformation in the first stage and a pattern-dependent scaling in the second stage. Analyses based on these pattern-color separable models suggest that the asymmetries are mediated mainly through a white-black mechanism and much less, if at all, through a red-green and yellow-blue mechanism.