Abstract
It is well known that a chromatic surround influences the perceived color of a stimulus. But little is known quantitatively about how perceived hue depends on the hue of the surround. In cone-opponent color space, chromaticities can be expressed in terms of spherical coordinates, and hue corresponds to polar angle. We measured changes in hue angle induced by a chromatic background, using asymmetric matching of 2-degree chromatic patches across different isoluminant backgrounds. One background was neutral gray, the other had a chromaticity corresponding to one of eight hue angles with fixed cone contrast with respect to the gray background. Subjects adjusted the hue angle of the match patch on the neutral background to match it to the test patch on the chromatic background. When plotted as a function of hue angle difference between test patch and background, induced hue angle changes showed a maximum around 41 ± 4 degrees, with maximal induced changes of 24 ± 3 degrees. The curves for different backgrounds were qualitatively similar, but the amount of induced hue change depended on the hue angle of the background, indicating that induction is weaker along the S-cone axis than along the M-L axis. The dependence on angular difference between stimulus and background is qualitatively similar to the well-known tilt effect, where changes in perceived angle of oriented stimuli are induced by surrounding orientations. This suggests similar mechanisms of contextual processing for quite different visual features such as orientation and color.