Abstract
The brightness or color appearance of a uniform gray region can be affected by a patterned surround. Munker-White effect and chromatic assimilation from patterned surround (e.g., Monnier & Shevell, 2004, Vision Research, 44, 849–56) are two examples. Here we compared the spatial configuration effect on these two chromatic context effects. We used an asymmetric matching task in which an observer was asked to match the appearance of a comparison patch along a predesignated color direction to a reference patch. The reference patch was either a ring superimposed on a bull eye surround (concentric square wave) for chromatic assimilation or a bar superimposed on a horizontal grating surround for Munker-White effect. The square wave surround (3.3 c/deg) was modulated along either isochromatic or one of the two isoluminant (M-L and S-cone modulation) directions. The contrast of surround for each color direction varied from near threshold to 4 times threshold of the surround modulated at that color direction. The comparison patch was either a ring or a bar on a uniform background. The uniform background was gray (CIE-xy =(0.33, 0.33)) with luminance 15 cd/m2. The reference and the comparison patches were also gray with luminance 20 cd/m2. The phase of the surround was either 0 or 180 deg relative to the stimuli center.
Compared with the uniform surround, the patterned surround shifted the perceived brightness or color of the reference patch. The amount of shift, when measured at the same color direction and contrast, was similar for both the bull eye and the grating surround. The amount of shift was a linear function of the surround contrast on log-log coordinates. Our result demonstrates a great similarity between the context effects produced by bull eye and grating surrounds. This implies that common mechanisms may underlie chromatic assimilation and Munker-White effect.
Supported by NSC 95-2413-H-002-001