Abstract
The apparent color contrast of a texture is reduced when it is surrounded by another texture with higher color contrast. This phenomenon is called color contrast-contrast. It is thought to be similar to the achromatic contrast-contrast phenomenon, in which the contrast of the center texture appears to be reduced when surrounded by a texture with higher contrast. The contrast-contrast phenomenon has long been thought to result from interactions between visual channels that encode contrast energy, but has recently been shown that it is actually subserved by luminance polarity selective units. In this study, we investigated whether color contrast-contrast is also selective to the polarity of each axis in the DKL color space, a color space defined by the two cone-opposite color channels (L-M and S-(L+M)). The stimuli were texture patterns composed of colored and elongated blobs, and the hue of the background in the texture was always 180 degrees off the blob in DKL color space. The hue angle of the blob in the center texture in DKL space were either of 45, 135, 225, and 315 deg. The hue angle of the blob in the surround texture was varied in 10 levels. We measured the point of subjective equality for perceived color contrast (chroma) of the center texture by using a staircase method. The apparent color contrast of the center texture was substantially reduced only when it was surrounded by textures of similar hue in the DKL color space, but not when it was surrounded by textures 180 degrees off hue from the center. This result suggests that color contrast-contrast is hue polarity selective as well as the achromatic simultaneous contrast-contrast, which is selective to luminance polarity.