Poster Session: Achromatic biases in noise images.

Abstract

In a previous study, Winkler et al. (Current Bio 2015) examined the effects of luminance on the perceived color categories selected for uniform square patches. When the square was equiluminant with the background, the patch appeared colored as soon as it was detected, while for increments or decrements, the range of chromaticities that were classified as achromatic was expanded and more strongly along bluish axes. Here we extended these results to examine the color appearance of spatially varying patterns, which contain a wide range of luminance levels. The images were 1/f luminance noise and were briefly alternated with a gray background with the same mean luminance. The noise was shown on each trial with a uniform chromaticity, which was varied across trials over a grid of values spanning the LvsM and SvsLM cone-opponent axes. Observers categorized each noise image as gray or one of the four unique (RGBY) or binary (RB,BG,GY,YR) hues. The perceived achromatic gamut for the noise again tended to vary along bluish-yellowish directions, but was markedly broader compared to the uniform patches. The broadening of the gray category may partly reflect attributions of some of the color to the illuminant, a tendency which may be stronger in the spatially variegated patterns.