Searching for variegated elements

Visual search performance was investigated for variegated elements that differed from each other either in space-average chromaticity (identical chromatic contrast; Experiment 1) or in the chromatic contrast of the variegation (identical space-average chromaticity; Experiment 2). Specifically, search performance was measured as a function of noise contrast articulated either along the same color direction or orthogonally from the signal (target) variegation. Target-to-distractor difference thresholds were estimated in a two-alternative forced-choice task with briefly presented displays. First, when the signal and noise variegations were articulated along the same direction in color space, elements that differed from each other in space-average chromaticity were less susceptible to noise compared to elements that differed in the contrast of the variegation. Second, orthogonal noise had little effect on threshold supporting independence between the mechanisms mediating these searches. Third, the effect of the noise was similar across the different chromatic directions as well as between observers (but still differed for the two types of variegation) when differences in sensitivity between the various color directions and between observers were taken into account. This last statement only holds because the color space was normalized for each participant.