Distractor heterogeneity, attention, and color in visual search

Experiments were designed to investigate the effects of set size and variation in the chromaticity of distractor stimuli on thresholds for detecting a target stimulus that differed from distractors only in chromaticity. Distractor chromaticities were selected from a line in the isoluminant color plane and targets were selected from lines approximately orthogonal to the distractor line. With uniform distractors thresholds increased with set size as predicted by a signal detection model. When targets and distractors were selected from lines parallel to the Cardinal directions in color space, thresholds were lower with variable distractors than with uniform distractors and variations in the location of the target along the distractor line had no effect on threshold. Results with diagonally oriented distractor lines were similar. Results suggest that many pairs of orthogonal directions in the isoluminant color plane represent independent color coding mechanisms that mediate search. Results also show that information in independent color coding mechanisms tuned to orthogonal directions in the isoluminant plane can be combined to facilitate detection of the target.