Chromaticity and luminance as coding dimensions in visual search

Visual search times were measured as a function of chromaticity and luminance differences between a target and distractor stimuli. Results showed that mean search time increased linearly with the number of distractors if the luminance difference between target and distractors was small but was roughly constant if the luminance difference was large. Similar results were previously found for chromaticity differences. With the number of distractor stimuli held constant, the mean search time decreased with increases in the difference between target and distractors, up to some critical difference. Further increases in target-distractor difference had little effect. Results were similar for targets defined by luminance and chromaticity. There was some advantage to combining luminance differences with chromaticity differences when the target was dimmer than the distractors. Generally there was no advantage for combining a chromaticity difference with a luminance difference when the target was brighter than the distractors.