Divided attention and visual search for simple versus complex features

Under what search conditions does attention affect perceptual processes, resulting in capacity limitations, rather than affecting noisy decision-making processes? Does parallel or serial processing cause the capacity limitations? To address these issues, we varied stimulus complexity, set size, and whether distractors were mirror images of the target. Both target detection and localization produced similar patterns of results. Capacity limitations only occurred for complex stimuli used in within-object conjunction searches. Parallel processing, rather than serial processing, probably caused these capacity limitations. Moreover, although mirror-image symmetry adversely affected early visual processing, it did not place additional demands on attention. (C) 2003 Elsevier Ltd. All rights reserved.