Mirror-image symmetry and search asymmetry: a comparison of their effects on visual search and a possible unifying explanation.

Visual search may be affected by mirror-image symmetry between target and non-targets and also by switching the roles of target and non-target. Do different attention mechanisms underlie these two phenomena? Can a unifying explanation account for both? We conducted two experiments to decompose processing into component parts, and compared results to competing models' predictions. Mirror-image search was unimpaired after target discrimination had been balanced across search conditions-results were consistent with an unlimited-capacity, decision noise model. Search asymmetry affected higher-level processing, however, resulting in capacity limitations that necessitated serial processing. A unifying explanation can account for these two seemingly unrelated phenomena.

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.

Perceptual processing and search efficiency of young and older adults in a simple-feature search task: a staircase approach.

The reasons that visual search may sometimes be difficult, especially for older adults, remain important research issues. This study investigated (a) whether age-related differences can occur in simple-feature search, (b) if so, whether slowing adequately accounts for these differences, (c) whether other perceptual/cognitive factors are involved, and (d) the role of perceptual strategies. The authors tested 15 young adults (ages 18-30) and 15 older adults (ages 65-78). The target was a red disc presented among red diamonds in an array of 16 or 36 items. The forced-choice staircase procedure emphasized perceptual processing while deemphasizing decision-making and psychomotor processing. Although perceptual slowing may affect older adults' search performance, the perceptual slowing model is not simple, and other perceptual/cognitive factors, such as spatial resolution and distractibility, also are implicated. Moreover, perceptual strategies involving perceptual grouping or suppression of distractors play a key role in explaining why search efficiency is actually better for the larger set size.