Testing the effects of perceptual grouping on visual search in older adults.

Visual search is to find targets while ignoring distractors. Previous studies established that a target is more difficult to identify if aligned collinearly with other items, called the collinear search impairment. Since older adults have lower perceptual grouping ability than younger adults, benefits in visual search may occur for older adults for they may be less distracted by the collinear distractors. Three experiments were carried out to compare 45 younger and 45 older healthy adults. Participants were asked to identify a local target either in the column with items collinearly aligned to each other (the overlapping condition) or in the background (the non-overlapping condition), and the response difference between the two conditions is the collinear search impairment. Results showed that both groups showed reliable search impairment specific to collinear distractor regardless of grouping difficulty and task demands, and the impairment strength increased with the grouping strength of the collinear distractor. Further analysis revealed that the response times of older adults increased in a multiplicative manner to that of younger adults, suggesting that longer response of older adults spread to multiple underlying processing including grouping and suppression of collinear distractors. Together, the results suggest that older adults were still distracted in visual search even when grouping was required on a distractor. Our findings also highlight how general slowing may delay suppression processing in visual search.