Age differences in same-different judgments as a function of multidimensional similarity.

Age deficits in visual search often are attributed to difficulties in comparing display items to target representations. In the presence-absence search paradigm, however, these comparisons are frequently confounded with age differences in the latency and velocity of saccadic eye movements, reductions in the useful field of view (FOV), and retention of information concerning previously searched locations. To circumvent these shortcomings, 20 young and 20 older adults were compared in the speed of their same-different judgments of two perifoveal stimuli. The two stimuli were either identical or varied along one or more of the dimensions of size, shape, and color. In both age groups, RT for correct "different" judgments increased with stimulus similarity, an effect which was more pronounced in the elderly subjects. Results suggest that age differences in free search are due, in part, to an age-related decline in the speed of evaluating object congruence.