Age differences in feature and conjunction search: Implications for theories of visual search and generalized slowing

Abstract

Reaction times (RTs), saccadic eye movements, and fixation durations were measured while older and younger observers searched visual displays for targets defined by a single feature, luminance contrast or orientation, as well as the conjunction of these two features. Target eccentricity was varied between approximately 4 and 14 deg. Age deficits generally increased in the more difficult conditions. the RT data indicated that age deficits were greatest for conjunction search and on target absent trials. the saccade data showed that on target present trials, age deficits were larger for more eccentric targets, especially in conjunction search. Fixation durations were related by a power function to the number of saccades made prior to a correct response. Whereas the exponent of these power functions was constnat across search condition and age group, the coefficient was larger for older adults. Thus at a fixed number of saccades, when old and young were presumably searching groups of equal size, the elderly took longer to process the information within that group. the RT, fixation duration, and saccade data of older observers were fit by a linear function based on the performance of young adults, and all dependent measures yielded essentially the same slowing function. This pattern was also found when the RT and saccade data from Scialfa, Thomas, and Joffe (1994) were reexamined. Results are discussed with reference to the generalized slowing hypothesis and models of visual search.