Age-related differences in the timing of stimulus and response processes during visual selective attention: performance and psychophysiological analyses.

In this study, age-related differences in the selection of visual information were investigated. Two groups of younger and older subjects performed focused- and divided-attention (i.e., visual search) tasks. In the focused-attention task, centrally presented target letters could be flanked by compatible or incompatible noise letters. In the visual-search task, targets could be cued or uncued, and target locations could be spatially compatible or incompatible with the responding hand. P3 latency, lateralized readiness potentials, the electromyogram, and reaction times were used to detect possible age-related differences in the timing of stimulus- and response-related processes during selective processing of information. In the focused-attention task, performance of older subjects showed greater interference by incompatible flankers than did that of younger subjects because of stronger response competition caused by partial activation of the incorrect response channel by the incompatible flankers. No evidence was found of specific age-related differences in the efficiency of visual search in a divided-attention task. Furthermore, in both tasks, younger subjects showed an earlier start of response execution (in the electromyogram) relative to the onset of response preparation (lateralized readiness potential) and a higher percentage of incorrect electromyographic activity than did older subjects.