Selective processing of two-dimensional visual stimuli in young and old subjects: electrophysiological analysis.

In this study, we compared selection of conjunctions of spatial frequency and orientation in young and old subjects, using performance and event-related brain potential (ERP) measures. Responses to target conjunctions were slightly but significantly slower in older subjects; lateralized readiness potential (LRP) onsets did not differ between groups. Older subjects made more false-positive responses to stimuli sharing only spatial frequency with the target. Difference waves associated with selection of separate dimensions included frontal positivity and occipital and central negativity and were 20-50 ms slower in older subjects. Later parts of these difference waves had smaller amplitudes in older subjects. Sensory discrimination, assessed through the effects of physical stimulus parameters on ERPs, was not clearly affected by age. Data are interpreted in terms of a relationship in older subjects between longer latencies of difference waves but equal LRP onsets and a higher false-alarm rate.