Ageing-related changes in the processing of attended and unattended standard stimuli.

Responses to standard stimuli presented during a dichotic listening task were analysed in 53 healthy subjects from 20 to 86 years of age. The aim was to determine whether N1 and P2 waves showed changes attributable to attention or more general changes underlying the electrophysiological processing of such stimuli under attended and unattended conditions. N1 was larger at midline frontal and central electrodes in middle-aged and in elderly subjects without changes in its topographical distribution. These changes were independent of attention. P2, which was also larger in middle-aged and in elderlies, showed scalp distribution changes depending on the direction of attention. The present results indicate the existence of general ageing-related changes in the processing of attended and unattended standard stimuli which may be related to inhibitory deficits (N1) and to changes in the orientation of electrical sources (P2).