Auditory selective attention in middle-aged and elderly subjects: an event-related brain potential study.

Reaction times (RTs) and event-related brain potentials (ERPs) were recorded in middle-aged (MA) and elderly (ELD) subjects performing an auditory selective attention task. Subjects attended to tone bursts of a specified pitch and ear of delivery and responded to occasional longer duration target tones (75 vs. 25 msec). Infrequent novel stimuli (computer synthesized sounds and digitized environmental noises) were also included in the stimulus sequence. No significant age-related differences were found in the speed or accuracy of target detection. However, in both groups, RTs were delayed (by more than 300 msec) to targets that followed novel sounds. The prolongation was greater following novel sounds in the attended ear, particularly in the ELD group. The effects of selective attention on ERPs to standard tones were isolated as negative difference waves (Nds) by substracting ERPs to non-attended stimuli from ERPs to the same signals when attended. Nds had similar amplitudes, latencies of onset (60 msec), and distributions in ELD and MA groups. In both groups, Nd waves were more prominent following right ear stimulation, reflecting possible hemispheric asymmetries of generators in posterior temporal regions. The mismatch negativity (MMN) was isolated by subtracting ERPs to standard tones from ERPs to deviant stimuli. MMN amplitudes were reduced in the ELD group. There was also a significant change in MMN distribution with age: the MMN was larger over the right hemisphere for MA subjects but larger over the left for ELD subjects. Elderly subjects showed a trend toward smaller P3 amplitudes and delayed P3 latencies, but group differences did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)