An event-related potential evaluation of involuntary attentional shifts in young and older adults.

Involuntary shifts in attention to irrelevant stimuli were studied in elderly and young volunteers during a dichotic-listening task. Event-related potentials and behavioral measures were recorded. Volunteers heard pairs of tones presented with 2 different stimulus onset asynchronies (SOAs). To-be-ignored tones were presented to the left ear, followed by to-be-attended tones to the right ear. Left-ear tones were a frequent standard (700 Hz) and an infrequent small (650 Hz) and large (500 Hz) deviant. Right-ear tones (1500 Hz) were presented with 2 equiprobable intensities. Volunteers responded to the lower intensity stimulus. Behavioral performance was impaired at the short SOA when to-be-ignored large deviants preceded to-be-attended targets, but more so for the elderly volunteers. Large deviants also elicited the mismatch negativity (MMN) and P3a for both age groups. It was concluded that the more impaired behavioral performance observed for the elderly was due to greater sensitivity to output from the MMN system by a frontal lobe system responsible for the maintenance of attentional focus.