Effect of age on interaural asymmetry of event-related potentials in a dichotic listening task.

Three groups of subjects, children, young adults, and elderly persons with presbyacusis, were tested in a directed attention, quasidichotic paradigm in which continuous speech was monitored for syntactically and/or semantically anomalous words. The task evoked an event-related potential (ERP) characterized by a positive peak in the latency region of 600 to 1,000 msec. ERPs were separately averaged for target-word-right and target-word-left conditions. Amplitude and latency measures at the peak of the global field power waveform were calculated. Amplitude was significantly larger in children than in either adult group. In children and young adults, both amplitude and latency measures were equivalent for target-right and target-left conditions, but in elderly persons, latency was significantly greater in the target-left than in the target-right condition. Topographic maps of amplitude at the peak of the ERP waveform showed maximal positivity symmetrically distributed around the midline centroparietal area in both right-attended and left-attended conditions. In elderly persons, however, maximal positivity in the left-attended condition was significantly delayed relative to maximal positivity in the right-attended condition. Results are consistent with previous findings of interaural asymmetry in a dichotic listening task in elderly persons.