Aging affects hemispheric asymmetry on a competing speech task.

This study examined the effects of aging on the hemispheric asymmetry of event-related potentials (ERPs) evoked by morphosyntactic anomalies in a competing speech paradigm. The experimental groups consisted of children, young adults, and elderly persons. The ERPs were recorded from 32 scalp sites while participants listened to a continuous narrative presented quasidichotically via loudspeakers. Participants responded when they heard an anomalous word embedded within a popular fairy tale. Anomalous words evoked a robust positivity in the 700- to 900-msec latency range in all participants. Comparison of area measures from waveforms at the lateral frontal, frontotemporal, temporal, temporoparietal, and parietal electrode sites revealed asymmetry in hemispheric positivity. In children and young adults, asymmetry peaked in the 600- to 800-msec range and favored the left hemisphere in both target-right and target-left conditions. In seniors, however, asymmetry peaked at 1100 msec, favored the left hemisphere in the target-right condition, and favored the right hemisphere in the target-left condition. These results support the concept that aging affects hemispheric asymmetry during linguistic processing.