Functional auditory development in preterm and full term infants.

Bilateral ABRs were recorded from 452 infants 32-45 weeks conceptional age. Differences in laterality, gender and appropriateness for gestational age were investigated in order to increase our understanding of developmental processes in early life. Rate effects were also studied in a subsample of infants (145 ears). All subjects were free of conditions known to affect ABR parameters. Left/right differences were evident for all ABR measures except the amplitude of wave I. Shorter interwave intervals and larger amplitudes were consistently observed on the right. Females exhibited shorter absolute latencies for waves III and V and larger wave I amplitudes than males. Small for gestational age (SGA) infants displayed shorter wave V latencies and interwave intervals relative to AGA infants. These differences, however, disappeared by term age whereas the contrasts in laterality persisted. Increasing the rate of stimulation reduced wave I amplitude irrespective of conceptional age and increased wave V amplitude prior to term. An increase in wave V latency was more pronounced at the higher rate on the left than the right. There was no interaction between rate and appropriateness for gestational age, although SGA infants had shorter wave V and interwave latencies. Our data indicate a slight but significant right ear advantage in the processing of auditory signals. Gender differences were apparent as well. While research on adults and older children have reported similar findings, no other studies to date have observed these results in neonates. The present work also lends support to the view that accelerated neurological development occurs in growth-retarded infants.