Effect of interstimulus interval and age on cortical auditory evoked potentials in 10-22-week-old infants

This study compares cortical auditory evoked potentials (CAEPs) at different interstimulus intervals (ISIs) in infants to determine the impact of stimulus rate on wave morphology. Infant CAEPs are dominated by a positive peak P1. We hypothesized that infant CAEPs would be more adult-like at longer ISI with P1, followed by negativity (labelled N450). Participants were 10 typically developing infants aged 10-13 weeks (N=4) and 20-22 weeks (N=6). CAEPs were measured in one recording session for/da/in quiet at 55 dB SPL for ISIs of 910, 1820, 3640 and 4550 ms in a randomized order. Recordings were complete at each ISI for 7-10 infants. Seven infants who completed all testing in quiet were also tested in continuous white noise (+5 dB signal-to-noise ratio) for the shortest ISI. P1 was observable in all infants; N450 was only present in the older infants. There appeared to be no ISI effect for younger or older infants, which is not consistent with ISI findings for adults and older children. The presence of N450 in the older infants only suggests that cortical maturational differences are evident in speech-evoked CAEPs in young infants. There were minimal effects of noise on P1 latency and amplitude. Results suggest different effects of ISI for very young infants than those observed in older infants and children. CAEPs are being used to measure hearing aid effectiveness in young infants and hence it is imperative that the effects of factors such as ISI are better understood.