Book Description

Purpose: This study was designed to investigate (1) the effects of age and hearing loss on auditory neural coding, (2) interrelationships between auditory evoked potentials (AEP) taking place at early and later stage of auditory processing, and (3) electrophysiological correlates of age-related declines in speech-in-noise perception. Methods: 30 young normal-hearing adults (YNH, M=21 years), 26 older adults with near-normal hearing (ONH, M=63.9 years) and 26 older adults with hearing loss (OHL, M=72.8 years) participated in the study. AMLR Pa and N1, P2 and N2 of ALLRs were recorded using two-channel electrode system. 500 Hz tone burst and syllable /ba/ were presented in quiet and in babble at the level of 90 Leq (dBA), accompanied by babble at the level of 65 Leq (dBA). Revised Speech Perception in Noise (R-SPIN) test was conducted to measure speech-in-noise perception. Results: ONH listeners demonstrated significantly enhanced Pa and N1 amplitudes and significantly prolonged Pa, P2 and N2 latencies compared with YNH listeners, indicating the effects of aging. OHI group demonstrated significantly prolonged N2 latencies compared with ONH group, indicating the effects of hearing loss. OHI listeners demonstrated significantly enhanced amplitudes and significantly prolonged latencies across all AEP components compared with YNH listeners, indicating that the combined effects may have stronger impacts on age-related changes in AEP morphology. Significant correlations between the amplitudes of Pa and each component of ALLRs were found in ONH and OHI groups, indicating that enhanced Pa amplitudes correspond with enhanced amplitudes of cortical responses in older listeners. Significant correlations between latencies of Pa and each component of ALLRs were found in all groups, indicating that prolonged Pa latencies correspond with prolonged latencies of cortical responses in all listeners. In both ONH and OHI groups, lower R-SPIN-LP scores are significantly correlated with enhanced Pa, P2, and N2 amplitudes and prolonged N2 latencies, particularly for syllable /ba/. Discussion and Conclusions: Interplay between effects of aging and hearing loss may have stronger impacts on morphological changes in the AEP waveforms. Amplitude-based interrelationships reflect age-related changes in a transfer of neural information between subcortical and cortical auditory network. Latency-based interrelationships indicate the association between neural timings at subcortical and cortical levels. Age-related enhancements of Pa, P2 and N2 amplitudes and age-related prolongations of N2 latencies may serve as electrophysiological correlates of age-related declines in SIN perception.