Aided cortical auditory evoked potentials in response to changes in hearing aid gain

Objective: There is interest in using cortical auditory evoked potentials (CAEPs) to evaluate hearing aid fittings and experience-related plasticity associated with amplification; however, little is known about hearing aid signal processing effects on these responses. The purpose of this study was to determine the effect of clinically relevant hearing aid gain settings, and the resulting in-the-canal signal-to-noise ratios (SNRs), on the latency and amplitude of P1, N1, and P2 waves. Design & Sample: Evoked potentials and in-the-canal acoustic measures were recorded in nine normal-hearing adults in unaided and aided conditions. In the aided condition, a 40-dB signal was delivered to a hearing aid programmed to provide four levels of gain (0, 10, 20, and 30 dB). As a control, unaided stimulus levels were matched to aided condition outputs (i.e. 40, 50, 60, and 70 dB) for comparison purposes. Results: When signal levels are defined in terms of output level, aided CAEPs were surprisingly smaller and delayed relative to unaided CAEPs, probably resulting from increases to noise levels caused by the hearing aid. Discussion: These results reinforce the notion that hearing aids modify stimulus characteristics such as SNR, which in turn affects the CAEP in a way that does not reliably reflect hearing aid gain.