Blog Archives

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.

from the International Journal of Audiology

Hearing aid noise reduction algorithms and the acquisition of novel speech contrasts by young children

A previous study by the authors concluded that digital noise reduction (DNR) does not have an influence on the acquisition of a second language in adults. On the basis of results from adult subjects, it was inferred that DNR is not likely to influence language acquisition in pre-verbal infants. The present study serves as an update to determine whether the tasks being modeled could be conducted with younger participants of 4-and 5-years of age, and whether similar results would be found. Two groups of normal-hearing, monolingual English-speaking children were presented with noise-embedded Hindi speech contrasts that were difficult to discriminate. One group listened to both speech items and noise processed with DNR while the other group listened to unprocessed speech in noise. To ensure task appropriateness, these results were also compared to measures from a third group composed of Hindi-speaking children of the same age. Results indicated that Hindi-speaking children performed better than English-speaking children, confirming age-appropriateness of the cross-language task, but that DNR did not enhance nor impair the acquisition of novel speech contrasts by young listeners.

from the Canadian Journal of Speech-Language Pathology and Audiology</p

human evoked cortical activity to signal-to-noise ratio and absolute signal level

The purpose of this study was to determine the effect of signal level and signal-to-noise ratio (SNR) on the latency and amplitude of evoked cortical activity to further our understanding of how the human central auditory system encodes signals in noise. Cortical auditory evoked potentials (CAEPs) were recorded from 15 young normal-hearing adults in response to a 1000 Hz tone presented at two tone levels in quiet and while continuous background noise levels were varied in five equivalent SNR steps. These 12 conditions were used to determine the effects of signal level and SNR level on CAEP components P1, N1, P2, and N2. Based on prior signal-in-noise experiments conducted in animals, we hypothesized that SNR, would be a key contributor to human CAEP characteristics. As hypothesized, amplitude increased and latency decreased with increasing SNR; in addition, there was no main effect of tone level across the two signal levels tested (60 and 75 dB SPL). Morphology of the P1-N1-P2 complex was driven primarily by SNR, highlighting the importance of noise when recording CAEPs. Results are discussed in terms of the current interest in recording CAEPs in hearing aid users.

from Hearing Research