The role of aided signal-to-noise ratio in aided speech perception in noise

Abstract

Despite advances in hearing aid technology and careful fitting processes, outcomes vary widely among hearing aid users, particularly in background noise. Predicting benefit with hearing aids is not easy to do, as many variables contributing to outcomes are not known. The general aim of this research is to explore a previously undefined variable in outcomes, the signal-to-noise ratio. The level of speech compared to the level of background noise (i.e., signal-to-noise ratio; SNR) has been linked to speech perception and quality of brain responses at the input stage of processing. However, hearing aid processing is likely to modify the SNR, therefore delivering an altered SNR version to the listener. This study first aims to quantify the amount of change in SNR made by hearing aid processing, and second, to use the SNR changes at the output of the hearing aid to predict changes in speech percpetion. Two groups were studied, normal and impaired hearing listeners. Our hypothesis is that speech perception is dependent in part on the SNR at the output of the hearing aid, since this is the signal entering the listener's auditory system. To test this hypothesis, we quantified the SNR at the output of the hearing aid using acoustic measures of the hearing aid output. We then correlated the changes in output SNR to changes in speech perception scores, measured in a background of noise. The results showed that hearing aids for both groups of listeners were changing the SNR from input to output by a small, but statistically significant, amount (mean change: -0.25 dB). However, the change in SNR was not predictive of changes in speech perception for either group. We discuss the limitations and generalizations of these results, as well as future directions for research.