Characterizing the effects of distorted tonotopy on neural coding and perception in sensorineural hearing loss

Abstract

Patients with similar audiograms often experience varying levels of difficulty with understanding speech in noisy listening environments, even with prescriptive amplification using state-of-the-art hearing aids. With audibility mostly restored by amplification, these suprathreshold differences are often attributed to degraded frequency selectivity (broadened cochlear tuning) due to sensorineural hearing loss (SNHL), and non-peripheral factors. However, evidence from recent animal models of noise-induced SNHL suggests that distorted tonotopy—i.e., hypersensitivity of the tails of cochlear frequency tuning curves—may be a significant contributor to degraded speech coding, particularly in the presence of background noise. In this study, a combination of behavioral measures, otoacoustic emissions, and electroencephalography (EEG) was used to investigate: (1) whether distorted tonotopy degrades the neural coding of speech in human listeners with SNHL as measured using EEG, and (2) whether variations in the degree of distorted tonotopy contribute to the large individual differences in perceptual outcomes that persist despite prescriptive amplification. Preliminary results from individuals with mild-to-moderate SNHL who listened to stimuli amplified by a hearing-aid simulator implementing individualized prescriptions suggest that distorted tonotopy (as measured using the tuning-curve tip-to-tail ratio) can indeed partly account for individual variations both in neural coding and behavior.