Perceptual Distortions in Aided Hearing-Impaired Listeners: Psychophysical Evidence of Excessive Loudness Growth and Altered Timbre Representation.

Hearing aid users often report that some everyday sounds are abnormally intrusive or salient. This issue may stem from distorted coding of sound features due to peripheral impairments and/or hearing aid processing. This study investigates whether aided hearing-impaired (aHI) listeners experience (1) abnormal loudness processing and (2) distorted timbre perception, both of which may contribute to this problem. In Experiment 1, we measured loudness functions using sounds varying in four timbre dimensions (brightness, spectral flux, attack time, roughness) in normal-hearing (NH) and aHI listeners. In Experiment 2, we assessed timbre perception via dissimilarity judgments based on a similar set of sounds. We tested NH listeners with and without a hearing loss simulator and a hearing aid simulator, as well as aHI listeners with the hearing aid simulator. The results of Experiment 1 revealed steeper loudness functions in aHI participants, in particular for low-to-moderate level sounds with center frequency above 1 kHz, suggesting that hearing aids fail to fully restore normal loudness growth above a certain degree of threshold loss. The characterization of timbre perception in aHI listeners obtained in Experiment 2 showed enhanced weighting of temporal envelope features, likely emphasized by hearing aid expansion at low level, as well as non-linear distortions in the perceptual coding of roughness. These findings suggest that both loudness and timbre dimensions are distorted in aided impaired hearing. We propose that these distortions may underlie the excessive salience of certain everyday sounds, though direct measurement of salience effects will be important in future work.