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. We hypothesize that 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. Participant groups included NH listeners with simulated hearing loss and hearing aids to better isolate contributing factors. Results revealed that hearing aids fail to restore normal loudness for low-level sounds, causing excessively steep loudness growth. Although brightness influenced loudness growth similarly across groups, the effect of attack time was specific to aHI listeners. The characterization of timbre perception in aHI listeners showed enhanced weighting of temporal envelope features, likely emphasized by hearing aid compression, 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 works.