Phase effects in masking in normal-hearing and hearing-impaired listeners

Abstract

Changes in the phase relationships between components in a harmonic tone complex masker can lead to large changes in masked threshold for long-duration sinusoids in normal-hearing listeners. The effect is reduced or absent in hearing-impaired listeners. This reduction could be due to a loss of peripheral compression, a change in the auditory filters’ phase response, or both. Signal thresholds were measured as a function of masker phase curvature, signal frequency, and masker fundamental frequency (F0). In contrast to previous studies, more than just two phase relationships were considered, allowing us to compare the overall phase response of impaired and normal ears. Peripheral compression was estimated in a separate experiment using a notched-noise masking technique. If changes in filter phase response can account for the differences between normal-hearing and hearing-impaired listeners, then certain phase relationships should produce large threshold differences even in hearing-impaired listeners. If peripheral compression is important, threshold differences in hearing-impaired listeners should emerge at very low F0s, due to the predicted interaction between peripheral compression and temporal processing at higher stages. Preliminary results suggest that the difference between normal-hearing and hearing-impaired listeners can be explained primarily in terms of peripheral compression. [Work supported by DFG and NIDCD.]