Loudness fluctuation and temporal masking in normal and hearing-impaired listeners

Abstract

The model of fluctuation strength as proposed by Fastl is based on the level difference ΔL between the maximum and minimum of the temporal masking pattern of dynamically varying sounds. Compared to normal-hearing subjects this level difference can be strongly reduced in hearing-impaired listeners. Recent findings, however, suggest that perceived fluctuations in hearing-impaired listeners are magnified by recruitment. Based on fitted loudness fluctuations—measured by a categorical scaling procedure—for each subject a ‘‘uniform loud noise’’ was generated, having equal loudness across all critical bands. These noises were amplitude modulated with different rates and depths. In experiment 1, subjects had to judge ‘‘how strong (not how fast) fluctuates the loudness’’ by marking one of seven verbal categories. In experiment 2, the ΔL’s of the various noises were measured by determining the thresholds in the envelope’s maximum and minimum. Although measured level differences were markedly reduced in the hearing impaired, the perceived loudness fluctuations are nearly the same for normal and hearing-impaired listeners. These results support the idea that the model of fluctuation strength can be applied to hearing-impaired listeners by transforming the difference in level into the corresponding individual difference in loudness. [Work supported by Geers.]