WDRC processing uses rapid, automatic gain adjustment to place more speech cues within the listener's audible range. Most hearing aids (> 80%) now offer WDRC, so over time this technology will be provided to most of the 6.2 million hearing aid wearers in the United States. However, WDRC processing does not always improve speech recognition over conventional amplification, perhaps because of distortions to the temporal properties of the speech signal. We are particularly interested in listeners with severe loss, who because of broader auditory filters may depend more heavily on temporal cues for recognition. Severely impaired listeners cannot communicate without acceptable amplification, so it is important not to distort usable information. Therefore, the long-term objectives of this project are to describe the effects of wide-dynamic range compression (WDRC) amplification on temporal cues for speech recognition and to assess the consequences of those changes for listeners with severe sensorineural hearing loss. The first Specific Aim is to compare speech recognition scores for WDRC versus linear amplification in a cohort of listeners with severe sensorineural hearing loss. Subjects will be fit with a master hearing aid using accepted clinical parameters and speech recognition measured under laboratory conditions. We will also analyze consonant error patterns, using a feature analysis. Our hypothesis is that listeners with severe loss fit with WDRC amplification will perform more poorly than listeners with mild-to-moderate loss, and that error patterns will indicate confusion of sounds that depend on temporal cues. The second Specific Aim is to describe the effects of WDRC on temporal cues essential for speech recognition. Recognition will be measured for speech processed to limit spectral information. Acoustic analysis of amplified speech will be used in conjunction with speech recognition scores to directly examine the extent of temporal cue distortion from WDRC and to determine an acceptable range of amplitude compression. The proposed project will also test the utility of quantifying amplitude envelope changes and the usefulness of these measures to predict recognition of WDRC-amplified speech. The third Specific Aim is to describe how spectral cue perception changes with increasing numbers of compression channels. We will use acoustic analysis in combination with vowel recognition. Our hypothesis is that listeners with severe loss who are less able to discriminate spectral details will show less degradation from larger numbers of compression channels.
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