An ongoing goal of our work has been to understand the effects of wide dynamic range compression (WDRC) amplification on temporal cues for speech recognition. WDRC is the default configuration in all digital aids, so the extent to which WDRC improves speech recognition dictates hearing aid benefit and use. However, WDRC can degrade the modulation properties of the signal, particularly the low-modulation rate (envelope) cues which are important for speech recognition. This project encompasses three sets of experiments that take a systematic approach to prescribing amplification parameters. The first specific aim is to define the extent to which envelope cues can be altered without degrading speech recognition. We will quantify how much envelope cues can be altered, particularly under conditions of spectral degradation similar to those experienced by listeners with hearing loss. We are most concerned with listeners with severe hearing loss who depend more on envelope cues, and who have received little attention in the literature. The second specific aim is to determine whether the acceptable level of envelope distortion depends on factors associated with degree of hearing impairment. The working hypothesis is that listeners who have reduced access to spectral cues, and therefore must rely more on envelope information, will have lower recognition scores due to the envelope alteration caused by WDRC. We will use several measures of ability to detect and use spectral differences necessary for speech recognition, which will be related to the speech-recognition changes due to envelope distortion. The third specific aim is to determine whether the acceptable amount of envelope distortion depends on the listening environment. We will consider the effect of two factors on the acceptable level of envelope distortion: effect of background noise and length of speech utterance. Ultimately, the goal of this work is to determine the range of compression values that maximize the restoration of audibility without distorting usable modulation cues.
Hearing loss is one of our most pervasive health problems but the only treatment option for most of those with hearing loss is a hearing aid. To improve hearing aid satisfaction and benefit and avoid distorting important speech cues, we need to choose appropriate processing parameters for each individual. The focus of this project is to determine hearing aid settings that will provide the best possible speech recognition for each individual under a variety of listening conditions.
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