The proposed research is designed to investigate the relationship between frequency analysis and speech recognition by hearing- impaired individuals. Abnormal auditory processing is often assumed to be responsible for reduced speech recognition observed in these listeners, without careful consideration of the concurrent effects of threshold elevation. It is possible that a strong association between these two conditions secondary to hearing impairment has not, as yet, been established because, with current techniques, evaluation of the frequency resolution of normal and impaired auditory systems is often performed without accounting for effects of threshold sensitivity, making an accurate estimate of functional auditory capabilities difficult. Experiment 1 will estimate the auditory filter width of normal-hearing and hearing- impaired listeners while controlling for differences in threshold sensitivity. Under conditions in which the frequency analysis of speech is likely to result in modifications of its spectral characteristics, speech recognition by normal-hearing listeners does not deteriorate. However, speech recognition by hearing-impaired listeners may not be as resistant to spectral modification. Experiment 2 will determine if consonant recognition by normal- hearing listeners is equivalent to performance or hearing-impaired listeners then the stimuli presented to normal listeners has been modified to approximate consonants processed by wide auditory filters. In addition, changes in frequency analysis may explain residual deficits in speech recognition which remain once threshold elevation and/or excessive masking is taken into account, or under difficult listening conditions. Experiment 3 will evaluate if diminished spectral contrasts in speech sounds resulting from widened auditory filters differentially affects normal-hearing and hearing-impaired listeners in their ability to understand speech in noisy environments. The results of these experiments will provide a clearer understanding of the dynamics of the auditory processing dysfunction imposed by sensorineural hearing loss and the magnitude of the effects on speech recognition for most hearing-impaired individuals.
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