This research addresses basic questions related to processing of auditory signals and recognition of speech by individuals with sensorineural hearing loss. At high signal levels, predicted improvement in speech recognition in noise is often not achieved by hearing-impaired individuals, suggesting that abnormal growth of masking of speech may be a consequence of peripheral hearing loss. Accordingly, if speech is amplified to assure maximum audibility, abnormal growth of masking may negate the benefit provided by the amplification system. The proposed research consists of four related projects, each of which examines fundamental properties of masking of pure tones and speech in normal- hearing and hearing-impaired human subjects, with the goal of providing an understanding of how abnormal masking relates to diminished speech recognition.
In Aim 1, masking of pure tones and speech is measured as a function of signal and masker level to test hypotheses concerning growth of masking at moderate and high signal levels.
Aim 2 measures growth of masking and growth of loudness in individuals with cochlear hearing loss to test hypotheses concerning relationships among masking, loudness, and growth of response in impaired auditory systems.
In Aim 3, unmasking (suppression) is measured psychophysically to assess its sensitivity as an indicator of cochlear function in the absence of threshold elevation.
In Aim 4, suppression is measured in subjects with cochlear hearing loss to determine how the absence of suppression interferes with speech recognition in noise. Results of these projects will extend our general understanding of mechanisms that account for differences between normal and impaired hearing. The projects are related to each other by their emphasis on studies of auditory processing of pure tones and speech at moderate to high signal levels. A better understanding of these abilities is necessary if hearing-impaired individuals are to achieve maximum benefit from amplified speech in adverse listening conditions.
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