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Active Research
Hearing Loss and the Perception of Complex Sounds
Principal Investigator: Marjorie R. Leek, PhD
Objective: To examine the preservation of temporal precision in auditory processing by hearing-impaired listeners, and how these measures relate to pitch perception.
Background: Auditory speech recognition by individuals with hearing loss requires recovery of the intended message from a distorted internal representation of the input stimulus. The preservation of precise temporal firing patterns in the auditory nervous system is necessary for the clear perception of pitch that supports recognition of speech and musical sounds, as well as for the ability of normal-hearing people to extract the speech signal from a noisy background. Hearing-impaired and normal-hearing listeners were asked to discriminate sounds that vary in the frequency spectrum, the temporal waveform envelope, and the temporal fine structure in the waveform. Experiments also estimated the amount of temporal “jitter” imposed by a damaged auditory system across different frequency ranges.
Findings: In a study of consonance and dissonance perception, people with hearing loss showed less difference between consonant tones and those that had a dissonant sound. This may result in music becoming distorted for these people, and may contribute to the difficulties they experience in identifying and separating different voices. Another study determined that hearing-impaired listeners were restricted in their ability to discriminate temporal waveforms with short durations, meaning the fine structure in speech waveforms may be indiscriminable to these people, which likely interferes with the ability to clearly understand speech. Finally, a third study indicated that hearing-impaired listeners could identify clear vowel tokens as well as normal-hearing people, but their identification of vowels that were acoustically more similar to everyday speech sounds (i.e., not clearly articulated) showed a great deal of ambiguity and variability. This indicates that vowel sounds in ongoing speech contribute to the overall difficulty that hearing impaired people have in understanding speech. An understanding of the interaction of factors such as impaired spectral and temporal processing with the acoustics of speech and music is critical to the potential ability to tailor programmable hearing aids to individual patients’ hearing losses.
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