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Dissertation
Upward spread of masking for pure tones and speech in normal-hearing and cochlear impaired listeners
Doctor of Philosophy (Ph.D.), University of Texas at Austin
1992
Abstract
The purpose of this research was to evaluate the upward spread of masking (USM) for pure tones and for words in seven young normal hearers and twelve young subjects with moderate cochlear hearing loss. Pure-tone thresholds were obtained with an intense low-frequency masker using a method-of-adjustment procedure. To quantify the USM, an USM index (USMI) was created based upon the subject's unmasked and masked thresholds, with respect to the median masked thresholds of the normal hearers. All hearing-impaired subjects had larger USMI values than normal-hearers.
Speech recognition thresholds (SRTs) for high-frequency-weighted monosyllables were obtained in quiet and at multiple levels of a speech-spectrum masker. The SRT functions were analyzed for SRTs in quiet (SRTQ) and in noise (SRTN). All hearing-impaired subjects produced higher SRTN than normal hearers. For the impaired subjects, SRTs were measured utilizing three different amounts of low-frequency energy (LFE) in the speech and noise complex. Ten of twelve subjects had their best SRTQ with the most LFE whereas seven subjects had their best SRTN with the least LFE.
For the hearing-impaired listeners, the USMI values were significantly, negatively correlated with the unmasked pure-tone thresholds and were significantly, positively correlated with the pure-tone threshold shifts. The SRTQ and the SRTN were not significantly correlated with each other. The USMI values were significantly, negatively correlated with the SRTQ and not significantly correlated with the SRTN or the change in SRTN with reduction of LFE.
These experiments support the previous research that individuals with moderate cochlear hearing impairment have excess USM and higher SRTN relative to that of normal hearers. The SRT experiment also showed that SRTs in a broadband noise for many, but not all, impaired listeners could be improved by highpass filtering of the signals. However, the USMI was not predictive of those individuals who benefited from reduction in LFE. The results support the use of adaptive highpass filters in hearing aids but further work is needed to determine measures that would predict individual speech recognition benefit.
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Details
- Title
- Upward spread of masking for pure tones and speech in normal-hearing and cochlear impaired listeners
- Creators
- Victor Bray - Drexel University, Audiology - 4 Year
- Contributors
- Linda M Thibodeau (Advisor) - The University of Texas at Austin
- Awarding Institution
- University of Texas at Austin
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Number of pages
- 236
- Resource Type
- Dissertation
- Language
- English
- Other Identifier
- 9798208035740; 991022207446404721