Perception of Spectral Contrast by Hearing-Impaired Listeners The ability to discriminate the spectral shapes of complex sounds is critical to accurate speech perception. Part of the difficulty experienced by listeners with hearing loss in understanding speech sounds in noise may be related to a smearing of the internal representation of the spectral peaks and valleys because of ... Research Article
Research Article  |   August 01, 2005
Perception of Spectral Contrast by Hearing-Impaired Listeners
 
Author Affiliations & Notes
  • Laura E. Dreisbach
    San Diego State University, San Diego, CA
  • Marjorie R. Leek
    Walter Reed Army Medical Center, Washington, DC
  • Jennifer J. Lentz
    Indiana University, Bloomington
  • Corresponding author: e-mail: ldreisba@mail.sdsu.edu
Article Information
Hearing & Speech Perception / Hearing Disorders / Speech, Voice & Prosody / Hearing / Research Articles
Research Article   |   August 01, 2005
Perception of Spectral Contrast by Hearing-Impaired Listeners
Journal of Speech, Language, and Hearing Research, August 2005, Vol. 48, 910-921. doi:10.1044/1092-4388(2005/063)
History: Received September 10, 2003 , Accepted December 16, 2004
 
Journal of Speech, Language, and Hearing Research, August 2005, Vol. 48, 910-921. doi:10.1044/1092-4388(2005/063)
History: Received September 10, 2003; Accepted December 16, 2004
Web of Science® Times Cited: 7

The ability to discriminate the spectral shapes of complex sounds is critical to accurate speech perception. Part of the difficulty experienced by listeners with hearing loss in understanding speech sounds in noise may be related to a smearing of the internal representation of the spectral peaks and valleys because of the loss of sensitivity and an accompanying reduction in frequency resolution. This study examined the discrimination by hearing-impaired listeners of highly similar harmonic complexes with a single spectral peak located in 1 of 3 frequency regions. The minimum level difference between peak and background harmonics required to discriminate a small change in the spectral center of the peak was measured for peaks located near 2, 3, or 4 kHz. Component phases were selected according to an algorithm thought to produce either highly modulated (positive Schroeder) or very flat (negative Schroeder) internal waveform envelopes in the cochlea. The mean amplitude difference between a spectral peak and the background components required for discrimination of pairs of harmonic complexes (spectral contrast threshold) was from 4 to 19 dB greater for listeners with hearing impairment than for a control group of listeners with normal hearing. In normal-hearing listeners, improvements in threshold were seen with increasing stimulus level, and there was a strong effect of stimulus phase, as the positive Schroeder stimuli always produced lower thresholds than the negative Schroeder stimuli. The listeners with hearing loss showed no consistent spectral contrast effects due to stimulus phase and also showed little improvement with increasing stimulus level, once their sensitivity loss was overcome. The lack of phase and level effects may be a result of the more linear processing occurring in impaired ears, producing poorer-than-normal frequency resolution, a loss of gain for low amplitudes, and an altered cochlear phase characteristic in regions of damage.

Acknowledgments
This work was supported by National Institutes of Health Grant DC RO1 00626 and was carried out under Department of Clinical Investigation Work Unit 2570. A preliminary report of this work was presented at the 139th Meeting of the Acoustical Society of America, June 2000, Atlanta, Georgia. All listeners participating in this research provided written informed consent prior to beginning the study. We are grateful to B. C. J. Moore for helpful suggestions and comments on an earlier version of this article. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense.
Portions of this work were presented at the Spring meeting of the Acoustical Society of America, Atlanta, Georgia, June 2000. The majority of this work was completed at the Army Audiology and Speech Center, Walter Reed Army Medical Center in Washington, D.C.
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