Temporal Envelope Changes of Compression and Speech Rate: Combined Effects on Recognition for Older Adults Purpose When understanding speech in complex listening situations, older adults with hearing loss face the double challenge of cochlear hearing loss and deficits of the aging auditory system. Wide-dynamic range compression (WDRC) is used in hearing aids as remediation for the loss of audibility associated with hearing loss. WDRC processing ... Research Article
Research Article  |   October 01, 2007
Temporal Envelope Changes of Compression and Speech Rate: Combined Effects on Recognition for Older Adults
 
Author Affiliations & Notes
  • Lorienne M. Jenstad
    University of British Columbia, Vancouver, British Columbia, Canada
  • Pamela E. Souza
    University of Washington, Seattle
  • Contact author: Lorienne M. Jenstad, School of Audiology and Speech Sciences, University of British Columbia, 5804 Fairview Avenue, Vancouver, British Columbia V6T 1Z3, Canada. E-mail: ljenstad@audiospeech.ubc.ca.
Article Information
Hearing & Speech Perception / Acoustics / Hearing Aids, Cochlear Implants & Assistive Technology / Special Populations / Older Adults & Aging / Speech, Voice & Prosody / Hearing / Research Articles
Research Article   |   October 01, 2007
Temporal Envelope Changes of Compression and Speech Rate: Combined Effects on Recognition for Older Adults
Journal of Speech, Language, and Hearing Research, October 2007, Vol. 50, 1123-1138. doi:10.1044/1092-4388(2007/078)
History: Received March 13, 2006 , Accepted December 18, 2006
 
Journal of Speech, Language, and Hearing Research, October 2007, Vol. 50, 1123-1138. doi:10.1044/1092-4388(2007/078)
History: Received March 13, 2006; Accepted December 18, 2006

Purpose When understanding speech in complex listening situations, older adults with hearing loss face the double challenge of cochlear hearing loss and deficits of the aging auditory system. Wide-dynamic range compression (WDRC) is used in hearing aids as remediation for the loss of audibility associated with hearing loss. WDRC processing has the additional effect of altering the acoustics of the speech signal, particularly the temporal envelope. Older listeners are negatively affected by other types of temporal distortions, but this has not been found for the distortion of WDRC processing for simple signals. The purpose of this research was to determine the circumstances under which older adults might be negatively affected by WDRC processing and what compensatory mechanisms those listeners might be using for the listening conditions when speech recognition performance is not affected.

Method Two groups of adults with mild to moderate hearing loss were tested: (a) young-old (62–74 years, n = 11) and (b) old-old (75–88 years, n = 14). The groups did not differ in hearing loss, cognition, working memory, or self-reported health status. Participants heard low-predictability sentences compressed at each of 4 compression settings. The effect of compression on the temporal envelope was quantified by the envelope difference index (EDI; T. W. Fortune, B. D. Woodruff, & D. A. Preves, 1994). The sentences were presented at three rates: (a) normal rate, (b) 50% time compressed, and (c) time restored.

Results There was no difference in performance between age groups, or any interactions involving age. There was a significant interaction between speech rate and EDI value; as the EDI value increased, representing higher amounts of temporal envelope distortion, speech recognition was significantly reduced. At the highest EDI value, this reduction was greater for the time-compressed than the normal rate condition. When time was restored to the time-compressed signals, speech recognition did not improve.

Conclusion Temporal envelope changes were detrimental to recognition of low-context speech for older listeners once a certain threshold of distortion was reached, particularly for rapid rate speech. For this sample tested, the effect was not age related within the age range tested here. The results of the time-restored condition suggested that listeners were using acoustic redundancy to compensate for the negative effects of WDRC distortion in the normal rate condition.

Acknowledgments
The research reported in this study was made possible by funding from the Canadian Institutes of Health Research (awarded to the first author) and National Institutes of Health Grant R01 DC006014 (awarded to the second author). We acknowledge Steve Armstrong and Gennum Corporation for providing the compression simulator, Sandra Gordon-Salant for providing advice on the speech materials, Marc Caldwell for assisting with data collection, and Lynne Werner and Christopher Moore for providing comments on design and analysis.
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