Subjective Judgments of Clarity and Intelligibility for Filtered Stimuli With Equivalent Speech Intelligibility Index Predictions The purpose of this investigation was to determine whether subjective judgments of clarity or intelligibility would be rated equally among conditions in which speech was equated for predicted intelligibility (using the Speech Intelligibility Index, SII) but varied in bandwidth. Twenty listeners with normal hearing rated clarity and intelligibility for sentence ... Research Article
Research Article  |   April 01, 1998
Subjective Judgments of Clarity and Intelligibility for Filtered Stimuli With Equivalent Speech Intelligibility Index Predictions
 
Author Affiliations & Notes
  • Laurie S. Eisenberg
    UCLA School of Medicine, Division of Head and Neck Surgery Los Angeles, CA
  • Donald D. Dirks
    UCLA School of Medicine, Division of Head and Neck Surgery, and West Los Angeles Veterans Administration Medical Center, CA
  • Sumiko Takayanagi
    UCLA Department of Linguistics Los Angeles, CA
  • Amy Schaefer Martinez
    UCLA School of Medicine, Division of Head and Neck Surgery Los Angeles, CA
  • Contact author: Laurie S. Eisenberg, Ph.D., House Ear Institute, 2100 West Third Street, Fifth Floor, Los Angeles, CA 90057. Email: leisenberg@hei.org
  • Currently affiliated with the House Ear Institute, Los Angeles, CA.
    Currently affiliated with the House Ear Institute, Los Angeles, CA.×
Article Information
Speech, Voice & Prosodic Disorders / Hearing Disorders / Hearing / Research Articles
Research Article   |   April 01, 1998
Subjective Judgments of Clarity and Intelligibility for Filtered Stimuli With Equivalent Speech Intelligibility Index Predictions
Journal of Speech, Language, and Hearing Research, April 1998, Vol. 41, 327-339. doi:10.1044/jslhr.4102.327
History: Received June 4, 1997 , Accepted October 10, 1997
 
Journal of Speech, Language, and Hearing Research, April 1998, Vol. 41, 327-339. doi:10.1044/jslhr.4102.327
History: Received June 4, 1997; Accepted October 10, 1997

The purpose of this investigation was to determine whether subjective judgments of clarity or intelligibility would be rated equally among conditions in which speech was equated for predicted intelligibility (using the Speech Intelligibility Index, SII) but varied in bandwidth. Twenty listeners with normal hearing rated clarity and intelligibility for sentence material (Hearing In Noise Test) in speech-shaped noise at six paired low- and high-pass filtered conditions in which SII was equated for each pair. For three paired conditions, predicted intelligibility increased as SII increased monotonically (0.3, 0.4, 0.5). In the remaining paired conditions, SII continued to increase monotonically (0.6, 0.7, 0.8) but predicted intelligibility was held at a maximal level (≥95%). Predicted intelligibility was estimated from the transfer function relating SII to speech recognition scores determined in preliminary experiments. Differences in ratings between paired low- and high-pass filtered sentences did not reach statistical significance for either clarity or intelligibility, indicating that the spectral differences at equivalent SIIs did not influence the judgments for either of the two dimensions. For conditions in which predicted intelligibility increased, both clarity and intelligibility ratings increased in a similar manner. For conditions in which predicted intelligibility was maximized, intelligibility ratings remained the same statistically across conditions while clarity ratings changed modestly. Although high correlations were observed between clarity and intelligibility ratings, intelligibility ratings were consistently higher than clarity ratings for comparable conditions. The results indicated that listeners with normal hearing produced clarity and intelligibility ratings for the same speech material and experimental conditions that were highly related but differed in magnitude. Caution is required when substituting clarity for intelligibility.

Acknowledgments
This research was supported (in part) by research grants 5 K08 DC 00083-05 and T32 DC00029-07 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health, and from Veterans Administration Rehabilitation Research and Development Grant C-432. The authors thank Sigfrid Soli and Michael Nilsson, of the House Ear Institute, for providing a recording of the original HINT sentences, and Chaslav Pavlovic, of ReSound Corporation, who provided the software used for the SII calculations, based on procedures recommended in the proposed ANSI Standard (ANSI S3.79-199x, Draft V3.0).
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