High-Level Psychophysical Tuning Curves Simultaneous Masking by Pure Tones and 100-Hz-Wide Noise Bands Research Article
Research Article  |   April 01, 1991
High-Level Psychophysical Tuning Curves
 
Author Affiliations & Notes
  • David A. Nelson
    Hearing Research Laboratory Departments of Otolaryngology and Communication Disorders University of Minnesota, Minneapolis
  • Todd W. Fortune
    Hearing Research Laboratory Departments of Otolaryngology and Communication Disorders University of Minnesota, Minneapolis
  • Requests for reprints should be sent to David A. Nelson, Ph.D., University of Minnesota, Department of Otolaryngology Medical School, 2630 University Avenue, S.E., Minneapolis, MN 55414.
Article Information
Hearing / Research Articles
Research Article   |   April 01, 1991
High-Level Psychophysical Tuning Curves
Journal of Speech, Language, and Hearing Research, April 1991, Vol. 34, 360-373. doi:10.1044/jshr.3402.360
History: Received October 20, 1989 , Accepted August 16, 1990
 
Journal of Speech, Language, and Hearing Research, April 1991, Vol. 34, 360-373. doi:10.1044/jshr.3402.360
History: Received October 20, 1989; Accepted August 16, 1990

Simultaneous-masked psychophysical tuning curves were obtained from normal-hearing listeners using low-level (20–25 dB SPL) probe tones in quiet and high-level (60 dB SPL) probe tones, both in quiet and in the presence of a broad-band background noise. The background noise was introduced to eliminate combination tones or combination bands and other off-frequency listening cues that exist at high levels. Tuning curves were obtained using pure-tone maskers and 100-Hz-wide narrow-band noise maskers for probe tones at 1000 and 4000 Hz. High-level tuning curves for pure-tone maskers demonstrated large discontinuities or “notches” on the low-frequency sides of the tuning curves. Broad-band background noise eliminated those notches, indicating that the notches were due to the detection of off-frequency listening cues at combination-tone frequencies. High-level tuning curves for 100-Hz-wide narrow-band maskers also demonstrated notches on the low-frequency sides. Those notches were eliminated with broad-band background noise, which indicates that combination bands strongly influenced the shapes of high-level tuning curves obtained with narrow-band maskers. The influence of combination bands was dependent upon test frequency. At 1000 Hz, combination bands had very little influence on the shapes of high-level tuning curves. At 4000 Hz, where the masker bandwidth was substantially less than the critical bandwidth, combination bands strongly affected the low-frequency sides of the tuning curves. In 2 subjects tested at a probe frequency of 2000 Hz with 100-Hz-wide masking bands, combination bands also influenced the lowfrequency sides of high-level tuning curves. The presence of combination-tone or combination-band cues essentially steepened the low-frequency slopes of tuning curves, resulting in sharper estimates of tuning. Comparisons of tuning curves obtained with pure-tone maskers and narrow-band maskers, in the same listeners, revealed that pure-tone maskers were more effective than narrow-band maskers when the masker frequencies were in the tail region of the tuning curve. The results of these experiments support the notion that tuning in the normal auditory system broadens notably with stimulus level, once off-frequency listening cues such as combination tones or combination bands are eliminated. The low-level simultaneously masked tuning curve demonstrates a sharp bandpass tuning characteristic, whereas the high-level simultaneously masked tuning curve in background noise demonstrates a broad low-pass tuning characteristic. It is argued that comparisons of tuning in impaired ears with tuning in normal ears should be made using estimates of tuning in normal ears that are not influenced by combination-tone or combination-band detection cues.

Acknowledgments
This research was supported in part by NIDCD grants DC00110 and DC00149. The authors wish to thank D. D. Greenwood and two anonymous reviewers for their extensive suggestions on an earlier version of this manuscript.
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