Tags

Type your tag names separated by a space and hit enter

Speech recognition in noise: estimating effects of compressive nonlinearities in the basilar-membrane response.
Ear Hear. 2007 Sep; 28(5):682-93.EH

Abstract

OBJECTIVES

This experiment was designed to estimate effects of cochlear nonlinearities on tonal and speech masking for individuals with normal hearing who have a range of quiet thresholds. Physiological and psychophysical evidence indicates that for signals close to the characteristic frequency (CF) of a place on the basilar membrane, the normal growth of response of the basilar membrane is linear at lower stimulus levels and compressed at medium to higher stimulus levels. In contrast, at moderate to high CFs, the basilar membrane responds more linearly to stimuli at frequencies well below the CF regardless of input level. Thus, the hypothesis tested was that masker effectiveness would change as a function of stimulus level consistent with the underlying basilar membrane response. Specifically, with a fixed-level speech signal and a speech-shaped masker that ranges from low to higher levels, the resulting response of the basilar membrane to the masker would be linear at lower levels and compressed at medium to higher levels. This would result in relatively less effective masking at higher masker levels. It was further hypothesized that the transition from linear to compressed responses to both tones and maskers would occur at higher levels for listeners with higher quiet thresholds than for listeners with lower quiet thresholds.

DESIGN

Tonal thresholds and speech recognition in noise were measured as a function of masker level. A 10-msec, 2.0-kHz tone was presented in a lower frequency masker ranging from 40 to 85 dB SPL. Moderate-level speech was presented in interrupted noise at six levels ranging from 47 to 77 dB SPL. To minimize differences in speech audibility that could arise during the "off" periods of the interrupted noise, a low-level steady-state "threshold-matching noise" was also present during measurement of speech recognition. Subjects were 30 adults with normal hearing with a 20-dB range of average quiet thresholds.

RESULTS

Tonal breakpoints (i.e., the levels corresponding to the transitions from linear to nonlinear responses) were significantly correlated with quiet thresholds, whereas slopes measured above the breakpoints were not. Speech recognition in noise was consistent with the hypothesis that the response of the basilar membrane to the masker was linear at lower levels and compressed at medium to higher levels, resulting in less effective masking at higher masker levels. That is, at lower masker levels, as masker level increased, mean observed speech scores declined as predicted using the articulation index, an audibility-based model. With further increases in masker level, mean scores declined less than predicted. Moreover, for subjects with higher quiet thresholds, masker effectiveness remained constant for a wider range of masker levels than for subjects with lower quiet thresholds, consistent with the hypothesis that the transition from linear to compressed responses occurred at higher levels. Finally, significant negative correlations were obtained between individual subjects' tonal and speech measures.

CONCLUSIONS

Results from tonal and speech tasks were consistent with basilar membrane nonlinearities and consistent with changes in nonlinearities with minor threshold elevations, providing support for their role in the understanding of speech in noise with increases in noise level.

Authors+Show Affiliations

Medical University of South Carolina, Charleston, SC 29425, USA. horwitar@musc.eduNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

17804982

Citation

Horwitz, Amy R., et al. "Speech Recognition in Noise: Estimating Effects of Compressive Nonlinearities in the Basilar-membrane Response." Ear and Hearing, vol. 28, no. 5, 2007, pp. 682-93.
Horwitz AR, Ahlstrom JB, Dubno JR. Speech recognition in noise: estimating effects of compressive nonlinearities in the basilar-membrane response. Ear Hear. 2007;28(5):682-93.
Horwitz, A. R., Ahlstrom, J. B., & Dubno, J. R. (2007). Speech recognition in noise: estimating effects of compressive nonlinearities in the basilar-membrane response. Ear and Hearing, 28(5), 682-93.
Horwitz AR, Ahlstrom JB, Dubno JR. Speech Recognition in Noise: Estimating Effects of Compressive Nonlinearities in the Basilar-membrane Response. Ear Hear. 2007;28(5):682-93. PubMed PMID: 17804982.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Speech recognition in noise: estimating effects of compressive nonlinearities in the basilar-membrane response. AU - Horwitz,Amy R, AU - Ahlstrom,Jayne B, AU - Dubno,Judy R, PY - 2007/9/7/pubmed PY - 2007/12/6/medline PY - 2007/9/7/entrez SP - 682 EP - 93 JF - Ear and hearing JO - Ear Hear VL - 28 IS - 5 N2 - OBJECTIVES: This experiment was designed to estimate effects of cochlear nonlinearities on tonal and speech masking for individuals with normal hearing who have a range of quiet thresholds. Physiological and psychophysical evidence indicates that for signals close to the characteristic frequency (CF) of a place on the basilar membrane, the normal growth of response of the basilar membrane is linear at lower stimulus levels and compressed at medium to higher stimulus levels. In contrast, at moderate to high CFs, the basilar membrane responds more linearly to stimuli at frequencies well below the CF regardless of input level. Thus, the hypothesis tested was that masker effectiveness would change as a function of stimulus level consistent with the underlying basilar membrane response. Specifically, with a fixed-level speech signal and a speech-shaped masker that ranges from low to higher levels, the resulting response of the basilar membrane to the masker would be linear at lower levels and compressed at medium to higher levels. This would result in relatively less effective masking at higher masker levels. It was further hypothesized that the transition from linear to compressed responses to both tones and maskers would occur at higher levels for listeners with higher quiet thresholds than for listeners with lower quiet thresholds. DESIGN: Tonal thresholds and speech recognition in noise were measured as a function of masker level. A 10-msec, 2.0-kHz tone was presented in a lower frequency masker ranging from 40 to 85 dB SPL. Moderate-level speech was presented in interrupted noise at six levels ranging from 47 to 77 dB SPL. To minimize differences in speech audibility that could arise during the "off" periods of the interrupted noise, a low-level steady-state "threshold-matching noise" was also present during measurement of speech recognition. Subjects were 30 adults with normal hearing with a 20-dB range of average quiet thresholds. RESULTS: Tonal breakpoints (i.e., the levels corresponding to the transitions from linear to nonlinear responses) were significantly correlated with quiet thresholds, whereas slopes measured above the breakpoints were not. Speech recognition in noise was consistent with the hypothesis that the response of the basilar membrane to the masker was linear at lower levels and compressed at medium to higher levels, resulting in less effective masking at higher masker levels. That is, at lower masker levels, as masker level increased, mean observed speech scores declined as predicted using the articulation index, an audibility-based model. With further increases in masker level, mean scores declined less than predicted. Moreover, for subjects with higher quiet thresholds, masker effectiveness remained constant for a wider range of masker levels than for subjects with lower quiet thresholds, consistent with the hypothesis that the transition from linear to compressed responses occurred at higher levels. Finally, significant negative correlations were obtained between individual subjects' tonal and speech measures. CONCLUSIONS: Results from tonal and speech tasks were consistent with basilar membrane nonlinearities and consistent with changes in nonlinearities with minor threshold elevations, providing support for their role in the understanding of speech in noise with increases in noise level. SN - 0196-0202 UR - https://www.unboundmedicine.com/medline/citation/17804982/Speech_recognition_in_noise:_estimating_effects_of_compressive_nonlinearities_in_the_basilar_membrane_response_ L2 - https://doi.org/10.1097/AUD.0b013e31812f7156 DB - PRIME DP - Unbound Medicine ER -