The interaural level difference (ILD) is a robust indicator of sound source azimuth, and human ILD sensitivity persists under conditions that degrade normally-dominant interaural time difference (ITD) cues. Nonetheless, ILD sensitivity varies somewhat with both stimulus frequency and interaural correlation (coherence). To further investigate the combined binaural perceptual influence of these variables, the present study assessed ILD sensitivity at frequencies 250–4000 Hz using stimuli of varied interaural correlation. In the first of two experiments, ILD discrimination thresholds were modestly elevated, and subjective lateralization slightly reduced, for both half-correlated and uncorrelated narrowband noise tokens relative to correlated tokens. Different from thresholds in the correlated condition, which were worst at 1000 Hz [Grantham, D.W. (1984). J. Acoust. Soc. Am. 75, 1191–1194], thresholds in the decorrelated conditions were independent of frequency. However, intrinsic envelope fluctuations in narrowband stimuli caused moment-to-moment variation of the nominal ILD, complicating interpretation of measured thresholds. Thus, a second experiment employed low-fluctuation noise tokens, revealing a clear effect of interaural decoherence per se that was strongly frequency-dependent, decreasing in magnitude from low to high frequencies. Measurements are consistent with known integration times in ILD-sensitive neurons and also suggest persistent influences of covert ITD cues in putative “ILD” tasks.
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June 2021
June 30 2021
Effects of interaural decoherence on sensitivity to interaural level differences across frequency
Andrew D. Brown
;
Andrew D. Brown
a)
1
Department of Speech and Hearing Sciences, University of Washington
, 1417 Northeast 42nd Street, Seattle, Washington 98105, USA
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Daniel J. Tollin
Daniel J. Tollin
2
Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora
, Colorado 80045, USA
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a)
Also at: Virginia Merrill Bloedel Hearing Research Center, University of Washington, Seattle, WA 98195, USA. Electronic mail: andrewdb@uw.edu, ORCID: 0000-0003-0838-2894.
J. Acoust. Soc. Am. 149, 4630–4648 (2021)
Article history
Received:
July 22 2020
Accepted:
May 10 2021
Citation
Andrew D. Brown, Daniel J. Tollin; Effects of interaural decoherence on sensitivity to interaural level differences across frequency. J. Acoust. Soc. Am. 1 June 2021; 149 (6): 4630–4648. https://doi.org/10.1121/10.0005123
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