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May 1988

Volume 83, Issue S1, pp. S1-S122

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back to top Session CCC. Psychological Acoustics VII: Multiear Phenomena and Models
Contributed Papers
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Creating a sound field for manipulating interaural level differences separately or independently of the interaural time differences and vice versa (A)

George F. Kuhn

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S121-S121 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Using two or more sources whose source strengths and relative phases can be controlled independently, a sound field can be generated in which the interaural pressure level differences (ILDs) and the interaural time differences (ITDs) can be controlled separately. Thus, for a fixed ILD, a range of ITDs, or vice versa, can be presented to the listener. Thus it appears possible to perform some localization experiments that had previously been confined to lateralization methods using earphones. Some calculated results for interaural time differences and interaural level differences, using two sources, will be presented.
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An adaptation model for source displacement in multiple‐source environments (A)

Gregory H. Wakefield

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S121-S121 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In general, the acoustic field at the two ears is not sufficient to support source localization for more than one source. Experiments on localization indicate that the co‐occurrence of two sources can lead to substantial source localization error that reflects either the ambiguity present in the acoustic field or some form of bias in the binaural processing of that acoustic field. It is shown that displacement of the perceived lateral position of a narrow‐band noise away from the lateral position of a narrowband interferer [G. H. Wakefield and N. F. Viemeister, J. Acoust. Soc. Am. Suppl. 1 76, S91 (1984)] does not lie on the surface of possible source positions supported by the acoustic field. Therefore, it does not appear that anomalous localization can be explained entirely with respect to ambiguities in the acoustic field. Instead, a modification of Stern's position variable is proposed to account for source displacement by introducing a frequency‐dependent form of spatial adaptation. Much, but not all, of our displacement data are consistent with an additive form of adaptation with a time constant of 25 ms in which the level of adaptation at a given position does not depend on excitation at other positions. The manner in which the model fails to predict displacement for long‐duration sources suggests the presence of a weaker adaptation across position.
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Binaural modulation detection (A)

D. Wesley Grantham and Sid P. Bacon

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S121-S121 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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A sinusoidally amplitude‐modulated (SAM) noise (modulation depth: 1.0) was used to mask another SAM noise, the signal, in a two‐interval forced‐choice experiment. Signal and masker modulation frequency were both either 4 or 32 Hz, and were added in quadrature. The same wideband noise carrier was used for both masker and signal (spectrum level: 15 dB SPL). The whole stimulus was filtered after modulation (either 4‐kHz low pass or 4‐kHz high pass). Modulation depth (m) of the signal was varied adaptively to track threshold. In the case of diotic presentation (Mo‐So), threshold m was about 0.30 for both modulation frequencies and both filtering conditions. In a binaural condition Mo‐Sm (masker presented to both ears and signal to only one ear) some subjects. showed a release from masking of up to 10 dB (m = 0.10), while others. showed none. The release from masking occurred for both filtering conditions, but only for the lower (4‐Hz) modulation rate. The results will be, discussed in relation to current models of binaural processing and the sluggish nature of the binaural system. [Work supported by NIH.]
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Detection of interaural phase shifts and level differences in portions of broadband noise (A)

William A. Yost

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S121-S121 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Versions of Cramer‐Huggins pitch stimuli were generated such that a narrow band (bandwidths ranged from 1–100 Hz) of a wideband, diotic noise (low‐passed filtered at 8000 Hz) was presented dichotically with an interaural phase shift or an interaural level difference. The threshold value for detecting a phase shift or a level difference in the dichotic, narrowband portion of the broadband noise was determined as a function of the center frequency of the dichotic, narrow band of noise and as a function of the bandwidth of the dichotic, narrow band of noise. A single‐interval procedure without feedback was used to estimate three point psychometric functions relating d′ to interaural phase or d′ to interauralevel difference. A random variation in the interaural level difference of the entire noise waveform was also used to force the listeners to use pitch as the cue for detection rather than some aspect of lateral position. The data will be discussed in terms of models of binaural processing and binaural pitch. [Work supported by NINCDS.]
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Lateralization on the basis of interaural envelope delays: The effect of component starting phase (A)

R. H. Dye, A. J. Niemiec, and M. A. Stellmack

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S122-S122 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Threshold interaural envelope delays were measured with a 2 AFC paradigm as a function of modulation frequency (fm = 25, 50, 100, 200, 300, 400, and 500 Hz) for three‐ and five‐component complexes whose center frequencies (fc) were equal to 4000 Hz. Comparisons were made between thresholds obtained when the starting phases were randomized and when they were all set to zero. The level of each component was approximately 50 dB SPL, and the signal duration was 200 ms with 10‐ms linear rise/decay times. While reductions in depth of modulation elevate threshold envelope delays [G. B. Henning, J. Acoust. Soc. Am. 55, 84–90 (1974)], no such effects were found for phase randomization even when modulation rates were low and all components fell within a critical band. This seems surprising in light of the fact that both reduce depth of modulation and phase randomization reduce the peak factors of the waveforms, which is commonly believed to interfere with entrainment by the peripheral auditory system. Efforts to reconcile the absence of phase effects with the deleterious effects of reduced depth of modulation will be presented. [Work supported by NIH/NINCDS and AFOSR.]
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Accruing binaural cues across frequency (A)

Thomas N. Buell and Ervin R. Hafter

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S122-S122 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Localizing a complex sound requires in part an analysis of the interaural difference of time (IDT) of the component frequencies. Above about 500 Hz, the IDT is constant across the frequency spectrum. This commonality may be used to group components that arise from a single source as well as segregating such components from those which arise from competing sources. Interactions across components can be shown by measuring changes in IDT thresholds when a target is lateralized in the presence of other simultaneous sounds. When the nontarget sound has a dissimilar IDT, thresholds may actually increase. This effect has been aptly termed “interference” [D. McFadden and E.G. Pasanen, J. Acoust. Soc. Am. 59, 634–639 (1976)]. In the present experiment, listeners detected an IDT in a 600‐Hz target tone both with and without the presence of a nontarget tone. Of special interest was the harmonic relation between target and nontarget. Among other factors, the results show that a simple relation such as 400 Hz can produce more interference than one that is nonharmonic, even when the interfering tone is closer to the target, e.g., 531 Hz. [Research supported by NIH.]
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Discrimination of direction in the free field (A)

Ervin R. Hafter, Thomas N. Buell, David A. Basiji, and Elizabeth E. Shriberg

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S122-S122 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The psychophysics of direct comparison (two‐alternative, forced choice) was applied to the study of localization. For complex signals, the interaural parameters presented by stimuli in the free field are more “natural” than those heard through earphones though more difficult to control. In this study, digital preprocessing was used to reverse the spectral characteristics of each loudspeaker to make its response uniform and indiscriminable. The listener sat in an anechoic chamber with his or her head optically fixed at the center of a semicircular array of speakers. The stimuli were trains of n filtered clicks (n = 1, 9, or 18) whose center frequencies were either 2050, 4050, or 6050 Hz. Interclick intervals (ICIs) were either 4 or 12 ms and levels were set so that a single click was 10 dB SL. Minimum audible angles (MAAs) were found to increase as the azimuth increased from 0 to 60 deg; performance was best at 2050 Hz. Studies of lateralization with earphones have led to speculations about “binaural adaptation,” a process whereby improvements in threshold with increased n depend on the click rate (1/ICI). Similar analyses show this also to be true for free‐field listening. [Research supported by the NIH.]
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Sound localization without interaural time or intensity differences (A)

Frederic Wightman, Doris Kistler, Marianne Arruda, and Linda Schwister

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S122-S122 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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In a series of localization experiments, blindfolded listeners were asked to give the apparent azimuth and elevation coordinates of 250‐ms broadband noise bursts. The noise bursts were spectrally shaped so that the spectrum level in each critical band was set randomly (from trial to trial) within a 20‐dB range. In a reference condition, the sounds were transduced by miniature loudspeakers placed at 36 locations in an anechoic chamber. Performance in this free‐field condition agreed with previous results in the literature except for an increased frequency of frontback reversals, which is felt to be the result of the lack of a visual frame of reference. In a control condition, digital techniques were used to synthesize headphone‐presented stimuli that were nearly identical, as measured in listeners' ear canals, to the free‐field stimuli. Localization performance with these stimuli was virtually the same as in free field, thus verifying the adequacy of the simulation. The digital filters used to synthesize the stimuli were then modified such that in one condition the interaural time differences were removed from all 36 stimuli, and in another condition the interaural amplitude differences were removed. In both of these conditions, localization performance was degraded. However, preliminary results suggest that the degradation caused by removal of interaural time differences is considerably greater than that caused by removal of interaural intensity differences. [Work supported by NIH, NSF, and NASA.]
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