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Apr 1991

Volume 89, Issue 4B, pp. 1851-2015

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back to top Session 8PP: Psychological and Physiological Acoustics: Localization and Binaural Processes
Contributed Papers
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Effects of age on auditory spatial resolution in the horizontal plane (A)

David W. Chandler and D. Wesley Grantham

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1994-1994 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The purpose of this research was to determine if auditory spatial resolution in the horizontal plane changes with age. Spatial resolution was measured in static conditions, represented by the minimum audible angle (MAA), and in dynamic conditions, represented by the minimum audible movement angle (MAMA). MAAs and MAMAs were measured for adult subjects 60 to 80 years of age with normal (or near normal) hearing thresholds. All measurements were obtained in a darkened anechoic chamber. Thresholds were measured as a function of stimulus bandwidth, center frequency, and listening azimuth, for both MAA and MAMA. Additionally, MAMAs were measured as a function of the velocity of the moving stimulus source. MAAs and MAMAs of the elderly will be compared with previous measurements for young normal adults that were obtained under the same stimulus conditions [D. W. Chandler and D. W. Grantham, J. Acoust. Soc. Am. Suppl. 1 87, S64 (1990)]. It is hypothesized that auditory spatial resolution in the horizontal plane diminishes with age because of generalized deficits of central nervous system processing. This diminished resolution should be reflected by poorer MAAs and poorer MAMAs among the elderly subjects than among the young, normal‐hearing subjects. [Work supported by NIH.]
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Monaural spatial resolution in the horizontal plane under dynamic and static listening conditions (A)

D. Wesley Grantham and David W. Chandler

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1995 (1991); (1 page) | Cited 1 time

Online Publication Date: 14 Aug 2005

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Auditory spatial resolution was measured in the horizontal plane for three normal‐hearing adult subjects in a darkened anechoic chamber. In all conditions, subjects' right ears were occluded by an EAR foam insert plug plus an external sound‐attenuating muff, providing a total of about 40 dB of attenuation. In the dynamic conditions, the minimum audible movement angle (MAMA) was measured—that is, the angular extent a moving target had to traverse to be just discriminable from a stationary target. In the static conditions, the minimum audible angle (MAA) was measured—that is, the minimum angular separation between two sequentially presented stationary targets that was just discriminable from a single stationary target presented twice in succession. In general, MAMAs and MAAs decreased as stimulus bandwidth increased from 0 Hz (pure tone at 3000 Hz) to wideband. MAAs were extremely variable across and within subjects (varying from 10° to 40° of arc). MAMAs for slow‐velocity targets (10°/s) were usually lower than MAAs measured for the same signals, a result that contrasts with the results from binaural resolution tasks [D. W. Chandler and D. W. Grantham, J. Acoust. Soc. Am. Suppl. 1 87, S64 (1990)]. These results suggest that specialized mechanisms sensitive to dynamic stimuli may play a role in monaural spatial resolution. [Work supported by NIH.]
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Monaural localization, revisited (A)

Frederic Wightman, Doris Kistler, and Marianne Arruda

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1995 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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There are numerous reports in the psychoacoustical literature that human listeners can localize sound sources reasonably well with one ear. Since interaural difference cues are presumably eliminated in monaural conditions, the so‐called “monaural spectral cues” introduced by pinna filtering are assumed to provide the information necessary for accurate localization in monaural conditions. In these experiments, listeners localize wideband noise bursts presented either in free‐field (with one ear occluded) or via headphones (with the signal to one phone either attenuated or disconnected). In the headphone conditions, pinna filtering effects are added digitally, such that the waveforms at a listener's eardrum are nearly the same as those produced by free‐field sources. The noise spectrum is scrambled from trial to trial to prevent learning. With the noise bursts presented at about 30 dB SL in free‐field, the results are consistent with other recent reports and suggest that some ability to localize, especially in the vertical direction, is retained in monaural conditions. However, when the identical stimuli are presented via headphones, there is no indication that sources can be localized monaurally. In other conditions, listeners localize constant spectrum stimuli, free‐field stimuli at 70 dB SL, and binaural headphone stimuli with one ear attenuated. Results from these conditions suggest that monaural localization in free‐field is most likely mediated by small head movements, a priori knowledge of the stimulus spectrum, and acoustical leakage through the ear‐occluding devices used to monauralize the listeners. [Work supported by NIH and NASA.]
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Influence of onset cues in lateralization (A)

Richard L. Freyman and Patrick M. Zurek

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1995 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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When pairs of clicks delivered binaurally via earphones are repeated to form a click train, interaural cues at stimulus onset can exert a strong influence on the perceived intracranial position of the entire stimulus [Saberi and Perrott, J. Acoust. Soc. Am. Suppl. 1 86, S11 (1989)]. This phenomenon has been observed most clearly under conditions in which the interaural time delays in the ongoing click trains—because they alternate between two values—are ambiguous. For example, when a single click pair with a 500‐μ‐time lead to the right is followed by a 250‐ms train consisting of alternating diotic and left‐leading click pairs, the entire stimulus is lateralized to the right. This paper will describe conditions in which onset cues dominate the perceived lateral position as well as those in which steady‐state cues determine the lateralization. It will also describe stimulus manipulations that appear to produce a release from the influence of the onset cues. For example, a brief silent gap inserted in the middle of a click train released the listener from the influence of the original onset, while a brief burst of binaural white noise presented during the middle of the click train did not. [Work supported by NSF and NIH.]
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Differential lateralization interference for interaural time and interaural level differences (A)

Laurie M. Heller and Virginia M. Richards

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1995 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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Lateralization thresholds were obtained in a 21FC task using 200‐ms noise bands presented with either an interaural time or level difference. The elevation in lateralization threshold (interference) caused by a simultaneously presented noise band was measured. When the ITD was applied to a 50‐Hz‐wide noise band centered at 500 Hz, there was minimal interference from a diotic 400‐Hz‐wide noise band centered at 4000 Hz. When the ITD was applied to the noise band centered at 4000 Hz, there was substantial interference from a diotic band of noise centered at 500 Hz [D. Mcfadden and E. G. Pasanen, J. Acoust. Soc. Am. 59, 634–639 (1976)]. In contrast, the interfering effect of a diotic noise band was greater when the ILD was applied to the 500‐Hz band of noise than when it was applied to the 4000‐Hz band of noise. A similar pattern of results was obtained when the ITD or ILD of the interfering band of noise was randomized from interval to interval, although randomization produced greater interference in all conditions. The complementary pattern of results for time and level differences favors an explanation based on averaging between simultaneous interaural parameters rather than a masking‐based explanation.
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Modeling of binaural discrimination of multiple sound sources: A contribution to the development of a “cocktail party processor” (A)

H. Slatky

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1995 (1991); (1 page)

Online Publication Date: 14 Aug 2005

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The human hearing system when being stimulated simultaneously by narrow‐banded signals from two loudspeakers at different locations is able to determine the directions of both sound sources. However, conventional models of binaural interaction which are based on interaural cross correlation in critical bands fail in discriminating the source directions. The reason is that the cross‐correlation functions at the output of the model display severe fluctuations in time. A revised binaural cross‐correlation model that contains an additional “recomputation mechanism” will be presented. This mechanism estimates directions and energies of sound sources from cross‐correlation functions fluctuating in time. Using this mechanism the results of relevant auditory experiments can be reproduced. This model has been applied to construct a cocktail party processor, which is able to enhance the signal‐to‐noise ratio considerably.
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Changing echo thresholds (A)

Richard Freyman, Rachel Clifton, and Ruth Litovsky

J. Acoust. Soc. Am. Volume 89, Issue 4B, pp. 1995-1996 (1991); (2 pages)

Online Publication Date: 14 Aug 2005

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Echo thresholds for a 4‐ms white noise burst were measured in an anechoic chamber with the leading loudspeaker located at 45° left and three lagging loudspeakers at 35°, 45°, and 55° right. The listener judged whether the echo sound came from the loudspeaker at 35° or 55° right by pressing one of two buttons; correct feedback was provided on every trial. This test noise burst was presented in isolation, or preceded by several conditions. Lead only had a train of nine noise bursts from the leading loudspeaker preceding the test noise burst; Lag only had a train from the lagging loudspeaker at 45° right; Precedence effect (PE) had a train from both leading and lagging loudspeaker at 45° left and right. The PE condition had the highest echo threshold (14.9 ms), followed by the isolated burst (11.2 ms), with the lowest threshold for Lead only (6.8 ms). Increased threshold under the PE condition indicated that repetition of the echo during the train was necessary to drive up echo threshold compared to the isolated burst. The single source train appeared to enhance the test burst echo following the train. [Work supported by NSF.]
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