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May 1987

Volume 81, Issue S1, pp. S1-S100

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back to top Session K. Psychological and Physiological Acoustics III: Binaural Processing
Contributed Papers
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Predictions for binaural masked detection with frozen‐noise maskers (A)

Gary C. Kline and H. Steven Colburn

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S27-S27 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Biomedical Engineering Department, 110 Cummington Street, Boston University, Boston, MA 02215 A model of binaural heating based on combinations of interaural time and intensity differences [Gabriel et al., J. Acoust. Soc. Am. Suppl. 1 74, S85 (1983)] was used to predict results obtained previously [R. H. Gilkey, D. E. Robinson, and T. E. Hanna, J. Acoust. Soc. Am. 78, 1207–1219 (1985)] in a binaural masked detection experiment with repeatable samples of masking noise. The narrow‐band model generates its decision variables through a linear combination of interaural time and intensity differences followed by a sluggishness filter (averager). A computer simulation of the model was used to predict the hit and false‐alarm rates for each of ten independent, frozen‐noise masker samples, and for target phase angles of 0 deg and 90 deg. Model predictions disagree with the experimental results in two respects. First, the false‐alarm rates predicted by the model show almost no variation across masker samples, while the experimental results show changes from 5% to 80%. This disagreement illustrates the inadequacy of the additive internal noise assumption of the model. Second, the model predicts changes in the hit rate as large as 80% when the tone phase changes from 0 to 90 deg for a given masker sample, while the experimental results show changes less than 20% for a given masker sample (although hit rates vary over a range of 75% across masker samples). This significant correlation in hit rates for these two phase angles is not easily explained within a model based on interaural differences since the interaural differences in the stimulus are uncorrelated for these phase angles. [Work supported by NIH.]
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Extending the position‐variable model: Dependence of lateralization on frequency and bandwidth (A)

Glenn D. Shear and Richard M. Stern

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S27-S27 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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The position‐variable model [R. M. Stern, Jr. and H. S. Colburn, J. Acoust. Soc. Am. 64, 127–140 (1978)] is extended to describe the subjective lateral position of tones as a function of frequency and ITD, and the lateralization of bandpass noise as a function of bandwidth, ITD, and interaural phase shift. The two major modifications made to the model are (1) the use of a frequency‐dependent form of the function that expresses the relative number of binaural coincidence detectors as a function of their characteristic delay and (2) additional processing of the display of interaural cross correlation to emphasize those regions of the function which exhibit peaks at the same internal delay across a range of frequencies. For most naturally occurring broadband stimuli, these regions indicate the set of primary modes of the corresponding cross‐correlation functions, thereby enabling the central processor to determine without ambiguity the value of ITD present in the stimulus. The extended model describes lateralization data for a much wider range of stimulus frequencies than the original model, which could only describe responses elicited by 500‐Hz tones. [Work supported by NIH.]
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The dependence of binaural detection and interaural discrimination on interaural time and intensity in normal and impaired listeners (A)

J. Koehnke and H. S. Colburn

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S27-S27 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Measurements of binaural performance by normal and hearing‐impaired listeners are reported for large reference values of interaural time delay (ITD) and interaural intensity difference (IID). NoSπ detection thresholds and just‐noticeable differences (jnds) in ITD and IID were measured with 1/3‐oct noise bursts at 500 and 4000 Hz, using reference ITDs and IIDs up to 600 μs and 34 dB. As expected, jnds and thresholds for normal and impaired subjects increase as the reference IID increases. In contrast, increasing the reference ITD shows relatively small effects for most subjects. The present data are consistent with those described previously [C. Passaro, J. Koehnke, and H. S. Colburn, J. Acoust. Soc. Am. Suppl. 1 79, S21–S22 (1986)] but are more pronounced with larger reference ITDs and IIDs. For example, performance is generally poorer for the impaired listeners than the normal listeners. Also, for both groups, measurements of IID jnds consistently result in smaller jnds for the canceling combinations of reference ITD and IID than reinforcing combinations. [Work supported by NIH.]
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Nonlinear spectral interferometry (NLSI): A new approach to modeling binaural hearing and aural communication channeling (A)

Nathan Cohen and Dean Cummins

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S27-S27 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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A biointerferometric model for spatial hearing is described in which binaural information is processed as an interferometric response via a nonlinear spectral transform of the cross‐correlation function. Relevant observables include phase delay, phase delay rate, visibility amplitude, and visibility phase. Our model accounts for a broad range of hearing phenomena including: (1) localization below diffraction limited frequencies by overtone generation at the cochlea; (2) localization acuity by superresolution of the synthesized beam; (3) beam synthesis by visibility plane sampling through overtone content in speech and cochlear response; (4) the binaural advantage in intelligibility through interferometric rejection and neuronally driven beam steering; and (5) transformation from phase to amplitude localization cues through loss of visibility phase above the phase‐locked frequency range. This model obviates the need for multiple cue and/or component models and has distinct advantages over other cross‐correlation models. Additional psychoacoustic tests to corroborate this NLSI model are described.
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The effect of head‐induced interaural time and level differences on speech intelligibility in noise (A)

A. W. Bronkhorst and R. Plomp

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S27-S28 (1987); (2 pages)

Online Publication Date: 13 Aug 2005

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The effect of interaural time delay (ITD) and acoustic headshadow on binaural speech intelligibility in noise was studied. A free‐field condition was simulated by presenting recordings, made with a KEMAR manikin in an anechoic room, through headphones. Recordings were made of speech, reproduced in front of the manikin, and of noise, emanating from seven angles in the azimuthal plane, ranging from 0° (frontal) to 180° in steps of 30°. From this noise, two signals were derived, one containing only ITD, the other containing only headshadow. Speech‐reception thresholds for sentences in noise for a group of normal‐hearing subjects showed that for noise azimuths between 30° and 150°, the gain due to ITD lies between 3.9 and 5.1 dB, while the gain due to headshadow ranges from 3.5 to 7.8 dB. A second experiment with similar stimuli, presented monaurally or with a 20‐dB interaural level difference, indicated that for noise with only headshadow, the gain relies on the ear presented with the most favorable signal‐to‐noise ratio, but decreases when the noise presented to the other ear becomes relatively loud.
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Motion aftereffects with horizontally moving sound sources (A)

D. Wesley Grantham and Lynn E. Luethke

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S28-S28 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Continuous sounds were presented in an anechoic chamber through two horizontally rotating loudspeakers that traversed a full 360° around the observer at ear level (distance: 1.5 m). At 10‐s intervals this “adaptation stimulus” was interrupted and a 750‐ms “probe stimulus” was presented from a pair of stationary loudspeakers (separated by 7.5°) 1.6 m in front of the observer. The probe could itself be stationary or could “move” (employing a stereophonic balancing algorithm) in either direction. During a run the adaptation stimulus was held at a constant velocity (− 200° to + 200°/s), while probes with velocities varying from − 10° to + 10°/s were presented in a random order. Observers judged the direction of motion (“left” or “right”) of each probe tone. When the frequency content of the adaptation stimulus was the same as that of the probe stimulus (either 500‐Hz low‐pass or 6300‐Hz high‐pass noise), stationary probes were consistently judged to move in the direction opposite to that of the adaptation stimulus. This effect increased with the velocity of the adaptor. Possible sensory and nonsensory mechanisms underlying this aftereffect will be discussed. [Work supported by NIH.]
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A comparison of the effects of time and intensity during the auditory brain‐stem response to lateralized clicks (A)

Mark Stephenson and William Melnick

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S28-S28 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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A group of 12 otologically normal subjects were presented with binaural clicks at 70 dB nHL. During one condition, subjects delayed the onset of the click to the left ear until a single image was percieved either midway between the center of the head and the right ear (referred to as the “midway” location), or until the image was perceived just at the right ear. In a second condition, subjects attenuated the click to the left ear until the acoustic image was lateralized either midway towards the right ear, or just at the right ear. These same stimuli conditions were then used to evoke auditory brain‐stem responses (ABRs). When clicks were lateralized midway, ABR latencies from delayed versus attenuated clicks were not significantly different. However, when clicks were lateralized just at the right ear, there were statistically significant differences between latencies from delayed versus attenuated clicks. There was also a consistent ordinal relationship noted: In nearly every case, delayed clicks yielded longer latencies than attenuated clicks. The clear perceptual equivalence observed psychoacoustically was not fully reflected in the corresponding auditory brain‐stem responses. [Work supported by AFOSR.]
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The duplex nature of the brain‐stem binaural interaction component: Frequency, rate, and intensity effects (A)

T. K. Parthasarathy and G. Moushegian

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S28-S28 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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As in a previous study [J. Acoust. Soc. Am. Suppl. 1 79, S6 (1986)], stimuli were varied to evaluate the binaural interaction component (BIC) of the auditory brain‐stem response (ABR) in normal hearing adults. In addition to a clicklike sound, tone bursts (0.5, 1.0, and 2.0 kHz), having two cycles of rise‐fall time and one of duration, were presented at two intensities (85 and 100 dB SPL). Binaural wave III and V amplitudes were smaller with shorter latencies than summed monaural amplitudes and latencies at both intensity levels of the click and 2.0‐kHz tone burst. Increasing stimulus rate produced longer latencies and smaller peak amplitudes of the binaural interaction components and concomitantly longer latencies and smaller wave III and V amplitudes of ABR. Wave V latency shift was greater at 85 than at 100 dB SPL, whereas the BIC exhibited greater latency shifts at 100 than at 85 dB SPL. The derived frequency following response (FFR) to 0.5 and 1.0 kHz [J. Acoust. Soc. Am. Suppl. 1 79, S6 (1986)] had shorter latencies and larger amplitudes at 100 than at 85 dB SPL. All of the findings suggest that the BIC, in conformity with the findings from medullary neuronal physiology, is differentially sensitive to rate, frequency, and intensity.
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Sound localization in the budgerigar and the interaural pathways (A)

Thomas Park, Kazuo Okanoya, and Robert Dooling

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S28-S28 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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Sound localization presents a problem for animals with small heads (closely spaced ears) and poor high‐frequency hearing. In recent tests of spatial resolving power, several small songbirds (i.e., great tit, canary, and zebra finch) show rather large minimum audible angles (MAA) on the order of 15–20 deg. These results are expected if conventional binaural time and intensity differences are used. Budgerigars (17‐mm interaural distance), on the other hand, demonstrate an MAA of about 5 deg, which approaches the excellent ability of the barn owl with a much larger head (50‐mm interaural distance). Recent work has suggested that interaural pathways connecting the two ears of birds could be involved in sound localization. Using latex injection medium, we have demonstrated interaural pathways in the budgerigar, canary, and zebra finch. Taken together, the results of these behavioral and anatomical studies indicate that the budgerigar may use the interaural pathway in sound localization.
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Performance of adult subjects on a dichotic speech test under both directed and free recall listening conditions (A)

Jane A. Baran and Frank E. Musiek

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S28-S29 (1987); (2 pages)

Online Publication Date: 13 Aug 2005

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Twenty‐five young adult subjects with negative otologic histories were administered a dichotic rhyme test under three different listening conditions: (1) free recall, (2) directed listening to the right ear, and (3) directed listening to the left ear. The dichotic rhyme test used is composed of 30 well‐aligned synthetic CVC words that were presented at 50 dB SL (re: speech reception thresholds). The nature of the test is such that under normal conditions (i.e., free recall), listeners tend to repeat either the word presented to the left ear or to the right ear. Normal performance is approximately 50% correct identification in each ear, with a slight right ear advantage evident. In an earlier investigation using a dichotic CV test, Keith et al. [Ear Hear. 6, 270–273 (1985)] demonstrated a clear left ear advantage on a directed left ear task and an obvious right ear advantage on a directed right ear task. In the present investigation, no significant differences in the test scores were observed when the right and left ear scores were compared with the same ear scores across the three test conditions. In all three test conditions, a slight right ear advantage was noted. The implications of these findings as they relate to our understanding of how dichotic stimuli are processed will be discussed.
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Monaural perception of the rapidly alternating speech perception test (RASP) (A)

Richard W. Harris, Ruth Kaspar, and Robert H. Brey

J. Acoust. Soc. Am. Volume 81, Issue S1, pp. S29-S29 (1987); (1 page)

Online Publication Date: 13 Aug 2005

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One test that claims to measure binaural fusion, and is routinely utilized as a measure of central auditory function, is the rapidly alternating speech perception (RASP) test. There has been some controversy over the clinical validity of this test. The purpose of this study was to investigate information contained in a single channel of the RASP. Twenty‐four normal hearing subjects listened to one channel of the RASP: twelve to channel 1, twelve to channel 2. Sentence scores for a single channel of the RASP ranged from 0% to 70%, with mean sentence scores for subjects listening to channels 1 and 2 of 37.72% and 20.8%, respectively. An ideal binaural fusion test would contain no, or very little, information when listening to only one channel. It is possible that a single channel of the RASP contains too much information. Many of the sentences were repeated correctly, in their entirety, by at least a few of the subjects listening to either channel in isolation, a task previously assumed to be possible only in the binaural condition.
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