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Apr 2007

Volume 121, Issue 4, pp. 1811-EL175

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Modeling comodulation masking release using an equalization-cancellation mechanism

Tobias Piechowiak, Stephan D. Ewert, and Torsten Dau

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2111-2126 (2007); (16 pages) | Cited 19 times

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This study presents an auditory processing model that accounts for the perceptual phenomenon of comodulation masking release (CMR). The model includes an equalization-cancellation (EC) stage for the processing of activity across the audio-frequency axis. The EC process across frequency takes place at the output of a modulation filterbank assumed for each audio-frequency channel. The model was evaluated in three experimental conditions: (i) CMR with four widely spaced flanking bands in order to study pure across-channel processing, (ii) CMR with one flanking band varying in frequency in order to study the transition between conditions dominated by within-channel processing and those dominated by across-channel processing, and (iii) CMR obtained in the “classical” band-widening paradigm in order to study the role of across-channel processing in a condition which always includes within-channel processing. The simulations support the hypothesis that within-channel contributions to CMR can be as large as 15 dB. The across-channel process is robust but small (about 2–4 dB) and only observable at small masker bandwidths. Overall, the proposed model might provide an interesting framework for the analysis of fluctuating sounds in the auditory system.
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43.66.Ba Models and theories of auditory processes
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Interaural fluctuations and the detection of interaural incoherence. II. Brief duration noises

Matthew J. Goupell and William M. Hartmann

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2127-2136 (2007); (10 pages) | Cited 6 times

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Listeners detected a small amount of interaural incoherence in reproducible noises with narrow bandwidths and a center frequency of 500 Hz. The durations of the noise stimuli were 100, 50, or 25 ms, and every one of the noises had the same value of interaural coherence, namely 0.992. When the nominal noise bandwidth was 14 Hz, the ability to detect incoherence was found to depend strongly on the size of the fluctuations in interaural phase and level for durations of 100 and 50 ms. For the duration of 25 ms, performance did not appear to depend entirely on fluctuations. Instead, listeners sometimes recognized incoherence on the basis of laterality. However, when the nominal bandwidth was doubled, leading to a greater number of fluctuations, detection performance at 25 ms resembled that at 50 ms for the smaller bandwidth. It is concluded that the detection of a small amount of interaural incoherence is mediated by fluctuations in phase and level for brief stimulus durations, so long as such fluctuations exist physically. This conclusion presents a promising alternative to models of binaural detection that are based on the short-term cross-correlation in the stimulus.
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43.66.Ba Models and theories of auditory processes
43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources

Loudness changes induced by a proximal sound: Loudness enhancement, loudness recalibration, or both?

Daniel Oberfeld

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2137-2148 (2007); (12 pages) | Cited 6 times

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The effect of a forward masker on the loudness of a target tone in close temporal proximity was investigated. Loudness matches between a target and a comparison tone at the same frequency were obtained for a wide range of target and masker levels. Contrary to the hypothesis by Scharf, Buus, and Nieder [J. Acoust. Soc. Am. 112, 807–810 (2002)] , these matches could not be explained by an effect of the masker on the comparison loudness, which was measured by loudness matches between the comparison and a fourth tone separated in frequency from the comparison and the masker. The data thus demonstrate that a forward masker has an effect on the loudness of a proximal target. The results are compatible with the suggestion by Arieh and Marks [J. Acoust. Soc. Am. 114, 1550–1556 (2003)] that the masker triggers two processes. The data indicate that the effect of the slower-decaying process resulting in a reduction in the loudness of a following tone saturates at masker-target level differences of 10–20 dB. The faster-decaying process causing loudness enhancement or loudness decrement has the strongest effect at a masker-target level difference of approximately 30 dB. A model explaining this mid-difference hump is proposed.
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43.66.Cb Loudness, absolute threshold
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

The time required to focus on a cued signal frequency

Bertram Scharf, Adam Reeves, and John Suciu

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2149-2157 (2007); (9 pages) | Cited 5 times

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How quickly can a listener focus on a single tonal cue that indicates the frequency of an upcoming signal? Initial measurements were made with frequency uncertainty (signal frequency varies randomly from trial to trial) and with certainty (same frequency on all trials). Measured by a yes–no procedure, thresholds for 40- and 20‐ms signals presented in continuous broadband noise at 50 dB SPL were higher in uncertainty than in certainty; the difference decreased monotonically from 5 dB at frequencies below 500 Hz to under 3 dB above about 2500 Hz. This decrease in the detrimental effect from uncertainty, which comes about with increasing signal frequency, may result from preferential attention to higher frequencies. In a second experiment, frequency again varied randomly, but each trial now began with a cue at the signal frequency. The critical variable was the delay from cue onset to signal onset. A delay of 352 ms eliminated the detrimental effect of frequency uncertainty at all frequencies. At the shortest delays of 52 and 82 ms the detrimental effect was reduced primarily at lower frequencies. Our analysis suggests that shifting focus to a cued frequency region, under optimal stimulus conditions, requires less than 52 ms.
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43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

The measurement problem in level discrimination

Daniel Shepherd and Michael J. Hautus

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2158-2167 (2007); (10 pages) | Cited 3 times

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There is disagreement among theorists over the exact measure to be used to quantify auditory level discrimination. It has been proposed that, for level discrimination tasks, the measure that is most linearly related to the sensitivity index, d′, will be the correct measure. The level difference (ΔL) and the Weber fraction (Θ) are both candidates, though the latter is sensitive to the physical unit in which it is expressed (e.g., pressure or intensity) while the former is not. Psychometric functions for level discrimination were obtained at a number of pedestal levels for 10-ms sinusoids (either 1000 or 6500 Hz) and broadband noise bursts. These functions were used to assess which of three measures: ΔL, Θ = Δp/p, or Θ = ΔI/I, is most nearly linearly related to d′. The results suggest that Δp/p is the measure that comes closest to being linearly related to d′.
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43.66.Fe Discrimination: intensity and frequency
43.66.Dc Masking
43.66.Ba Models and theories of auditory processes
43.66.Yw Instruments and methods related to hearing and its measurement
43.66.Cb Loudness, absolute threshold

Comparison of level discrimination, increment detection, and comodulation masking release in the audio- and envelope-frequency domains

Paul C. Nelson, Stephan D. Ewert, Laurel H. Carney, and Torsten Dau

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2168-2181 (2007); (14 pages)

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In general, the temporal structure of stimuli must be considered to account for certain observations made in detection and masking experiments in the audio-frequency domain. Two such phenomena are (1) a heightened sensitivity to amplitude increments with a temporal fringe compared to gated level discrimination performance and (2) lower tone-in-noise detection thresholds using a modulated masker compared to those using an unmodulated masker. In the current study, translations of these two experiments were carried out to test the hypothesis that analogous cues might be used in the envelope-frequency domain. Pure-tone carrier amplitude-modulation (AM) depth-discrimination thresholds were found to be similar using both traditional gated stimuli and using a temporally modulated fringe for a fixed standard depth (ms = 0.25) and a range of AM frequencies (4–64 Hz). In a second experiment, masked sinusoidal AM detection thresholds were compared in conditions with and without slow and regular fluctuations imposed on the instantaneous masker AM depth. Release from masking was obtained only for very slow masker fluctuations (less than 2 Hz). A physiologically motivated model that effectively acts as a first-order envelope change detector accounted for several, but not all, of the key aspects of the data.
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43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Dc Masking

Lateralization discrimination of interaural time delays in four-pulse sequences in electric and acoustic hearing

Bernhard Laback, Piotr Majdak, and Wolf-Dieter Baumgartner

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2182-2191 (2007); (10 pages) | Cited 18 times

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This study examined the sensitivity of four cochlear implant (CI) listeners to interaural time difference (ITD) in different portions of four-pulse sequences in lateralization discrimination. ITD was present either in all the pulses (referred to as condition Wave), the two middle pulses (Ongoing), the first pulse (Onset), the last pulse (Offset), or both the first and last pulse (Gating). All ITD conditions were tested at different pulse rates (100, 200, 400, and 800 pulses/s pps). Also, five normal hearing (NH) subjects were tested, listening to an acoustic simulation of CI stimulation. All CI and NH listeners were sensitive in condition Gating at all pulse rates for which they showed sensitivity in condition Wave. The sensitivity in condition Onset increased with the pulse rate for three CI listeners as well as for all NH listeners. The performance in condition Ongoing varied over the subjects. One CI listener showed sensitivity up to 800 pps, two up to 400 pps, and one at 100 pps only. The group of NH listeners showed sensitivity up to 200 pps. The result that CI listeners detect ITD from the middle pulses of short trains indicates the relevance of fine timing of stimulation pulses in lateralization and therefore in CI stimulation strategies.
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43.66.Pn Binaural hearing
43.66.Ts Auditory prostheses, hearing aids
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Sensitivity to binaural timing in bilateral cochlear implant users

Richard J. M. van Hoesel

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2192-2206 (2007); (15 pages) | Cited 35 times

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Various measures of binaural timing sensitivity were made in three bilateral cochlear implant users, who had demonstrated moderate-to-good interaural time delay (ITD) sensitivity at 100 pulses-per-second (pps). Overall, ITD thresholds increased at higher pulse rates, lower levels, and shorter durations, although intersubject differences were evident. Monaural rate-discrimination thresholds, using the same stimulation parameters, showed more substantial elevation than ITDs with increased rate. ITD sensitivity with 6000 pps stimuli, amplitude-modulated at 100 Hz, was similar to that with unmodulated pulse trains at 100 pps, but at 200 and 300 Hz performance was poorer than with unmodulated signals. Measures of sensitivity to binaural beats with unmodulated pulse-trains showed that all three subjects could use time-varying ITD cues at 100 pps, but not 300 pps, even though static ITD sensitivity was relatively unaffected over that range. The difference between static and dynamic ITD thresholds is discussed in terms of relative contributions from initial and later arriving cues, which was further examined in an experiment using two-pulse stimuli as a function of interpulse separation. In agreement with the binaural-beat data, findings from that experiment showed poor discrimination of ITDs on the second pulse when the interval between pulses was reduced to a few milliseconds.
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43.66.Pn Binaural hearing
43.66.Ts Auditory prostheses, hearing aids
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Ba Models and theories of auditory processes

Similar patterns of learning and performance variability for human discrimination of interaural time differences at high and low frequencies

Yuxuan Zhang and Beverly A. Wright

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2207-2216 (2007); (10 pages) | Cited 10 times

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Sound source localization on the horizontal plane is primarily determined by interaural time differences (ITDs) for low-frequency stimuli and by interaural level differences (ILDs) for high-frequency stimuli, but ITDs in high-frequency complex stimuli can also be used for localization. Of interest here is the relationship between the processing of high-frequency ITDs and that of low-frequency ITDs and high-frequency ILDs. A few similarities in human performance with high- and low-frequency ITDs have been taken as evidence for similar ITD processing across frequency regions. However, such similarities, unless accompanied by differences between ITD and ILD performance on the same measure, could potentially reflect processing attributes common to both ITDs and ILDs rather than to ITDs only. In the present experiment, both learning and variability patterns in human discrimination of ITDs in high-frequency amplitude-modulated tones were examined and compared to previously obtained data with low-frequency ITDs and high-frequency ILDs. Both patterns for high-frequency ITDs were more similar to those for low-frequency ITDs than for high-frequency ILDs. These results thus add to the evidence supporting similar ITD processing across frequency regions, and further suggest that both high- and low-frequency ITD processing is less modifiable and more noisy than ILD processing.
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43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources

The effect of impedance on interaural azimuth cues derived from a spherical head model

Bradley E. Treeby, Roshun M. Paurobally, and Jie Pan

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2217-2226 (2007); (10 pages) | Cited 3 times

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Recent implementations of binaural synthesis have combined high-frequency pinna diffraction data with low-frequency acoustic models of the head and torso. This combination ensures that the salient cues required for directional localization in the horizontal plane are consistent with psychophysical expectations, regardless of the accuracy or match of the high-frequency cues, or the fidelity of experimental low-frequency information. This paper investigates the effect of a nonrigid boundary condition on the surface pressure and the resulting interaural cues used for horizontal localization. These are derived from an analytical single sphere diffraction model assuming a locally reacting and uniformly distributed impedance boundary condition. Decreasing the magnitude of a purely resistive surface impedance results in an overall decrease in the sphere surface pressure level, particularly in the posterior region. This produces nontrivial increases in both the interaural level and time difference, especially for sound source directions near the interaural axis. When the surface impedance contains a reactive component the interaural cues exhibit further changes. The basic impedance characteristics of human hair and their incorporation into the sphere diffraction model are also discussed.
Show PACS
43.66.Pn Binaural hearing
43.66.Qp Localization of sound sources
43.20.Fn Scattering of acoustic waves

The role of the external ear in vertical sound localization in the free flying bat, Eptesicus fuscus

Chen Chiu and Cynthia F. Moss

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2227-2235 (2007); (9 pages) | Cited 7 times

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The role of the external ear in sonar target localization for prey capture was studied by deflecting the tragus of six big brown bats, Eptesicus fuscus. The prey capture performance of the bat dropped significantly in the tragus-deflection condition, compared with baseline, control, and recovery conditions. Target localization error occurred in the tragus-deflected bat, and mainly in elevation. The deflection of the tragus did not abolish the prey capture ability of the bat, which suggests that other cues are available used for prey localization. Adaptive vocal and motor behaviors were also investigated in this study. The bat did not show significant changes in vocal behaviors but modified its flight trajectories in response to the tragus manipulation. The tragus-deflected bat tended to attack the prey item from above and had lower tangential velocity and larger bearing from the side, compared with baseline and recovery conditions. These findings highlight the contribution of the tragus to vertical sound localization in the free-flying big brown bat and demonstrate flight adaptations the bat makes to compensate altered acoustic cues.
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43.66.Qp Localization of sound sources
43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
43.66.Pn Binaural hearing
43.60.Jn Source localization and parameter estimation
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Effects of carrier pulse rate and stimulation site on modulation detection by subjects with cochlear implants

Bryan E. Pfingst, Li Xu, and Catherine S. Thompson

J. Acoust. Soc. Am. Volume 121, Issue 4, pp. 2236-2246 (2007); (11 pages) | Cited 27 times

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Most modern cochlear-implant speech processors convey speech-envelope information using amplitude-modulated pulse trains. The use of higher-rate carrier pulse trains allows more envelope detail in the signal. However, neural response properties could limit the efficacy of high-rate carriers. This study examined effects of carrier rate and stimulation site, on psychophysical modulation detection thresholds (MDTs). Both of these variables could affect the neural representation of the carrier and thus affect perception of the modulation. Twelve human subjects with cochlear implants were tested. Phase duration of symmetric biphasic pulses was modulated sinusoidally at 40 Hz. MDTs were determined for monopolar stimulation at two carrier rates [250 and 4000 pulses/s (pps)], three stimulation sites (basal, middle, and apical), and five stimulus levels (10%, 30%, 50%, 70%, and 90% of the dynamic range). MDTs were lower for 250 pps carriers than for 4000 pps carriers in 71% of the 180 cases studied. Effects of carrier rate were greatest at the apical stimulation site and effects of stimulation site on MDTs depended on carrier rate. The data suggest a distinct disadvantage to using carrier pulse rates as high as 4000 pps. Stimulation site should be considered in evaluating modulation detection ability.
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43.66.Ts Auditory prostheses, hearing aids
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Cb Loudness, absolute threshold
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