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May 1988

Volume 83, Issue S1, pp. S1-S122

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back to top Session N. Psychological Acoustics II: Masking, Modulation and Modulation Masking
Contributed Papers
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Changes in the masked thresholds of brief tones produced by preceding bursts of bandpass and notched noise (A)

Robert P. Carlyon

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S34-S34 (1988); (1 page) | Cited 1 time

Online Publication Date: 13 Aug 2005

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Thresholds were measured for 5‐ms 1‐kHz tones masked by synchronous bursts of noise containing a spectral notch centered on the signal frequency. These thresholds were reduced by prior exposure to a 200‐ms burst of a “priming stimulus,” which had the same spectral shape as the masker. This masking release was greatest for notch widths extending between 20%–30% on either side of the signal frequency, and was absent when the masker and primer contained no notch. A smaller masking release could be obtained with primers consisting of only the lower band of a notched noise masker, and, to a lesser extent, of the higher band alone. A primer consisting of a narrow band of noise centered on the signal frequency produced an increase in masking, which could not be attributed to forward masking of the tone. The effects of all of these primers were independent of the 30‐dB range of primer levels studied, ruling out an explanation in terms of peripheral adaptation. The results are consistent with the presence of an active neural mechanism that enhances the internal representation of newly arriving energy in a previously unstimulated frequency region. Temporal parameters of the masking release were also studied.
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Comodulation masking release with delayed signal onsets (A)

Beverly A. Wright and Dennis McFadden

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S34-S34 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The detectability of a 1250‐Hz, 50‐ms signal was assessed in a comodulation masking release (CMR) setting. One 50‐Hz noise band (the “masker”) was centered at 1250 Hz; other noise bands were centered at 850, 1050, 1450, and 1650 Hz (the “cue” bands). The masker and/or cue bands were gated prior to the onset of the signal by an amount (“fringe”) that was varied across blocks of trials. The noise bands and the signal always ended together. The temporal envelopes of the noise bands were all correlated, all correlated except for the masker band, or all uncorrelated. When all of the noise bands were gated synchronously, the CMR grew from 1 dB in the burst condition to 7 dB for a 450‐ms fringe, due to a greater improvement in detectability in the correlated condition compared to the uncorrelated and all‐uncorrelated conditions. When the cue bands were gated before the masker, the average CMR was larger (4–6 dB) than when the masker was gated before the cue bands (2–4 dB). These differences in improvement with increasing fringe duration may be attributable to differences in neural adaptation in the correlated and uncorrelated conditions. [Work supported by NINCDS Grant NS15895.]
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Comodulation masking release (CMR) as a function of masker bandwidth, signal duration, and modulator bandwidth (A)

Gregory A. Schooneveldt and Brian C. J. Moore

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S34-S34 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Thresholds were measured for a 2000‐Hz signal masked by continuous noise varying in bandwidth from 50 to 3200 Hz in 1‐oct steps. For random noise maskers, thresholds increased with increasing bandwidth up to 400 Hz and then remained approximately constant. When the masker was amplitude modulated by a low‐pass noise, so as to produce coherent envelope fluctuations across frequency, thresholds decreased as the masker bandwidth was increased beyond 200 Hz, giving a CMR. For a 400‐ms signal duration, the CMR for masker bandwidths greater than 400 Hz increased from 2.4 to 12.3 dB as the modulator bandwidth was decreased from 400 to 12.5 Hz in 1‐oct steps. For modulator bandwidths of 50 Hz or less, a release from masking of 3.5 to 7.3 dB occurred even for maskers with bandwidths of 50 and 100 Hz, less than the critical bandwidth at 2000 Hz. For a modulator bandwidth of 12.5 Hz, the CMR decreased from 12.3 to 5.3 dB as the signal duration was decreased from 400 to 25 ms in 1‐oct steps. When the signal duration was less than 100 ms, there was no release from masking for masker bandwidths less than 400 Hz. The results suggest that, for maskers with fluctuating envelopes, across‐channel comparisons can reduce signal thresholds even for short signals, but an extra within‐channel process can produce a release from masking for long signals. This second process may reflect the ability of subjects to detect a change in the statistical properties of the envelope of the stimulus when the signal is added to the masker.
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Signal threshold as a function of the relative modulation depth between on‐frequency and flanking masker components (A)

John H. Grose and Joseph W. Hall, III

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S34-S34 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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It is apparent that the mechanism underlying comodulation masking release (CMR) relies on the existence of temporal fluctuations in the masker envelope. This raises the question of how much fluctuation is necessary to facilitate CMR. The present experiment addresses this question by measuring psychometric functions relating signal threshold to depth of flanker band modulation using sinusoidally amplitude‐modulated pure tones as masker components. In the first set of conditions, the on‐frequency component had a constant modulation depth of 100%, while the depth of the flanking components was varied between 100% and 0%. As expected, signal threshold improved monotonically as depth of flanker band modulation increased. In the second set of conditions, the on‐frequency component had a constant modulation depth of 63%, while the depth of the flanking components was either 100%, 63%, or 0%. Results to date suggest that signal threshold is lowest when the flanking components have the same depth of modulation as the on‐frequency component. [Research supported by AFOSR.]
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Gap detection in a narrow‐band noise with either a comodulated or a noncomodulated flanking band (A)

John H. Grose and Joseph W. Hall, III

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S34-S35 (1988); (2 pages)

Online Publication Date: 13 Aug 2005

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Comodulation masking release (CMR) suggests that the auditory system is sensitive to across‐frequency differences in modulation pattern. This raises the question of whether it is as sensitive to modulation differences due to the absence of activity (a silent interval) as it is to the presence of additional activity (a signal). If so, gap detection in a narrow‐band noise would be expected to be better in the presence of a comodulating flanking band than in the presence of a noncomodulating flanking band. The present study was designed to test this hypothesis. Gap detection was measured in a 30‐Hz‐wide narrow‐band noise centered at 1 kHz. A second 30‐Hz band of noise, centered at either 500 Hz or 1.5 kHz, was then added that was either comodulated or noncomodulated with the 1‐kHz band. While gap detection deteriorated with the addition of a second noise band, it appeared to do so more for the noncomodulated case than for the comodulated case. [Research supported by AFOSR.]
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Cross‐channel effects in amplitude‐modulation detection (A)

Stanley Sheft and William A. Yost

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S35-S35 (1988); (1 page) | Cited 2 times

Online Publication Date: 13 Aug 2005

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Sensitivity to low‐frequency sinusoidal amplitude modulation (AM) at a single‐component frequency of an equal‐amplitude tonal complex was investigated. All masker components of the complex were modulated with a fixed depth at the same frequency as the probe. The phase between probe and masker envelopes was varied across conditions. For a two‐component complex, the change in performance as a function of frequency separation (Δf) depended on the envelope phase relationship. With a 2‐kHz probe carrier, the slopes of the AM threshold versus Δf functions are more gradual than would be predicted by envelope interaction in a single‐frequency channel. Consistent with AM detection models incorporating broad predetection filtering, performance may be affected by detection of changes in the overall modulation pattern. When the probe and masker envelopes differ, adding masker components at the fringes of the two‐component complex can lead to an improvement in probe AM detection. This result suggests that the detection of the modulation pattern of an individual component in a tonal complex may be aided by enhancing cross‐channel differences in modulation.
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Complex sound discrimination: Predictions of the EWAIF model (A)

L. L. Feth, L. J. Stover, and R. A. Gerren

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S35-S35 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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The envelope‐weighted average of instantaneous frequency (EWAIF) model of auditory perception has been successfully applied to simple, two‐component signals, simultaneously amplitude‐ and frequency‐modulated tones, and even to the complex signals used in the early “profile analysis” work. The EWAIF model predicts performance from a calculation of the envelope‐weighted average of the instantaneous frequency fluctuations inherent in almost every complex periodic sound. When the model is in error, it generally predicts better performance than our listeners achieve. A revised version of the EWAIF model incorporates a temporal processing window. The revised model was tested by comparing its predictions with listeners' performance in a frequency‐change discrimination task. The experiment requires the listener to distinguish a smooth frequency glide from a discrete, multistep transition over the same trajectory. The listeners' ability to distinguish the glide from the multistep transition, in a 2IFC task, decreased to chance as the number of steps increased. The EWAIF model performance follows that of the listeners, given the appropriate choice of temporal window parameters. [Work supported by AFOSR and NIH.]
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Detecting amplitude modulation of sinusoidal carriers (A)

William A. Yost and Stanley Sheft

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S35-S35 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Listeners were asked to detect sinusoidal amplitude modulation (SAM) of one carrier tone (the target carrier) in the presence of a second carrier tone (the masking carrier) that also had SAM. The depth of modulation required to detect the presence of SAM of the target carrier was measured as a function of the difference in the frequency of amplitude modulation for the two carriers (modulator frequencies ranged from 4 to 100 Hz), the frequency separation between the two carriers (200‐ to 3000‐Hz separation), and the phase of the sinusoidal modulator of the masker carrier relative to the phase of the sinusoidal modulator of the target carrier. In half of the conditions, the frequency of the target carrier was greater than the frequency of the masker carrier, while, for the other half of the conditions, the frequency of the target carrier was less than that of the masker carrier. The data will be discussed in terms of the strategies employed by the auditory system in processing temporal modulation of complex sounds. The data indicate that the auditory system uses a wideband mode for processing temporal modulation, such that there is a great deal of interaction across widely separate frequency channels. [Work supported by the NINCDS.]
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Modulation masking patterns (A)

Sid P. Bacon, D. Wesley Grantham, and Luann E. Van Campen

J. Acoust. Soc. Am. Volume 83, Issue S1, pp. S35-S35 (1988); (1 page)

Online Publication Date: 13 Aug 2005

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Modulation thresholds for sinusoidally amplitude‐modulated (SAM) broadband noise were obtained for modulation frequencies from 2 to 512 Hz using a two‐interval, forced‐choice adaptive procedure. The noise carrier was on continuously throughout a block of trials, and was modulated for 500 ms in one of the two observation intervals. Thresholds were obtained in quiet and in the presence of a SAM broadband noise masker. In the masking conditions, the same noise carrier, presented at a spectrum level of 15 dB SPL, was used for the signal and the masker. The masker was modulated in both of the 500‐ms observation intervals. The modulation frequency of the masker was 4, 16, or 64 Hz; its modulation depth (m) was 0 (no modulation), 0.5, or 1.0. For a given masker modulation frequency, the modulation masking patterns generally were bandpass, with the greatest amount of masking occurring when the signal and masker modulation frequencies were the same. With a few consistent exceptions, there was a monotonic relation between masker modulation depth and amount of masking (the greater the modulation depth the greater the amount of masking). These data indicate a tuning of the auditory system for the detection of modulation. [Work supported by NIH.]
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