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The Journal of the Acoustical Society of America 11/1996; 100(4 Pt 1):2547-50. · 1.55 Impact Factor
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ABSTRACT: This study examined the effects of multicomponent, random-frequency maskers and broadband-noise maskers on intensity discrimination at 1000 Hz. Maskers and signals were 200 ms, presented simultaneously. In the first set of conditions, thresholds were measured for the detection of a 1000-Hz tone in the presence of 40 or 60 dB SPL random-frequency or noise maskers, with extensive training of listeners with the random-frequency masker to assure stable effects of masker-frequency uncertainty. The random-frequency maskers had two, six, or ten components chosen at random from a large frequency range (300-3000 Hz, excluding a 160-Hz band around 1000 Hz). For these maskers, performance across the four listeners was very similar, showing large effects of masker-frequency uncertainty. For noise maskers, performance matched predictions for energy-based masking. In the second and third sets of conditions, intensity discrimination was measured at 1000 Hz for pedestals ranging from 40 to 80 dB SPL, first in isolation and then in the presence of the maskers. The pattern of results for intensity discrimination in quiet showed the expected near miss to Weber's Law, but poorer performance than typically observed. The addition of broadband-noise maskers had little effect on performance. However, random-frequency maskers degraded performance in nearly all conditions, with the size of the effect dependent on the level of the pedestal relative to the masker. Considering the pedestal as a tonal masker, the data were fitted with various models of combined masking. A simple power-law model provided excellent fits, with exponents ranging from 0.24 to 0.35 for the multicomponent maskers, but 1.0 (linear) for the noise. The results support models positing that the effects of individual maskers undergo nonlinear transformation before they are added, independent of the mechanisms which produce these effects. Because random-frequency maskers presumably produce informational (uncertainty-based) masking, the nonlinearity in this case appears central rather than peripheral.
The Journal of the Acoustical Society of America 11/1996; 100(4 Pt 1):2289-98. · 1.55 Impact Factor
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D L Neff
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ABSTRACT: Large amounts of simultaneous masking can be produced by changing the frequency content of multicomponent maskers with each presentation. Much of this masking appears to be informational, that is, produced by stimulus uncertainty. This study examined whether relatively simple changes in the properties or presentation mode of the signal could increase the saliency of the signal and reduce this masking. The number of masker components varied from 2 to 100 across conditions. The reference signal was a 200-ms, 1000-Hz sinusoid, presented monaurally with the masker. Across experiments, changes in masking relative to the reference condition were examined for different signal types (amplitude-modulated, quasifrequency-modulated, or narrow-band noise), durations (100 or 10 ms), and presentation modes (diotic, dichotic, or cross ear). The use of AM and NBN signals improved performance more consistently than the QFM signal, which degraded performance for some listeners. Lower masking in the reference condition for these listeners may have limited the effects of signal type. Dichotic (versus monaural) presentation produced larger reductions in masking for more listeners and conditions. Comparisons to results with broadband maskers and other patterns in the data, however, suggest the dichotic advantage may not clearly reflect a reduction of masking due to uncertainty. Separating masker and signal onset/offset times by shortening signal duration produced the largest and most consistent reductions in masking produced by masker-frequency uncertainty.
The Journal of the Acoustical Society of America 11/1995; 98(4):1909-20. · 1.55 Impact Factor
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ABSTRACT: Individual differences were examined for 49 listeners in a simultaneous-masking task with random-frequency, multicomponent maskers and a 1000-Hz signal. Across conditions, the maskers were broadband noise or complexes of 2-100 sinusoids whose frequencies were randomly chosen with each presentation. Maskers were equal rms waveforms, presented at 60 dB SPL. Thresholds for the multicomponent maskers spanned a range of up to 59 dB across listeners within conditions without distinct groupings. When divided into quartiles, mean thresholds for listeners in the lowest quartile increased monotonically with the number of masker components and peaked below values produced by broadband noise. Listeners in the upper quartile had nonmonotonic functions with a broad peak around 10-20 components, with values above those produced by broadband noise. Quiet thresholds and masked thresholds for the broadband-noise masker did not distinguish "high-" from "low-threshold" groups. Lowering masker uncertainty (frequencies randomized between but not within trials) or introducing temporal differences by shortening the signal both improved performance by as much as 40 dB, dependent on the masking produced with maximum uncertainty. Training effects within experiment (excluding an initial training period) were examined for all listeners and for five listeners across two consecutive experiments. Eleven of forty-nine listeners (22%) showed systematic improvement averaging 12 dB within experiment, independent of high or low original thresholds. For the five tested longer, four improved by 5 dB or more in at least one condition, but the change in performance occurred primarily during initial training for the second experiment. The large individual differences documented present a challenge to the development of models for masking produced by masker-frequency uncertainty.
The Journal of the Acoustical Society of America 08/1995; 98(1):125-34. · 1.55 Impact Factor
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ABSTRACT: Simultaneous maskers comprised of a few random-frequency sinusoids can produce considerable informational (uncertainty-based) masking if the component frequencies are drawn from a wide range and changed with each stimulus presentation. The present experiments examined the effect on informational masking of removing masker energy from large frequency regions around the signal. Threshold for a 1000-Hz signal was measured in the presence of maskers comprised of 2, 4, 6, 10, 50, or 100 random-frequency sinusoids, notched-noise, or two fixed-frequency sinusoids. The multicomponent maskers had a maximum frequency range of 300-3000 Hz, typically excluding a 160-Hz band around the signal. In comparison conditions, masker frequencies were limited to the high or low side of the signal, or the gap around the signal was progressively widened. Four listeners showed substantial informational masking which was not eliminated even by extreme spectral gaps in the maskers. Four other listeners showed much smaller effects of masker uncertainty across all conditions. Notched-noise measures of auditory-filter width did not distinguish the two subject groups, but indices of processing efficiency were typically poorer for the high-threshold listeners, as were measures of both the width and processing efficiency of presumed "attentional filters" under conditions of masker-frequency uncertainty.
The Journal of the Acoustical Society of America 01/1994; 94(6):3112-26. · 1.55 Impact Factor
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D L Neff
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ABSTRACT: Large amounts of simultaneous masking can be produced when the frequency content of multicomponent maskers is changed with each presentation. This study examined whether such masker uncertainty also influences forward masking. The forward maskers were a 1000-Hz sinusoid, a broadband noise, and tonal complexes composed of 2-100 sinusoids drawn at random from a 300 to 3000-Hz range. A 10-ms signal at 1000 Hz followed the offset of 200-ms, 60 to 80-dB maskers with delays of 4-32 ms. For comparison, simultaneous-masked thresholds were measured for a 200-ms signal at 1000 Hz for a subset of conditions or taken from an earlier study. Unlike simultaneous masking, forward masking showed little effect of masker uncertainty. As confirmed by fitting a three-parameter descriptive model of forward masking, the pattern of results was similar for the sinusoidal, noise, and multicomponent forward maskers and there was no reduction in masking with decreased masker uncertainty. Performance in simultaneous masking improved to equal that in forward masking when the signal was shortened from 200 to 10 ms. Thus temporal disparities between masker and signal can offset the effects of spectral uncertainty and help separate the relative contribution of peripheral versus more central processes.
The Journal of the Acoustical Society of America 04/1991; 89(3):1314-23. · 1.55 Impact Factor
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ABSTRACT: When more than one sinusoid is used as a masker, more masking is observed than would be predicted by a simple combination of their individual effects. This masking is dramatically increased when the masker components vary in frequency and intensity with each presentation. These studies manipulated several masker parameters under conditions of high masker uncertainty, examining the effect of excluding critical-band components, fixing or randomizing component amplitudes and frequencies, and narrowing the frequency range of the components. The signal was always a 200-ms, 1000-Hz sinusoid, presented simultaneously with the 200-ms masker. Removing critical-band components reduced the amount of masking, but considerable masking remained that appears to be nonperipheral in origin. Fixing masker frequencies across the two intervals of a trial greatly reduced the masking observed, whereas fixing masker amplitudes had no effect. Reducing the frequency range from 5000 to 2700 Hz generally increased the masking observed, but appeared to depend on other masker parameters. Summaries across ten listeners show individual differences that are resistant to extensive training. It is difficult to account for most of the masking observed in terms of masker energy falling near the region of the signal.
The Journal of the Acoustical Society of America 06/1988; 83(5):1833-8. · 1.55 Impact Factor
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Perception & Psychophysics 06/1987; 41(5):409-15. · 1.37 Impact Factor
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D L Neff
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ABSTRACT: In some forward-masking conditions, signal thresholds may be elevated by the listener's inability to distinguish the signal from the preceding masker. In this study, such "confusion" effects are investigated for both sinusoidal and narrow-band noise forward maskers combined with sinusoidal signals of varying duration. Results for the sinusoidal maskers show effects of off-frequency listening for brief signals and possibly small effects of confusion for longer signals. Results for the narrow-band noise maskers show a marked influence of confusion over a wide range of signal durations. This range is in good agreement with that predicted from previous work with "pulsing" maskers [D. Neff, J. Acoust. Soc. Am. 78, 1966-1976 (1985)]. These results suggest that studies using narrow-band noise forward maskers or studies of psychophysical suppression should include direct tests for confusion effects in key conditions.
The Journal of the Acoustical Society of America 06/1986; 79(5):1519-29. · 1.55 Impact Factor
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D L Neff
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ABSTRACT: In forward masking, performance may be affected by confusion, that is, by the difficulty of discriminating a suprathreshold signal from the preceding masker. This study investigated confusion effects for forward maskers composed of repeated bursts of a 100-Hz sinusoid followed by sinusoidal signals; such "pulsing" maskers produce confusion when the properties of the signal are identical to those of an individual masker "pulse." The level, frequency, and duration of the signal relative to an individual masker pulse, as well as offset-onset delay, were varied to determine the minimum change necessary to eliminate confusion. For maskers composed of 20-ms pulses, confusion was eliminated by changes in signal level of 5 dB or changes in signal frequency of 30 to 40 Hz. For maskers composed of 10-, 20-, or 40-ms pulses, confusion was eliminated by signal delays of 8 to 16 ms or by signal durations less than half or greater than twice the masker-pulse duration. Results with adaptive procedures designed to measure confusion-free or confusion-determined thresholds suggest that confusion effects can be minimized or avoided by extensive listener training with a procedure in which the signal and masker are not presented at similar intensities.
The Journal of the Acoustical Society of America 01/1986; 78(6):1966-76. · 1.55 Impact Factor
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ABSTRACT: Masked thresholds for a 1000-Hz sinusoidal signal were measured as a function of masker level in both forward and simultaneous masking for two types of maskers: a 1000-Hz sinusoid and a narrowband noise, 60-Hz wide, centered at 1000 Hz. In forward masking, the noise masker produced much steeper growth-of-masking functions than the sinusoid. Presenting a contralateral broadband noise "cue" with the forward masker dramatically reduced the slope of masking for the noise masker but did not influence results for the sinusoidal masker. The noise remained the more effective masker. The amount of masking produced by combinations of equally effective narrowband-noise and sinusoidal maskers was compared to that produced by each masker individually with and without the contralateral cue. No additional masking beyond that predicted by energy summation was measured for forward masking. Additional masking beyond energy-sum predictions was measured for analogous conditions in simultaneous masking. Comparisons of results obtained with and without the contralateral cue suggest that signal thresholds in the presence of narrowband-noise forward maskers can reflect nonperipheral auditory processes.
The Journal of the Acoustical Society of America 01/1984; 74(6):1695-701. · 1.55 Impact Factor
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ABSTRACT: Pitch shifts in sinusoids as a function of intensity result in systematic response biases and differences in performance in forced-choice frequency-discrimination tasks. Two approaches are described for converting these effects to a measure of pitch shift in Hz using standard signal-detection-theory assumptions. To illustrate these approaches, forced-choice frequency-discrimination data were obtained for three listeners at 250 and 4000 Hz, with six intensities from 40 to 90 dB SPL. The resulting pitch-shift estimates are in good agreement with adjustment data obtained from the same listeners. Collection and analysis of the forced-choice data can be greatly simplified by using an adaptive procedure. Pitch-shift estimates obtained in this way for two of the three listeners are in good agreement with the other estimates.
The Journal of the Acoustical Society of America 01/1983; 72(6):1812-20. · 1.55 Impact Factor
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Perception & Psychophysics 06/1982; 31(5):493-501. · 1.37 Impact Factor
