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Jan 2003

Volume 113, Issue 1, pp. 1-660

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Effect of amplitude modulation coherence for masked speech signals filtered into narrow bands

Emily Buss, Joseph W. Wall, III, and John H. Grose

J. Acoust. Soc. Am. Volume 113, Issue 1, pp. 462-467 (2003); (6 pages) | Cited 7 times

Online Publication Date: 08 Jan 2003

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Introduction of masker amplitude modulation (AM) can improve signal detection in a number of paradigms. In some cases this advantage depends on the coherence of modulation across a relatively wide frequency range. In the experiments described below, observers were asked to identify masked spondee words produced by a single male talker. The target spondees and masking noise were filtered into nine narrow bands, and the coherence of AM of either the speech signal or noise masker was manipulated. Inherent modulation of the masker bands was manipulated via assignment of real and imaginary values to the associated components of each band in the frequency domain, and AM of speech bands was achieved via multiplication with envelopes extracted from these maskers. Responses were based on two alternatives, four alternatives, or open response sets. The effect of masker AM coherence was highly dependent upon the size of the response set: coherent AM was associated with better thresholds in a two-alternative response set, but poorer thresholds in an open response set. Results with AM speech did not depend critically upon the across-frequency temporal synchrony of AM imposed on the speech material. © 2003 Acoustical Society of America.
Show PACS
43.66.Dc Masking
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.72.Dv Speech-noise interaction

Detection and direction-discrimination of diotic and dichotic ramp modulations in amplitude and phase

Caroline Witton, Michael I. G. Simpson, G. Bruce Henning, Adrian Rees, and G. G. R. Green

J. Acoust. Soc. Am. Volume 113, Issue 1, pp. 468-477 (2003); (10 pages)

Online Publication Date: 08 Jan 2003

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When the source of a tone moves with respect to a listener’s ears, dichotic (or interaural) phase and amplitude modulations (PM and AM) are produced. Two experiments investigated the psychophysical characteristics of dichotic linear ramp modulations in phase and amplitude, and compared them with the psychophysics of diotic PM and AM. In experiment 1, subjects were substantially more sensitive to dichotic PM than diotic PM, but AM sensitivity was equivalent in the dichotic and diotic conditions. Thresholds for discriminating modulation direction were smaller than detection thresholds for dichotic AM, and both diotic AM and PM. Dichotic PM discrimination thresholds were similar to detection thresholds. In experiment 2, the effects of ramp duration were examined. Sensitivity to dichotic AM and PM, and diotic AM increased as duration was increased from 20 ms to 200 ms. The functions relating sensitivity to ramp duration differed across the stimuli; sensitivity to dichotic PM increased more rapidly than sensitivity to dichotic or diotic AM. This was also reflected in shorter time-constants and minimum integration times for dichotic PM detection. These findings support the hypothesis that the analysis of dichotic PM and AM rely on separate mechanisms. © 2003 Acoustical Society of America.
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43.66.Pn Binaural hearing
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