The effects of bandwidth on the detection of narrow- and wide-band auditory signals.
Item
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Title
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The effects of bandwidth on the detection of narrow- and wide-band auditory signals.
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Identifier
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AAI8820843
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identifier
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8820843
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Creator
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Bernstein, Richard Saul.
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Contributor
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Adviser: David H. Raab
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Date
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1988
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Experimental
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Abstract
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Since Fletcher's classic paper on auditory masking, theorists have usually assumed that listeners base their decisions on some internal representation of stimulus energy and that critical bandwidths represent limits of integration. An energy-detection model (without internal filtering) predicts that threshold should increase with masker bandwidth at a rate of approximately 5 dB per decade increase in masker bandwidth. Empirical estimates of this rate are usually larger than this theoretical value.;The model also predicts that threshold will vary inversely with the bandwidth of a noise signal. The predicted rate depends on the relationship between signal and masker bandwidths. This study determined the detectability of signals with bandwidths that were sub-critical ("narrow") and supra-critical ("wide") in the presence of maskers of various bandwidths. Since predictions depend on bandwidth, synthetic noises with nearly rectangular spectra were employed.;For both narrow- and wide-band signals, increasing masker bandwidth resulted in elevation of signal threshold until some critical bandwidth was exceeded. Thresholds of narrow-band signals increased at the rate of 8 dB per decade increase in masker bandwidth, whereas thresholds of wide-band signals increased at a rate of 25 dB. These critical bandwidths were found to vary with signal bandwidth suggesting that listeners adjust the bandwidth of the detection process in accord with the spectrum of the signal.;Threshold was found to vary inversely with signal bandwidth. When signal and masker had the same bandlimits, threshold improved at the rate of 3 dB per decade increase in bandwidth. On the other hand, and for all signals, when masker bandwidth exceeded the signal's critical width, threshold improved at the rate of 7 dB.;The addition of a bandwidth-dependent variance term to an energy-detection model improved the ability of the model to predict thresholds of narrow-band signals. This variance is due to internal processing. The modified model also predicted the effect of signal bandwidth on threshold. However, the effect of masker bandwidth on thresholds of wide-band signals was greater than predicted. Suggesting that the spectral contours of these signals are enhanced by a operation which adjusts the gain of each critical band.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
