AUDIOLOGY JAPAN
Online ISSN : 1883-7301
Print ISSN : 0303-8106
ISSN-L : 0303-8106
Frequency Distribution of Two-tone Suppression in Forward Masking
I. Preliminary Experiment
Genzo IsojimaTakao Suzuki
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1985 Volume 28 Issue 1 Pages 14-26

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Abstract

This preliminary experiment is concerned with the frequency distribution of two-tone suppression. The first masker M1 (suppressee) was a narrowband noise centered and fixed at 3kHz (F1) with 200Hz bandwidth and spectrum level -10-30dB in SPL, the second masker M2 (suppressor), also was a narrow-band noise with 200Hz bandwidth and spectrum level -15-40dB in SPL. Levels of the stimulus components (suppressee and suppressor) were the experimental parameters. In all experiments the threshold of a 15ms probe tone (fixed at 3kHz) following a 600ms M1 was determined as a function of central frequency (F2) of a 600ms M2. The suppressor central frequency F2 ranged from 1.4 to 6kHz.
At appropriate levels and frequencies all subjects showed significant suppression both for F2>F1 and for F2<F1. For F2<F1 than for F2>F1, however, suppression was more prominent. Also, suppression occured at higher suppressee level than at lower suppressor levl for F2>F1 at appropriate suppressor levels and suppressee levels. Suppression was found to decrease to zero as F2 approached F1. Suppression showed at the suppressor frequencies ranging from just above or below the critical band of F1 to well beyound the 2-3 critical bands. The amount of suppression depended on both suppressor level and suppressee level in a way accounted for the Duifhuis' model of two-tone suppression. For spectrum levels of suppressor as low as 40dB in SPL, the effect of levels on suppression was linear, i.e., suppression magnitude was seen to be a monotonically increasing function. These results have demonstrated effects similar to two-tone suppression in auditory-nerve fibers in psychophysical experiments in humans.
In most of the psychophysical experiments, however, signal frequency has been equal to masker frequency. Thus, there is little information about the frequency distribution of suppression effects. This is main factor investigated in the next papers.

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© Japan Audiological Society
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