AUDIOLOGY JAPAN
Online ISSN : 1883-7301
Print ISSN : 0303-8106
ISSN-L : 0303-8106
Frequency Distribution of Two-Tone Suppression in Forward Masking
IV. Level Effect of Suppressor
Genzo IsozimaTakao Suzuki
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1987 Volume 30 Issue 6 Pages 764-777

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Abstract

Frequency distribution of two-tone suppression was measured in forward masking and the comparison of the psychophysical and physiological results were examined. In each experiment, the masked threshold of 15ms probe tone caused by the addition of a 600ms second masker (M2) to a 600ms first masker (M1) was determined as a function of probe frequency. M1 and M2 were noises with 200Hz bandwidth. The spectrum levels (No, L1, L2) of maskers varied from -10dB to 50dB SPL by 10dB step.
In each experiment, probe tones were filtered with a bandwidth of two thirds of each critical band.
The results were as follows:
Frequency distribution of two-tone suppression was not dependent on the levels of M1 or M2. However, amount of suppression was dependent of the difference in intensity between two maskers, L1, L2 or overall, respectively. Also, frequency distribution of suppression indicated that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. There was a systematic increase in rates of suppression growth for suppressors as L1 or L2 increased and suppression were greatest in high-F2 and least in low-F2. Thus, suppression magnitudes were always dependent on only the intensity of M2. Suppression was observed at all F1 (0.7-3kHz) and was dependent on the phase of the masker components or the phase between the masker and the probe tones. Characteristics of suppression were not in conflict with the assumption that this effect is caused by the variable component suppressing the other masker component. Suppression of primary neurons indicated that suppression was generated as the results of interations occuring within hair cells, and stereocilliary-tectorial structures, however, implied that psychophysical suppression added inhibition of the cochlear nuclei to suppression primary neurons.

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© Japan Audiological Society
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