Forward maskingによる2音抑制の周波数分布

II. 抑制音の周波数効果

抄録

These experiments are concerned with the frequency distribution of two-tone suppression in forward masking. In each experiment the threshold of a 15ms probe tone following a 600ms narrow-band noise masker was determined as a function of probe frequency. Probe threshold was measured for a fixed narrow-band noise centered at 3kHz with 200Hz bandwidth and spectrum level of 20dB in SPL with and without a suppressing narrow-band noise with 200Hz bandwidth and spectrum level of 40dB in SPL whose central frequency was systematically varied. The suppression, measured as a reduction in probe threshold produced by adding the suppressing narrow-band noise, was found to have three components.
First, frequency distribution of suppression was limited to a narrow range of probe frequencies around 3kHz and does not reflect a simple reduction in the level of suppression noise, i.e., part of the suppression can be attributed to reduction of the effective level of the suppressed noise in a particular region. Second, for central frequency (F2) of the suppressing noise below central frequency (F1) of the suppressed noise, the suppressed frequency region lies around 0.6 to 0.85F1 and F2 above F1 the suppressed frequency region lies around 1.30t 1.9F1.
However, they are in disagreement with the notion proposed by Javel et al. (1978) that suppression magnitude is related to the frequency difference between the travelling wave peaks for F2 and F1 on the basilar membrane. Third, these data indicated that there is much more suppression for F2<F1 than F2>F1.
This effect can be explained with the help of the Hall's nonlinear model on the basiler membrane. These data are in general agreement with previously published reports of physiological suppression behavior, and they support the concept that the suppression is generated primarily as a result of interactions occurring within hair cells or stereo-ciliary-tectrial structures.