2-tone suppression is observed in cochlear microphonic potentials of the human cochlea which are obtained by electrocochleography. The significant reduction of cochlear microphonic potentials takes place within only a relatively narrow frequency band and the frequency dependence is rather sharp. The frequency to produce maximum suppression (dip) is higher than the probe frequency but it is not found at a lower frequency. Dip frequency is systematically increased according to an approximately linear rule when the probe tone frequency increases. The ratio between dip and probe tone frequency is almost 2, 7. The effect of suppression is dependent only on the ratio of the intensities (P2/P1) for the specific intensities of the probe tone in this study. According to this experiment it is demonstrated that the basilar membrane motion of the human cochlea has nonlinear character. 2-tone suppression and combination tone in humans is produced by nonlinearity of the basilar membrane motion the same as the results observed in animal and mechanical model.
