Phase-dependent suppression of transient evoked and distortion product otoacoustic emissions by a low-frequency tone

The subjective recording of the masked threshold of short acoustical stimul i with a loud tone of 30 Hz (phase audiogram) has been used for the clinica l diagnosis of endolymphatic hydrops (EH). In normally-hearing subjects, a marked modulation of the threshold was found, depending on the phase of the low-frequency tone. A very small dependence was found in patients with Men iere's disease, due to the micromechanical changes in the basilar membrane (BM). The same phase relationship becomes apparent in low-frequency suppres sion of otoacoustic emissions. The amplitudes of TEOAEs are controlled by t he phase-dependent displacement of the BM. The suppressed TEOAEs have to be measured separately in each phase relationship. During recording of suppre ssed DPOAEs, the low-frequency suppressor is permanently superimposed on th e pair of primary tones. After time averaging and a moving short-time FFT, the spectral values of the DPOAEs are obtained depending on the phase of th e low-frequency tone. Modulation depends also on the masker level, the leve ls of the primary tones, and on their frequency range. The method of low-fr equency suppressed DPOAEs is an objective method to diagnose EH and could b e a useful tool in human inner ear research.