Evaluating a cochlear transducer function and its operating point from low-frequency modulated distortion-product otoacoustic emissions simulated in a cochlear model

Distortion-product otoacoustic emission (DPOAE) offers a noninvasive objective diagnosis of the functional state of the cochlear amplifier. Bian, Chertoff, and Miller [J. Acoust. Soc. Am. 112, 198-210 (2002)] proposed a technique for estimating a cochlear transducer function from DPOAEs modulated by a low-frequency (LF) high-intensity bias tone. It was assumed that DPOAE generation is defined by a single nonlinearity driven directly by the input pressure in the ear canal and maintained that for low-intensity primary tones, the lower cubic (2f1-f2) and quadratic (f2-f1) components of DPOAEs are proportional to the third and second derivatives, respectively, of the proposed transducer function. Here, a two-dimensional nonlinear model of the human cochlea is employed to simulate and analyze the bias-tone experiments performed by Bian et al. and others. Using our model, it is shown that modulation of the time course of the DPOAE signal by the bias tone is not directly related to the third or second derivatives of the transducer function. Instead, it is observed that those changes significantly depend on the decrease in the amplitude of the basilar membrane responses at the primary tone frequencies and on the distribution of DPOAE sources. An alternative interpretation of DPOAE amplitude modulation by a LF bias tone is proposed.