Analysis of the f2-f1 and 2f1-f2 distortion components generated by the hair cell mechanoelectrical transducer: Dependence on the amplitudes of the primaries and feedback gain

This paper describes the pattern of f(2) - f(1) and 2f(1) - f(2) components at the output of the nonlinear hair cell mechanoelectrical transducer when the input consists Of two sinusoidal signals. The mechanoelectrical transd ucer was represented by a second-order Boltzmann function. It is shown that -some experimental observations, which have been cited to prove the existen ce of two discrete sources of distortion product otoacoustic emissions in t he cochlea, can be produced by a single nonlinearity. These observations in clude the pattern of magnitude: and phase "notches" in the growth functions of the distortion product otoacoustic emissions when measured in the two-d imensional space of the amplitudes of the two primaries. A single saturatin g nonlinearity also explains the distinctive response of the distortion pro duct otoacoustic emissions to the decreasing gain Of the cochlear amplifier . A possible basis for the differences in distortion product otoacoustic em issions, which have been measured in humans and rodents, is discussed. (C) 1999 Acoustical Society of America. [S0001-4966(99)03811-4].