Analysis of Level Dependence of 2f ₁ – f ₂ Component of Otoacoustic Emissions Using Nonlinear 2D Cochlear Model

A two-dimensional nonlinear cochlear model was used to study the dependence of the nonlinear-distortion component of cubic distortion product otoacoustic emissions (DPOAEs) on the levels of the primary tones: f ₁ , f ₂. DPOAE was simulated for a fixed frequency ratio between the primaries f ₂ /f ₁ = 1.2 and for two amplification gains at f ₂ of 1.2, 2.4 and 4.8 kHz. The simulated optimal primary levels depend on frequency. Loss of the gain affects the optimal levels at the lowest intensities for which the DPOAE amplitude would fall below the noise level in real experiments. The nonlinear force acting in the model as a source of DPOAEs along the basilar membrane (BM) was calculated. Simulations showed that the nonlinear force spreads over a wide part of the length of BM, especially at large levels of the primaries and low f ₂. Contributions along the source length may cancel each other out if the phase difference between them is half a cycle. This contributes to saturation of the DPOAE amplitude and causes notches.

© 2018 The Author(s). Published by S. Hirzel Verlag · EAA. This is an open access article under the terms of the Creative Commons Attribution (CC BY 4.0) license (https://creativecommons.org/licenses/by/4.0/).