Two-tone distortion products in a nonlinear model of the basilar membrane

Two‐tone distortion products were studied in a computational model of the basilar membrane into which second‐ and third‐order nonlinearities had been introduced. The displacement patterns produced by distortion products $f_2{\mathrm{-\; f}}_1$ and ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ resemble, in the neighborhood of the characteristic place for the frequency in question, displacement patterns produced by tones delivered at the stapes. This is not the case for distortion product ${\text{2f}}_2{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_1$ . The dependence of both the amplitude and phase of distortion products $f_2{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_1$ and ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ on frequency spacing and amplitude of the two primary tones has features in common with results from psychophysical experiments. The ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ distortion product shows a nonmonotonic behavior similar to that demonstrated in psychophysical experiments. The phase of the ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ distortion product changes with intensity in a manner similar to that observed psychophysically. In the model, a cancellation‐tone method overestimates the amplitude of the ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ distortion product, again in agreement with results from psychophysical experiments. These areas of agreement between the model and psychophysical data support the notion that psychophysically observed distortion products ${\text{2f}}_1{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_2$ and (under some conditions) $f_2{\mathrm{\hspace{0.17em}-\hspace{0.17em}f}}_1$ are the result of nonlinear mechanical properties of the basilar membrane.