Simple oscillator model of frequency dependence of cochlear two-tone suppression

A simple oscillator model is proposed to investigate the frequency dependence of cochlear two-tone suppression (2TS), which is the cochlear response to a tone decrease when a second sound is simultaneously presented. The frequency dependence of 2TS exhibits two characteristics. First, the shapes of the input-output (IO) curves as a function of the input levels of the two tones depend on the frequency ratio of the two tones. Second, the temporal features of suppressed responses vary with the frequency ratio. To account for 2TS, the saturation function is widely used; however, it cannot explain the frequency dependence of cochlear 2TS. Transmission line models can reproduce the frequency dependence of cochlear 2TS. It has been suggested that complicated cochlear mechanics generate 2TS in the transmission line model. The model proposed in this study includes a one-degree-of-freedom oscillator and feedback via the saturation function, which produces basic cochlear properties such as amplification, frequency selectivity, and compressive nonlinearity in the model. Simulations show that the transmission line model and our proposed model can reproduce the frequency dependence of 2TS in the IO functions and temporal responses, indicating that the frequency dependence of 2TS requires basic cochlear properties such as amplification, frequency selectivity, and compressive nonlinearity, which are involved in saturating the feedback.