Possible mechanisms of cochlear two-tone suppression represented by vector subtraction within a model

Abstract

This paper investigates possible mechanisms of cochlear two-tone suppression (2TS) in models of the hair cell transducer and the cochlea. The hair cell transducer model can be represented by a saturation function. To simulate cochlear mechanics, a nonlinear transmission line cochlear model is used. The mechano-electric transducer curve of the outer hair cell (OHC) is regarded as the source of nonlinearity in cochlear mechanics. The saturation function approximated by a power series can explain 2TS in the OHC transducer model. However, this mathematical formulation cannot account for cochlear 2TS because the cochlear mechanics is more complicated than the saturation in the OHC transducer. To clarify two-tone interference graphically, it is expressed as a residual vector, the entries of which are the frequencies of the probe and suppressor. In this construct, the stronger of two tones introduced to the system nonlinearly reduces the output by vector subtraction. The model accomplished 2TS and displayed similar horizontal and vertical residual vectors. These analytical results suggest that 2TS is obtained from simple interference between the probe and the suppressor in the cochlear mechanics with nonlinear variation of the OHC transducer current.