On the origins of the compressive cochlear nonlinearity

Various simple mathematical models of the dynamics of the organ of Corti in the mammalian cochlea are analysed. The models are assessed against their ability to explain the compressive nonlinear response of the basilar membrane. The speci fic models considered are: phenomenological Hopf and cusp normal forms, a recently-proposed description combining active hair-bundle motility and somatic motility, a reduction thereof, and finally a new model highlighting the importance of the coupling between the nonlinear transduction current and somatic motility. The overall conclusion is that neither a Hopf bifurcation nor cusp bifurcation are necessary for realistic compressive nonlinearity. Moreover, two physiological models are discussed showing compressive nonlinearities similar to experimental observations without the need for tuning near any bifurcation