Waves in a three-dimensional model of the cochlea

The conventional travelling wave theory of the cochlea assumes that only a single “slow” wave, which determines the overall response in the cochlea, can propagate. Various different mechanisms, such as longitudinal coupling in the fluid or the basilar membrane, BM, may give rise to other types of wave. In this paper the wave finite element method is used to predict all possible waves in a three-dimensional model of the passive cochlea using an orthotropic plate model for the BM, in terms of wave mode shape and wavenumber as a function of position along the cochlea. Mode conversion in waves can then be explored by decomposing results from a full finite element model. It is found that only one wave, the slow wave, is dominant basal to the characteristic place and then a higher order fluid mode starts to make a significant contribution to the overall response when system damping is small