Frequency-domain analysis of cochlear gain reduction due to disruptions in the outer hair cell feedback loop

Abstract

A frequency domain equivalent model was implemented to match the small-signal responses produced by a time-domain cochlear mechanics model [Liu and Neely (2010)]. In the present model, the outer hair cell feedback is characterized by physical parameters, including a hair-bundle transduction ratio (HBTR) and a prestin-associated capacitance (PAC). When either of them is reduced, the model predicts lowered magnitude responses along the cochlea; however, HBTR and PAC seem to play different roles in facilitating cochlear amplification. It appears that the gain drops more drastically with respect to reduction in the HBTR, whereas the degradation is more graceful with respect to lack of prestin. Simulation also suggests that HBTR is more crucial for high-frequency hearing whereas PAC boosts up low frequency responses. Finally, we present attempts on modifying the frequency-domain model iteratively to simulate nonlinear responses. The saturating cochlear responses to high-intensity tones can be predicted by the frequency domain model as long as HBTRs are adjusted appropriately. Currently, high precision is achieved (as compared against time-domain simulation) by usage of Fourier series analysis in determining the HBTR adjustment factor. This numerical approach has a potential to accelerate simulation by orders of magnitude. Its physical meaning will also be discussed.