Abstract
Stimulus-Frequency Otoacoustic emissions (SFOAEs) are sounds that are generated by the cochlea and carry signatures of cochlear mechanisms and amplification. Although SFOAEs are not thought to contribute to the sensitivity of the hearing process, they provide valuable non-invasive information about cochlear function and potentially can be used in the clinical assessment of sensory-neural hearing loss. The source of SFOAE is thought to be due to the travelling wave reflected by local impedance roughness which is due to random perturbations of the organ of Corti structures (Shera and Zweig, 1993). While the active process of the outer hair cells (OHCs) tunes the peak of the traveling wave, the source of the random perturbations in generating SFOAEs is not well established. In the present work, random perturbations around baseline model parameters (e.g., Young's moduli and geometrical parameters of the basilar membrane (BM), reticular lamina (RL), outer hair cells (OHCs) as well as their gain factor (the ratio of the axial force that OHC generates due to the shear force on OHC stereocilia) were studied in a finite-element model of the mouse cochlea. Consistent with experimental measurements, the model successfully produces SFOAE magnitudes and phase delays, without significantly affecting cochlear tuning. The model SFOAE amplitude and phase are more sensitive to perturbations in BM Young's modulus and thickness and to OHC gain than to RL Young's modulus and thickness and OHC Young's moduli. Irregularities of OHC gain factor seems to be a plausible source of the SFOAEs because not only their distribution varies along the cochlear length but also their functionality is vulnerable. The model also confirms that the SFOAE magnitude increases, approximately linearly with the perturbation of BM Young's modulus.