Investigating the effect of change in cochlear micromechanics and activity levels on stimulus frequency otoacoustic emissions phase-gradient delay.

Stimulus frequency otoacoustic emissions (SFOAEs), which are sounds emitted by the cochlea at the frequency of the stimulus, have been used as a noninvasive measure of cochlear function. The gradient of the SFOAE phases characterizes the latency of emission and is associated with the frequency selectivity and sharpness of tuning of the mammalian cochlea. However, whether the phase-gradient delay of SFOAE can be used as a indicator of cochlear tuning and sensitivity reliably when the proper-ties of the cochlea change remains unclear. The objective of this study is to address this question by varying cochlear model activity, tectorial membrane (TM) properties and organ of Corti (OoC) micromechanical properties to change cochlear tuning. In this work, a three-dimensional gerbil cochlear model that couples mechanical, electrical and acoustic domains with cochlear roughness has been used. The roughness is implemented on outer hair cells (OHCs) force acting on the basilar membrane (BM). Parameters that control the activity levels, TM longitudinal coupling and OoC impedance are varied. The results show that changes in sharpness of tuning due to reduction in cochlear activity and TM longitudinal coupling can be detected by using SFOAE phase-gradient delay. However, changes in cochlear tuning due to changes in OoC impedance are not necessarily reflected by corresponding changes in SFOAE phase-gradient delay. [ABSTRACT FROM AUTHOR]