Middle ear ossicles motion at hearing thresholds with air conduction and bone conduction stimulation

Abstract

Hearing threshold data with bone conduction and air conduction stimulation are combined with physiological and mechanical measurements of the middle ear ossicles vibration to compute the vibration level of the ossicles at threshold stimulation. By comparing the displacements of the stapes footplate with the two stimulation modalities and assuming the vibration of the stapes footplate to be the input to the cochlea when stimulation is by air conduction, the importance of middle ear ossicles inertia with bone conduction stimulation is evaluated. Given the limitations of the analysis, the results indicate that the inertia of the middle ear is not an important contribution to the perception of BC sound for frequencies below 1.5 kHz; it seems to contribute to perception of bone conducted sound between the frequencies 1.5 and 3.5 kHz. At frequencies above 4 kHz, the analysis failed since the input to the cochlea is probably not through the oval window with bone conduction stimulation. Comparison of basilar membrane vibration data verified the calculations for frequencies between 0.8 and 3.5 kHz. It was also found that the fluid flow at the round window, rather than at the oval window, reflects the stimulation of the basilar membrane with bone conduction stimulation.