On the sound pressure distribution in the inner ear during bone conduction stimulation

During air conduction (AC), intracochlear sound pressures in the scala vestibuli and scala tympani differ significantly, enabling the determination of differential pressure as a key indicator for auditory perception. In bone conduction (BC), however, these pressures are of similar magnitude and exhibit variability due to the motion of the inner ear and interactions among different BC mechanisms. Using a finite element model, we investigated intracochlear sound pressure distributions during BC and AC, separately analyzing rigid body motion and oval window (OW) input. Our results reveal distinct pressure patterns and directionality for rigid body motion, fundamentally differing from those associated with (AC-related) OW input. Basic acoustic principles further clarify the fluid dynamics underlying these distributions. The findings underscore the need to superimpose pressure contributions from various BC mechanisms in a location-dependent manner to fully understand the inner ear's response. These results provide insight into the variability of measurement results published in the literature, and they highlight the challenges of isolating the pressure driving the basilar membrane traveling wave using intracochlear probes. Further investigations are needed to reconcile theoretical models for AC and BC stimulation and to improve the interpretation of experimental data.