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

Area of Science:

• Auditory physiology
• Biomechanics of hearing
• Otoacoustic emissions

Background:

• Understanding bone conduction (BC) sound perception is crucial for diagnosing hearing loss.
• The role of middle ear ossicle mechanics in BC hearing is not fully elucidated.
• Previous models often simplify or neglect the inertial effects of the ossicles.

Purpose of the Study:

• To compute ossicle vibration levels at hearing threshold for both air and bone conduction.
• To evaluate the contribution of middle ear ossicle inertia to BC sound perception.
• To determine the primary cochlear input pathway for BC stimulation.

Main Methods:

• Combined hearing threshold data (air and bone conduction) with middle ear ossicle vibration measurements.
• Calculated ossicle vibration levels at threshold stimulation.
• Compared stapes footplate displacements between air and bone conduction modalities.
• Analyzed basilar membrane vibration data for verification.

Main Results:

• Middle ear inertia is not significant for BC sound perception below 1.5 kHz.
• Ossicle inertia appears to contribute to BC sound perception between 1.5 kHz and 3.5 kHz.
• Analysis failed above 4 kHz, suggesting oval window is not the primary cochlear input for BC.
• Basilar membrane vibration data validated calculations from 0.8 kHz to 3.5 kHz.
• Fluid flow at the round window, not the oval window, reflects basilar membrane stimulation in BC.

Conclusions:

• Middle ear inertia plays a frequency-dependent role in bone conduction hearing.
• The primary cochlear input for BC stimulation shifts from the oval window at lower frequencies to potentially the round window at higher frequencies.
• Further research is needed to fully understand BC mechanisms, especially at higher frequencies.