Sound pressure in the external auditory canal during bone-conduction testing

Area of Science:

• Audiology
• Bioacoustics
• Hearing Science

Background:

• Bone-conduction (BC) hearing tests assess auditory function by transmitting sound vibrations through the skull to the inner ear.
• The external auditory canal (EAC) can contribute to sound transmission during BC measurements, potentially confounding results.
• Optimizing BC vibrator placement is crucial for accurate hearing sensitivity assessment.

Purpose of the Study:

• To compare sound pressure levels (SPLs) in the external auditory canals (EACs) resulting from bone-conduction (BC) stimulation at different cranial placements.
• To investigate the effect of vibrator placement (forehead vs. mastoid) on interaural SPL differences in the EAC.
• To determine if forehead placement can minimize unwanted EAC contributions to BC hearing measurements.

Main Methods:

• Measured SPLs in the EACs of 16 normal-hearing subjects.
• Used BC stimulation at 500, 1000, 2000, and 4000 Hz.
• Applied the BC oscillator to either the forehead or the mastoid process.

Main Results:

• Significantly higher SPLs were recorded in the EAC for mastoid stimulation compared to forehead stimulation at 1000, 2000, and 4000 Hz.
• Mastoid placement resulted in significantly greater ipsilateral EAC SPLs at 2000 and 4000 Hz.
• Forehead placement showed no significant interaural differences in EAC SPLs.

Conclusions:

• Forehead placement of a BC vibrator generates lower SPLs in the EAC than mastoid placement.
• Forehead placement may reduce the influence of the EAC on BC hearing sensitivity measurements.
• This finding has implications for improving the accuracy and reliability of BC audiometry.