Occlusion Effect in Response to Stimulation by Soft Tissue Conduction-Implications.

Miriam Geal-Dor,Cahtia Adelman,Shai Chordekar,Haim Sohmer

doi:10.3390/audiolres10020012

Miriam Geal-Dor, Cahtia Adelman + Show 2 more

Open Access

https://doi.org/10.3390/audiolres10020012

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Abstract

To gain insight into the broader implications of the occlusion effect (OE—difference between unoccluded and occluded external canal thresholds), the OE in response to pure tones at 0.5, 1.0, 2.0 and 4.0 kHz to two bone conduction sites (mastoid and forehead) and two soft tissue conduction (STC) sites (under the chin and at the neck) were assessed. The OE was present at the soft tissue sites and at the bone conduction sites, with no statistical difference between them. The OE was significantly greater at lower frequencies, and negligible at higher frequencies. It seems that the vibrations induced in the soft tissues (STC) during stimulation at the soft tissue sites are conducted not only to the inner ear and elicit hearing, but also reach the walls of the external canal and initiate air pressures in the occluded canal which drive the tympanic membrane and excite the inner ear, leading to hearing. Use of a stethoscope by the internist to hear intrinsic body sounds (heartbeat, blood flow) serves as a clear demonstration of STC and its relation to hearing.

Highlights

The most common mode of hearing is by air conduction (AC)—i.e., by alternating condensation and rarefaction air pressures arising from the sound producing structure, which are conducted to the ear, reaching the tympanic membrane, causing its vibration, and that of the middle ear ossicles, inner ear fluid pressures, etc
The two-way ANOVA showed that there was a significant difference in the occlusion effect between the lower frequencies compared to the higher frequencies (p < 0.001), and that there was no significant difference between the occlusion effect for the two soft tissue conduction (STC) sites compared to the two bone conduction (BC) sites
This study has shown for the first time that the occlusion effect can be elicited in response to stimulation delivered to soft tissue sites (STC), to BC stimulation

Summary

Introduction

The most common mode of hearing is by air conduction (AC)—i.e., by alternating condensation and rarefaction air pressures arising from the sound producing structure (e.g., natural voice, loud speaker, musical instrument, etc.), which are conducted to the ear, reaching the tympanic membrane, causing its vibration, and that of the middle ear ossicles, inner ear fluid pressures, etc. Bone conduction (BC) stimulation is elicited by a vibrator applied to skull bone, usually the skin over the mastoid or forehead, and it is used to differentiate between a conductive hearing loss (in which AC thresholds are elevated and BC thresholds are normal) and a sensori-neural hearing loss (in which both AC and BC thresholds are elevated). This differentiation was based on the assumption that BC stimulation excites the inner ear directly. A special bone vibrator eliciting osseous BC is used as a hearing aid in some cases of hearing loss (bone anchored hearing aid)

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