Bilateral Bone Conduction Amplification in Noise – The Role of Spectral Release from Masking
2Institute of Audiology and Clinical Neurophysiology, Schneider Children’s Medical Center
3Department of Otorhinolaryngology, Rabin Medical Center
4Sackler Faculty of Medicine, Tel Aviv University
Introduction: Bone conduction hearing devices are indicated for conductive hearing loss as well as for sensorineural single sided deafness. Bilateral hearing loss adversely affect speech understanding in noise and sound localization. It is questionable whether bilateral amplification with bone conduction devices will improve hearing in noise, as interaural attenuation via bone conduction is considered negligible in low frequencies.
Objectives: The aim of this study was to evaluate the effect of bilateral bone conduction hearing aids in subjects with bilateral conductive hearing loss.
Methods: Thirty normal hearing subjects were included. Bilateral pseudo-conductive hearing loss of >35db was induced using earplugs and earmuffs. Bone conduction hearing aids (Contact-Mini, BMH-Tech, Austria) were placed over the mastoid bilaterally. Blinded comparison of unilateral vs. bilateral amplification was performed in different signal to noise ratio (SNR) settings and different locations of the noise. A validated Hebrew version of Hagerman sentences, as well as questionnaires assessing noise disturbance and ‘ease of listening’ were used.
Results: Objective and subjective measures were similar for unilateral and bilateral amplification when both signal and noise were presented from the front. However, bilateral amplification was superior to unilateral amplification when signals were presented from the front and noise was presented from both sides (SNR-10: 92% vs. 84%, p=0.001; SNR-15: 84% vs, 78%, p=0.005). Blinded questionnaires demonstrated that bilateral amplification was beneficial – 81% of subjects answered that hearing was easier with bilateral amplification; 55% vs 9% answered that noise was more disturbing with unilateral vs. bilateral amplification, respectively.
Conclusions: Bilateral amplification with bone conduction devices can improve hearing in noise in specific conditions. Improvements include better speech understanding, better sound quality and reduced noise disturbance.
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