Multimodal Stimulation Using Bone Conduction for Tinnitus Therapy

Abstract

Tinnitus is the perception of sounds with no external source. Several techniques to manage tinnitus exist, including tinnitus masking. This study investigated the potential of using bone conduction to deliver tinnitus masking, instead of through the traditional air conduction route. Auditory and somatosensory perceptions are known to be intricately related including in their central processing. Somatosensory manipulations are also documented to alter tinnitus characteristics for some individuals. Multimodal integration of vibrotactile and auditory sensations using bone conduction may therefore effectively alter the intensity required for the masking noise of an individual’s tinnitus. It was hypothesised that the intensity required for tinnitus masking may be reduced when using bone conduction, especially at the lower frequencies where vibrotactile perceptions can be felt. The group consisted of twelve subjects (mean age of 55.00 years; 6 males, 6 females) with chronic and continuous tinnitus. Ear-specific minimum masking levels at different frequencies ranging from 125 Hz to 8 kHz were determined when using in-ear air conduction transducers and bone conduction transducers. Threshold-adjusted noise prescriptions were calculated to account for the headphones’ output variability across the frequency range. A battery of measures were also taken to assess participants’ relationship with tinnitus and their hearing to evaluate tinnitus therapy effectiveness by using questionnaires, otoscopy, pure tone audiometry, and psychoacoustic tinnitus tests. No significant differences were found between the minimum masking levels required when using the two different transducers, including when compared at each frequency. This has implications for clinical practice – as bone conduction transducers are as effective as traditional air conduction transducers, clinicians should consider the potential advantages of bone conduction transducers for tinnitus therapy for clients who prefer not to be fitted with hearing aids, including the ability to maintain awareness of one’s sound environment, and the absence of occlusion that earphones cause. Significant correlations also infer that proportionately lower masking levels were required at frequencies with more hearing loss for both transducers but especially when delivered using bone conduction. Age may also be involved in this relationship; older tinnitus sufferers required less tinnitus masking at these higher frequencies with more hearing loss. Loudness recruitment is likely responsible. Proportionate distributions of sound should therefore be prescribed across frequencies when using hearing aids for sound therapy, especially for older patients.