Abstract
Bone-anchored hearing aids are a widely used method of treating conductive hearing loss, but the benefit of bilateral implantation is limited due to interaural cross-talk. The present study measured the phase and level of pure tones reaching each cochlea from a single, mastoid placed bone transducer on normal hearing participants. In principle, the technique could be used to implement a cross-talk cancellation system in those with bilateral bone conductors. The phase and level of probe tones over two insert earphones was adjusted until they canceled sound from a bone transducer (i.e., resulting in perceived silence). Testing was performed in 50-Hz steps between 0.25 and 8 kHz. Probe phase and level results were used to calculate inter-cochlear level and phase differences. The inter-cochlear phase differences of the bone-conducted sound were similar for all three participants showing a relatively linear increase between 4 and 8 kHz. The attenuation characteristics were highly variable over the frequency range as well as between participants. This variability was thought to be related to differences in skull dynamics across the ears. Repeated measurements of cancellation phase and level of the same frequency produced good consistency across sessions from the same participant.
Highlights
Nolan and Lyon (1981) raised the question of whether sound transmitted by BC is received at the same intensity at the ipsilateral and contralateral cochleae and how this “transcranial attenuation” varied with frequency
Our results identified a greater accumulation of phase cycles than Stenfelt and Goode (2005a). It is unclear why there were differences between the two experiments, one possible explanation for the difference relates to intracranial pressure (ICP)
Using a single BT and ER2 headphones, we have demonstrated that it is possible to achieve repeatable phase results in both the ipsilateral and contralateral ears in binaurally hearing participants on multiple separate testing sessions over a large frequency range from 0.25–8 kHz
Summary
Nolan and Lyon (1981) raised the question of whether sound transmitted by BC is received at the same intensity at the ipsilateral and contralateral cochleae and how this “transcranial attenuation” varied with frequency. Studies which have focused on the transcranial attenuation properties of the skull have used various methods with many investigating the difference in hearing threshold in a single-sideddeafness group when placing a BT on the mastoid bone of the hearing side and the deaf side (Nolan and Lyon, 1981; Stenfelt, 2012). Studies such as this have shown that there is considerable variability in attenuation from À23 to 37 dB across listeners and frequencies (Stenfelt, 2012). This research is mainly beneficial in investigating appropriate masking thresholds for BC sound rather than giving precise inter-cochlear level differences produced by a BT in a particular fixed location
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