Psychoacoustic measurements of bone conducted sound

Abstract

Bone-conduction hearing aids (BCHAs) are a widely used method of treating conductive hearing loss, but the benefit of bilateral implantation is severely limited due to interaural cross-talk. In theory two BCHAs could deliver improved stereo separation using cross-talk cancellation. Sound vibrations from each BCHA would be cancelled at the contralateral cochlea by an out-of-phase signal of the same level from the psilateral BCHA. In order to achieve this the phase and level of sound at each cochlea needs to be known. A method to measure the level and phase required for these cancellation signals was developed and cross-validated with a second technique that combines air- and bone-conducted sound in normal hearing subjects. Levels measured with each method differed by <1 dB between 3-5 kHz. The phase results also corresponded well for the cancelled ear (11° mean difference). The newly developed method using only bone transducers is potentially transferable to a clinical population. To demonstrate cross-talk cancellation tone and speech reception thresholds (TRT and SRT) were investigated with and without unilateral cross-talk cancellation. Band limited noise was emitted from one BT whilst signal +/- cancellation signal was produced by the other. Benefits of cross-talk cancellation under this atypical listening situation were found to be 12.08 and 13.7 dB for TRT and SRT thresholds. In order to estimate the potential benefits of cross-talk cancellation in spatially realistic environments, phase and level elements of impulse responses from a BAHA 4 were convolved with speech. This found that cross-talk cancellation had the potential to lower SRTs in a clinical population by approximately 4.4 dB. Future work will focus on real-time processing and examine using a clinical population