Psychoacoustic measurements of bone conducted sound

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

Three-Year Follow-Up with the Bone Conduction Implant

Background: The bone conduction implant (BCI) is an active transcutaneous bone conduction device where the transducer has direct contact to the bone, and the skin is intact. Sixteen patients have been implanted with the BCI with a planned follow-up of 5 years. This study reports on hearing, quality of life, and objective measures up to 36 months of follow-up in 10 patients. Method: Repeated measures were performed at fitting and after 1, 3, 6, 12, and 36 months including sound field warble tone thresholds, speech recognition thresholds in quiet, speech recognition score in noise, and speech-to-noise thresholds for 50% correct words with adaptive noise. Three quality of life questionnaires were used to capture the benefit from the intervention, appreciation from different listening situations, and the ability to interact with other people when using the BCI. The results were compared to the unaided situation and a Ponto Pro Power on a soft band. The implant functionality was measured by nasal sound pressure, and the retention force from the audio processor against the skin was measured using a specially designed audio processor and a force gauge. Results: Audiometry and quality of life questionnaires using the BCI or the Ponto Pro Power on a soft band were significantly improved compared to the unaided situation and the results were statistically supported. There was generally no significant difference between the two devices. The nasal sound pressure remained stable over the study period and the force on the skin from the audio processor was 0.71 \ub1 0.22 N (mean \ub1 1 SD). Conclusion: The BCI improves the hearing ability for tones and speech perception in quiet and in noise for the indicated patients. The results are stable over a 3-year period, and the patients subjectively report a beneficial experience from using the BCI. The transducer performance and contact to the bone is unchanged over time, and the skin area under the audio processor remains without complications during the 3-year follow-up

Communications Biophysics

Contains research objectives, summary of research and reports on three research projects.National Institutes of Health (Grant 5 PO1 GM14940-04)National Institutes of Health (Grant 5 TOl GM01555-04)National Aeronautics and Space Administration (Grant NGL 22-009-304

Progress Report No. 15

Progress report of the Biomedical Computer Laboratory, covering period 1 July 1978 to 30 June 1979