Comparison between bone-conducted ultrasound and audible sound in speech recognition.

Conclusion: This study showed that it is possible to transmit language information using bone-conducted ultrasound (BCU) in normal-hearing subjects. Our results suggest the possibility of a difference in speech recognition between BCU and air-conducted audible sound (ACAS).

Objective: Ultrasound was audible when delivered by bone conduction. Some profoundly deaf subjects as well as normal-hearing subjects can discriminate BCU whose amplitude is modulated by different speech sounds. These findings suggest the usefulness of developing a bone-conducted ultrasonic hearing aid (BCUHA). However, the characteristics of BCU are still poorly understood. The aim of the present study was to compare BCU and ACAS in terms of their associated speech perception tendency and to investigate the different perceptual characteristics of BCU and ACAS.

Subjects and methods: Speech discrimination tests using both BCU and ACAS were performed with normal-hearing subjects. BCU and ACAS were compared for intelligibility and hearing confusion.

Results: With BCU, the maximum percentage correct totaled about 75%. Our comparison of the hearing confusion with ACAS and BCU according to the individual syllabic nuclear group showed a clear difference in the incorrect rates. In addition, the stimulus nuclear groups were often perceived in other nuclear groups in BCU.