The basic study on communication aids for the profoundly deaf using ultrasound hearing

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The perception mechanism of bone-conducted ultrasound (BCU) was investigated. The central auditory system of BCU was studied using PET (positron emission tomography) and magnetoencephalography (MEG). Its peripheral mechanism was investigated by means of calculation of the inner head acoustic field and the study on ultrasonic masker and dynamic range of BCU.1. Using three-dimensional PET, the cortical areas activated by BCU were measured from five profoundly deaf subjects and normal-hearing subjects. The medial portion of the primary auditory cortex of the profoundly deaf subjects as well as normal volunteers was significantly activated. These results suggest that extra-cochler routes convey information to the primary auditory cortex and can therefore produce detectable sound sensation even in the profoundly deaf.2. The effects of stimulus duration for 30 kHZ BCU were compared with those for air-conducted 1 kHz tone bursts by MEG. As a result, significant differences in the growth were … More observed below the saturation points. The results indicated a possibility that there were some differences in the central auditory system between BCU and audible sound.3. The phenomenon physically occurring within the head for bone-conducted sound of various stimulation locations has been calculated using finite-difference time-domain (FDTD) technique. The results showed that there was a large difference between the inner head acoustic field for BCU and bone-conducted audible sound.4. The mount of masking produced by 27-, 30- and 33-kHz bone-conducted ultrasonic maskers for air-conducted high-frequency sounds was measured in the frequency range of 8-18 kHz. The results showed that the air-conducted signals of 10-14 kHz were strongly masked by the ultrasonic maskers. And the dynamic range for BCU was clearly narrower than that for audible sounds. These results suggest that perception of BCU depends on inner hair cell activity induced by ultrasound, and did not depend on enhancement by the outer hair cells. Less