Objective Assessments of Bone-conducted Ultrasonic Hearing-aid (BCUHA) by Magnetoencephalography: A Study on Discrimination Capability of Multi-channel Inputs

Bone-conducted ultrasound (BCU) is perceived even by those who are profoundly sensorineural deaf. A novel hearing-aid using BCU perception, which transmits amplitude-modulated ultrasound by bone-conduction, has been developed for the profoundly deaf. To assess and optimize the bone-conducted ultrasonic hearing-aid (BCUHA), the characteristics of BCU perception need to be better specified. This study verified the discrimination capability of two-channel BCUs presented to the both left and right mastoids in the both normal-hearing and profoundly deaf subjects by evaluating the laterality of the auditory evoked cortical activities. In normal-hearing subjects, Nlm responses, the most prominent deflections peaking about 100 ms after the sound onset, evoked by the contralateral stimuli were larger in amplitude and shorter in latency than those evoked by the ipsilateral stimuli for BCUs as well as audible sounds. The same phenomena were also observed for BCUs in profoundly deaf subjects. These results suggest that two-channel BCUs were separately localized and provide a rationale to develop a multichannel BCUHA.