Effects of modulation method and presentation part on distantly-presented bone-conducted ultrasonic perception

Ultrasounds can be heard clearly by bone-conduction, and this "bone-conducted ultrasound (BCU)" can transmit speech using amplitude-modulation. Additionally, BCU can be heard even on distal parts of the body e.g., the neck, trunk, and upper limbs. Previous studies have suggested that "distantly-presented BCU" is expected to be applied to a audio device that can selectively transmits sound information to a specific user who touches the vibrator. In this study, to assess the effects of the stimulus placement on the perception of distantly-presented BCU, acceleration of vibration in the external auditory meatus and hearing threshold were investigated. Also, the effect of the method of amplitude-modulation on Japanese monosyllable articulation were examined. The results showed that the more complex the presentation part, the more the ultrasound was attenuated, and factors other than distance attenuation were significant in the forearm. Further, the modulation method had significant effects on speech perception; DSB-TC and Transposed showed higher articulation than DSB-SC and SSB. These results provide useful information to develop a novel audio device using distantly-presented BCU.