The effect of amplitude-modulation methods and speaker gender on monosyllable articulation by distantly-presented bone-conducted ultrasound

Bone-conducted ultrasound (BCU) can be heard and can transmit speech information using amplitude-modulation (AM). Additionally, BCU can be heard even on distal-parts of the body; e.g., the neck, trunk, and upper limbs. Since transmission path of the distantly-presented BCU is much longer and complicated than the ordinary-BCU presented to the head, it may contain tissues with strong nonlinearity like cartilages and generate some amount of self-demodulation components. Previous studies have indicated that the self-demodulation components contribute to improve the hearing of distantly-presented AM-BCU, however, self-demodulation components are thought to be affected by AM-methods and modulator characteristics. In this study, effects of the AM-methods and the speaker-gender on distantly-presented AM-BCU hearing were assessed by Japanese mono-syllable articulation testsin seven normal-hearing subjects. The articulation generally decreased as the presentation location moved away from the head, whereas the neck showed higher than the mastoid in some conditions. Effects of AM-methods on the articulationwere similarto those observed in the previous study on ordinary-BCU (DSB-TC ≒ Transposed ≫ SSB, DSB-SC). Also, female-voice showed higher articulation than male-voice, especially in the distal locations. The results suggested that self-modulation components have significant effect, although the AM-methods affect dominantly on hearing of the distantly-presented AM-BCU.