Frequency-discrimination and speech-perception characteristics of bone-conducted sound presented to the facial parts

Bone-conducted (BC) sound is typically presented to the mastoid process of the temporal bone or the condyle process of the mandible. However, a method of presenting BC sound to facial parts such as the nose and cheek have also been investigated recently. Since the face is one of the most complex structures in the human body, slight differences in the presentation parts of the vibrator will also change the perception and propagation mechanism. However, the characteristics of BC sound presented to the face have not yet been studied in detail. We have previously discussed the differences in perception (hearing thresholds) and propagation characteristics among facial parts. Here, to test the frequency-discrimination ability, we measured difference limens for frequency. We also conducted monosyllable articulation tests in Japanese to assess the speech-perception characteristics when BC sounds are presented to various facial (nasal, infraorbital region, zygomatic, jaw angle, and chin) and conventional (mastoid and condyle process) parts. The results obtained showed that the frequency resolution and intelligibility of the facial parts were about the same as those of the conventional parts. It is indicated that practical frequency information and speech perception are possible with BC devices attached to certain facial parts.