Characteristics of Frequency Resolution and Speech Perception Using Bone Conduction on Different Human Facial Parts*

In conventional bone-conduction (BC) devices, a vibrator is typically attached to the mastoid process of the temporal bone or the condyle process of the mandible. However, BC-sound presentations to facial parts such as the nose and cheek have also been investigated recently. As the face is the among the most complex structures of the human body, transmission of sounds using BC on different facial parts are likely to show different perception and propagation characteristics than those presented to conventional parts. However, the characteristics of BC sound presented to different part of the face have not yet been studied in detail. To test the frequency discrimination ability, we measured difference limens for frequency (DLFs). 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 of a normal-hearing subject. The results suggest that, at least in the parts investigated in the current study, the frequency resolution and intelligibility of the facial parts were about the same as those of the conventional parts. These results indicate that practical frequency information and speech perception are possible with BC devices attached to different facial parts.