Effect of occlusion effects by bone-conduction sound on speech perception assessed by monosyllable articulation test and confusion in phoneme perception

Bone conduction (BC) has been applied to hearing aids for conductive hearing loss, earphones, and other audio devices including ones presenting sound to the face. One of the important characteristics of BC is the "occlusion effect (OE)", a phenomenon that low-frequency sound are perceived as being enhanced when the ear canal is occluded. Our previous study examining OE in facial parts reported that the OE in some facial parts was larger than OE in parts conventionally used. In this study, we conducted monosyllable articulation tests using bone-conducted speech with subjects' ear canal open and occluded, and investigated confusion in phoneme perception to evaluate the effect of OE on perception in the mastoid process, condylar process, nasal bone, and infraorbital region. The results showed that OE increased articulation. However, its effect varied depending on stimulus location and acoustic characteristics of the phonemes, and even confusions among unvoiced consonants even increased by OE. These findings are useful for optimizing BC devices using OE.