Jianwu Dang Kiyoshi Honda
ATR Human Information Processing Res. Labs., 2-2 Hikaridai Seikacho Soraku-gun, Kyoto, 619-02 Japan
Hisayoshi Suzuki
Shizuoka Univ., 3-5-1 Jouhoku, Hamamatsu, 432 Japan
Morphological measurements of the nasal and paranasal cavities were performed to speculate on the acoustic properties of the human nasal tract. The magnetic resonance imaging (MRI) technique was used to measure the three-dimensional structure of the vocal tract. The area function of the nasal tract was calculated from seven subjects at rest. The whole vocal tract was measured from five subjects during sustained pronunciation of nasal consonants. A marked morphological difference was observed between these data and the previous data particularly in the middle portion of the nasal tract. The previous data measured from cadaver specimens have a wide cavity in the middle portion possibly due to absent or dehydrated mucous membrane, while these data show narrow passages caused by thick mucosa. It was confirmed by an experiment that the above difference was reproducible by applying an adrenaline-like agent onto the nose. The acoustic transfer function was calculated from these data, and the speech sound, recorded soon after MRI scan, was used to evaluate the transfer function. The results indicate that the asymmetry of two nostrils can cause an extra pole-zero pair, and suggest that the paranasal cavities can play an important role in shaping spectral characteristics of human nasal cavities.