Three dimensional vocal tract shapes of three males and three females were measured from the magnetic resonance images that were taken during sustained phonation of the five Japanese vowels. Dimensional differences in the vocal tract length of the subjects were quantitatively measured by dividing the entire vocal tract into the oral, the pharyngeal and the laryngeal sections. To investigate main factors that contribute to the differences of the formant patterns, uniform and non-uniform normalization methods were applied to the vocal tract shapes. The formant frequencies were also computed from the normalized area functions and compared. The results show that the physiological dimensions of the vocal tract continuously distributed from females to males. The normalization experiments suggest that the non-uniform scaling of the vocal tract was not significant and back/front cavity volume in addition to the vocal tract length is an important factor to describe speaker individualities.
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