Detailed morphological analysis of mandarin sustained steady vowels

One of important issues for speech production is to investigate the relation of acoustic features and fine morphological structures of the vocal tract. This study aims to examine morphological characteristics of Mandarin sustained vowels using a female vocal tract MRI data. To do so, image preprocessing, teeth superimposition, segmentation and volume reconstruction are carried out on the MRI volumetric images to extract 3D vocal tract shapes. Then area functions are extracted from vocal tract shapes by re-slicing the vocal tract with a set of grid planes. Nine Mandarin vowels are divided into three groups based on the size rate of pharyngeal/oral cavity. Detailed analysis of these area functions are performed within the groups. The morphological characteristics of the laryngeal cavity and side branches (namely the bilateral piriform fossae, epiglottic valleculae and inter-dental spaces) are also discussed. To evaluate morphological measurements, a comparison is carried out between formants measured from real speech sounds and those calculated ones from these area functions. Results suggested that the calculated formants are consistent with natural speech with a mean error of 4.6%.