Midsagittal Images.
Quantitative models of the human speech production system are needed for a better understanding of our cognitive abilities and for the development of high-quality speech synthesizers and automatic speech recognition systems. In previous studies, information regarding the vocal tract geometry during speech production has been mainly derived from lateral x-ray data. The main limitations of x-rays include radiation risks and difficulty in accurately deducing the cross-sectional morphology from mid-sagittal profiles.
Magnetic resonance imaging (MRI) is a powerful tool in obtaining the vocal-tract geometry and does not involve any known radiation risks. The images have good signal to noise ratio, are amenable to computerized 3-D modeling, and provide excellent structural differentiation. In addition, the tract (airway) area and volume can be directly calculated. The low image sampling rate, however, has restricted MRI use to the study of sustained speech sounds, corresponding to `static' tract shapes. In addition, the high expense associated with using MRI equipment, has restricted its use in speech research. Previous MRI studies have been mostly limited to vowels and nasal consonants.
In this study, articulatory data are obtained from Magnetic Resonance Images (MRI) and Dynamic Electropalatography (EPG). MRI reveals the 3D geometry of the vocal tract while EPG is important for studying articulatory dynamics. The modeling approach is based on estimation theory, acoustics, and signal-processing techniques and uses the data obtained from the unified set of measurements described above.
We have gained access to the Medical Imaging Facilities at Cedars Sinai Hospital and have collected MR images in the sagittal, coronal, and axial planes using a GE 1.5 Tesla SIGNA machine. Four phonetically-trained, native American English speakers [2 males (MI, SC) and 2 females (AK, PK)] served as subjects. Coronal and axial scans were used to obtain area functions of the front and back regions, respectively, while sagittal scans were used for length measurements. 3D models were used to measure the volumes of the sublingual cavities, piriform sinuses, and the entire vocal tract.
In addition to obtaining valuable estimates of the area functions and volumes, the MRI data illustrated inter-speaker differences in tongue shapes. So far, we have obtained images while speakers sustained vowels, fricatives, and liquids.
Supported by NSF grant number IRI-9503089.
MRI, Speech Production Modeling.
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