A three-dimensional linear articulatory model of velum based on MRI data

In the framework of studies on nasality, we have attempted to develop a 3-D articulatory model of velum. Sets of 25 sagittal MRI images have been collected for one French subject sustaining 46 articulations. Contours of the velum have been manually drawn from these images; a common 3-D triangular mesh has then been fitted to these contours in order to constitute 3-D representations of the velum outline. This resulted in 46 meshes of 5239 vertices defined by their 3-D coordinates.In order to develop a velum model free of the influence of the tongue, the analysis was first limited to the 28 articulations where no tongue - velum contact occurs: it was found that the first component extracted from these data by Principal Component Analysis can explain as much as 79% of the variance of the complete 3-D shape of the velum, while the second component was meaningless in terms of articulatory movements. It was also found that the same model could explain 71% of the variance for the corpus of the 18 articulations where tongue - velum contact occurs. It was finally shown that the vertical coordinate of a single flesh point attached to the downward face of the velum is enough to predict the complete 3-D shape of the free velum