A three-dimensional articulatory model of the velum and nasopharyngeal wall based on MRI and CT data.

An original three-dimensional (3D) linear articulatory model of the velum and nasopharyngeal wall has been developed from magnetic resonance imaging (MRI) and computed tomography images of a French subject sustaining a set of 46 articulations, covering his articulatory repertoire. The velum and nasopharyngeal wall are represented by generic surface triangular meshes fitted to the 3D contours extracted from MRI for each articulation. Two degrees of freedom were uncovered by principal component analysis: first, VL accounts for 83% of the velum variance, corresponding to an oblique vertical movement seemingly related to the levator veli palatini muscle; second, VS explains another 6% of the velum variance, controlling a mostly horizontal movement possibly related to the sphincter action of the superior pharyngeal constrictor. The nasopharyngeal wall is also controlled by VL for 47% of its variance. Electromagnetic articulographic data recorded on the velum fitted these parameters exactly, and may serve to recover dynamic velum 3D shapes. The main oral and nasopharyngeal area functions controlled by the articulatory model, complemented by the area functions derived from the complex geometry of each nasal passage extracted from coronal MRIs, were fed to an acoustic model and gave promising results about the influence of velum movements on the spectral characteristics of nasals.