An inversion procedure from formant trajectories to central motor commands is presented here. It first involves the inference of vocal tract shapes by the inversion of an articulatory-to-acoustic model of the vocal tract. This many-to-one problem is solved by minimising the jerk of the articulatory parameters. Articulatory trajectories in different parts of the vocal tract are extracted from sagittal contours. Dynamic properties of speech articulators are then modelled by a second-order system, and articulatory movements are controlled by shifting the equilibrium position of the system. The inversion of this second model thus provides motor command sequences for a given articulatory trajectory. This procedure is applied to vowel reduction. The results suggest that the observed acoustic variability can be explained with an invariant motor command sequence associated with a specific dynamic parameterisation of the movement.
Bibliographic reference. Loevenbruck, Helene / Perrier, Pascal (1993): "Vocalic reduction : prediction of acoustic and articulatory variabilities with invariant motor commands", In EUROSPEECH'93, 85-88.