ABSTRACT
Elastic lip shape greatly varies in order to control speech sounds. We introduce a lip-dynamics model for exploring speech articulatory movements. The shapes of the lip-rounding muscle (orbicularis oris), jaw and maxillar bones, and skin surface were extracted from three-dimensional magnetic resonance imaging (MRI) data, and then the locations of the perioral muscles were defined based on the MRI data. To represent fine deformation patterns of lip shape, the orbicularis oris muscle was subdivided into eight regions. Nine perioral muscles and five jaw muscles were implemented to reproduce large lip deformation. Muscle dynamics consist of a force generator and visco-elastic components, and all passive dynamics are represented by a mass-spring meshed network. This model enables us to reproduce dynamical perioral movements by specifying arbitrary muscle inputs. Using this model, we have succeeded in reproducing lip protrusion only by activating peripheralis parts of the upper and lower lip muscles, the possibility of which was predicted by a previous EMG study. We also demonstrate other natural lip deformations obtained from several muscle activation patterns and discuss the important aspects of modeling studies for understanding the mechanisms of speech motor control.
