Study On Mechanism Of Lip Protrusion Based On Magnetic Resonance Imaging And Finite Element Modeling

The lips are one of the articulators for producing speech sounds,and also contribute to the generation of phonetic information to be visually perceived by the listeners.For this reason,lip gestures for speech provide a useful research topic for investigating multimodal aspects of speech production and perception.Rapid and accurate gestures can be performed by the lips,whereas the mechanism underlying such large degrees of freedom in labial gestures is still unclear.Among them,lip protrusion is the most underexplored because there is no known mechanism to cause such a shape.The manner by which the lips alter the shape of the vocal tract is similar to that of the tongue,in that the action of both organs involves a large deformation of soft tissue consisting mainly of muscle,without the mechanical support of a rigid skeletal structure.The efficient way to overcome the difficulties in investigating lip deformation mechanisms is to synthetically reproduce lip movements using a 3D physiological model.This study aims at exploring physiological mechanisms of lip protrusion based on muscle visualization and finite element simulation of lower lip deformation.In this thesis,we review anatomical and physiological findings of the lip muscles in detail and propose a possible mechanism of lip protrusion.A special focus is placed on the peripheral part of the orbicularis oris among the lip muscles because it is located closer to the lip's oral surface.This geometry suggests enhancement of lip tissue convexity by medial shortening of the teeth-side lip tissue disproportionately.This hypothesis was examined by a simulation using a physiological model of the lower lip and jaw built based on high-resolution magnetic resonance imaging(MRI)data.Lower lip deformation obtained by the simulation conforms to the hypothesis of lip tissue advancement with enhanced anterior convexity.