A mechanical deformation model of the tongue during speech production considering personalized anatomical structure

Abstract

In the previous studies, several tongue models have been developed to investigate the relationship between the contraction of tongue muscles and the deformation of the tongue during speech. However, the tongue deformation is highly subject-specific and their modellings are insufficient to uncover the detailed mechanism. In this study, a mechanical tongue model considering personalized anatomical structure of tongue myofiber is proposed. A set of reference geometries of tongue and jaw is constructed from the medical images of computer tomography (CT) and the magnetic resonance imaging (MRI) for a Japanese male adult. In addition, we reflect the information of tongue myofiber orientations evaluated from the medical images of diffusion tensor imaging (DTI) on the model using a smoothing extrapolation technique. The tongue deformation is calculated by solving a force-equilibrium equation using a continuous Galerkin finite element method with a hyperelastic material, where the deformation is driven by active contraction of the tongue muscles. We examined the tongue deformations under several contraction conditions during speech and confirmed reasonable numerical reproductions of actual tongue motion and shape. These results indicate that the proposed model reflecting personalized information including myofiber orientations has a potential to identify the tongue muscle contractions in speech production.