Categorical variation in lip posture is determined by quantal biomechanical-articulatory relations

A study that was conducted to examine why the lips should adopt such different postures in an attempt simply to modulate degree of constriction is presented. The lip musculature is modeled using a transversely anisotropic FEM material. The transverse direction of each element is interpolated from the muscle fiber path and represents the muscle's line-of-action. Stress is added in the transverse direction to represent passive muscle stress and active muscle stress. Different initial muscle settings produce regions in which large variations in input activation yield stably different degrees of constriction, all corresponding to the feature of labial. The article concludes that language speakers use these quantal regions in biomechanical-articulatory space to control constriction degree at the lips.