Biomechanical simulation of lip compression and spreading

Abstract

Researchers have proposed that human movements exploit regions of biomechanical stability, allowing targets to be reliably achieved in the face of noisy, everyday conditions (e.g., Loeb 2012). Previous biomechanical simulation studies have demonstrated that this property holds for various speech postures of the lips (Stavness et al. 2013; Gick et al. 2020). These studies, however, have omitted two cross-linguistically common lip postures: compression, where the aperture between the lips is narrowed without accompanying protrusion (e.g., Catford 1982), and spreading, where the corners of the lips are drawn back. Previous empirical work has met with difficulty in quantifying the muscle activations that generate these postures due to the interdigitation of lip muscles (Blair and Smith 1986). The present study presents biomechanical simulation results using the Artisynth platform, which allows movements of the face and vocal tract to be simulated as a function of muscle activation (Lloyd et al. 2012). These simulations identify muscle groupings sufficient to produce lip compression and spreading, and provide insight into which of these groupings generate the quantal properties observed in other lip postures. The results complement past experimental findings, and provide a starting point for future modeling and experimentation.