Shaping by Stiffening: A Modeling Study for Lips

Abstract

On the basis of simulations carried out with a finite element biomechanical model of the face, the influence of the muscle stress stiffening effect was studied for the protrusion/rounding of the lips produced with the Orbicularis Oris (OO). It is shown that the stress stiffening effect influences lip shape. When stress stiffening is modeled, the variation in the crucial geometrical characteristics of the lips shows a clear saturation effect as the OO activation level increases. Similarly, for a sufficient amount of OO activation, a saturation effect is observed when stiffening increases. In both cases, differences in lip shaping associated with the absence or presence of stiffening have consequences for the spectral characteristics of the speech signal obtained for the French vowel /u/. These results are interpreted in terms of their consequences for the motor control strategies underlying the protrusion/rounding gesture in speech production.

Speech function of the oropharyngeal isthmus: a modelling study

“…In this sense, OPI function indeed seems analogous to the lips, where discrete, task-specific mechanisms have been described as being used to produce different-sized constrictions; mechanisms of this kind, associated with distinct muscle combinations, have been described as producing biomechanically nonlinear or quantal-like effects (Fujimura 1989; Nazari et al 2011; Gick et al 2011) similar to those observed here for the OPI. Such effects have been used to explain why different lip shapes are associated with different areas (degrees) of constrictions in speech (e.g., flat-shaped lips for complete closures, but rounded, protruded lips for vowels; Gick et al 2011).…”

Visuomotor and Audiomotor Processing in Continuous Force Production of Oral and Manual Effectors

“…Lip elevation for force control may have limited the lips to use all the necessary muscular components needed to minimize variation of force. Changes in stiffness may influence the shape of the lips, such as pursing the lips (Nazari, Perrier, Chabanas, & Payan, 2011). Our findings indicating no increase in CV in the finger as force level increased and a decrease in CV as force increased in the lip may reflect different controls of stiffness between the effectors.…”

A Biomechanical Modeling Study of the Effects of the Orbicularis Oris Muscle and Jaw Posture on Lip Shape

“…This muscle plays a central role in the production of the lip protrusion and rounding gestures (Nazari et al, 2011). These gestures are essential for rounded vowels such as /u/, /o/ or /y/, and for closing labial gestures, which represent the key articulatory feature of bilabial stops such as /b/ and /p/.…”