This paper presents a biomechanical model of the face to simulate orofacial movements in speech and non-verbal communication. A 3D finite element model, based on medical images of a subject, is presented. A hyperelastic Mooney-Rivlin constitutive law accounts for the non-linear behaviour of facial tissue. Muscle fibres are represented by piece-wise uniaxial tensile element that generate force. The stress stiffening effect, an increase in the stiffness of the muscles when activated, is modelled by varying the constitutive law of the tissue with the level of activation of the muscle. A large number of facial movements occurring during speech and facial mimics are simulated. Results show that our modelling approach provides a realistic account of facial mimics. The differences between dynamic vs. quasi-static simulations are also discussed, proving that dynamic trajectories better fit experimental data.

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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.

Method: Our methodology is based on computer simulations with a sophisticated biomechanical model coupling the jaw, tongue and face. First, the influence of Orbicularis Oris (OO) muscle geometry is analyzed. We assessed how changes to the OO anatomical implementation, in terms of depth (from epidermis to the skull) and peripheralness (proximity to the lip horn center), affected lip protrusion, lip spreading and lip area. Second, we evaluated the capability of the lip/jaw system to generate protrusion and rounding, or labial closure for different jaw heights.Results: (1) A highly peripheral and moderately deep OO implementation is most appropriate for achieving protrusion and rounding; (2) a superficial implementation facilitates closure; (3) protrusion and rounding requires a high jaw position; (4) labial closure is achievable for various jaw heights.Conclusions: Our results provide a quantitative assessment of how physical characteristics of the speech motor plant can determine regularities and variability in speech articulations across humans and over time.

Mothers’ constitute is a very important part of infants’ social environment and mediate their experience with the surrounding world. Postpartum depression, which is considered one of the most common and important psychiatric disorders, affects 10–15% of mothers, its causes are different. By investigating various sources, some effects of this disorder have been observed on the cognitive development of children, particularly among boys, such as language, intelligence quotient (IQ), and behavioral problems. Thus, it is imperative to study the effects of postpartum depression on children’s growth and development and to identify methods of reducing these effects. This review indicates that postpartum depression in mothers reduces children’s cognitive performance. The adverse effects of postpartum depression on children’s development seem to be mediated by the mother’s interpersonal behavior and the infant gender. The review of previous studies shows that postpartum depression reduces children’s cognitive performance by impairing maternal mental and behavioral care.

In situations where automatic mesh generation is unsuitable, the finite element (FE) mesh registration technique known as mesh-match-and-repair (MMRep) is an interesting option for quickly creating a subject-specific FE model by fitting a predefined template mesh onto the target organ. The irregular or poor quality elements produced by the elastic deformation are corrected by a 'mesh reparation' procedure ensuring that the desired regularity and quality standards are met. Here, we further extend the MMRep capabilities and demonstrate the possibility of taking into account additional relevant anatomical features. We illustrate this approach with an example of biomechanical model generation of a speaker's face comprising face muscle insertions. While taking advantage of the a priori knowledge about tissues conveyed by the template model, this novel, fast and automatic mesh registration technique makes it possible to achieve greater modelling realism by accurately representing the organ surface as well as inner anatomical or functional structures of interest.

Material properties of the human tongue tissue have a significant role in understanding its function in speech, respiration, suckling, and swallowing. Tongue as a combination of various muscles is surrounded by the mucous membrane and is a complicated architecture to study. As a first step before the quantitative mechanical characterization of human tongue tissues, the passive biomechanical properties in the superior longitudinal muscle (SLM) and the mucous tissues of a bovine tongue have been measured. Since the rate of loading has a sizeable contribution to the resultant stress of soft tissues, the rate dependent behavior of tongue tissues has been investigated via uniaxial tension tests (UTTs). A method to determine the mechanical properties of transversely isotropic tissues using UTTs and inverse finite element (FE) method has been proposed. Assuming the strain energy as a general nonlinear relationship with respect to the stretch and the rate of stretch, two visco-hyperelastic constitutive laws (CLs) have been proposed for isotropic and transversely isotropic soft tissues to model their stress-stretch behavior. Both of them have been implemented in ABAQUS explicit through coding a user-defined material subroutine called VUMAT and the experimental stress-stretch points have been well tracked by the results of FE analyses. It has been demonstrated that the proposed laws make a good description of the viscous nature of tongue tissues. Reliability of the proposed models has been compared with similar nonlinear visco-hyperelastic CLs.

The DLM accounted for the characteristics of the λ model. Biomechanically, no clear differences were found between the DLM and a Hill-type model. Accurate evaluations of the λ model, based on the comparison between data and simulations, are now possible with 3-D biomechanical descriptions of the speech articulators because of the DLM.