Mohammad Ali Nazari

Bio: Mohammad Ali Nazari is an academic researcher from University of Tehran. The author has contributed to research in topics: Finite element method & Support vector machine. The author has an hindex of 11, co-authored 39 publications receiving 364 citations. Previous affiliations of Mohammad Ali Nazari include University of Grenoble & Centre national de la recherche scientifique.

Simulation of dynamic orofacial movements using a constitutive law varying with muscle activation

Abstract: 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. Muscles fibres are represented by piece-wise uniaxial tensile elements, which generate force. The stress stiffening effect, an increase of 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 versus quasi-static simulations are also discussed, proving that dynamic trajectories better fit experimental data.

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.

A biomechanical modeling study of the effects of the orbicularis oris muscle and jaw posture on lip shape

Abstract: Purpose: The authors' general aim is to use biomechanical models of speech articulators to explore how possible variations in anatomical structure contribute to differences in articulatory strategies and phone systems across human populations Specifically, they investigated 2 issues: (a) the link between lip muscle anatomy and variability in lip gestures and (b) the constraints of coupled lip/jaw biomechanics on jaw posture in labial sounds Method: The authors used a model coupling the jaw, tongue, and face First, the influence of the orbicularis oris (OO) anatomical implementation was analyzed by assessing how changes in depth (from epidermis to the skull) and peripheralness (proximity to the lip horn center) affected lip shaping Second, the capability of the lip/jaw system to generate protrusion and rounding, or labial closure, was evaluated for different jaw heights Results: Results showed that a peripheral and moderately deep OO implementation is most appropriate for protrusion and rounding; a superficial implementation facilitates closure; protrusion and rounding require a high jaw position; and closure is achievable for various jaw heights Conclusions: Models provide objective information regarding possible links between anatomical and speech production variability across humans Comparisons with experimental data will illustrate how motor control and cultural factors cope with these constraints

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

Abstract: Purpose The authors' general aim is to use biomechanical models of speech articulators to explore how possible variations in anatomical structure contribute to differences in articulatory strategie...

Finite element speaker-specific face model generation for the study of speech production

Abstract: 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.

A theory of speech motor control and supporting data from speakers with normal hearing and with profound hearing loss

Abstract: A theory of the segmental component of speech motor control is presented, followed by supporting data. According to the theory, speech movements are programmed to achieve auditory/acoustic goals. The goals are determined partly by "saturation effects", which are basic characteristics of speakers' production systems that make it possible to produce a sound output that has some relatively stable acoustic properties despite a somewhat variable motor input. The programming of articulatory movements to achieve auditory goals utilizes an internal model (or "mapping") of relations between articulatory configurations and their acoustic consequences. The internal model is acquired and maintained with the use of auditory feedback. The supporting data for this theory come from experiments on speakers with normal hearing, cochlear implant users and a patient with neurofibromatosis-2.

What is tensor analysis

Abstract: I have read with much interest and pleasure “What is tensor analysis?” by Doctor Banesh Hoffmann and his article is the best elementary analysis of the subject which I have seen.

Human sound systems are shaped by post-Neolithic changes in bite configuration

Abstract: Linguistic diversity, now and in the past, is widely regarded to be independent of biological changes that took place after the emergence of Homo sapiens We show converging evidence from paleoanthropology, speech biomechanics, ethnography, and historical linguistics that labiodental sounds (such as "f" and "v") were innovated after the Neolithic. Changes in diet attributable to food-processing technologies modified the human bite from an edge-to-edge configuration to one that preserves adolescent overbite and overjet into adulthood. This change favored the emergence and maintenance of labiodentals. Our findings suggest that language is shaped not only by the contingencies of its history, but also by culturally induced changes in human biology.

Coupled hard―soft tissue simulation with contact and constraints applied to jaw―tongue―hyoid dynamics

Abstract: We present an open-source physical simulation system suitable for efficient modeling of anatomical structures composed of both hard and soft tissue components, interconnected by point-wise attachments, contact, and other constraints. Specific attention is paid to the computational formulation needed for the coupled simulation of rigid and deformable structures, and a constraint-based mechanism is described for attaching these together. As an application of this system, we then present a novel 3D dynamic model of the jaw-tongue-hyoid complex, consisting of an FEM model of the tongue, rigid jaw, and hyoid structures, point-to-point muscle actuators, and constraints for bite contact and the temporomandibular joints. Several simulations are presented showing combined jaw-tongue actions and demonstrating the effects of coupled jaw-tongue-hyoid dynamics.