A 3D biomechanical vocal tract model to study speech production control: How to take into account the gravity?

This paper presents a modeling study of the way speech motor control can deal with gravity to achieve steady-state tongue positions. It is based on simulations carried out with the 3D biomechanical tongue model developed at ICP, which is now controlled with the Lambda model (Equilibrium-Point Hypothesis). The influence of short-delay orosensory feedback on posture stability is assessed by testing different muscle force/muscle length relationships (Invariant Characteristics). Muscle activation patterns necessary to maintain the tongue in a schwa position are proposed, and the relations of head position, tongue shape and muscle activations are analyzed

Modeling the production of VCV sequences via the inversion of a biomechanical model of the tongue

A control model of the production of VCV sequences is presented, which consists in three main parts: a static forward model of the relations between motor commands and acoustic properties; the specification of targets in the perceptual space; a planning procedure based on optimization principles. Examples of simulations generated with this model illustrate how it can be used to assess theories and models of coarticulation in speech

Influences of tongue biomechanics on speech movements during the production of velar stop consonants: a modeling study

This study explores the following hypothesis: forward looping movements of the tongue that are observed in VCV sequences are due partly to the anatomical arrangement of the tongue muscles and how they are used to produce a velar closure. The study uses an anatomically based 2D biomechanical tongue model. Tissue elastic properties are accounted for in finite-element modeling, and movement is controlled by constant-rate control parameter shifts. Tongue raising and lowering movements are produced by the model with the combined actions of the genioglossus, styloglossus and hyoglossus. Simulations of V1CV2 movements were made, where C is a velar consonant and V is [a], [i] or [u]. If V1 is one of the vowels [a] and [u], the resulting trajectories describe movements that begin to loop forward before consonant closure and continue to slide along the palate during the closure. This prediction is in agreement with classical data published in the literature. If V1 is vowel [i], we observe a small backward movement. This is also in agreement with some measurements on human speakers, but it is also in contradiction with the original data published by Houde (1967). These observations support the idea that the biomechanical properties of the tongue could be the main factor responsible for the forward loops when V1 is a back vowel. In the left [i] context, it seems that additional factors have to be taken into considerations, in order to explain the observations made on some speaker

The Distributed Lambda Model (DLM): A 3-D, Finite-Element Muscle Model Based on Feldman's Lambda Model; Assessment of Orofacial Gestures

International audiencePurpose: The authors aimed to design a distributed Lambda model (DLM), which is well-adapted to implement three-dimensional (3-D) Finite Element descriptions of muscles. Method: A muscle element model was designed. Its stress-strain relationships included the active force-length characteristics of the Lambda model along the muscle fibers, together with the passive properties of muscle tissues in the 3-D space. The muscle element was first assessed using simple geometrical representations of muscles in form of rectangular bars. Then, it was included in a 3-D face model, and its impact on lip protrusion was compared with the impact of a Hill-type muscle model. Results: The force-length characteristic associated with the muscle elements matched well with the invariant characteristics of the Lambda model. The impact of the passive properties was assessed. Isometric force variation and isotonic displacements were modeled. The comparison with a Hill-type model revealed strong similarities in terms of global stress and strain. Conclusion: The DLM accounted for the characteristics of the Lambda model. Biomechanically no clear differences were found between the DLM and a Hill-type model. Accurate evaluations of the Lambda model, based on the comparison between data and simulations, are now possible with 3-D biomechanical descriptions of the speech articulators because to the DLM

Uncontrolled Manifolds in Vowel Production: Assessment with a Biomechanical Model of the Tongue

International audienceMotor equivalence is a key feature of speech motor control, since speakers must constantly adapt to various phonetic contexts and speaking conditions. The Uncontrolled Manifold (UCM) idea offers a theoretical framework for considering motor equivalence. In this framework coordination among motor control variables is separated into two subspaces, one in which changes in control variables modify the acoustic output and another one in which these changes do not influence the output. Our work develops this concept for speech production using a 2D biomechanical model of the tongue, coupled with a jaw and lip model, for vowel production. We first propose a representation of the linearized UCM based on orthogonal projection matrices. Next we characterize the UCMs of various vocal tract configurations of the 10 French oral vowels using their perturbation responses. We then investigate whether these UCMs describe phonetic classes like phonemes, front/back vowels, rounded/unrounded vowels, or whether they significantly vary across representatives of these different classes. We found they clearly differ between rounded and unrounded vowels, but are quite similar within each category. This suggests that similar motor equivalence strategies can be implemented within each of these classes and that UCMs provide a valid characterization of an equivalence strategy

Biomechanics of the orofacial motor system: Influence of speaker-specific characteristics on speech production

International audienceOrofacial biomechanics has been shown to influence the time signals of speech production and to impose constraints with which the central nervous system has to contend in order to achieve the goals of speech production. After a short explanation of the concept of biomechanics and its link with the variables usually measured in phonetics, two modeling studies are presented, which exemplify the influence of speaker-specific vocal tract morphology and muscle anatomy on speech production. First, speaker-specific 2D biomechanical models of the vocal tract were used that accounted for inter-speaker differences in head morphology. In particular, speakers have different main fiber orientations in the Styloglossus Muscle. Focusing on vowel /i/ it was shown that these differences induce speaker-specific susceptibility to changes in this muscle's activation. Second, the study by Stavness et al. (2013) is summarized. These authors investigated the role of a potential inter-speaker variability of the Orbicularis Oris Muscle implementation with a 3D biomechanical face model. A deeper implementation tends to reduce lip aperture; an increase in peripheralness tends to increase lip protrusion. With these studies, we illustrate the fact that speaker-specific orofacial biomechanics influences the patterns of articulatory and acoustic variability, and the emergence of speech control strategies

Vocal tract growth from birth to adulthood, applications for articulatory studies in infants and biomechanical modeling of the vocal apparatus

International audienceThe growth of the vocal apparatus is far from linear, and reflects several important changes during ontogeny. How are children able to reach acoustic targets in such a context? To counterbalance the nonuniform growth of the vocal tract, adequate motor control of the supra-laryngeal articulators is crucial. Therefore, prior to understand the development of speech production, not only in the acoustic space, but in respect with the articulatory-to-acoustic relationships evolution, it is crucial to study vocal tract morphology