A three-dimensional (3D) biomechanical model of the tongue and the oral cavity, controlled by a functional model of muscle force generation (lambda-model of the equilibrium point hypothesis) and coupled with an acoustic model, was exploited to study the activation of the tongue and mouth floor muscles during the production of French cardinal vowels. The selection of the motor commands to control the tongue and the mouth floor muscles was based on literature data, such as electromyographic, electropalatographic, and cineradiographic data. The tongue shapes were also compared to data obtained from the speaker used to build the model. 3D modeling offered the opportunity to investigate the role of the transversalis, in particular, its involvement in the production of high front vowels. It was found, with this model, to be indirect via reflex mechanisms due to the activation of surrounding muscles, not voluntary. For vowel /i/, local motor command variations for the main tongue muscles revealed a non-negligible modification of the alveolar groove in contradiction to the saturation effect hypothesis, due to the role of the anterior genioglossus. Finally, the impact of subject position (supine or upright) on the production of French cardinal vowels was explored and found to be negligible.

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BackgroundLearning to perform new movements is usually achieved by following visual demonstrations. Haptic guidance by a force feedback device is a recent and original technology which provides additional proprioceptive cues during visuo-motor learning tasks. The effects of two types of haptic guidances-control in position (HGP) or in force (HGF)–on visuo-manual tracking (“following”) of trajectories are still under debate.Methodology/Principals FindingsThree training techniques of haptic guidance (HGP, HGF or control condition, NHG, without haptic guidance) were evaluated in two experiments. Movements produced by adults were assessed in terms of shapes (dynamic time warping) and kinematics criteria (number of velocity peaks and mean velocity) before and after the training sessions. Trajectories consisted of two Arabic and two Japanese-inspired letters in Experiment 1 and ellipses in Experiment 2. We observed that the use of HGF globally improves the fluency of the visuo-manual tracking of trajectories while no significant improvement was found for HGP or NHG.Conclusion/SignificanceThese results show that the addition of haptic information, probably encoded in force coordinates, play a crucial role on the visuo-manual tracking of new trajectories.

An assessment of a target-based control model of speech production using Feldman's Equilibrium Point Hypothesis is presented. It consists of simulations of articulatory movements during Vowel-to-Vowel sequences with a 2D biomechanical tongue model. In the model the main muscles responsible for tongue movements and tongue shaping in the mid-sagittal plane are represented. The elastic properties are accounted through a Finite-Element modeling, while force generation principles are implemented according to the non-linear force-length Invariant Characteristics proposed by Feldman.Movement is produced through control variable shifts at rates that are constant throughout each transition. The external contours of the model are adjusted to approximate X-ray data collected on a native speaker of French, and it is inserted in the vocal tract contours of the speaker. Thus, from tongue shapes generated with the model, it was possible to produce formant trajectories compatible with the speaker's acoustic space. It permitted a comparison of simulations with real data collected on the speaker in the kinematic and acoustic domains. Emphasis is put on the realism of synthesized formant trajectories, and on the potential influence of biomechanical tongue properties on to measurable kinematic features. ZusammenfassungWir stellen eine Bewertung eines Sprachproduktionsmodells vor, das das Konzept von phonetischem Ziel einschliesst, und auf der Equilibrium Point Hypothesis von Feldman beruht. Dafiir wurden artikulatorische Bewegungen in vokalischen Reihenfolgen mit einem zweidimensionalen Zungenmodell simuliert. In diesem Modell wurden die Muskeln eingeschlossen, deren Wirkungen auf die Zungengestalt in der sagitalen Ebene die wichtigsten sind. Durch die Methode der endlichen Elemente wurden die elastischen Eigenschaften der Zunge modellisiert, und die muskullire Kraft entspricht Feldmans unlinearen "Kraft-Lange unveranderlichen Kurven". Die Bewegung wurde

Abstract. Finite Element mesh generation remains an important issue for patient specific biomechanical modeling. While some techniques make automatic mesh generation possible, in most cases, manual mesh generation is preferred for better control over the sub-domain representation, element type, layout and refinement that it provides. Yet, this option is time consuming and not suited for intraoperative situations where model generation and computation time is critical. To overcome this problem we propose a fast and automatic mesh generation technique based on the elastic registration of a generic mesh to the specific target organ in conjunction with element regularity and quality correction. This Mesh-Match-and-Repair (MMRep) approach combines control over the mesh structure along with fast and robust meshing capabilities, even in situations where only partial organ geometry is available. The technique was successfully tested on a database of 5 pre-operatively acquired complete femora CT scans, 5 femoral heads partially digitized at intraoperative stage, and 50 CT volumes of patients' heads. In the latter case, both skin and bone surfaces were taken into account by the mesh registration process in order to model the face muscles and fat layers. The MMRep algorithm succeeded in all 60 cases, yielding for each patient a hex-dominant, Atlas based, Finite Element mesh with submillimetric surface representation accuracy, directly exploitable within a commercial FE software.

The brain deformation that occurs during neurosurgery is a serious issue impacting the patient "safety" as well as the invasiveness of the brain surgery. Model-driven compensation is a realistic and efficient solution to solve this problem. However, a vital issue is the lack of reliable and easily obtainable patient-specific mechanical characteristics of the brain which, according to clinicians' experience, can vary considerably. We designed an aspiration device that is able to meet the very rigorous sterilization and handling process imposed during surgery, and especially neurosurgery. The device, which has no electronic component, is simple, light and can be considered as an ancillary instrument. The deformation of the aspirated tissue is imaged via a mirror using an external camera. This paper describes the experimental setup as well as its use during a specific neurosurgery. The experimental data was used to calibrate a continuous model. We show that we were able to extract an in vivo constitutive law of the brain elasticity: thus for the first time, measurements are carried out per-operatively on the patient, just before the resection of the brain parenchyma. This paper discloses the results of a difficult experiment and provide for the first time in vivo data on human brain elasticity. The results point out the softness as well as the highly non-linear behavior of the brain tissue.

This paper aims at characterizing the mechanical behavior of two human anatomical structures, namely the tongue and the cheek. For this, an indentation experiment was provided, by measuring the mechanical response of tongue and cheek tissues removed from the fresh cadaver of a 74 year old woman. Non-linear relationships were observed between the force applied to the tissues and the corresponding displacements. To infer the mechanical constitutive laws from these measurements, a finite element (FE) analysis was provided. This analysis aimed at simulating the indentation experiment. An optimization process was used to determine the FE constitutive laws that provided the non-linear force/displacements observed during the indentation experiments. The tongue constitutive law was used for simulations provided by a 3D FE biomechanical model of the human tongue. This dynamical model was designed to study speech production. Given a set of tongue muscular commands, which levels correspond to the force classically measured during speech production, the FE model successfully simulated the main tongue movements observed during speech data.