A unifying framework for the identification of motor primitives

Chiovetto E, d’Avella A, Giese MA. A unifying framework for the identification of motor primitives. Plos One. Submitted

Whole-body motor strategies for balancing on a beam when changing the number of available degrees of freedom

Chiovetto E, Huber M, Righetti L, Schaal S, Stenard D, Giese MA. Whole-body motor strategies for balancing on a beam when changing the number of available degrees of freedom. In: Annual meeting of the Progress on Motor Control Society. 2015

Revisiting the Body-Schema Concept in the Context of Whole-Body Postural-Focal Dynamics

The body-schema concept is revisited in the context of embodied cognition, further developing the theory formulated by Marc Jeannerod that the motor system is part of a simulation network related to action, whose function is not only to shape the motor system for preparing an action (either overt or covert) but also to provide the self with information on the feasibility and the meaning of potential actions. The proposed computational formulation is based on a dynamical system approach, which is linked to an extension of the equilibrium-point hypothesis, called Passive Motor Paradigm: this dynamical system generates goal-oriented, spatio-temporal, sensorimotor patterns, integrating a direct and inverse internal model in a multi-referential framework. The purpose of such computational model is to operate at the same time as a general synergy formation machinery for planning whole-body actions in humanoid robots and/or for predicting coordinated sensory–motor patterns in human movements. In order to illustrate the computational approach, the integration of simultaneous, even partially conflicting tasks will be analyzed in some detail with regard to postural-focal dynamics, which can be defined as the fusion of a focal task, namely reaching a target with the whole-body, and a postural task, namely maintaining overall stability

An Ensemble Analysis of Electromyographic Activity during Whole Body Pointing with the Use of Support Vector Machines

We explored the use of support vector machines (SVM) in order to analyze the ensemble activities of 24 postural and focal muscles recorded during a whole body pointing task. Because of the large number of variables involved in motor control studies, such multivariate methods have much to offer over the standard univariate techniques that are currently employed in the field to detect modifications. The SVM was used to uncover the principle differences underlying several variations of the task. Five variants of the task were used. An unconstrained reaching, two constrained at the focal level and two at the postural level. Using the electromyographic (EMG) data, the SVM proved capable of distinguishing all the unconstrained from the constrained conditions with a success of approximately 80% or above. In all cases, including those with focal constraints, the collective postural muscle EMGs were as good as or better than those from focal muscles for discriminating between conditions. This was unexpected especially in the case with focal constraints. In trying to rank the importance of particular features of the postural EMGs we found the maximum amplitude rather than the moment at which it occurred to be more discriminative. A classification using the muscles one at a time permitted us to identify some of the postural muscles that are significantly altered between conditions. In this case, the use of a multivariate method also permitted the use of the entire muscle EMG waveform rather than the difficult process of defining and extracting any particular variable. The best accuracy was obtained from muscles of the leg rather than from the trunk. By identifying the features that are important in discrimination, the use of the SVM permitted us to identify some of the features that are adapted when constraints are placed on a complex motor task

Evidence for Composite Cost Functions in Arm Movement Planning: An Inverse Optimal Control Approach

An important issue in motor control is understanding the basic principles underlying the accomplishment of natural movements. According to optimal control theory, the problem can be stated in these terms: what cost function do we optimize to coordinate the many more degrees of freedom than necessary to fulfill a specific motor goal? This question has not received a final answer yet, since what is optimized partly depends on the requirements of the task. Many cost functions were proposed in the past, and most of them were found to be in agreement with experimental data. Therefore, the actual principles on which the brain relies to achieve a certain motor behavior are still unclear. Existing results might suggest that movements are not the results of the minimization of single but rather of composite cost functions. In order to better clarify this last point, we consider an innovative experimental paradigm characterized by arm reaching with target redundancy. Within this framework, we make use of an inverse optimal control technique to automatically infer the (combination of) optimality criteria that best fit the experimental data. Results show that the subjects exhibited a consistent behavior during each experimental condition, even though the target point was not prescribed in advance. Inverse and direct optimal control together reveal that the average arm trajectories were best replicated when optimizing the combination of two cost functions, nominally a mix between the absolute work of torques and the integrated squared joint acceleration. Our results thus support the cost combination hypothesis and demonstrate that the recorded movements were closely linked to the combination of two complementary functions related to mechanical energy expenditure and joint-level smoothness

Deciphering the functional role of spatial and temporal muscle synergies in whole-body movements

International audienceVoluntary movement is hypothesized to rely on a limited number of muscle synergies, the recruitment of which translates task goals into effective muscle activity. In this study, we investigated how to analytically characterize the functional role of different types of muscle synergies in task performance. To this end, we recorded a comprehensive dataset of muscle activity during a variety of whole-body pointing movements. We decomposed the electromyographic (EMG) signals using a space-by-time modularity model which encompasses the main types of synergies. We then used a task decoding and information theoretic analysis to probe the role of each synergy by mapping it to specific task features. We found that the temporal and spatial aspects of the movements were encoded by different temporal and spatial muscle synergies, respectively, consistent with the intuition that there should a correspondence between major attributes of movement and major features of synergies. This approach led to the development of a novel computational method for comparing muscle synergies from different participants according to their functional role. This functional similarity analysis yielded a small set of temporal and spatial synergies that describes the main features of whole-body reaching movements

Hyperbolic Bundles and the Gromov-Lawson-Thurston Conjec-ture.

Um importante problema em aberto em geometria hiperbólica é saber quando um fibrado de discos sobre uma superfície orientável possui métrica completa de curvatura constante negativa. A conjectura Gromov-Lawson-Thurston diz que um fibrado de discos M → S sobre uma superfície fechada conexa orientável S de gênero g ≥ 2 admite tal métrica se, e somente se, ΙeM/XSΙ ≤1. No artigo (ANANIN; CHIOVETTO, 2018), construímos novos exemplos nos quais ΙeM/XSΙ = ⅗, melhorando assim a maior cota superior conhecida anteriormente (ΙeM/XSΙ = ½, devida a Feng Luo (LUO, 1992) e obtida em 1992). Nesta dissertação, apresentamos o artigo (ANANIN; CHIOVETTO, 2018An important open problem in hyperbolic geometry is to decide whether a disc bundle over an orientable surface can be equipped with a complete metric of constant negative curvature. The Gromov-Lawson-Thurston Conjecture says that a disk bundle M → S over a closed orientable surface S of genus g ≥ 2 admits such metric if, and only if, ΙeM/XSΙ ≤ 1. On the article (ANANIN; CHIOVETTO, 2018), we build new bundles M → S satisfying ΙeM/XSΙ = ⅗, thus improving the former maximum known bound ΙeM/XSΙ - ½, due to Feng Luo (LUO, 1992) and obtained in 1992). In this thesis, we present the paper (ANANIN; CHIOVETTO, 2018)