198 research outputs found

    CONTRIBUTION OF VELOCITY CONGRUENCY AND APPARENT STIFFNESS TO INTERFERENCE OF BIMANUAL RHYTHMIC-DISCRETE MOVEMENTS.

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    Many actions feature rhythmic and discrete movements, individually or in combinations. Rhythmic movements are defined as those having no clearly defined start and end-point, while discrete movements have a definite starting and ending posture. Performing a discrete movement against a base rhythm by the contralateral limb typically speeds up the rhythmic movement -- indicating the presence of bimanual coupling. While bimanual rhythmic/rhythmic interaction has been studied extensively in the field, understanding of the interaction between discrete and rhythmic movements has been less represented. In this thesis, I examined two potential sources of interlimb interference during rhythmic-discrete bimanual actions: 1) velocity congruence of the limbs, 2) co-contraction level of the synergist muscles. Hypothesis 1 predicted that the extent of rhythmic-discrete interference depends on the discrepancy between the velocities of the rhythmic and discrete movements, such that faster discrete movement would speed up the rhythmic movement and vice versa. Hypothesis 2 predicted that speeding up the rhythmic movement following the discrete response would be associated with increased muscle co-contraction in the rhythmic limb because higher apparent stiffness typically increases the natural frequency of oscillations. To address these hypotheses, I used a computational model of upper limb movements proposed by Ronsee et al. that allows simulation of both unimanual and bimanual rhythmic and discrete movements using the central pattern generator (CPG) concept. Discrete movement with an amplitude of 60 deg was simulated in two velocity conditions: Slow (peak velocity: 163 deg/s) and Fast (249 deg/s), these values differed by approximately 20% from the peak velocity of the rhythmic movement. Phase discrete movement initiation within rhythm was also manipulated. Dependent measures included rhythmic movement period, amplitude, phase, and level of co-contraction following the initiation of the discrete response were examined. The results showed that 1) the velocity of the discrete movement does not account for the changes of rhythmic behavior and (2) the level of co-contraction and the period shift of the rhythmic arm do not co-vary. However, the results suggested that the response of the rhythmic arm is dependent of the rhythmic movement\u27s phase during which the discrete movement is initiated

    Activation and inhibition of bimanual movements in school-aged children

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    The development of motor activation and inhibition was compared in 6-to-12 year-olds. Children had to initiate or stop the externally paced movements of one hand, while maintaining that of the other hand. The time needed to perform the switching task (RT) and the spatio-temporal variables show different agerelated evolutions depending on the coordination pattern (inor anti-phase) and the type of transition (activation, selective inhibition, non selective inhibition) required. In the anti-phase mode, activation perturbs the younger subjects' responses while temporal and spatial stabilities transiently decrease around 9 years when activating in the in-phase mode. Aged-related changes differed between inhibition and activation in the antiphase mode, suggesting either the involvement of distinct neural networks or the existence of a single network that is reorganized. In contrast, stopping or adding one hand in the in-phase mode shows similar aged-related improvement. We suggest that selectively stopping or activating one arm during symmetrical coordination rely on the two faces of a common processing in which activation could be the release of inhibitio

    Comparing unilateral and bilateral upper limb training: The ULTRA-stroke program design

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    <p>Abstract</p> <p>Background</p> <p>About 80% of all stroke survivors have an upper limb paresis immediately after stroke, only about a third of whom (30 to 40%) regain some dexterity within six months following conventional treatment programs. Of late, however, two recently developed interventions - constraint-induced movement therapy (CIMT) and bilateral arm training with rhythmic auditory cueing (BATRAC) - have shown promising results in the treatment of upper limb paresis in chronic stroke patients. The ULTRA-stroke (acronym for Upper Limb TRaining After stroke) program was conceived to assess the effectiveness of these interventions in subacute stroke patients and to examine how the observed changes in sensori-motor functioning relate to changes in stroke recovery mechanisms associated with peripheral stiffness, interlimb interactions, and cortical inter- and intrahemispheric networks. The present paper describes the design of this single-blinded randomized clinical trial (RCT), which has recently started and will take several years to complete.</p> <p>Methods/Design</p> <p>Sixty patients with a first ever stroke will be recruited. Patients will be stratified in terms of their remaining motor ability at the distal part of the arm (i.e., wrist and finger movements) and randomized over three intervention groups receiving modified CIMT, modified BATRAC, or an equally intensive (i.e., dose-matched) conventional treatment program for 6 weeks. Primary outcome variable is the score on the Action Research Arm test (ARAT), which will be assessed before, directly after, and 6 weeks after the intervention. During those test sessions all patients will also undergo measurements aimed at investigating the associated recovery mechanisms using haptic robots and magneto-encephalography (MEG).</p> <p>Discussion</p> <p>ULTRA-stroke is a 3-year translational research program which aims (1) to assess the relative effectiveness of the three interventions, on a group level but also as a function of patient characteristics, and (2) to delineate the functional and neurophysiological changes that are induced by those interventions.</p> <p>The outcome on the ARAT together with information about changes in the associated mechanisms will provide a better understanding of how specific therapies influence neurobiological changes, and which post-stroke conditions lend themselves to specific treatments.</p> <p>Trial Registration</p> <p>The ULTRA-stroke program is registered at the Netherlands Trial Register (NTR, <url>http://www.trialregister.nl</url>, number NTR1665).</p

    Toward simple control for complex, autonomous robotic applications: combining discrete and rhythmic motor primitives

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    Vertebrates are able to quickly adapt to new environments in a very robust, seemingly effortless way. To explain both this adaptivity and robustness, a very promising perspective in neurosciences is the modular approach to movement generation: Movements results from combinations of a finite set of stable motor primitives organized at the spinal level. In this article we apply this concept of modular generation of movements to the control of robots with a high number of degrees of freedom, an issue that is challenging notably because planning complex, multidimensional trajectories in time-varying environments is a laborious and costly process. We thus propose to decrease the complexity of the planning phase through the use of a combination of discrete and rhythmic motor primitives, leading to the decoupling of the planning phase (i.e. the choice of behavior) and the actual trajectory generation. Such implementation eases the control of, and the switch between, different behaviors by reducing the dimensionality of the high-level commands. Moreover, since the motor primitives are generated by dynamical systems, the trajectories can be smoothly modulated, either by high-level commands to change the current behavior or by sensory feedback information to adapt to environmental constraints. In order to show the generality of our approach, we apply the framework to interactive drumming and infant crawling in a humanoid robot. These experiments illustrate the simplicity of the control architecture in terms of planning, the integration of different types of feedback (vision and contact) and the capacity of autonomously switching between different behaviors (crawling and simple reaching

    Особливості активності м’язів людини при виконанні циклічних бімануальних рухів з різною організацією циклів

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    Згідно з характеристиками ЕМГ, підданих повному випрямленню та низькочастотній фільтрації, досліджували координацію центральних моторних команд, що надходять до м’язів плечового пояса та плеча під час реалізації циклічних бімануальних рухів у горизонтальній площині, близьких до таких при парному веслуванні. Тестувалося виконання трьох моторних завдань: рухи в зручному для тестованого темпі (ЗТ), рухи в максимальному темпі (МТ) та рухи зі зворотним зв’язком (ЗЗ), коли тестований мав можливість відслідковувати темп рухів і кути обертання одного з важелів установки. До важелів могли прикладатися зовнішні навантаження двох рівнів у напрямку «від себе». Встановлено, що під час виконання тесту ЗТ темп «веслування» в разі прикладання більшого навантаження був вищим, ніж у разі меншого опору. Середній рівень ЕМГ м’язів в умовах більшого рівня навантаження при виконанні тесту ЗТ був вищим, ніж при виконанні тесту ЗЗ. Рівень активації м’язів під час виконання тесту МТ не залежав істотно від рівня зовнішнього навантаження. Рівень спряження ЕМГ-активності однойменних м’язів лівої та правої рук мав тенденцію до зниження в умовах наявності зорового ЗЗ. Припускається, що в умовах дії такого зв’язку посилюється когнітивний вплив на виконання рухового завдання і сам тип руху наближується до дискретного.According to the characteristics of EMGs subjected to full-wave rectification and low-pass filtering, we examined coordination of central motor commands coming to muscles of the shoulder belt and shoulders in the course of realization of cyclic bimanual movements within a horizontal plane (close to those in sculling). The performance of different motor tasks was tested: (i) movements at a comfortable stroke rate (CSR); (ii) movements at a maximum rate (MR), and (iii) movements with the feedback (FB) information, where the subject could trace the movement rate and angles of rotation of one lever of the experimental set. Two levels of external loading could be applied to the levers of the set (“oars”) in the direction counteracting efforts developed by the subject within the pulling phase. It was found that, in realization of the CSR test, the movement rate was greater at a higher loading than that in the case of a smaller mechanical resistance. The mean level of EMGs of the examined muscles under conditions of a higher loading in realization of the CSR test was greater than that in the FB test. The level of activation of the muscles in the course of the MR test demonstrated no dependence of the level of external loading. The level of correlations between EMG activities of similar muscles of the left and right upper limbs demonstrated a trend toward lowering under conditions of the presence of visual FB. It is supposed that the cognitive influence upon realization of the motor tasks is intensified under the above conditions, and the type of the performed movements becomes closer to the discrete mode

    Dynamical Movement Primitives: Learning Attractor Models for Motor Behaviors

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    Nonlinear dynamical systems have been used in many disciplines to model complex behaviors, including biological motor control, robotics, perception, economics, traffic prediction, and neuroscience. While often the unexpected emergent behavior of nonlinear systems is the focus of investigations, it is of equal importance to create goal-directed behavior (e.g., stable locomotion from a system of coupled oscillators under perceptual guidance). Modeling goal-directed behavior with nonlinear systems is, however, rather difficult due to the parameter sensitivity of these systems, their complex phase transitions in response to subtle parameter changes, and the difficulty of analyzing and predicting their long-term behavior; intuition and time-consuming parameter tuning play a major role. This letter presents and reviews dynamical movement primitives, a line of research for modeling attractor behaviors of autonomous nonlinear dynamical systems with the help of statistical learning techniques. The essence of our approach is to start with a simple dynamical system

    Dynamic primitives of motor behavior

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    We present in outline a theory of sensorimotor control based on dynamic primitives, which we define as attractors. To account for the broad class of human interactive behaviors—especially tool use—we propose three distinct primitives: submovements, oscillations, and mechanical impedances, the latter necessary for interaction with objects. Owing to the fundamental features of the neuromuscular system—most notably, its slow response—we argue that encoding in terms of parameterized primitives may be an essential simplification required for learning, performance, and retention of complex skills. Primitives may simultaneously and sequentially be combined to produce observable forces and motions. This may be achieved by defining a virtual trajectory composed of submovements and/or oscillations interacting with impedances. Identifying primitives requires care: in principle, overlapping submovements would be sufficient to compose all observed movements but biological evidence shows that oscillations are a distinct primitive. Conversely, we suggest that kinematic synergies, frequently discussed as primitives of complex actions, may be an emergent consequence of neuromuscular impedance. To illustrate how these dynamic primitives may account for complex actions, we brieflyreviewthree typesof interactivebehaviors: constrained motion, impact tasks, and manipulation of dynamic objects.United States. National Institutes of Health (T32GM008334)American Heart Association (11SDG7270001)National Science Foundation (U.S.) (NSF DMS-0928587

    Coordination of unimanual continuous movements with external events

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