1,721,187 research outputs found
Learning, retention and slacking: a model of the dynamics of recovery in robot therapy
No full textQuantitative descriptions of the process of recovery of motor functions in impaired subjects during robot-assisted exercise might help to understand how to use these devices to make recovery faster and more effective. Linear dynamical models have been used to describe the dynamics of sensorimotor adaptation. Here, we extend this formalism to characterize the neuromotor recovery process. We focus on a robot therapy experiment that involved chronic stroke survivors, based on a robot-assisted arm extension task. The results suggest that modeling the recovery process with dynamical models is feasible, and could allow predicting the long-term outcome of a robot-assisted rehabilitation treatment
Effect of assistive forces on speed-accuracy trade-off in reaching movements: Model and experiments
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Direct measurement of ankle stiffness during quiet standing: implications for control modelling and clinical application
No full textIn this study, we describe a device for the direct measurement of intrinsic ankle stiffness in quiet standing. It consists of a motorised footplate mounted on a force platform. By generating random sequences of step-like disturbances (1° amplitude, 150 ms duration) and measuring the corresponding displacements of the center of pressure in the antero-posterior direction, we obtained torque-rotation patterns after aligning, averaging, and scaling the postural responses. Such patterns were used for estimating the value of the ankle stiffness, which was normalized as a fraction of the critical value. In order to be confident that the measurements addressed the intrinsic ankle stiffness and were not affected in a significant way by the reflex activation of the muscles in response to the test disturbances, we performed the estimates in different ways: least squares estimates with time windows of different widths and an instantaneous estimate at the time in which the angular acceleration vanishes. The statistical analysis showed that there is no significant difference among the different methods of estimate and the inspection of the electromyographic activity in response to the perturbations showed that at least two of the estimates were certainly outside the possible influence of reflex patterns. The intrinsic ankle stiffness was evaluated to be 64 ± 8% of the critical stiffness for test disturbances of the order of 1°. We argue that this figure identifies the lower bound of the range of values which characterise normal sway in quiet standing, whereas the upper bound is given by the estimates performed with much smaller test disturbances [1] which yield a higher value: 91 ± 23%. The two estimation paradigms (with very small and very large test disturbances, respectively) are complementary also because they behave in a different way as regards the sensitivity to a bias torque: it is close to zero in the Loram & Lakie’s paradigm, whereas it is significant in our paradigm. Thus, as the bias grows, it appears that the range of stiffness values is narrowed and is pushed towards the upper bound. There is a clear potential for the clinical application of these methods, in the sense that the identification of the range of stiffness values used by a patient is a measurable index of motor organisation/reorganisation
Muscle activities in similar arms performing identical tasks reveal the neural basis of muscle synergies
No full textAre the muscle synergies extracted from multiple electromyographic signals an expression of neural information processing, or rather a by-product of mechanical and task constraints? To address this question, we asked 41 right-handed adults to perform a variety of motor tasks with their left and right arms. The analysis of the muscle activities resulted in the identification of synergies whose activation was different for the two sides. In particular, tasks involving the control of isometric forces resulted in larger differences. As the two arms essentially have identical biomechanical structure, we concluded that the differences observed in the activation of the respective synergies must be attributed to neural control.TN
Quantifying performance and variability in reward-based motor skill learning
No full textThis study investigates motor skill learning in a specific situation in which the only information provided on performance consists of a reward signal. Subjects performed a point-to-point movement. After the end of the movement we displayed a score based on the distance from a hidden via-point - the maximum score corresponds to the via-point belonging to the trajectory path. The score was the sole information available on task performance and subjects got no additional clues of how to make it high. The task is highly redundant, as infinite trajectories are compatible with the maximum score. We specifically looked at how subjects explore the task space and how they exploit task redundancy to maximize their performance. We also compared the experimental data with the solution predicted by an optimal feedback control model. The main findings were that (i) movement outcomes are largely determined by the subject-specific history of exploration; (ii) during learning, path variability gradually decreased; (iii) for the majority of subjects the point of minimum variability gradually gets closer to the point at minimum distance from the hidden via-point; and (iv) overall, subjects don't converge to the 'optimal control' solution
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