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Sara Agosta, Lorella Battelli, Antonino Casile; Neuronal Encoding of movement kinematics during action observation: a TMS study. Journal of Vision 2011;11(11):689. doi: https://doi.org/10.1167/11.11.689.
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© ARVO (1962-2015); The Authors (2016-present)
Several studies compellingly show that the human motor system is active during action observation. According to the direct-matching hypothesis this activation reflects a covert simulation of the observed action, possibly for the purpose of action or intention understanding. A prediction of this proposal is that the activation of the motor system during action observation should be modulated by the degree of similarity between the observed movement and those that can be actually produced by humans. We tested this prediction by measuring the excitability of the observer's motor system during the observation of human movements either complying or violating the 2/3 power law. The 2/3 power law is an empirical law stating that during curvilinear movements the instantaneous velocity of the end effector is related to the local curvature of the path by a power law with an exponent of two-thirds. Interestingly, it has been shown that, even after extensive training, humans cannot produce movements that violate this kinematic invariant. For our experiment, we first motion captured the movements of a human subject while he was moving his arms along curvilinear trajectories. We then animated computer characters with either the original movements or with a version of them that was manipulated so as to violate the 2/3 power law. On each trial, motor evoked potentials (MEPs) induced by single-pulse TMS were recorded simultaneously from the First right Dorsal Interosseus (FDI) and the right Extensor Digitorum Communis (EDC) while participants were passively observing videos showing the computer characters performing normal or distorted movements. Preliminary results suggest that the amplitude of the MEPs, an indirect measure of the excitability of the observer's motor system, is modulated by the degree of compliance of the observed movements with the 2/3 power law.
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