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Jan Jastorff, Simon Clavagnier, Gyorgy Gergely, Guy A. Orban; Investigating action understanding: Activation of the middle temporal gyrus by irrational actions. Journal of Vision 2010;10(7):1092. doi: https://doi.org/10.1167/10.7.1092.
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© ARVO (1962-2015); The Authors (2016-present)
Performing goal directed actions towards an object according to contextual constraints has been widely used as a paradigm to assess the capacity of infants to evaluate the rationality of others' actions. Here we used fMRI to visualize the cortical regions involved in the assessment of action rationality. To this end, we scanned 15 participants, showing videos of human actors reaching over a barrier to grasp a fruit. The conditions were arranged according to a 2x2 factorial design by either changing the height of the barrier, or the height of the arm trajectory. The conditions were: 1) low barrier with high arm trajectory, 2) high barrier with high arm trajectory, 3) low barrier with low arm trajectory and 4) high barrier with low arm trajectory. Thus, in the first three conditions the arm trajectory was not adapted to the height of the barrier, rendering the action non-rational. Directly after scanning, participants rated the rationality of the videos and the ratings of a given subject were directly used to model the contrasts for that subject. Random effects analysis, combining these contrast images from all subjects, showed bilateral activation of the posterior middle temporal gyrus (pMTG). In contrast to rationality, the height of the barrier was indicated amongst others by the activity of the EBA. An additional control experiment, showing random dot texture patterns, animated with exactly the same local motion present in the original videos, confirmed that pMTG activation was related to rationality and not to low level differences in the videos. Our pMTG activations were imbedded in the STS regions processing the kinematics of observed actions [Jastorff & Orban, 2009]. These results together with those of Saxe et al  suggest that rationality is assessed initially by purely visual computations, combining kinematics of the action with visual elements of the context.
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