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Expectations facilitate perception of expected stimuli but may hinder perception of unexpected alternatives. Here, we consider how prior expectations about others' intentions are integrated with visual kinematics over time in detecting the intention of an observed motor act (grasp-to-pour vs. grasp-to-drink). Using rigorous psychophysics methods, we find that the processes of ascribing intentions to others are well described by drift diffusion models in which evidence from observed movements is accumulated over time until a decision threshold is reached. Testing of competing models revealed that when kinematics contained no discriminative intention information, prior expectations predicted the intention choice of the observer. When kinematics contained intention information, kinematics predicted the intention choice. These findings provide evidence for a diffusion process in which the influence of expectations is modulated by movement informativeness and informative kinematics can override initial expectations., (Copyright © 2018 The Authors. Published by Elsevier B.V. All rights reserved.)

Observation of others' actions has been proposed to provide a shared experience of the properties of objects acted upon. We report results that suggest a similar form of shared experience may be gleaned from the observation of pantomimed grasps, i.e., grasps aimed at pretended objects. In a weight judgment task, participants were asked to observe a hand reaching towards and grasping either a real or imagined glass, and to predictively judge its weight. Results indicate that participants were able to discriminate whether the to-be-grasped glass was empty, and thus light, or full, and thus heavy. Worthy of further investigation, this finding suggests that by observing others' movements we can make predictions, and form expectations about the characteristics of objects that exist only in others' minds., (Copyright © 2017 The Author(s). Published by Elsevier B.V. All rights reserved.)

Body movement provides a rich source of cues about other people's goals and intentions. In the present research, we investigate how well people can distinguish between different social intentions on the basis of movement information. Participants observed a model reaching toward and grasping a wooden block with the intent to cooperate with a partner, compete against an opponent, or perform an individual action. In Experiment 1, a temporal occlusion procedure was used as to determine whether advance information gained during the viewing of the initial phase of an action allowed the observers to discriminate across movements performed with different intentions. In Experiment 2, we examined what kind of cues observers relied upon for the discrimination of intentions by masking selected spatial areas of the model (i.e., the arm or the face) maintaining the same temporal occlusion as for Experiment 1. Results revealed that observers could readily judge whether the object was grasped with the intent to cooperate, compete, or perform an individual action. Seeing the arm was better than seeing the face for discriminating individual movements performed at different speeds (natural-speed vs. fast-speed individual movements). By contrast, seeing the face was better than seeing the arm for discriminating social from individual movements performed at a comparable speed (cooperative vs. natural-speed individual movements, competitive vs. fast-speed individual movements). These results demonstrate that observers are attuned to advance movement information from different cues and that they can use such kind of information to anticipate the future course of an action., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The aim of the present study is to ascertain whether in a social context the kinematic parameters are influenced by the stance of the participants. In particular, we consider two basic modes of social cognition, namely cooperation and competition. Naïve subjects were asked either to cooperate or to compete with a partner (a professional female actor), whose attitude could be either congruent or incongruent with the task instructions. Thus, on congruent conditions, subjects cooperated or competed with a partner showing a congruent cooperative or competitive attitude. On incongruent trials, the partner assumed an attitude that was manifestly in contrast with the instruction: competitive for the cooperative task, cooperative for the competitive task. We hypothesized that this mismatch between partner's attitude and instruction would produce a sort of unexpected social situation, affecting the kinematics of reach-to-grasp movement performed by the agents. If cooperative and competitive kinematic patterns are sensitive to the partner's attitude, then we should expect that an incongruent attitude have the potency to determine a reversal in kinematic patterning. Results revealed that for the incongruent trials the specific kinematic patterns for cooperation and competition found for the congruent conditions where modified according to the incongruent attitude assumed by the model actor. We suggest that this 'attitude' contagion is part of a sophisticated system that allows us to infer about the intention to act in a social context.

The aim of the present study is to elucidate the influence of context on the kinematics of the reach-to-grasp movement. In particular, we consider two basic modes of social cognition, namely cooperation and competition. In two experiments kinematics of the very same action - reaching-to-grasp a wooden block - were analyzed in two different contexts provided by a cooperative task and competitive task. For the 'cooperation' tasks two participants were required to reach and grasp their respective objects and to cooperate to join the two objects in specific configurations in the middle of the working surface. For the 'competition' tasks, the two participants had to compete to place their own object first in the middle of the working surface. Results revealed specific kinematic patterns for cooperation and competition which were distinct from similar actions performed by each participant in isolation. Further, during the cooperation tasks, a high level of correlation between key kinematical parameters of the two participants was found. In accordance with evidence from neuroimaging, developmental and social psychology our results suggest the existence of motor patterns which reflect the intention to act in a social context.