Infants make predictions about actions they observe already during the first year of life. To investigate the role of the motor system in predicting the end state of observed actions, 12-month-old infants were shown movies of ordinary and extraordinary object-directed actions. The stimuli displayed a female actor who picked up an everyday object (a cup or a phone) and brought it to either her mouth or her ear. In this way, a similar movement could be ordinary (e.g., cup to mouth) or extraordinary (e.g., phone to mouth) depending on the object used. Infants' EEG and eye movements were recorded. We found a significantly stronger motor activation, indicated by a stronger desynchronization in the mu-frequency band over fronto-central areas, during observation of extraordinary compared to ordinary actions. This is explained within the computational framework of Kilner, Friston, and Frith (2007), who suggest that the motor system is used to generate predictions about actions we observe. If the observed action deviates from the initially expected path, additional predictions have to be generated, resulting in a stronger motor activation during perception of extraordinary actions. In sum, it appears that from early in life, the motor system is involved in making predictions about how an observed action will end.

Previous research demonstrates that from early in life, our cortical sensorimotor areas are activated both when performing and when observing actions (mirroring). Recent findings suggest that the adult motor system is also involved in detecting others’ rule violations. Yet, how this translates to everyday action errors (e.g., accidentally dropping something) and how error‐sensitive motor activity for others’ actions emerges are still unknown. In this study, we examined the role of the motor system in error monitoring. Participants observed successful and unsuccessful pincer grasp actions while their electroencephalography was registered. We tested infants (8‐ and 14‐month‐olds) at different stages of learning the pincer grasp and adults as advanced graspers. Power in Alpha‐ and Beta‐frequencies was analysed to assess motor and visual processing. Adults showed enhanced motor activity when observing erroneous actions. However, neither 8‐ nor 14‐month‐olds displayed this error sensitivity, despite showing motor activity for both actions. All groups did show similar visual activity, that is more Alpha‐suppression, when observing correct actions. Thus, while correct and erroneous actions were processed as visually distinct in all age groups, only the adults’ motor system was sensitive to action correctness. Functionality of different brain oscillations in the development of error monitoring and mirroring is discussed.

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Previous research investigated the contributions of target objects, situational context and movement kinematics to action prediction separately. The current study addresses how these three factors combine in the prediction of observed actions. Participants observed an actor whose movements were constrained by the situational context or not, and object-directed or not. After several steps, participants had to indicate how the action would continue. Experiment 1 shows that predictions were most accurate when the action was constrained and object-directed. Experiments 2A and 2B investigated whether these predictions relied more on the presence of a target object or cues in the actor’s movement kinematics. The target object was artificially moved to another location or occluded. Results suggest a crucial role for kinematics. In sum, observers predict actions based on target objects and situational constraints, and they exploit subtle movement cues of the observed actor rather than the direct visual information about target objects and context.

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