Motor activation during observation of unusual versus ordinary actions in infancy.

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.