Motor activation during observation of unusual versus ordinary actions in infancy

TLDR

Infants can predict observed actions within their first year, a process explained by Kilner, Friston, and Frith’s computational framework that posits the motor system generates predictions about actions. The study examined whether the motor system predicts the end state of observed actions by showing 12‑month‑old infants ordinary and extraordinary object‑directed action movies. The experiment presented infants with a female actor performing ordinary (cup to mouth) or extraordinary (phone to mouth) object‑directed actions while recording EEG and eye movements, and modeled that deviations from expected paths trigger additional motor predictions reflected in increased mu‑frequency desynchronization. Infants showed significantly stronger motor activation—evidenced by greater mu‑frequency desynchronization—when observing extraordinary actions, indicating that the motor system is engaged in predicting action outcomes from early life.

Abstract

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.