The study explores infants' ability to generate on-line predictions about others' action goals through the recruitment of motor resonance mechanisms. To this aim, electromyography was recorded from mouth-opening suprahyoid muscles (SM) of 9-month-old infants while watching a video of an adult agent reaching-to-grasp an object and bringing it either to mouth or head. The results demonstrated, for the first time, that at the age of 9 months there is a dynamic mirror modulation of SM activity by action observation, with the infant's muscles responsible for the action final goal being recruited from the action outset. The comparison with the responses of 6-month-olds tested on the same task showed that in younger and older infants there is a different chronometry of the SM activation with respect to the different phases of the observed action (i.e., bringing vs. grasping, respectively). Results suggest that motor resonance mechanisms triggered within the infants' motor system by action observation undergo gradual development during the first year of life. They also indicate that motor resonance may reflect anticipation of the agent's intention based on the goal of the action.
Keywords: Action understanding; Cognitive development; Grasping skills; Infancy; Motor resonance.
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