Action priming with biomechanically possible and impossible grasps: ERP evidence from 6-month-old infants.

Coding the direction of others' gestures is a fundamental human ability, since it allows the observer to attend and react to sources of potential interest in the environment. Shifts of attention triggered by action observation have been reported to occur early in infancy. Yet, the neurophysiological underpinnings of such action priming and the properties of gestures that might be crucial for it remain unknown. Here, we addressed these issues by recording electroencephalographic activity (EEG) from 6-month-old infants cued with spatially non-predictive hand grasping toward or away from the position of a target object, i.e., valid and invalid trials, respectively. Half of the infants were cued with a gesture executable by a human hand (possible gesture) and the other half with a gesture impossible to be executed by a human hand. Results show that the amplitude enhancement of the posterior N290 component in response to targets in valid trials, as compared to invalid trials, was present only for infants seeing possible gestures, while it was absent for infants seeing impossible gestures. These findings suggest that infants detect the biomechanical properties of human movements when processing hand gestures, relying on this information to orient their visual attention toward the target object.