Verbal social primes alter motor contagion during action observation.

We investigated whether prosocial and nonsocial word primes prior to action observation modify subsequent initiation and execution of the observer's own reach-to-grasp actions. Participants observed a model performing exaggeratedly curved (vertical deviation) or natural straight reaches to a vertical dowel and always performed a straight reach to a dowel themselves. Observing curved movements slowed initiation times and increased the vertical deviation of the participants' movements. Observing curved movements enhanced vertical deviation only in the prosocial word primes condition. We suggest that social context priming can modulate initiation of movement as well as the extent of motor contagion (in this case, the extent of vertical deviation) between model and observer.