Fig. 1. Spatial-compatibility task used to test whether action representations are shared. Participants
observed pictures of a hand pointing left or right (A), and were instructed to respond to the color
of the ring on the index finger, ignoring the direction in which the finger was pointing. In the group
condition (B, left panel), each participant responded to one color. In the individual condition (B, right
panel) participants performed the same task alone, responding to one color and not responding to the
other color. On compatible trials, the irrelevant pointing stimulus corresponded to the location of the
required action. On incompatible trials, the pointing stimulus referred to the other’s action (joint
condition) or to no action (individual condition). Response times (RT) on incompatible trials in the
joint condition (left graph) were slowed because the pointing stimulus activated a representation of the
action at the other’s command.