FIGURE 1.

In the mirror game paradigm, two players are instructed to “create movements together, like a conversation in movements,” holding two handles on two parallel tracks (A) taking turns leading, following, or jointly improvising (with no designated leader). (B) Their movements are sampled at 50 Hz and at a spatial resolution of 0.94 mm. The majority of the time, players display a (C) leader–follower pattern, in which the follower (red) shows ‘jitter’ corrective motions around the leader’s (blue) smooth trajectory. Players can also attain moments of (D) co-confident pattern, in which the two players have highly synchronized smooth motion tracks, with no jitter, indicative of the fact that they are moving as a coupled unit rather than reactively.