Figure 1. Experimental conditions.

Left, upper panel. Example of communicative signal trial (single frame). Agent A asks agent B to squat down; agent B squats down. B is presented using limited-lifetime technique and masked with temporally scrambled noise dots. Left, lower panel. Example of individual signal trial (single frame). Agent A turns around; agent B squats down. Right panel. Representation of the three timing sets (‘+0’, ‘+20’ and ‘+40’). The duration of the action of agent A (black line) and B (gray line) in both the communicative and the individual condition is 148 frames (4933 ms). Triangles indicate key kinematic landmarks characterizing the observed action sequences. The black triangles represent the moment in time in which A's hand begins to move up to signal B the up/down movement path (first change in the vertical position compared to frame 0 of the right wrist dot). The gray triangles represent the moment when B starts to squat down (first change in the vertical position compared to frame 0 of the right hip dot). Dashed lines represent static frames added to equate stimulus duration across timing sets.