Figure 1.

Experimental design (adapted from Zillekens et al. (2019))

(A) Experimental conditions. In the communicative condition (COM; top row), agent A performs a communicative action. In the left panel, agent B is present and reacts in accordance to it (signal trial). In the right panel, agent B is replaced by randomly moving dots (noise trial). In the individual condition (IND; bottom row), agent A performs an individual action. Agent B is again either present (left panel) or replaced by noise (right panel). The gray silhouettes serve illustrative purposes and were not visible for participants. The occurrence of a Bayesian ghost (indicated in blue) is defined by a false alarm (FA) in the communicative noise trial (i.e., the participant indicated that agent B was present when in fact noise dots were presented). The number of false alarms is illustrated in Figure S1.

(B) Structure of experimental trials. Jittered inter-trial-intervals (ITI) preceded a fixation cross appearing at the subsequent position of agent A. Following this, the video of the two point-light agents started. The video duration as well as agent B’s onset varied depending on the specific actions performed. The analyzed time segments are illustrated in color: (1) 1-s before agent B’s onset (red): Participants passively observed agent A, who either performed an individual or communicative gesture; (2) 1-s after agent B’s onset (gray): Participants passively watched the responding agent B or noise dots; and (3) 1-s before the response (blue): Participants decided whether the masked agent B was present or absent and indicated their choice with a button press.