2.3.2. Procedure

C. Social motor experiment: Two cubes (printed with a blue or a red line) were disposed on the sides of agrid that was situated in the centre of the scene. The two actors played one after the other by moving the cube towards the middle of the grid (termed ‘bank’) or by rotating it so that it remains in its previous place.

Here, each motor act directly denoted the social intention of the player: each player could either cooperate with the other one, by moving the cube towards the central bank (transport), or defect, by leaving the cube in its previous place (rotate). Consequently, there were four possible combinations of intentions, or strategies: either both players cooperated (transport/transport) or defected (rotate/rotate), or the first player defected and the second cooperated (rotate/transport), or the first player cooperated and the second defected (transport/rotate).

For each trial, participants were instructed to observe the incomplete movie and infer what the second player’s action was. Participants responded by pressing, as quickly and as accurately as possible, one of the two keyboard buttons corresponding to the two possible actions (T for ‘transport’, or R for ‘rotate’) susceptible to achieve the second player’s intention (defect or cooperate). Once a response was given, the next trial started.

D. Social superordinate experiment: Four cubes (one blue and three red ones) were placed in the centre of the scene. Actors played in turn with the goal to vertically align three cubes among the four available ones. The goal of the first player was to align the three cubes according to the color red, irrespective of the orientation (configuration 1 or Ico1). The goal of the second player was to align the cubes according to the orientation, irrespective of the color (configuration 2 or Ico2). Finally, a third configuration could be obtained by aligning the cubes according to both the orientation and the color (configuration 3 or Ico3).

To win the game, each player depended upon the other player’s manipulation. As in the social motor experiment, the two social intentions were of a defective or a cooperative nature. However, in the present experiment, the social intention was denoted by the sequence of the players’ motor acts (i.e. the final configuration: Ico1, 2 or 3), rather than by the single action performed by each player. Each configuration was associated with a defective or a cooperative strategy that could be equally achieved by rotating or transporting the cube. Each player could therefore adopt a defective strategy by manipulating the cube in such a way that it prevented the creation of a configuration, or adopt a cooperative strategy in order to achieve a configuration. The resulting four possible combinations of strategies therefore led to different final configurations: either both players defected or cooperated (Ico3), or the first player defected and the second cooperated (Ico1), or the first player cooperated and the second defected (Ico2).

Participants were instructed to infer the social superordinate intention of the second playerby pressing, as quickly and as accurately as possible, one of the two keyboard buttons corresponding to the two possible actions (T for ‘transport’, or R for ‘rotate’) congruent with the second player’s social intention (defect or cooperate). Once a response was given, the next trial started.