Four-way mirror game
For this initial analysis, we calculated the average velocity of all the markers (quantity of motion, QoM) for each player. The QoM’s of the players were then correlated with those of the other players, to evaluate the overall synchronicity in the game. A more detailed analysis was conducted on the finger tip movements. The Euclidean norm of the acceleration of the extended fingers was calculated, to obtain their accelerations along the trajectories. is allowed easy comparisons between players, as only the magnitude of the accelerations was preserved, and not the direction. This method allows us to analyse the relationships between the players in more detail.
This video shows the first four-way game from to different perspectives.
For this video, all four players' bodies have been rotated so that the first game can be observed from the players' perspective.
The second game has higher QoM peaks than the first, indicating that participants were conducting larger sudden movements (Figure 3).
Figure 1. First game, quantity of motion in each player, calculated from all markers.
Figure 2. First game, cross-correlations of finger norm accelerations for each pair.
Figure 3. Second game, quantity of motion in each player, calculated from all markers.
In the second game, we also see a more coherent cross-correlation structure (Figure 4). Participants are numbered in clock-wise direction, so the adjacent numbered players are standing next to each other in the game. Looking at the peaks that are closest to the lag 0, we can see that they all are from dyads of adjacent players. us players seem to follow the players next to them more closely than players they are facing.
Figure 4. Second game, cross-correlations of finger norm accelerations for each pair.
If we zoom in to some of the peaks in the QoM graph, we can see the anatomy of these larger movements: who initiated them, who followed and at how large were the lags. Figures three and four show two of these peaks.
Figure 5. Details of QoM peaks. Top: first game; Bottom: second game.
 Tommi Himberg, Maija Niinisalo, and Riitta Hari. 2015. Coordination of Fluent Hand-Movements in Dyads. RPPW15, Amsterdam, Netherlands.
 Michael J. Hove and Jane L. Risen. 2009. It’s All in the Timing: Interpersonal Synchrony Increases Affiliation. Social Cognition 27, 6 (2009), 949–960. DOI:10.1521/soco.2009.27.6.949
 Lior Noy, Erez Dekel, and Uri Alon. 2011. The mirror game as a paradigm for studying the dynamics of two people improvising motion together. Proceedings of the National Academy of Sciences 108, 52 (2011), 20947–20952. DOI:10.1073/pnas.1108155108
 Henri Tajfel. 1982. Social psychology of intergroup relations. Annual review of psychology 33, 1 (1982), 1–39.
 Piercarlo Valdesolo, Jennifer Ouyang, and David DeSteno. 2010. The rhythm of joint action: Synchrony promotes cooperative ability. Journal of Experimental Social Psychology 46, 4 (2010), 693–695.