Szymanski, C., Brick, T. R., Perdikis, D., Müller, V., Karch, J., & Lindenberger, U.
On neural synchronization during interpersonal action coordination. (under review entitled ‘Neural Synchronization during Reciprocal and Parallel Dyadic Gaming’ at Frontiers in human neuroscience).
Background. The recent interactive turn in social neuroscience has
highlighted the importance of interpersonal interaction for the development and functioning of social cognition (De Jaegher, Di Paolo, & Gallagher, 2010; Gallotti & Frith, 2013; Schilbach et al., 2013; Sebanz et al., 2006). Studies using EEG hyperscanning have repeatedly revealed interpersonally synchronized patterns during interpersonal action coordination. Yet, consensus is lacking if this inter-brain synchronization is characteristic for social interaction in that it reflects shared cognitive action plans (Sänger et al., 2011) or if it mainly reflects the similarity of two person’s motor output. To shed light on this core question of the current hyperscanning literature, we designed a novel computer-game paradigm to compare inter-brain phase synchronization during reciprocal, interactive interpersonal action coordination and during parallel, non-interactive interpersonal action coordination, preserving the same behavioral dynamics.
Figure 9.
A. Example display of the paradigm ‚Stay with me’. B. Experimental set-up in the electro- magnetically shielded cabin. A B
Aims. We aimed to disentangle the relative impacts of (A) interpersonal
interaction and (B) input/output similarity on inter-brain phase synchronization during interpersonal action coordination.
Hypothesis. From the current hyperscanning literature it is unclear if inter-
brain phase synchronization solely reflects the similarity of perceptual input and motor output between two individuals or if it is further modulated by the presence of social interaction. We thus hypothesized that inter-brain phase synchronization would differentiate (A) between conditions that differ in output similarity and thus behavioral dynamics. We had no a-priori hypothesis on the sensitivity of inter-brain phase synchronization for social interaction and thus asked the research question if inter-brain phase synchronization would differentiate (B) between reciprocal and parallel interpersonal coordination.
Methods. We had 13 male-male and 15 female-female dyads take part in
this EEG hyperscanning study. We designed the novel interactive virtual game ‚Stay with me‘ to disentangle the relative impacts of interpersonal interaction and input/output similarity on inter-brain phase synchronization during action coordination (Figure 9). By recording behavioral patterns during reciprocal coordination and replaying these recorded patterns in later trials, this paradigm enabled us to compare reciprocal interactive coordination and parallel non-
Figure 10. Results of a linear mixed model analysis for the effect of condition on circle distance.
Figure 11. Histogram of the ratings of control across conditions registered at the end of each interactive trial. Dotted lines represent average rating per condition.
interactive coordination following the same behavioral dynamics. The participants’ task was to navigate a virtual circle to (A) avoid collisions with moving virtual squares and (B) to align their circle with the second circle on the screen. Our four conditions differed with respect to the second circle’s movements. While in reciprocal the second participant real-time controlled the second circle, in replay the second circle displayed the movement path of a circle recorded during a previous reciprocal trial from the same dyad, in a identical square environment. In repIay other the second circle was a replay of a recording during a reciprocal trial from a different dyad. In alone, there was no second circle and participants only had to avoid collisions with the squares (intra-personal coordination only). We calculated number of square collisions per trial as a measure of intra-personal coordination, circle distance in pixel per trial as a measure of interpersonal coordination and movement similarity and inter-brain phase coherence (IPC) as a measure of inter- brain phase synchronization. We used linear mixed models to assess differences in behavioral performance and IPC between conditions.
Figure 12. Results of a linear mixed model analysis for the effect of condition,on IPC in the phi range (8- 12Hz, right centro-parietal electrode connections).
Figure 13. Grand average IPC values per frequency bin and condition.
Results. Analyses of our behavioral measures showed that behavioral
dynamics followed the same general movement patterns in all four conditions with small differences between reciprocal and replay and larger differences between reciprocal and alone (Figure 10). Participants reported ‚mutual control’ over circle movements for all conditions (Figure 11). We did not observe any differences in inter-brain phase synchonization between reciprocal interpersonal action coordination (reciprocal) and parallel interpersonal action coordination (replay) and thus our results give a negative answer to our second research question (B) for this study. We did however observe differences between alone and reciprocal, specifically in the alpha range in right centro-parietal electrode pairings and thus the results support our research hypothesis (A) for this study (Figure 12). Moreover, we observed a strong negative logarithmic relation between IPC and frequency band (Figure 13). On the behavioral level, subjects experienced reciprocal interpersonal coordination as well as parallel interpersonal coordination following the same behavioral dynamics as mutual teamwork (Figure 11). Additionally, our results on changes in coordination performance between playing alone and playing as a team replicated and extended an effect reported earlier in the literature (Bahrami et al. 2010). Due to the conceptualization of our paradigm, our task was more difficult in the three interpersonal conditions than in the alone condition. However, the degree of performance decrement was correlated with the skill difference between the two players in a dyad. The more two partners in a dyad differed in their coordination skills, the more the better player’s performance deteriorated, while there was no systematic effect on the weaker player’s performance change (Figure 14).
Conclusion. Inter-brain phase synchronization in the alpha range in right
centro-parietal electrode pairings has previously been associated with interpersonal interactivity (Tognoli et al., 2007a). Our results instead suggest that this ‚phi’ frequency and region may be particularly sensitive to the behavioral dynamics of an interaction. The results of our study suggest that interactive coordination is not systematically different, either experientially or neurally, from parallel coordination that is characterized by the same behvaioral dynamics. More generally, our evidence supports the idea that inter-brain phase synchronization may be seen as a
Figure 14. Effect of teamwork on coordination performance.
neural measure of behavioral dynamics that embodies characteristic (motor) information about an interaction.