Interpersonal Body and Neural Synchronization

Supplementary Information

Interpersonal body and neural synchronization

as a marker of implicit social interaction

Kyongsik Yun, Katsumi Watanabe, and Shinsuke Shimojo

Correspondence to:

Figure S1. Raw single-trial time-series data of finger position in (A) the pre-training test and (B) the post-training test (along the X-axis from left to right).

Fingertip movement synchronization increased after the training (two-tailed paired t-test, t(9)=2.51, p<0.03).

Figure S2. Body movement synchrony in control conditions.

(A) Average cross correlation coefficients of fingertip movements in non-training session for 8 times (blue: session 1 and 2, red: session 7 and 8, faint blue and red: standard errors). No significant difference in fingertip synchrony was found between the session 1 and 2 (pre-non-training sessions) and the session 7 and 8 (post-non-training sessions) (two-tailed paired t-test,p=0.99, n=10, age: 21.4±3.72). Thus, mere accumulation of test experiences was excluded as a factor for the increased synchrony. (B) Average cross correlation coefficients of fingertip movements in interaction with a dot moving on a computer display (blue: pre-training, red: post-training, faint blue and red: standard errors). No significant difference in fingertip synchrony was found between the pre- and post-training (two-tailed paired t-test,p=0.68, n=10, age: 21.4±3.72). (C) Average cross correlation coefficients of fingertip movements in interaction with a recorded video of another subject (blue: pre-training, red: post-training, faint blue and red: standard errors). No significant difference in fingertip synchrony was found between the pre- and post-training (two-tailed paired t-test,p=0.47, n=10, age: 20.8±3.29). Results are shown as means ±s.e.m.

Figure S3. Topography of the phase synchrony connections in the control analysis with randomly shuffled pairs.

Phase synchrony between all 84 cortical ROIs of the two random shuffled participants for cross-validation (Left brain: leader, right brain: follower) in (A) theta (4~7.5Hz) and (B) beta (12~30Hz) frequency range.Disrupted only inter-brain, not intra-brain, synchrony connections in the random shuffling cross-validation analysis confirmed that these connections were not by chance or artifact, but were due to the paired face-to-face interaction during the cooperative training session (phase randomization surrogate statistics, p<0.000001). Phase synchrony patterns between the leader and the follower are shown in (C) theta and (D) beta frequency range. The functional connectivity patterns were significantly different (phase randomization surrogate statistics, p<0.000001). Stronger connectivity in the leader compared with the follower shown in red. Stronger connectivity in the follower compared with the leader shown in blue.

Table S1. Correlations of the fingertip movement synchrony changes (post – pre-training session) with each pair’s averaged scores of social anxiety scale (Spearman’s rho, *p<0.05, n=22, male participants only, ages =24.3±4.9).

Supplementary Methods

Control Experiments

We performed three additional control conditions, consisting of (1) eight consecutive non-training sessions (i.e. the same as the pre- and the post-training sessions), (2) oneparticipant interacting with a dot moving on a computer screen which was based on recorded finger movements from a previous participant and (3) one participant interacting with a recorded video of another subject. In (1), we did not find a significant increasein fingertip synchrony between pre-non-training and post-non-training sessions (two-tailed paired t-test,p=0.99, n=10, age: 21.4±3.72) (Figure S1A). The results suggest that the mere repetition of test sessions (in the absence of interpersonal training) is not sufficient to increase fingertip synchrony. Moreover, we did not find any significant difference in fingertip synchrony between the pre- and post-training sessions in the other control conditions, either (2) witha dot moving (two-tailed paired t-test,p=0.68, n=10, age: 21.4±3.72) (Figure S1B), or (3) with a recorded video of another subject (two-tailed paired t-test,p=0.47, n=10, age: 20.8±3.29) (Figure S1C). Furthermore, a similar study with the leader blindfolded in the training sessions did not find a significant increase in the fingertip synchrony between the pre- and post-training sessions7. These control results suggest that non-social and non-responsive training cannot increase the fingertip synchrony.

We didfind significant differences in EEG activity between the pre- and post-training sessions in the main experiment (Figure 2A and 2B), but not in our additional controls tasks, either with a participant following a dot on the computer screen or with a recorded video of another subject (nonparametric permutation test, p>0.05).
SupplementaryReferences

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