## 3 Results
### Proximal Performance Data Analysis  
In order to characterize the musical gestures and motion, we computed the z-scored values of all features (kinetic energy, body twist index, and metrical centroid) recorded during the performance at different expressive intents with the presence or not of a virtual audience. Based on the marginality principle, we considered only a linear model containing main effects of both the expressive intents and the social factor as well as the interaction between these factors (\(F_{kineticenergy}(5,18)=39.78,p=4.1\times 10^{-9}\), \(R_{adjusted}^{2}=0.89\) & \(F_{BTI}(5,18)=6.77,p=0.001,R_{adjusted}^{2}=0.55\), \(F_{metrical centroid}(5,17)=16.58\), \(p=5.17\times 10^{-6},R_{adjusted}^{2}=0.78\)).  
Figure 1: Motion and acoustic features computed: (**A**) Chronograph of the motion capture data for one excerpt played in front of an audience while exaggerating expressive intent. (**B**) Kinetic energy associated with movements of all the markers for the excerpt depicted in (**A**). (**C**) 3D view of the motion capture and the line associated with the pelvis and shoulder. (**D**) Transversal view of the motion capture data and the angle computed between the line from the pelvis and shoulders. (**E**) Computation of Body Twist Index. The angle between the aforementioned lines is computed over the duration of the excerpt. The Body Twist Index consists of the average of all values comprised in the top quantile (above the quantile 75 value). (**F**) Sound profile of the performance of the Scherzo of [PERSON]’s Symphony No.9 in D minor, op.125. (**G**) Corresponding autocorrelogram with tracking of the metrical structure. (**H**) Corresponding metrical centroid curve (Copyright [PERSON], [PERSON] et al., 2013 [73]).  
Both motion features increased with stronger expressive intents in the absence of the social factor (Figure 2). When the audience was present, while the kinetic energy still increased with the expressive intent, the difference with the other social condition was not significant. When comparing the presence and absence of the audience, the impact of the social factor only appeared for the deadpan expressive condition for the BTI. In this case, the presence of the audience was characterized by a significant increase in the \"twist\" angle (\(F_{BTI,DP,Social}(1,18)=5.41,p=0.032\)). Noteworthy was the significant difference for the BTI in the deadpan and exaggerated condition when the audience was present or not. The BTI value increased in the deadpan condition with the presence of an audience while it was diminished in the exaggerated condition (\(F_{BTI,DP/EXAG,Social}(1,18)=5.64,p=0.028\)).  
In the case of the acoustic feature, metrical centroid, we observed a different pattern when the virtual audience was absent (Figure 2). When asked to play with a \"projected\" expressive intent, the metrical centroid of the performance was significantly greater, meaning that the more elementary metrical levels predominated (i.e., very fast levels corresponding to very fast rhythmical values). It was however lower for both the \"deadpan\" and \"exaggerated\" conditions, contrarily to the linear increase observed in motion features. The effect of the social factor was highlighted in the increase of the beats per minute of the metrical centroid for every expressive intent, especially for the \"exaggerated\" condition where this increase was significant (\(F_{MetCent,EXAG,Social}(1,17)=9.24,p=0.007\)).