## 4 Discussion
### Absence of an audience  
We observed that different expressive intents were characterized by different quantities of body movements, as already demonstrated in the literature, in the absence of an audience [43; 54]. Specifically, this study explored two features, the kinetic energy and newly developed body twist index, highlighting that energetic movements and wider body twists were associated with the magnitude of the expressive intent. Both features were increasing with the different expressive intents. Generally, it was revealed that musicians tended to make more movements when playing expressively [54]. This absence of the audience allowed them to fully twist and put more energy into their gestures. When analyzing the sound produced, the metrical centroid representing the metrical structure of the piece was also impacted by the different expressive manners. However, its value did not linearly increase between deadpan, projected and exaggerated expressive intents. The projected expressive intent was characterized by the highest value for the metrical centroid feature. This highlighted the predominance of faster notes within the musical piece. The other two expressive intents could be symbolized by longer notes or slow pulsations. In the case of the deadpan style, this suggested a more controlled way of playing, while emphasizing on a regular and slower beat. When musicians were exaggerating, the excessive expressive intent was marked on both slower and faster pulsations at different timing driving the decrease in the centroid value. As musicians dedicated more attention to  
Figure 4: Impact of the interaction of the computed features: (**A**,**C**) kinetic energy (red); and (**B**,**D**) metrical centroid (blue); and the presence of an audience on: (**A**,**B**) the perceived emotional intensity; and (**C**,**D**) the perceived authenticity (deadpan: DP, projected: PROJ, and exaggerated: EXAG) (\(p<0.01\), \({}^{\star}\)\(p<0.05\), \({}^{\star\ast}\)\(p<0.01\), \({}^{\star\ast}\)\(p<0.001\)). their expressive intent, they change the way they played a certain piece. This confirms the phenomenon of performance expression [57; 58]. When studying participants' perception of emotional intensity and authenticity, both ratings were affected significantly by the different expressive intents in the absence of an audience. Ratings were significantly increasing with the expressive conditions showing greater emotional intensity and authenticity in the exaggerated condition. The study of the impact of the physical attributes of the performance on the perception of emotional intensity and authenticity was conducted using feature values instead of the well-documented expressive conditions. The perception associated to stimuli with no virtual audience displayed was in line with the feature values obtained for different expressive intent. The deadpan (low kinetic energy and low metrical centroid), projected (medium kinetic energy and high metrical centroid), and exaggerated (high kinetic energy and medium metrical centroid) conditions are perceived, respectively, as relatively low, medium and high emotional intensity and authenticity. They showed a tripartite distribution of values which would fit with the three expressive conditions [43]. Before addressing the impact of the social factor on participants' ratings, we also noted the high correlation between authenticity and emotional intensity. Two conclusions can be drawn from such results. Firstly, the difficulty to discriminate between both ratings might be due to an underlying link between them. In music, authenticity represents an important part of the performance to make the listener feel the desired emotions [60]. Secondly, such link should be further untangled with a different experimental setup. We propose the use of \"fake\" stimuli, where musicians would fake the emotion felt and performed. This could for example be conducted by using mood induction procedures for \"real\" emotion stimuli while asking musicians to fake the rest of the stimuli.