## 3 Results
### Distal Participant Data Analysis
#### 3.2.2 Effect of the Motion and Acoustic Features and the Presence of an Audience  
Perceived authenticity and emotional intensity were also modeled using the motion and acoustic features computed on the material recorded. Three models were computed using, respectively, one of the three features, energy kinetic, body twist index, and metrical centroid. The interaction of the features, used here as continuous predictors, and the fixed effect representing the presence of an audience were used in these models. The participants and the musicians were used as random effects. When comparing such model with models with no interaction, only the models for kinetic energy and metrical centroid were significantly improving the model accuracy for both emotional intensity (kinetic energy: \(\chi^{2}(4,N_{trials}=875)=13.572\), \(p=0.011\), \(AIC=7649.9\), \(BIC=7707.2\), \(R_{m}^{2}=0.8\), \(R_{c}^{2}=0.42\), metrical centroid: \(\chi^{2}(4,N_{trials}=875)=32.133\), \(p=1.8\times 10^{-6}\), \(AIC=7653.7\), \(BIC=7711\), \(R_{m}^{2}=0.08\), \(R_{c}^{2}=0.43\)) and authenticity (kinetic energy: \(\chi^{2}(4,N_{trials}=875)=12.339\), \(p=0.018\), \(AIC=7750.3\), \(BIC=7817.6\), \(R_{m}^{2}=0.105\), \(R_{c}^{2}=0.42\), metrical centroid: \(\chi^{2}(4,N_{trials}=875)=35.714\), \(p=3.31\times 10^{-7}\), \(AIC=7760.5\), \(BIC=7817.8\), \(R_{m}^{2}=0.10\), \(R_{c}^{2}=0.42\)).  
When the musician was playing in front of an empty room, the recorded material was rated as more emotionally intense and authentic as the kinetic energy was increasing. The stimuli associated with higher value for kinetic energy were significantly rated higher for both dependent variables (intensity: \(\chi^{2}_{EmoInt,Low/MidKinEn,Absence}(1,N_{trials}=875)=4.368\), \(p=0.036\), \(\chi^{2}_{EmoInt,Mid/HighKinEn,Absence}(1,N_{trials}=875)=4.948\), \(p=0.026\); and authenticity: \(\chi^{2}_{Autth,Low/MidKinEn,Absence}(1,N_{trials}=875)=6.66\), \(p=0.009\), \(\chi^{2}_{Autth,Mid/HighKinEn,Absence}(1,N_{trials}=875)=4.47\), \(p=0.034\)) In the case of metrical centroid, mid-range values were rated as more intense and authentic compared to extreme values (Figure 4). The rating associated with lower values were significantly different from the high values, while the high values were significantly (and marginally in the case of authenticity) different from the mid values (intensity: \(\chi^{2}_{EmoInt,Low/HighMetCent,Absence}(1,N_{trials}=875)=16.473\), \(p=4.9\times 10^{-5}\), \(\chi^{2}_{EmoInt,Mid/HighMetCent,Absence}(1,N_{trials}=875)=5.288\), \(p=0.021\); and authenticity: \(\chi^{2}_{Autth,Low/HighMetCent,Absence}(1,N_{trials}=875)=21.277\), \(p=3.9\times 10^{-6}\), \(\chi^{2}_{Autth,Mid/HighMetCent,Absence}(1,N_{trials}=875)=3.773\), \(p=0.052\)).  
The introduction of an audience in front of the musicians influenced how the musicians performed (Figure 2) but also brought significant changes in how intense and authentic the performance was perceived. Those changes highlighted the emergence of a bipartite distribution of our data instead of the tripartite grouping of the expressive intents (Figure 4). For both the authenticity and the emotional intensity, the two levels of the bipartite distribution were significantly different from each another (intensity: \(\chi^{2}_{EmoInt,KinEn,Low/HighKinEn,Audience}(1,N_{trials}=875)=59.625\), \(p=1.14\times 10^{-14}\), \(\chi^{2}_{EmoInt,Low/HighMetCent,Audience}(1,N_{trials}=875)=36.056\), \(p=1.91\times 10^{-9}\), authenticity: \(\chi^{2}_{Autth,Low/HighFeatKinEn,Audience}(1,N_{trials}=875)=81.819\), \(p<2.2\times 10^{-16}\), \(\chi^{2}_{Autth,Low/HighMetCent,Audience}(1,N_{trials}=875)=48.918\), \(p=2.6\times 10^{-12}\)). The values of the features at which the separation occurred was calculated. It corresponds at \(6.73\times 10^{-3}\) W for the kinetic energy (\(kineticenergy_{min}=2.207\times 10^{-3}\) W and \(kineticenergy_{max}=0.0304\) W) and 308.18 BPM for the metrical centroid (\(metricalcentroid_{min}=260.48\) BPM and \(metricalcentroid_{max}=335.57\) BPM).