# Camera-Sourced Heart Rate Synchronicity: A Measure of Immersion in Audiovisual Experiences
## 4 Results
### Physiological Analyses  
In this section, the camera-sourced heart rate is initially analysed. Subsequently, this analysis is reproduced using the ECG sensor heart rate data. Finally, a post hoc analysis is performed on both the camera-sourced data and ECG-sourced data. The ISC-HR was calculated using Equation (1), shown in Section 2.3. Figure 5 shows the ISC-HR value distributions for both groups. The median ISC-HR value was higher in the group receiving the high-end audio presentation. However, using the permutation test described in Section 3.5, this difference was assessed as being not statistically significant (difference in median = 0.020, \(p\) = 0.491). Visual inspection of the camera-sourced ISC-HR data shown in Figure 5 suggested that there was one outlier within the high-end group. This participant had a much lower ISC-HR value than the others within the same group and had the highest average heart rate out of all participants in the study (103 BPM). Moreover, their HR appeared to be slowly decelerating throughout the audiovisual experience. With the participant removed, the permutation test evaluated that the difference in median was still not statistically significant (difference in median = 0.027, \(p\) = 0.360). All heart rate data, including that pertaining to the statistical outlier, is visualised in the code repository [67]. Figure 4: Distribution of the response to questions asked after the audiovisual experience. The questions are shortened; in the survey, they appear as: “I found the presence of the heart rate monitor negatively impacted my viewing experience”, “I found the presence of the camera negatively impacted my viewing experience”, “I found the brightness of the room negatively impacted my viewing experience”, and “I found all the questions easy to understand”. The ISC-HR feature was recalculated using the ECG-sourced HR data and compared between groups. The median ISC-HR value was higher in the group receiving the high-end audio presentation. However, using the permutation test described in Section 3.5, this difference in the median was assessed as being not statistically significant (difference in median = 0.032, \(p\) = 1.000). Visual inspection of the ECG-sourced ISC-HR values in Figure 5 appears to show the same outlier found using the camera-sourced data, as well as another statistical outlier who also had a much lower ISC-HR value than the other participants in the high-end audio presentation group. With the common outlier removed, the ISC-HR feature was recalculated, and the permutation test again assessed the between-group differences in the median as insignificant (difference in median = 0.034, \(p\) = 0.780). With both of these outliers removed, the difference in median ISC-HR between groups is not significant when using either the camera-measured heart rate data (difference in median = 0.0312, \(p\) = 0.314) or ECG sensor heart rate data (difference in median = 0.044, \(p\) = 0.773). To further assess the performance of the camera approach, MAE and PCC values were calculated through a comparison of the camera and ECG-sourced HR data for each participant. The mean MAE and PCC values were 1.522 BPM and 0.782. The range of MAE and PCC values were 0.650 BPM to 4.420 BPM and 0.330 to 0.960, respectively. The participant with the lowest PCC value, between ECG and camera-sourced HR, was the ISC-HR outlier in the high-end group, who only appeared when analysing the ECG-sourced feature. The PCC between the ISC-HR values calculated using the camera-sourced heart rate data and the ECG-sourced heart rate data was calculated as 0.868 and 0.907 for the participants in the high-end and basic conditions, respectively. Seeking an alternative means of validation regarding the relationship between immersion and heart rate synchronicity, ISC-HR values were compared with the immersion scores from the questionnaire. Figure 6 visualises this comparison, highlighting two clear outliers who recorded the highest and lowest self-report immersion scores using the questionnaire.