## 4 Analysis
### Facial Action Analysis
Figure 8: Box plot showing the distribution of PCC values quantifying the relationship between the expected target facial action signal and the camera-measured signal for each illumination condition. Each cross, in the overlaid swarm plot, shows an individual value within the distribution. The means and standard deviation of the distributions are as follows: Bright (mean: 0.46, std: 0.12), Medium (mean: 0.42, std: 0.14), Dark (mean: 0.37, std: 0.12). Figure 7: Box plot showing the distribution of MAE values quantifying the difference between the expected target facial action signal and the signal camera-measured signal for each illumination condition. Each cross, in the overlaid swarm plot, shows an individual value within the distribution. The means and standard deviation of the distributions are as follows: Bright (mean: 0.82, std: 0.10), Medium (mean: 0.84, std: 0.10), Dark (mean: 0.88, std: 0.08). Figure 10: Box plot showing the distribution of PCC values quantifying the relationship between the expected target facial action signal and camera-measured signal for each attempt at the facial actions task instructed by the film. Each cross, in the overlaid swarm plot, shows an individual value within the distribution. The means and standard deviation of the distributions are as follows: First (mean: 0.87, std: 0.10), Second (mean: 0.84, std: 0.10), Third (mean: 0.84, std: 0.09). \begin{table}
\begin{tabular}{c c c c c} \hline \multicolumn{5}{c}{**FAC Distributions for Comparison**} & \multicolumn{2}{c}{\(\boldsymbol{t}\)**-Test (A vs. B)**} \\ \hline
**Metric** & **Condition A** & **Condition B** & \(\boldsymbol{t}\) & \(\boldsymbol{p}\) \\ \hline PCC & Dark & Medium & \(-2.299\) & 0.033 \\  & Dark & Bright & \(-4.109\) & **<0.001** \\  & Medium & Bright & \(-2.156\) & 0.044 \\ \hline MAE & Dark & Medium & 2.428 & 0.025 \\  & Dark & Bright & 3.977 & **0.001** \\  & Medium & Bright & 1.566 & 0.134 \\ \hline \end{tabular}
\end{table} 
Table 5: Results of dependent t-tests assessing differences in mean for the performance metric distributions between illumination conditions, for automatic FAC. Statistically significant differences in mean are shown in bold. Figure 9: Box plot showing the distribution of MAE values quantifying the difference between the expected target facial action signal and the camera-measured signal for each attempt at the facial actions task instructed by the film. Each cross, in the overlaid swarm plot, shows an individual value within the distribution. The means and standard deviation of the distributions are as follows: First (mean: 0.39, std: 0.13), Second (mean: 0.43, std: 0.14), Third (mean: 0.43, std: 0.12). Through visual inspection of the camera-measured signals, it appeared that there are three characteristic errors. First, on average, the camera-measured facial action was of lower intensity than that expressed by the model. Second, _OpenFace 2_ often measures facial actions with an intensity between zero and one, whereas the expected signal is never assessed in this range of values. This is due to [PERSON]'s system defining a magnitude of one being the minimum observable intensity [46]. In Figure 11, both of these characteristic errors can be seen. The third characteristic error is that the camera-measured signal appears to make small erratic changes, even when the facial expression does not appear to change in the associated video recording. In Figure 12, the power spectral density of the target signal measured by _OpenFace 2_ is shown for all data collected under each of the three illumination settings. It has been suggested that the fastest micro-expressions last no longer 65 ms [71]. In all three cases, there appear to be frequency components representative of movements lasting less than this duration (15.38 Hz).