## 2 Materials and Methods
### Procedure and Data Acquisition  
Prior to testing, each subject was left in the experimental room for 20 min to allow the baseline skin temperature to stabilize. The recording room was set at a standardized temperature (23 \({}^{\circ}\)C) and humidity (50-60%) by a thermostat.  
To perform the experiment, a static driver simulator was used (Figure 1a). It was composed of driver's seat, steering wheel, clutch, brake, and gas pedals, and gearshift. To display the scenario, three 27 inch monitors were used. The total video resolution for the stimulation was 5760 \(\times\) 1080 pixels. The distance between the driver and road screen was approximately 1.5 m. Participants' horizontal view angle was 150 degrees. The simulator could produce starter and engine sounds, left and right signal indicators, and flashers and wiper blades. In this study, the sound of the engine, starter, and lights switches were provided.  
Participants sat comfortably on the seat of the driving simulator during both acclimatization and measurement periods.  
The software used for driving simulation was City Car Driving, Home Edition software (version 1.5) [35] (Figure 1b). The experimental protocol consisted of performing a driving simulation lasting 45 min in an urban context. The experimental conditions were set a priori to ensure the adverse driving condition and guarantee the uniformity of the experimental protocol for all the subjects. An overview of the experimental setting of City Car Driving software is reported in Table 1.  
\begin{table}
\begin{tabular}{l l l} \hline \hline \multicolumn{1}{c}{**City Car Driving Settings**} & \multicolumn{2}{c}{**Conditions**} \\ \hline \multirow{4}{*}{Weather} & • Season: Autumn \\  & • Weather & • Weather condition: Foggy \\  & • Time of the day: Daytime & • \\  & • Traffic density: 50\% & \\ \multirow{4}{*}{Traffic} & • Traffic behavior: Intense traffic & \\  & • Fullness of traffic: 60\% & \\ \multirow{4}{*}{Territory} & • Area: New city & \\  & • Location: Modern district & \\ \cline{1-1}  & \multirow{4}{*}{Dangerous change of traffic: Often} & \\ \cline{1-1}  & • Emergency braking of the car ahead: Often & \\ \cline{1-1} \cline{2-3} \multirow{2}{*}{Emergency situations} & • Pedestrian crossing the road in a wrong place: Often & \\ \cline{1-1}  & • Accident on the road: Often & \\ \cline{1-1}  & • Dangerous entrance of the vehicle into the oncoming lane: Rarely & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental settings of the driving software City Car Driving.  
Figure 1: Experimental setting for the proposed study: (**a**) driving simulator, lateral view; (**b**) screenshot of the software used for the driving simulation: City Car Driving [34].  
The conditions reported in Table 1 were selected to induce stress in the participants. In particular, the settings associated to traffic and emergency situations guaranteed non-comfortable driving, since the participants were often experiencing non-monotonous situations.  
During the execution of the experimental protocol, ECG signals and visible and thermal IR videos were acquired.  
The ECG signals were recorded by means of AD Instruments PowerLab system using the lead configuration determined by the Standard Limb Leads (i.e., electrodes positioned at the right arm (RA), left arm (LA), and left leg (LL)) [36].  
Visible and thermal IR videos were acquired by the depth camera Intel RealSense D415 and FLIR Boson 320 LW IR thermal camera, respectively. The technical characteristics of the two acquisition devices are summarized in Table 2.  
For the purpose of this study, the two imaging devices were held together and aligned horizontally. Figure 2 shows the entire imaging acquisition system.