# Feature Extraction and Evaluation for Driver Drowsiness Detection Based on Thermoregulation
## 2 Materials and Methods  
### Study Design and Participants  
The data of 19 healthy subjects between 20 years old and 27 years old who volunteered to perform a driving test were used in this study. Each participant was asked to drive in a driving simulator while physiological variables related to thermoregulation were monitored. To simulate a monotonous driving experience, a PlayStation 3 and racing game (Gran Tourismo 5) were used together with a compatible steering wheel as well as acceleration and brake pedals (Logitech Driving Force EX). The race track named \"Special Stage 7\" was selected because it represents an empty highway at night. Additionally, a speed limit of 80 km/h was imposed. This setup was installed in a climate-controlled room of 2.3 by 3.6 m, where the temperature was held constant at 23 \({}^{\circ}\)C and the relative humidity kept at 50%. The constant thermal environment was deemed realistic since similar conditions have been reported in experimental measurements performed on the road [23].  
Every participant arrived at the test facility at around 21:00. After an introduction to the setup and the purpose of this study, the volunteer was equipped with the different sensors (see Section 2.2. Data Collection). Subsequently, the driving simulation started between 21:30 and 22:15. The subjects performed the driving test in either one of the following conditions. In a first series of experiments, the lights inside the climate-controlled room were dimmed and there was no communication between the subject and the researcher present to follow up the measurements and the driver's state. The driving simulation was stopped after a maximum duration of 2.5 h or until the driver was too sleepy to continue driving in a normal way. In a second set of experiments, the lights inside the room were left on and communication between the researcher and the participant was allowed. It has been shown that exposure to light elicits acute physiological effects in humans such as an increase in alertness, suppression of melatonin, and an increase in T\({}_{\text{C}}\)[24]. In line with the hypothesis by [PERSON] et al. [19], the thermoregulatory changes are thought to be related to the alerting effects instead of a direct relation between light exposure and thermoregulation. Evidently, the purpose of this second protocol was to increase the chances of staying alert during the simulation. However, the participants were not forced to stay alert. For these measurements, a maximum duration of 1.5 h was set in advance. The maximum duration was set to 1.5 h because this was the average in the first set of experiments. In other words, the first group of participants became-on average-too sleepy to drive after 1.5 h under the first conditions. Figure 1 visualizes the timing of the experiments and shows the driving simulator that was set up in the climate-controlled room.  
In total, 26 people completed the driving simulation. However, the data of 7 participants were excluded due to missing sensor data (i.e., in 3 simulation data collection were not stored correctly) and/or limited duration of the driving simulation (i.e., 5 participants were falling asleep within 40 min to 60 min after the start). In case a participant became too drowsy to drive within 1 hour, it was assumed that the process of sleep onset started before entering the simulator. As a result, the analysis was applied to a dataset of 10 participants who performed the first protocol and 9 subjects who performed the second version. Afterwards, we checked whether this first group actually experienced drowsiness during the test and the second group did not (see Section 2.2. Data Collection).  
The study was approved by the Social and Societal Ethics Committee (SMEC) of the KU Leuven (case number G-2019 04 1632) and all participants provided written informed consent before starting the driving test.  
Figure 1: Timing of the driving experiment (**a**) and a photo of the driving simulator installed in the climate-controlled room (**b**).