## 3 Results and Discussion
### Analysis Results of EEG Measurement  
Figure 10 shows the EEG analysis results in the prefrontal lobe of the subject according to the cabin and vent discharge air temperature with an average solar radiation of 516 W/m\({}^{2}\). Figure 10a shows the variations of the relative \(\theta\)-wave, SMR wave, \(\beta\)-wave and CI, and \(\beta/\alpha\) in the prefrontal lobe of the driver. At the indoor temperature of 25 \({}^{\circ}\)C, the relative \(\theta\)-wave was high, while the relative SMR and \(\beta\)-wave were relatively low. The relative \(\theta\)-wave was the highest because the drivers were sitting on a chair in a comfortable environment at a ready state. Moreover, because there was no fatigue for driving, the relative SMR and \(\beta\)-wave values were also the lowest. The relative \(\theta\)-wave decreased and relative SMR and \(\beta\)-wave slightly increased when the subject started to drive at a cabin temperature of 35 \({}^{\circ}\)C without vent cooling. This is because the body of the subject felt uncomfortable when the driver moved from a comfortable condition to a hot condition. However, it was considered a relatively small change because of the delay of the body response to adapt to this condition for the sudden temperature change. The relative SMR wave was the highest at cabin and vent discharge air temperatures of 30 and 16.5 \({}^{\circ}\)C because the experiment was conducted continuously under high-temperature conditions. The relative SMR wave shows the concentration and slight tension of the driver. In these temperature ranges, the subject was in a state of slight tension; thus, the subject was considered to have a high level of concentration during driving. Afterwards, at a cabin and vent discharge air temperature of 22.5 \({}^{\circ}\)C, the relative \(\theta\)-wave increased, while the relative SMR and \(\beta\)-wave tended to decrease. This means that the fatigue of the driver increased because of the long driving time and drowsiness; thus, the concentration during driving was reduced. The relative \(\theta\)-, SMR, and \(\beta\)-waves are the indicators of the concentration of the subject. Based on these values, the concentration index (CI) and relative \(\beta/\alpha\) at the prefrontal lobe were calculated, as shown in Figure 10b. At an indoor temperature of 25 \({}^{\circ}\)C, the concentration was the lowest, and the relative \(\beta/\alpha\) was also low because the subject was in a comfortable state and doing nothing. The concentration showed a tendency to increase when the driver started to drive at a cabin temperature of 35 \({}^{\circ}\)C without vent cooling, and the relative \(\beta/\alpha\) also increased. Concentration increased at first because of the focus on driving by the subject. The reason for the increase in the relative \(\beta/\alpha\) is that the subject was nervous because of discomfort caused by the high-temperature environment without vent cooling. Both the concentration and relative \(\beta/\alpha\) of subjects were relatively low at cabin and vent discharge air temperatures of 32.5 and 14.5 \({}^{\circ}\)C, respectively, because the driver felt comfortable; however, the concentration on driving was reduced, owing to slight drowsiness. When the cabin and vent discharge air temperatures were 30 and 16.5 \({}^{\circ}\)C, concentration was the highest, and the relative \(\beta/\alpha\) showed an increasing trend. When the cabin and vent discharge air temperatures were 25 and 20.5 \({}^{\circ}\)C, concentration tended to decrease, and the relative \(\beta/\alpha\) was the highest. This is considered to be a condition that requires the driver to rest because the concentration of the subject during driving was reduced due to a long driving time and the high stress during driving. Figure 11 displays the relative \(\alpha\)- and \(\beta\)-waves of the driver in the occipital lobe according to the cabin and vent discharge air temperature with a maximum and average solar radiation of 1251 and 516 W/m\({}^{2}\), respectively.