# Physiological and Behavioral Changes of Passive Fatigue on Drivers during On-Road Driving
## 3 Results
### Eye Movement Indicators  
Analysis of drivers' horizontal gaze dispersion reported a significant main effect of driving stages, \(F(2,62)=3.97\), \(p<0.05\), \(\mathrm{n_{P}^{2}}=0.11\) (see Figure 8a). The post hoc test showed  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Indicator (Unit)** & **Stage** & **Stage** & **Stage** & **Stage** & **Stage** \\  & **I** & **II** & **Stage** & **I vs. II** & **II vs. III** & **I vs. III** \\ \hline \multirow{4}{*}{\begin{tabular}{c} Eye \\ movement \\ \end{tabular} } & Subjective fatigue level measured & 2.34 (0.87) & 3.06 (0.95) & 3.53 (0.84) & *** & ** & *** \\  & \begin{tabular}{c} Horizontal gaze dispersion (m) \\ \end{tabular} & 0.13 (0.04) & 0.14 (0.04) & 0.15 (0.05) & n.s. & n.s. & * \\  & \begin{tabular}{c} Vertical gaze dispersion (m) \\ \end{tabular} & 0.14 (0.04) & 0.13 (0.03) & 0.14 (0.04) & n.s. & * & n.s. \\  & \begin{tabular}{c} Pupil diameter (mm) \\ \end{tabular} & 3.58 (0.91) & 3.68 (0.97) & 3.73 (1.07) & n.s. & n.s. & * \\ \hline \multirow{4}{*}{\begin{tabular}{c} Driving \\ Performance \\ \end{tabular} } & Mean speed (km/h) & 81.52 (4.42) & 79.99 (4.28) & 85.68 (5.83) & n.s. & *** & *** \\  & Standard deviation of speed & 4.13 (2.24) & 4.75 (2.12) & 4.83 (2.62) & n.s. & n.s. & n.s. \\ \cline{1-1}  & \
\begin{tabular}{c} Speed compliance (\%) \\ \end{tabular} & 0.28 (0.19) & 0.27 (0.13) & 0.16 (0.15) & n.s. & ** & ** \\ \cline{1-1}  &
\begin{tabular}{c} Standard deviation of steering \\ angle (degree) \\ \end{tabular} & 1.01 (0.16) & 1.19 (0.16) & 1.06 (0.16) & *** & ** & n.s. \\ \cline{1-1}  & Steering hold frequency (Hz) & 2.68 (0.75) & 2.46 (0.73) & 2.73 (0.79) & *** & ** & n.s. \\ \hline \hline \end{tabular} Note.* indicates \(p<0.05\); ** indicates \(p<0.01\); *** indicates \(p<0.001\); n.s. indicates not significant.  
\end{table}
Table 4: Overview changes of eye movement and driving performance caused by passive fatigue in different driving stages [\(M\) (\(SD\))].  
Figure 7: Subjective fatigue level under three stages. (Note: Error bars in this and all following graphs represent standard errors. Two asterisks (**) indicate \(p<0.01\), and three (***) indicate \(p<0.001\)).  
that drivers' gazes were considerably more dispersed in the horizontal dimensions in stage III than in stage I, \(t(31)=2.80\), \(p<0.05\), [PERSON]'s \(d=0.50\).  
Significant differences have also been reported in drivers' vertical gaze dispersion, \(F(2,\,62)=4.24\), \(p<0.05\), \(\eta_{\rm p}^{2}=0.12\) (see Figure 8b). The post hoc test indicated that a broader vertical gaze dispersion appeared in stage III than in stage II, \(t(31)=2.60\), \(p<0.05\), [PERSON]'s \(d=0.46\). The density contour plots based on the intersection coordinates of three-dimensional gaze direction and vertical plain z = 0.9 in Figure 9 further visualize these tendencies.  
Pupil diameters of drivers as shown in Table 3 became greater as time went by, \(F(2,\,62)=3.44\), \(p<0.05\), \(\eta_{\rm p}^{2}=0.10\) (see Figure 8c). The difference between stage III and stage I has been proven to reach significance, \(t(31)=2.54\), \(p<0.05\), [PERSON]'s \(d=0.45\).