Investigating the Effects of Downhill Roads on Driver’s Eye Movements

Despite the increasing popularity of self-driving cars, researchers in the transportation industry continues to prioritize accident prevention and safety improvement. This study inspects the influence of driving experience and gender on the driver’s gaze and pupil behaviors while descending a downhill. The data in this paper was collected by equipping ten subjects Tobii Pro glasses II in a series of experiments designed to track their gaze and pupil behavior in a downhill road section. The statistical and Python-based data analysis shows that novice drivers pay more attention to the instrument panel on the downhill road, and their pupils’ diameter is larger at both the top and bottom of the hill. In addition, female drivers pay more attention to the instrument panel than male drivers do during downhill tasks. Finally, more accurate formulas can be obtained by considering the experience and gender of drivers through logistics regression. This study has important theoretical significance for discovering the driver’s target search process and improving the driver assistance system.


Introduction
In the recent years, driving private cars has become the most common mode of transportation.In the process of driving, when there is a danger or safety impact, the eyes will make a corresponding response and show a certain rule.The Eye is the main device for the human body to obtain information from the outside world.According to studies, vision is one of the most important senses in providing external information, accounting for about 80%~90% [1].In the 1970s, Sabey et al. [2] in the United Kingdom and Treat et al.[3] in the United States conducted two investigations on the causes of accidents, and proposed that their research confirmed that human factors accounted for 90% of accidents, and human perception played a leading role in human factors.
Driver experience and gender are also important influences on driving behavior.The likelihood of driving rage decreases with the increase in driving years and increases with the increase in annual driving miles [4].Male drivers with significant driving experience are expected to overestimate their driving performance.The combined effect of gender and driving distraction is evident in the driving patterns of male drivers [5].Novice drivers pay more attention to the right visual field during turning, and switch back and forth more frequently in each visual field area [6].In the process of straight-line driving, the eye movement behavior of female drivers is more similar to that of novice drivers, while the male drivers' is similar to that of experienced drivers [7].
The research of domestic and foreign researchers on drivers with different experience and gender mainly focus on the accident scene, driving style, different environment, and road, etc.At present, there is relatively little research on the behaviors of drivers with different experiences and gender in 2. Related works Numerous research findings currently indicate a strong correlation between the eye movement behavior of drivers and their experience and gender.
May Jorella Lazaro et al. divided intersections into three dangerous situations and divided drivers into two groups of experienced and novice drivers for experiments to determine the difference in stress level and attention function between experienced and novice drivers in dangerous situations related to intersections.Studies have found that experienced drivers are more sensitive to environmental changes and risks when driving.Even under higher pressure, their attention level and driving performance are not affected [8].Larry B. Nabatilan et al. studied the visual behaviors of experienced drivers and novice drivers in simple and complex driving tasks, using eye-movement tracking technology and found that that the novice drivers fixated more on the dashboard area than on the front and center view.On the other hand, the experienced drivers fixated more on the front and center as compared to the dashboard area [9].Zhao Liang et al. used a driving simulator and eye-movement tracking technology to record the eye-movement characteristics of drivers during simulated car operations.After analyzing the driving characteristics of the drivers, they found that the staring range of the novice driver is not as large as that of the experienced driver, and driving experience has an impact on driving behavior [10].
More and more people find it crucial to use new devices to capture eye movement data for driving behavior.On this basis, we consider the eye movement behavior of different drivers on downhill roads.

Methodology
We designed and conducted a set of experiments under natural driving conditions at Weishui Vehicle Test Centre, Chang'an University, China.In the experiments, the drivers drove a small automatic transmission car, and we asked the drivers to drive in the uphill and downhill sections.In fact, driving uphill and downhill is part of our broader driving behavior.The driver diagram is shown in Figure 1.Since the experiment was conducted in China, all the cars drove on the right side of the road with the steering wheel on the left side of the car, and all the drivers wore a high-precision device, Tobii Pro Glasses II, throughout the experiment [11].An experimental snapshot is shown in Figure 2.
As shown in Table 1, we asked ten drivers to take the test, and all ten individuals who participated in the study possessed valid driver's licenses.Novice drivers are defined as those who have driven less than 1,000 kilometers, while experienced drivers are defined as those who have driven more than 1 million kilometers.Each driver repeated the experiment ten times [6].
As shown in Figure 3, we divide the view window into four different areas [12], the Main View, the Left View, the Right View, and the Instrument Panel View, while creating the area of interest (AOI).After the AOI is created, it is fixed in the driver's field of vision and does not change even if the driver turns his head.

4.Analysis and discussion
Due to objective reasons, the left view and right view obtained too little data during data collection, so we only analysed the driver data of the instrument panel and main window area.Before the experiment, all the data were tested for normality and homogeneity of variance, and it was found that the data did not meet the requirements of normality and homogeneity of variance.Therefore, the Mann-Whitney U test in the non-parametric test was selected for fixation behavior data.

4.1Fixation behavior analysis
Mann-Whitney U test results of the two Windows grouped by experience level are shown in Table 3.
In the downhill road section, the average fixation time of drivers with different experiences on the instrument panel area was statistically different, but there was no significant difference in other test data.In the main window area, there are significant differences in the average fixation duration, first fixation duration, and visit count, but no significant differences in the other indicators.Therefore, we conclude that there is little difference between novice drivers and experienced drivers in the instrument panel gaze behavior during downhill, but novice drivers have longer average fixation duration on the instrument panel; however, drivers with different experiences have different fixation behaviors on the main window in the downhill road.Novice drivers pay more attention to the main window, and the fixation duration are longer.
There may be two reasons for the above conclusion: first, the speed of the downhill section is easy to be too fast.Novice drivers pay more attention to the speed value on the instrument panel to ensure that they can reach the bottom of the slope smoothly; Second, novice drivers are more nervous and focused on the road ahead, leading to a longer fixation duration at the main window, but the lack of driving consciousness may lead to confusion of sight and more visits.In contrast, experienced drivers are more relaxed and start out paying more attention to their surroundings and road conditions, thus paying less attention to the main window.
Mann-Whitney U test results of the two Windows grouped by gender are shown in Table 4.There were major differences between male and female drivers in the average visit duration and fixation count at the instrument panel area during the downhill, but no noteworthy differences were found in other test data.In the main window area, there were significant differences in average fixation duration, average visit duration, fixation count, and the visit count, but no significant differences in other indicators.Therefore, we conclude that, in the process of downhill, female drivers have a longer average visit duration and more fixation counts on the instrument panel.Different genders have some differences in their fixation behavior on the main window on the downhill road, which is mainly reflected in the female drivers, because they visit the main window more frequently and for a longer average fixation duration, while male drivers have a longer average visit duration.
There are two possible reasons for this conclusion.First, female drivers may be more conservative in driving style than male drivers, paying more attention to speed control on downhill roads, and thus paying more attention to the instrument panel.Second, female drivers may pay more attention to the environment and road conditions around the road, so they spend more time in different areas, resulting in more visits to the main window area and a longer average fixation duration.In the study, most of the male drivers are experienced drivers, so they may be calmer in the downhill section.Especially, after they are familiar with the road conditions in the middle and late periods, the surrounding attention will be reduced, and thus the visit time in the main view will be longer.
*p<0.1, **p<0.05,***p<0.01,n.s.: not significant Combined with the analysis of different experienced drivers, it can be concluded that female drivers' fixation behavior is more similar to that of novice drivers on a downhill road, while male drivers' fixation behavior is more similar to that of experienced drivers.

Analysis of pupil diameter
The Mann-Whitney U test was conducted on the pupil diameter of drivers with different experiences at the top and bottom of the slope, which was sorted out as shown in Table 5.It was found that novice drivers and experienced drivers had statistically significant differences in pupil diameter during the downhill.The difference is not only at the top of the hill but also at the bottom of the hill.Interestingly, the changes in pupil diameter during the downhill were more pronounced in novice drivers, as they exhibited a greater response compared to experienced drivers.According to psychological behavioral studies on changes in pupil diameter, pupil dilation is associated with encountering emotional stimuli such as anxiety and tension, as well as with tasks requiring more mental effort.
Based on the above analysis, the following conclusions can be drawn: 1. Novice drivers show more stress and attention when driving downhill.Therefore, whether at the top or bottom of the slope, the pupil diameter of the left and right eyes is larger than that of experienced drivers.
2. According to the test environment, two possible reasons are proposed for the phenomenon that novice drivers have a larger pupil diameter in their left eye.Firstly, the novice driver is required to complete a left turn before the downhill task, so more attention is required at the top of the hill to ensure that the left turn can be completed, resulting in a larger pupil diameter in the left eye.Secondly, after completing the downhill task, the driver needs to complete a right-angle left turn task immediately.The transition time between the two tasks is short, so the driver needs to pay attention to the left environment as soon as possible at the bottom of the slope, which results in the pupil diameter of the left eye being larger than that of the right eye.In such environments and stressful tasks, novice drivers are less able to handle, and are more stressed and attentive than their counterparts, and thus have larger pupil diameters.
The next step is to distinguish drivers' pupil diameter changes by gender in Table 6.Research shows that when male and female drivers are driving downhill, only at the top of the hill do female drivers have a noteworthy difference in the diameter of their right eye pupil.Specifically, female drivers had a larger pupil diameter in their right eye at the top of a hill.For this reason, we carried out the analysis in the natural environment.
First, considering Chinese driving regulations and customs, the driver's seat is situated on the left side of the vehicle, while driving in China is conducted on the right-hand side of the road.Women tend to be shorter in height and upper body length, so they need to pay more attention to whether the right side of the vehicle is safe and whether there are no violations, so they are more sensitive to the right side of the road.
Second, the driver needs to make a left turn before entering a downhill section.Female drivers are more cautious and sensitive to dangerous situations because of the large amount of green vegetation around them.Therefore, when the vehicle on the top of the hill keeps to the right and makes a left turn, female drivers will pay more attention to prevent the right tire from exceeding the safe range, so they focus more on the road conditions on the right.Therefore, the pupil diameter of female drivers' right eye was larger at the top of the hill, while there was no major difference in other conditions.
By comparing the pupil behavior of female drivers with that of male drivers with different experience levels, it is found that the pupil behavior of female drivers is more similar to the staring behavior of novice drivers, while the staring behavior of male drivers is more similar to that of experienced drivers.

Conclusion
From the perspective of fixation behavior, for drivers with different experiences on the downhill road, the main difference is that novice drivers pay more attention to the instrument panel and the main window.Specifically, the novice drivers have longer average fixation duration to the instrument panel, more visits to the main window, and longer access time.
The differences between male and female drivers in gaze behavior in the downhill section are mainly as follows: female drivers visit the instrument panel for a longer average time and more frequently compared to their counterparts; On the main window, female drivers had more average fixation time and visits, while male drivers had longer average visits to the main window.
In terms of pupil diameters, novice drivers have larger pupil diameters in both the left and right eyes at the top and bottom of slopes compared to the experienced drivers.The difference in pupil diameter of drivers of different genders is only apparent in the right eye at the top of the hill because it's larger for female drivers.
Based on the above results, it can be inferred that: the eye movement behavior of female drivers on downhill roads is similar to that of novice drivers, both of which pay more attention to information on the instrument panel.With the increase in experience, drivers will pay less attention to the instrument panel on the downhill road.The driver should control the speed better in the downhill process and pay less attention to the instrument panel and more attention to the main window.
However, due to the reasons of experimental conditions, the number of selected subjects is small, and there is no balance between experience and gender.In addition, due to inappropriate light and use, the data collection of eye movement equipment in the test of some drivers is not perfect, which leads to the inability to refer to the left and right visual field data for analysis in the study on the fixation behavior of the downhill road.

Figure 3 .
Figure 3.The AOIs set for eye movement analysis.As shown in Table2, for each AOI, the following eye movement indicators could be obtained: Average Fixation Duration (AFD), Fixation Count (FC), Average Visit Duration (AVD), Visit Count (VC), and First Fixation Duration (FFD), as well as the driver's pupil diameter.
[1] Zhang G，Application of Eye Movement Analysis Technology in Aviation Safety Electronic Technology 51 166-167 [2] Sabey B E and G C Staughton，INTERACTING ROLES OF ROAD ENVIRONMENT VEHICLE AND ROAD USER IN ACCIDENTS Ceste I Mostovi [3] Treat J R，Tri-level Study of the causes of the traffic accidents Research Findings 1 [4] Zhang X, X Qu, D Tao and H Xue，The association between sensation seeking and driving outcomes: A systematic review and meta-analysis Accident Analysis and Prevention 123 [5] Yang Y and Song S，Meta Analysis of the Correlation Between Driving Experiences and Driving Anger Industrial Safety and Environmental Protection 44 42-47 [6] Wu B, S Nishimura, Q Jin and Y Zhu,2020 Analyzing Eye-movements of Drivers with Different Experiences When Making a Turn 16th International Conference on Mobility, Sensing and Networking (MSN) [7] Shen N, Y Zhu, C Z Oroni and L Wang,2021 Analysis of Drivers' Eye movements with Different Experience and Genders in Straight-line Driving 19th IEEE International Conference on Dependable, Autonomic and Secure Computing 907-911 [8] Jorella L M, Y M Hwan and K Sungho，Stress-level and attentional functions of experienced and novice young adult drivers in intersection-related hazard situations International Journal of Industrial Ergonomics 90 [9] Nabatilan L B, F Aghazadeh, A D Nimbarte, C C Harvey and S K Chowdhury，Effect of driving experience on visual behavior and driving performance under different driving conditions Cognition, Technology & Work 14 [10] Zhao L and Hu J,2007 The eye tracking and driving behavior International Conference on Transportation Engineering 6 [11] Wu B, Y Zhu, S Nishimura and Q Jin，Analyzing the Effects of Driving Experience on Prebraking Behaviors Based on Data Collected by Motion Capture Devices IEEE Access 8 197337-197351 [12] Wu B, S Nishimura, Q Jin and Y Zhu,2019 Culture-based color influence paths analysis by using eye-tracking devices 2019 IEEE Intl Conf on Dependable, Autonomic and Secure Computing 66-71

Table 1 .
Details of subjects in the experiments.

Table 3 .
Results of Mann-Whitney U Test.

Table 5 .
Mann-Whitney U test of pupil diameter in drivers with different experience.

Table 4 .
Results of Mann-Whitney U Test.

Table 6 .
Mann-Whitney U test of pupil diameter in drivers with different gender.