## 4 Results and Discussions
### Impact Factor Analysis
#### 4.3.1 The Effect of Individual Characteristic Factors on Cognitive Load
It is evident from the figure that drivers in Vehicle Type 1 have a relatively higher eye height, with most sample points distributed above 0.7, while drivers in Vehicle Types 2 and 3 have a lower eye height, which may be related to the design of the driver's seat. When the eye height approaches 0.8, it negatively impacts the cognitive load, with Brand 1 showing a stronger negative correlation between blind spot image height and cognitive load. This could be attributed to its shorter vertical central display screen and smaller proportion of blind spot image display, making eye height have a more significant impact on the driver's ability to capture information. Conversely, when the eye height is lower or higher, the cognitive load positively correlates with eye height, with Brands 1 and 3 exhibiting stronger positive correlations than Brand 2, suggesting that a longer vertical height of the central display screen is more likely to induce changes in the driver's cognitive load. As depicted in Figure 12, the SHAP values for all brands under the right lane change scenario are concentrated between \(-\)0.004 and 0.002, indicating a minimal influence of vehicle type on driver cognitive load in this scenario. In contrast, Brand 2 is more likely to reduce driver cognitive load during left lane changes compared to Brand 3, as Brand 2 provides more accessible information when a blind spot appears on the left side during left lane changes. This finding is not contradictory to previous discussions on lane change directions, since the spatial overlap between the blind spot image and the left rearview mirror during left lane changes is low, and they do not share the same line of sight. Figure 13 illustrates that Position 3 positively affects driver cognitive load under low traffic flow but negatively impacts it under high traffic flow. This is speculated to be due to Position 3's blind spot image being prone to obstruction. Under low traffic flow, drivers can easily observe the blind spot image in time, but under high traffic flow, its vulnerability to obstruction hinders timely observation, leading to increased driver cognitive load. Figure 11: Height–vehicle type dependence scatter plot. Figure 12: Road Type–Vehicle type dependence scatter plot. Figure 13: Traffic flow–location dependence scatter plot. Figure 14 shows a stark contrast in Position 3's impact based on the direction of lane changes. During right lane changes, the SHAP values are concentrated between \(-0.015\) and \(-0.02\), indicating an increased likelihood of cognitive load. In contrast, during left lane changes, the SHAP values are between 0.005 and 0.02, suggesting a reduced cognitive load. This may be attributed to the ease of capturing information in Position 3 when simultaneously observing the rearview mirror and blind spot during left lane changes, which involves a larger scanning range. Figure 15 demonstrates that Position 2, with a larger distance between the blind spot and the central display screen, has SHAP values concentrated above 0, while Positions 1 and 3, with shorter distances, have SHAP values concentrated below 0. This suggests that Position 2 is more likely to effectively reduce drivers' cognitive load compared to Positions 1 and 3, which is consistent with previous analyses.