## 4 Results and Discussions
### Impact Factor Analysis  
#### 4.3.1 The Effect of Individual Characteristic Factors on Cognitive Load  
The average absolute value of the SHAP value indicates the degree of influence of that feature on cognitive load, with a larger value suggesting a greater impact on cognitive load. A feature density scatter plot is plotted as shown in Figures 9 and 10:  
As depicted in the figure, each row represents a feature factor. The horizontal axis corresponds to the SHAP value for each sample of that factor. A positive SHAP value indicates a positive impact on the time buffer, which translates to reduced cognitive load; a negative SHAP value indicates the opposite. The color of the sample points indicates the magnitude of the feature itself, with redder colors representing higher values and bluer colors representing lower values. The analysis of the results is as follows:  
1. Vehicle Type:  
Most points for the vehicle type feature fall near SHAP = 0, indicating a minimal impact on cognitive load. The blind spot imaging design of Brand 3 has a negative impact on cognitive load, potentially due to the excessively long vertical length of the central display screen. 2. Blind Spot Design Features:  
Blind spot design is divided into two parts. Firstly, the position of the blind spot image, represented by the distance and location indicators, shows a positive correlation between distance and time buffer, suggesting that a shorter distance between the blind spot and the  
Figure 10: Feature density scatter plots for Experiment 2. Figure 9: Feature density scatter plots for Experiment 1.  
steering wheel center results in a lower cognitive load within a certain range. This could be attributed to a shorter scanning path for drivers to quickly capture the blind spot image and retrieve information, resulting in a lower cognitive load. The correlation between location and time buffer is significant, with Location 2 positively correlated and Location 1 negatively correlated, indicating that Location 2 reduces driver cognitive load compared to Location 1, consistent with previous analysis. The SHAP values for Location 3 are evenly distributed on both sides of 0, indicating no significant impact on driver cognitive load. Secondly, the size of the blind spot image and its proportion of the central display screen are determined by the vehicle type, which, according to Analysis (1), has an insignificant impact on cognitive load. However, Brand 3 displays different blind spot images during left and right lane changes, necessitating further analysis. Environmental Factors:  
Overall, traffic environmental factors align with BLOR results: the traffic flow is negatively correlated with the time buffer, indicating increased cognitive load with higher traffic flow; left lane changes show a significant positive correlation with the time buffer, while right lane changes show the opposite, suggesting reduced cognitive load during left lane changes compared to right lane changes; expressways positively correlate with the time buffer, while urban roads have limited correlation with cognitive load, indicating a potential reduction in driver cognitive load on expressways. Driver Characteristics:  
Sample points representing higher eye heights are concentrated near 0, indicating minimal impact on cognitive load when drivers have higher eye heights. Conversely, lower eye heights significantly impact drivers' cognitive load. Interaction Effects  
To calculate the SHAP values under the interaction of multiple variables, we focus on analyzing the combined influence of blind spot image features and other factors. As shown in Figure 11, the horizontal axis represents the eye height, and the vertical axis represents the SHAP value for eye height. The color of the sample points indicates three different vehicle brands, where the vehicle type can reflect characteristics such as the size of the blind spot image design and its proportion on the central display screen.