Nonlinear effect of urban visual environment on residents’ psychological perception——An analysis based on XGBoost and SHAP interpretation model

Mental health issues have become a significant factor affecting residents’ lives and societal development. Studying the relationships between the urban visual environments and residents’ psychological perceptions can significantly improve residents’ mental health. This study employed the DeepLab-v3 deep learning model via semantic segmentation on street view images of the main urban area of Lanzhou, China to obtain eight urban visual environment indicators. A generative adversarial model was used to score the psychological perceptions of street-view images, and six psychological perception datasets were then obtained using a random forest model. Using the XGBoost and SHAP models, this study analyzed the key indicators, impact mechanisms, and optimal thresholds of the urban visual environment on psychological perception. This study identified comprehensive psychological perceptions and highlighted the most crucial indicators. The results showed that sky openness, green view index, sidewalk ratio, and transportation facilities ratio were the core indicators of the urban visual environment affecting comprehensive psychological perception. A nonlinear relationship exists between urban visual environments and psychological perceptions. The thresholds for the green view index to enhance safety and beauty perception are 0–0.1 and 0.1–0.2, respectively. The thresholds for the sidewalk ratio to enhance safety perception and suppress boredom perception were 0–0.019 and 0–0.0125, respectively. The thresholds for sky openness to enhance wealth, vitality, and beauty perceptions are 0.5–0.7, 0.45–0.7, and 0.4–0.6, respectively. The threshold for the pedestrian ratio to enhance vitality perception was 0–0.001. The thresholds for the transportation facilities ratio to suppress depression and boredom perceptions were 0–0.01. The optimal thresholds for positively impacting comprehensive psychological perception were 0.5–0.6 for sky openness, 0–0.0125 for sidewalk ratio, and 0–0.01 for transportation facilities ratio, respectively. These findings provide theoretical support for incorporating psychological perception needs and green view index into planning and management. Additionally, they provide threshold recommendations for urban street design guidelines.