How does the visual environment influence pedestrian physiological stress? Evidence from high-density cities using ambulatory technology and spatial machine learning

Revealing the phased impacts of the visual environment on physiological stress in outdoor environments can facilitate accurate and practical planning strategies towards healthy and sustainable living environments. This study adopted ambulatory sensing to monitor high spatiotemporal physiological stress from skin conductance level (SCL) and analyzed the association between the visual environment and the SCL in high-density environments. The multi-level visual environment was quantified from isovist and street view images. The most influential lags for each visual exposure factor were identified. Furthermore, multiple linear regression (MLR) and geographical random forest (GRF) were established to examine the effects of the lagged visual exposure factors on SCL. Particularly, the GRF can explore spatial nonstationary and complex relationships. The MLR (R2 = 0.466) suggests that exposure to trees, sky, and sign symbols can relieve stress. The GRF with 5 visual exposure factors can explain 87.4% of the spatial variance of SCL. This study confirms the effectiveness of monitoring pedestrians' stress in high-density cities and the phased and non-instantaneous impacts of the visual environment. The results have practical implications in urban design at both district and site levels for a sustainable and psychologically friendly urban environment.