Effects of underground green walls on human cognitive performance and physiological responses: A virtual reality simulation study

Urban densification has made underground retail, transit and workspace indispensable, yet their absence of daylight and monotonous scenery compromise thermal comfort and heighten psychological stress. Whether vertical greening offsets these deficits remains quantitatively unresolved. In a climate-controlled underground chamber, 72 university students were randomly assigned to 5 %, 15 % or 25 % green-view-index (GVI) walls. Thermal comfort vote (TCV), 4 neurobehavioural metrics and physiological strain (blood pressure [BP], heart rate [HR], oxyhemoglobin saturation [SpO 2 ], eardrum temperature [ET]) were recorded pre- and post-exposure. Compared to the pre-intervention phase, TCV increased monotonically with GVI, reaching significance only at 25 % (+0.25, P < 0.05). The same dose yielded the largest reductions in reaction time (η²p = 0.31–0.38) and significant decreases in systolic BP (−1.91 mmHg) and HR (−1.98 bpm); smaller effects were observed at 5 % and 15 % (η²p < 0.14; BP −0.33/−0.82 mmHg; HR −0.11/−0.35 bpm). Our study establishes dose-response evidence that increasing green-wall density in underground environments systematically enhances thermal comfort and accelerates cognitive restoration while attenuating physiological stress, offering actionable thresholds for biophilic design in underground spaces.