Quantifying threshold effects of physiological health benefits in greenspace exposure

Abstract

Despite the existence of discussions regarding the dose-response relationship between greenspace exposure (GE) and physiological health benefits (PHB), the threshold effects of GE have not been adequately addressed. Here we present the hypothesis of a PHB threshold model for GE, which introduces the concepts of efficiency threshold and benefits threshold and incorporates calculations of the area under the curve of the ground (AUCg) and the area under the curve of the increase (AUCi). To test the validity of this model, a pilot study was conducted over four days in a typical greenspace during the spring and summer seasons. Electroencephalogram was continuously measured as the physiological indicator, while meteorological and demographic factors were collected. The results suggest that (1) the PHB threshold model is applicable across different experimental groups and seasons, while also being influenced by multiple factors (such as meteorological factors). (2) Case study had shown that the efficiency threshold can be reached within 4 min and the benefit threshold within 12 min, demonstrating that the thresholds for GE can be achieved within a short period of time. Moreover, the mean AUCg and AUCi were lower in summer compared to spring, and meteorological factors such as lower heat stress index were found to be associated with higher PHB. (3) Besides, the proposed conceptual framework based on the “reality-virtual” dimension and the “subject-object” perspective needs further investigation to explore GE thresholds. The model provides insights into the optimal and maximum PHB that can be achieved through GE and also enriches the theoretical basis of research on GE.