Restorative Potential and Working Memory Capacity of Exposure to Vegetation in Indoor Built Environments

Abstract

This research seeks to understand how natural elements – specifically, vegetation in the indoor environment - influence people’s ability to restore attention and working memory capacity. Previous research demonstrates the benefits of nature on human beings in various ways. For instance, numerous studies show the positive effects of nature on stress reduction (Hartig, Mang, & Evans, 1991; Ulrich et al., 1991) and attention restoration (Staats, Kieviet, & Hartig, 2003). However, most of these studies focus on the effect of nature in outdoor settings. Relatively few studies focus on the presence of natural elements indoors. This is an important gap in the literature because people spend most of their time indoors. A few studies on indoor environments have focused on the benefits of vegetation (Kiyota, 2009; Raanaas, Patil, & Hartig, 2010; Shibata & Suzuki, 2001, 2002, 2004); however, they emphasized the effects of the vegetation and did not delve into the impact of the amount of vegetation on these effects.In response, this research explores how people perceive and are influenced by vegetation, the built environment, and vegetation within the built environment. To this end it employs surveys, tasks, and electroencephalography (EEG). EEG has been widely used to investigate people’s attention and restoration. The increased and extreme changes of alpha and theta activity measured by EEG (Aftanas & Golocheikine, 2001; Basar et al., 2001; Chen et al., 2020; Grassini et al., 2019; Jacobs & Friedman, 2004) are widely accepted as a neurophysiological indicator of attention and restoration. During the experiments in this study, participants were seated in designated spaces for EEG recordings, and then presented with a series of photos of various built environments with nature elements. After each EEG recording, they were asked to answer a survey (PRS-11; Pasini et al, 2014) about the spaces and images that they observed, and then perform a cognitive task (the backward digit span task). The results revealed that indirect and symbolic visual contact with vegetation had a significant association with restorative potential and working memory capacity. Furthermore, varied levels of exposure to vegetation showed significant quantitative impact on peoples’ restoration and attention. Qualitative findings from perceived restorativeness scores (PRS-11), backward digit span task scores, and EEG alpha and theta relative power spectrum density (PSD) suggest that indoor vegetation can benefit peoples’ well-being and productivity, by increasing restoration and working memory capacity. We discovered that when there is 12% or more vegetation in an indoor space, the restorative potential was closely equivalent to full nature. Also, we found that working memory capacity is most effective in the range of 24 - 36% vegetation in indoor built environment settings. Lastly, in situ environment (indirect visual contact with vegetation) showed stronger beta relative PSD compared to image viewing (symbolic visual contact with vegetation). This dissertation seeks to establish guidelines for reference by the designers and decision-makers of urban built environments to achieve the maximum positive benefits of biophilic design, and more specifically, to promote the physical and mental health benefits of vegetation for dwellers.