Exposure to natural environments can improve the functioning of working memory, attentional control, and cognitive flexibility

Stevenson, M., Schilhab, T., & Bentsen, P. (2018). Attention Restoration Theory II: A systematic review to clarify attention processes affected by exposure to natural environments. Journal Of Toxicology And Environmental Health, Part B, 21, 227-268. https://doi.org/http://dx.doi.org/10.1080/10937404.2018.1505571

This paper presents an updated systematic review of the literature focusing on attention processes affected by exposure to natural environments. Results of an earlier review conducted by Ohly and colleagues in 2013 raised awareness of ambiguity surrounding directed attention and concerns about how cognitive restoration was tested. The primary aim of this current review was to expand understanding of directed attention and to remove the ambiguity uncovered through the previous review.  This review also explored the influence of assessment measures and procedures on the findings of attention restoration research.

Attention Restoration Theory (ART) is based on the understanding that the ability to concentrate – or voluntarily direct attention -- is a limited ability. After a period of directed attention, people begin to experience "attention fatigue" and are then less effective in performing cognitive tasks. According to ART, exposure to certain types of environments (referred to as “restorative environments”) can lead to improved cognitive performance by restoring a limited cognitive resource. Natural environments tend to be restorative in this regard.

This updated systematic review included a subset of the studies in the Ohly et al. review, along with ART studies published between July 2013 and November 2017. While there were only 52 months during this time period, there were considerably more ART studies published after July 2013 than before. All of the studies included in this review were experimental or quasi-experimental, used an objective measure of cognitive performance, and included exposure to nature. The combined studies yielded 49 individual outcome measures, which were then grouped into 8 cognitive domains: working memory, attentional control, visual attention processes, vigilance, cognitive flexibility, impulse control, processing speed, and other emerging domains. The type of exposure to the natural environment experienced by study participants was broad, including both passive viewing of nature scenes on a computer screen and active outdoor engagement with nature in real environments. Some of the studies included a fatigue-inducing task prior to exposure to nature; others did not. Fatigue-inducing tasks are thought to create more "restoration potential."

Combining the results of 46 studies showed that exposure to a natural environment improved performance in the domains of working memory, attentional control, and cognitive flexibility. Improved performance ranged from low to moderate level effects. Actual exposure to natural environments significantly influenced effect sizes of all three domains compared to virtual exposures. Differences in the typical lengths of exposure may have influenced these effects. Exposure to actual environments tended to be considerably longer than exposure to virtual environments. There were no clear findings on how participants' restoration potential affected the cognitive restoration outcomes.

This updated literature review and meta-analysis provides evidence that certain cognitive processes (working memory, cognitive flexibility and attentional control) may be improved after exposure to nature. While it's not possible to quantify how much attention restoration occurs in each of these areas, it is possible to identify ways in which directed attention is restored during tasks within these cognitive domains. A Directed Attention framework is presented as a possible resource for further ART research. Other recommendations for future studies are offered as well.

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