" The results of the most recent such study were published in Psychological Science at the end of 2008. A team of University of Michigan researchers, led by psychologist Marc Berman, recruited some three dozen people and subjected them to a rigorous, and mentally fatiguing, series of tests designed to measure the capacity of their working memory and their ability to exert top-down control over their attention. The subjects were then divided into two groups. Half of them spent about an hour walking through a secluded woodland park, and the other half spent an equal amount of time walking along busy down town streets. Both groups then took the tests a second time. Spending time in the park, the researchers found, “significantly improved” people’s performance on the cognitive tests, indicating a substantial increase in attentiveness. Walking in the city, by contrast, led to no improvement in test results.
The researchers then conducted a similar experiment with another set of people. Rather than taking walks between the rounds of testing, these subjects simply looked at photographs of either calm rural scenes or busy urban ones. The results were the same. The people who looked at pictures of nature scenes were able to exert substantially stronger control over their attention, while those who looked at city scenes showed no improvement in their attentiveness. “In sum,” concluded the researchers, “simple and brief interactions with nature can produce marked increases in cognitive control.” Spending time in the natural world seems to be of “vital importance” to “effective cognitive functioning. "

― Nicholas Carr , The Shallows: What the Internet Is Doing to Our Brains