n 1984, a researcher named Roger Zurich noticed a curious pattern among patients who were recovering from gallbladder surgery at a suburban hospital in Pennsylvania. Those who had been given rooms overlooking a small stand of deciduous trees were being discharged almost a day sooner, on average, than those in otherwise identical rooms whose windows faced a wall. The results seemed at once obvious—of course a leafy tableau is more therapeutic than a drab brick wall—and puzzling. Whatever curative property the trees possessed, how were they casting it through a pane of glass?
In the late nineteenth century, the pioneering psychologist and philosopher William James proposed a distinction between “voluntary” and “involuntary” attention. When you cross a busy intersection or pore over a spreadsheet, you are depleting finite reserves of voluntary, directed attention. The antidote is not, as one might first guess, to sit quietly in a darkened room. “The environment has to have some kind of stimulation to activate your involuntary attention—your fascination,” Berman said. Urban environments can certainly elicit involuntary attention (honking horns in Times Square), but they do so in a harsh, peremptory way that requires voluntary attention to override. Natural environments, on the other hand, provide what Berman calls “softly fascinating stimulation.” Your eye is captured by the shape of a branch, a ripple in the water; your mind follows.
As a doctoral student at the University of Michigan, a decade ago, Berman conducted a study in which he sent volunteers on a fifty-minute walk through either an arboretum or city streets, then gave his subjects a cognitive assessment. Those who had taken the nature walk performed about twenty per cent better than their counterparts on tests of memory and attention. They also tended to be in a better mood, although that didn’t affect their scores. “What we’re finding is that you don’t have to like the interaction with nature to get the benefits,” Berman said. Some of the walks took place in June, whereas others took place in January; most people didn’t particularly enjoy trudging through the harsh Michigan winter, but their scores jumped just as much as in the summer trials. Not surprisingly, those whose directed attention is most depleted seem to get the biggest benefits: an end-of-workday nature romp probably packs a greater restorative punch than one first thing in the morning, and the boost is five times bigger in people who have been diagnosed with clinical depression.