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The less city you can see through the trees, the better for your brain, new research suggests.

Last month we explained how parks can restore much of the mental fatigue imposed on our brains by the busy city. The psychological evidence for this concept, known as the "attention restoration theory," is quite clear. What would be great to know, as I noted at the end of that post, is precisely how many trees it takes to recover the cognitive strains of urban life.

Well sometimes the gods of semi-obscure-hybrid-behavior-nature-academic-publications listen to your calls. In an upcoming issue of the journal Landscape and Urban Planning, a group of Finnish researchers describe recent work that just so happens to address our exact curiosity. They conclude that restoration reaches peak potential when every inch of the city — which they term the "urban matrix" — escapes our vision:

Our results showed that perceived restorativeness in urban forests was strongly affected by closure of view to the urban matrix through the forest vegetation. This means that perceived restorativeness was higher inside the forest with a closed (i.e. no) view to the urban matrix as compared to semi-closed and open views.

For the study, the researchers identified nine patches of boreal forest in greater Helsinki that bordered the "urban matrix" — in this case either a housing development (some single-family units, some flats) or an urban road with a steady flow of traffic. Within each nature site the researchers found three viewing points that offered a clear open look at the urban matrix (below, A and B), a partial glimpse (C), or no view of the road or homes at all (D).

Next, they recruited 66 people of all ages from the metropolitan area. Each study participant visited two of the viewing points at one of the nature patches and completed a questionnaire on the restorative potential of that particular site. The results followed a clear linear pattern: as one's view of the urban matrix increased, the perceived cognitive restorativeness of the park decreased. (There was no statistical difference between a view of the road and that of the homes.)

The work lacks a bit of force for its methods. While the researchers focused on "attention restoration theory," they provided only a questionnaire of perceived restorativeness as opposed to direct cognitive tests of attention. The questionnaire they used has been validated in previous empirical settings, but it's certainly a weaker measurement than, say, the "backwards digit-span task" used by other psychologists studying urban parks.

Still the findings provide urban planners with some nice food for thought. The most intriguing conclusion to be drawn here is that the size of an urban park isn't nearly as important as the density of its vegetation. Even when a nature site borders an urban road or housing development, it can function as a restorative place so long as it offers easy access to a dense interior. In other words, the ultimate goal is not to see the city for the trees.

Image via Hauru, K., et al. Closure of view to the urban matrix has positive effects on perceived restorativeness in urban forests in Helsinki, Finland. Landscape Urban Plan. (2012), http://dx.doi.org/10.1016/j.landurbplan.2012.07.002.

Photo credit: drpnncpptak /Shutterstock

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