the importance of nature...to the mind

I just saw a report on a study that showing that time spent moving around in nature, observing nature, improved the subjects' attention and focus by up to 20%. Observing pictures of nature had a similar effect. However walking around in an urban setting had no such effect. Nature speaks to a primal part of our mind that understands it directly, often without words. Does any one besides me think the current incidence of ADD might have something to do with nature deficit in children?