Ongoing research is examining ways in which the incidence of DAF can be decreased, and suggests that exposure to the natural environment may aid in the reduction of DAF symptoms. A number of researchers have investigated Directed Attention Fatigue recently. Leading contributors include Rachel and Stephen Kaplan, environmental psychologists at the University of Michigan. Rachel and Stephen Kaplan are credited with much of the research relating to Directed Attention Fatigue and were the first to discover that extended periods of focused attention can lead to DAF. Their research suggests that Directed Attention Fatigue can be alleviated with exposure to nature. Together, the Kaplans devised the Attention restoration theory (ART), which states that a person is better able to maintain focused directed attention after spending time in the natural environment.