I've heard this described as focused vs diffuse mode thinking. Focus on a problem for some time then move on to something else to allow the diffuse mode to continue the work.

Salvador Dali used this method by sitting in a chair while holding a key in his hand. He would then try to nap in that position. When the key would fall from his hand onto a plate he put next to the chair, the sound would wake him up and he would often have fresh ideas about his problem.