Cell Phones and Driving

Well, Mr. Scientist, you are onto something. The human mind has limitations. (duh statement). When our minds reach saturation (different for each person), it begins to ignore or filter out what it thinks is non-essential. I think you are right about our abilities to preserve our vested interest (hobby) while driving. Get too involved in a conversation and certain things can "take a backseat".
I read a story from Col. Robin Olds. He was leading a flight of F-4's in Vietnam. As they got close to the target, he and his other pilots started turning off certain equipment. To keep their minds focused on the objective , they turned off some of the distracting sensory inputs. (IFF warnings, SAM warning, etc)