I thought this link was interesting. Psychologists have determined that a small subset of people, about 2.5% of the general population, are capable of maintaining their driving efficiency while talking on a cellphone. The authors of the story seem convinced that it is a superior multitasking ability that allows the 2.5% to accomplish this, but I have an opposite theory. I think that 2.5% of people can drive while on the cellphone because they cannot multitask well.
I think I am a member of the 2.5% subgroup who can drive and talk on the phone at the same time. My loved ones will tell me I shouldn't anyway, and I have no evidence to back up this claim, but there it is nonetheless. Here is why I think so. Anyone who has talked to me while I am driving probably is aware of and annoyed by the fact that I periodically cease responding or paying attention to the conversation. Like completely stop paying attention; I might as well put the phone down on the seat.
The person on the phone with me might not appreciate what is causing the lack of attention, but it is obvious to me: it happens when any temporary situation arises on the road that complicates the driving situation at all. If another driver is being unpredictable and I am watching them, or I am making a turn or changing lanes, looking for a landmark, anything. As soon as I am doing something beyond just driving in a straight line at constant speed I cease functioning in the phone conversation precisely because I cannot multitask. When the situation on the road resolves, then my attention can shift back to the conversation.
The authors of the above study could easily test this. All they would have to do is measure conversational engagement of the driver at different parts of the course. If my theory is correct, driver engagement in the phone conversation should plummet when the driver is encountering some variations in the obstacle course.