Chatting on the cell phone while driving can be hazardous, even when you use a hands-off kit. And it is not because of radiation levels either--the human brain just seems to lack sufficient RAM.
A study published in the NeuroImage journal tried to gauge brain activity while people performed one complex task, and a combination two such tasks, showed that brain activity does not increase with the tasks.
Instead, it remains fairly constant, and less attention is devoted to each task, resulting in a lowering of performance.
The tasks chosen were a language skill, and mentally rotating objects in space. These are carried in the temporal lobe and the parietal lobe respectively, which are also the two areas of the brain that come into play when talking, and driving.
Volunteers for the study managed to maintain accuracy, but their speed dropped off, which showed Dr Marcel Just, who led the research, that there is only so much a human can do at one time.
"You can't just keep piping new things through," Just, a co-director of the Center for Cognitive Brain Imaging at Carnegie Mellon University, told the New York Times.
And since humans, unlike computers, do not enjoy the benefits of Moore's Law, we're probably going to have to equip our cars with computing capabilities.
On the positive side, conversing with a passenger is less dangerous than chatting on the cell phone, as passengers will probably be able to see tricky situations developing and know when to keep quiet, whereas the person on the other end of a line will just continue to talk.