They may also be distracted to the point that their engaged brains no longer process much of the information that falls on their retinas, which leads to slower reaction times and other driving problems.

Image Credit... Stuart Bradford

At the University of Utah, Dr. Strayer and his colleagues use driving simulators to study the effects of cellphone conversations. A simulator’s interior looks like that of a Ford Crown Victoria, and a computer allows researchers to control driving conditions. Study participants are asked to drive under a variety of conditions: while talking on a hand-held phone or a hands-free one, while chatting with a friend in the next seat, and even after consuming enough alcohol to make them legally drunk.

While in the simulator, drivers are asked to complete simple tasks, like driving for several miles along a highway and finding a particular exit, or navigating local streets where they must brake for traffic lights, change lanes and watch for pedestrians. How fast they drive, how well they stay in their lane, driving speed and eye movement are closely monitored.

The Utah researchers have also placed electrodes on participants’ scalps to gauge how they process information. Similar studies, using brain imaging, have been done at Carnegie Mellon.

The studies show that cellphone conversations are highly distracting compared with other speaking and listening activities in the car.

One might think that listening to talk radio or an audio book would degrade driving skill; it does not. (A quiz after the driving test confirmed that the drivers were really paying attention to the programs.)

Likewise, it is easy to equate talking to a friend on a cellphone with talking to a friend in the passenger seat. But a December report in The Journal of Experimental Psychology: Applied debunked that notion. Utah researchers put 96 drivers in a simulator, instructing them to drive several miles down the road and pull off at a rest stop. Sometimes the drivers were talking on a hands-free cell phone, and sometimes they were chatting with a friend in the next seat.