Don't try to tell Manbir Sodhi that using a hands-free cell phone does not affect driving. He knows better and has the data to prove it. Sodhi, an industrial engineer at the University of Rhode Island, and his colleague Jerry Cohen, a psychologist, mounted eye-tracking devices on the heads of a group of volunteers before they headed into traffic. Usually, a driver's eyes flit about, wandering from road to mirror to traffic and back. For a simple task, such as reading the odometer, the eyes track downward and to the left, pause briefly, and return to the road. But give a driver a mentally demanding tasksuch as reciting a list from memory while talking on a hands-free deviceand that pattern of scanning goes away. Instead, there is virtually no eye movement: The driver just stares at the bumper of the car ahead or at the median. The problem is not the cell phone per se. "It's the complex cognitive tasks that affect the driver," says Sodhi. The solution, he suggests, is a dose of common sense: Avoid any demanding activity, whether negotiating with the boss or resetting the radio, when your full attention should be on driving.