For years, psychologists who study driving and attention have argued that switching to "hands free" is not a real solution to the hazards caused by yakking on the mobile in the car. "The impairments aren't because your hands aren't on the wheel. It's because your mind isn't the road," says David Strayer, professor of psychology at the University of Utah, whose research has found driving while talking on a cellphone to be as dangerous as driving drunk.
Now neuroscience is showing your mind literally isn't on the road. The overtaxed driver's poor brain doesn't distinguish between a conversation that takes place on an iPhone or a Bluetooth headset. In both cases, the chatting driver is distracted, putting herself, her passengers, other drivers, bicyclists and pedestrians at risk.
Say there's an 18-wheeler to your right, an R.V. to your left, and suddenly a call comes in from that motormouth client in Kansas City. As the client's voice starts buzzing in your ear, the activity in the parts of your brain keeping your car in your lane declines.
"Forty percent of your attention is drawn away when you're on the phone," says Marcel Just, a psychologist who directs Carnegie Mellon's Center for Cognitive Brain Imaging. That goes for you too, Mr. Multitasker.
In one experiment at the Center for Cognitive Brain Imaging, a test subject lies down inside a magnetic resonance imaging (MRI) machine, and uses a simulator to drive a car along a winding road, like playing a video game. While steering, the driver hears a voice in his earphones making statements, and has to decide whether they're true or false, while continuing to pilot the car. Listening and driving make demands on different parts of the brain. Yet, apparently, there are finite resources to go around. "You have two moderately automatic tasks, executing concurrently and drawing on the same resource pool," explains Just.
When the voice in the headphones starts talking, researchers can see the parts of the brain devoted to driving get distracted. One part of the brain that's important for driving is the parietal lobe, which, for instance, helps a driver make the car's trajectory fit the curvature of the road. "There is much less activity if someone is talking to you, so you take the curve less precisely and less well," says Just. A similar reduction in activity occurs in the visual cortex, which helps a driver analyze how fast things are going by and see what's coming up ahead. When that voice chimes in on the headphones, "your analysis of the visual scene is less thorough. You'd be more likely to miss a sign, or not as quick to read a complex sign," says Just.