Hands-free call not safer

You know the shot: Seen from above, the hero (or villain) is hurtling down the freeway, top down, one hand on the wheel and the other clutching a cell phone to his ear. It's Hollywood's image of how deals are made, dates are broken and gossip is shared, at 104km per hour.

That shot will now be history. California motorists - as well as those in Washington state, where a similar law was recently passed - will be prohibited from talking on hand-held cellular phones while driving.

Most, however, will likely continue their wireless business using headsets, speakers or other hands-free devices.

California Governor Arnold Schwarzenegger says the new law will reduce accidents. "Getting people's hands off their phones and onto their steering wheels will save lives and make California's roads safer," he said earlier this month.

That, however, is not what the research finds. Scientists say that when mixing cell phones and driving, the number of hands available for the tasks is not the limiting factor.

Instead, it's a driver's attention and processing capacity. These are often stretched beyond safe limits when someone juggles the complex tasks of negotiating traffic and conversing with another remotely. "There are limits to how much we can multitask, and that combination of cell phone and driving exceeds the limits," says David Strayer, a University of Utah psychologist who has found that by many measures, drivers yakking on cell phones are more dangerous behind the wheel than those who are drunk, whether the conversation is carried on by handset or headset.

In a 2005 study, published in the journal Human Factors, Strayer put 41 adult drivers through four sessions in a simulator, re-creating realistic driving conditions along a 88km stretch of freeway.

Slow response

Over three days, the subjects took the wheel in various ways: sober and off-the-phone; legally under the influence of orange-juice-and-vodka cocktails; while talking with a research assistant by hand-held cell phone; and chatting over a hands-free cell phone device. The result: Compared with drivers exceeding the legal blood alcohol limit, users of cell phones - hand-held or hands-free - reacted 18 per cent more slowly to braking by the car in front and were more likely to be in a rear-end collision.

What's more, the talkers seemed to compensate for their slowed response time by falling farther behind the car in front - a pattern likely to slow traffic and exacerbate congestion.

"And you don't get any better with practice," Strayer adds. In his lab, subjects who reported they often use a cell phone when driving "show every bit as much impairment" than those who do so infrequently.

Although no studies looked at the safety of cell phone chatter by drivers of manual-transmission cars, Strayer acknowledged that stick-shifters may reap immediate safety improvements by switching to a hands-free device for cell phone calls.

Marcel Just, a neuroscientist at Carnegie Mellon University in Pittsburgh, conducted brain imaging of 29 young adults to gauge the cognitive demands of simultaneously driving and listening. Lying in a functional magnetic resonance imaging machine, the subjects steered a simulated car down a winding road.

The study, published in April in the journal Brain Research, found that subjects who were allowed to navigate undisturbed showed robust activity in the brain's parietal lobe, a region long associated with spatial sense, distance calculations and judgments that require a person to calculate his whereabouts in a broader physical environment. When the task of listening to the sentences was added, blood flowed to different parts of the brain generally involved in the processing of language. As those language areas came alive, activity in the parietal lobe declined by almost 40 per cent.

Brain traffic

While engaged in the listening task, drivers simultaneously listening to sentences veered off the road and onto the shoulder almost 50 per cent more often than those allowed to focus uniquely on driving.

"Before we ever ran any of these studies, some thought, 'Well, these were two independent tasks, performed by two independent brain areas'," Just says. But certain brain regions are very likely critical to both tasks, he adds, and the flow of traffic in the multitasking brain appears to have slowed as a result. "It can only do so much at a time."

If listening is demanding, talking appears to be even harder, especially when the other person isn't in the car. In a study published in June in the journal Experimental Psychology, University of South Carolina psychologist Amit Almor put 47 subjects in a surround-sound console and had them detect visual shapes on a monitor or use a mouse to track a moving target on a screen.

When the subjects listened to prerecorded narratives, their attention to the visual task before them dipped significantly. But as they then answered questions about what they'd seen, or even just prepared to speak, their attention to the task on the screen didn't dip - it plummeted.

"It has not anything to do with manipulating the phone or holding it," Almor says. "It's the attentional demands of conversation that matters." Those demands shoot up, he adds, when drivers expect to contribute to conversations.

Some researchers fear that the new law may cause more traffic accidents, not fewer, because they envision more distractions for many motorists.

- Los Angeles Times-Washington Post News Service