It's not the cell phone -- it's the brain

Drivers overloaded, researchers warn

Science

July 22, 2005|By Mariana Minaya | By Mariana Minaya,Sun Staff

Think twice about answering your cell phone while you're behind the wheel -- even if it's a hands-free model. Scientists now say there's evidence our brains can't concentrate on a phone conversation and driving at the same time.

A groundbreaking study published last week in the British Journal of Medicine shows that drivers who talk on a cell phone are four times as likely as nonusers to have an accident that sends them to the hospital -- regardless of the type of phone they use.

"Human beings are able to hold so many things in our mind at once, and apparently a phone conversation is a significant source of distraction. It makes it difficult for us to focus fully on the driving task," said Anne McCartt, co-author of the study and vice president for research at the U.S. Insurance Institute for Highway Safety.

The National Highway Traffic Safety Administration estimates up to 4 million crashes annually are related to some kind of driver inattention, including cell phone use.

The American Automobile Association agrees that cell phone conversations, regardless of the type of phone, can be a distraction to drivers, said Amanda Knittle, a spokeswoman for its Mid-Atlantic branch.

But why is talking on the phone -- even if it's hands-free -- so dangerous? Drivers have talked to their passengers and driven with blaring radios for years without the kinds of risk associated with cell phones.

A Johns Hopkins University psychologist thinks he has the answer. His research shows that the brain can fully concentrate on either a visual task such as driving, or an audio task like listening to a cell phone conversation -- but not both at once.

Steven Yantis said a cell phone conversation is riskier than talking to a passenger because the person on the other end of the line may not know you're driving. The person on the cell phone can't see that you're approaching a difficult intersection. And unlike the radio, a cell phone conversation demands an immediate response.

"There are real limitations in our ability to handle multiple sources of information, even though most of the time we get by," said Yantis, who used magnetic resonance imaging (MRI) scanners to measure the brain's ability to process visual and auditory information.

"Most of us have had a close one. All it takes is for one of those events to occur at the wrong time for you to be in an accident," he said.

The cell phone study conducted in the Australian city of Perth by the U.S. Insurance Institute for Highway Safety involved about 500 mildly to moderately injured motorists who agreed to give researchers access to copies of their phone bills.

Three major Australian cell phone companies cooperated. Researchers tried to conduct the study here but said U.S. wireless carriers were unwilling to release customers' records under any circumstances.

The scientists checked cell phone use in the hours leading to the accidents, as well as at different times during the previous week. It was the first study of its kind to use real drivers and real phone records at the time of a crash, compared with the driving simulators used in most earlier studies. And it confirmed earlier findings that showed a fourfold increase in accident risk.

The Hopkins study, published in The Journal of Neuroscience, used MRI scanners to examine brain activity in 11 participants. They watched a screen displaying a rapidly changing sequence of numbers and letters, while listening to three different voices speaking numbers and letters on headphones.

Occasionally, the test subjects would be asked to divert their attention from the screen to the audio, or vice versa.

When participants focused on the screen, the back of their brains, which control visual functions, indicated increased activity. When they focused on the voice, the sides of the brain, which control auditory functions, showed increased activity.

The researchers discovered that when attention was focused on vision, it decreased the brain activity in the audio area, and vice versa.

"It helps explain why it is that people tend to respond more slowly to visual events when talking on the phone, why they miss critical events like headlights coming on. The brain has a reduced capacity," said Yantis, a professor of psychological and brain science and co-author of the study.

Ed Awh, associate professor of psychology at the University of Oregon, said the study coincides with other research on how the brain works.

"It makes sense," he said. "There is a tradition of experiments that have looked at people's ability to do multiple things at once. Typically, it is in fact harder to do two things than to do one thing."

Researchers also discovered that other parts of the brain, called the parietal and prefrontal cortex, release a burst of activity to control the shift in attention from vision to hearing. Previously, scientists thought they controlled only visual shifts of attention.

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