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Talking while turning left is a recipe for disaster, study finds

Published February 28, 2013

Ever feel like your head’s going to explode when you’re trying to turn left at a hectic intersection and tell the boss, via that Bluetooth device looped over your ear, that it’s not your fault sales have tanked?

Your brain may be trying to tell you something while you’re driving. It appears that turning left at a busy intersection and talking on a hands-free cellphone is a recipe for disaster.

The human brain has a hard time dealing with the stressful decision-making, involved in a busy left-turn situation, at the same time as it is processing a distracting conversation. For drivers talking on those hands-free devices “that could be the most dangerous thing they ever do on the road,’’ said Dr. Tom Schweizer, a neuroscientist at St. Michael’s Hospital and lead researcher in a just-published study on distracted driving.

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Statistics indicate that the most serious traffic accidents occur when drivers are turning left at busy intersections, he said.

And the danger isn’t limited to talking on a hands-free cellphone — it could just as easily be from an in-car heated conversation with a real person, or even from a radio talk show that has passionately engaged a driver, said Schweizer. “Anything that you are actively listening to could potentially take some (brain) resources away from the primary task of driving.’’

Researchers in the study published online Feb. 28 in the journal Frontiers in Human Neuroscience, were able to show for the first time that making a left-hand turn involves a large amount of brain activation — much more than driving on a straight road for instance, or making a right turn.

They put seven women and nine men, ages 20 to 30, and with an average of seven years of driving experience apiece, through a driving simulation exercise while they were wearing headphones and monitored by an MRI. All of the participants were right-handed and used a functional steering wheel and pedals. They were taken through a series of increasingly difficult driving manoeuvres.

Eventually they had to decide when to turn left safely in a busy oncoming traffic situation, six times. At the same time as they were doing this, they had to answer a series of distracting true-false questions asked through their headphones. When this happened, the MRI images showed that blood moved from the posterior visual cortex of the brain, which controls sight, to the prefrontal cortex, which controls decision-making.

The study gives “real-time neuroimaging evidence” which supports previous behavioural observations that suggest “multi-tasking while driving may compromise vision and alertness,” Schweizer said.

A left-hand turn is demanding, visually, he said, and involves looking at oncoming traffic and lights, watching for pedestrians, assessing and co-ordinating.

Add to that the distraction of an insistent conversation, whether it’s hands free or someone in the car, and “your visual area shuts down significantly, which obviously is key to performing the manoeuvre,’’ he said.

What people might take from the study is that while driving, they need to “focus on the task at hand,’’ he said. “Hands free isn’t brains free.”

He told the Star that it was surprising to see “just how much of the brain came online when you’re doing a left-hand turn. It was almost the entire brain lighting up. It really proves the point that there are a limited amount of brain resources. Because that left-hand turn in the intersection is so demanding, something’s got to give when you’re distracted. And it just so happens that what gives is your visual cortex, which is processing the visual information. That, potentially, is quite a dangerous mix.”

None of the participants in the simulated driving exercise had an accident while making their left turns. Schweizer speculates they may have been helped by the fact that they are from a generation that has commonly used hand-held gaming devices and may have faster reflexes. The researchers made the exercise difficult, but not impossible, he said.

Schweizer said he intends to do a similar study with stroke patients and also an older age group.

The study was financed by the Natural Sciences and Engineering Research Council of Canada and the Ontario Ministry of Economic Development and Innovation.

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