02/28/2013 11:03 am ET

Talking While Making Left Turns Is Distracting, Study Finds

A new brain imaging study makes a pretty compelling case for not talking on the phone while driving -- even if you're using a hands-free headset.

Researchers from St. Michael's Hospital found that if a driver talks on the phone while making a left turn, even when it's on a hands-free device, there is decreased activation in the brain region responsible for vision control, and increased activation in the brain region responsible for decision-making.

In other words, left-hand turns require a lot of attention from your brain, and talking on the phone -- even if you're trying to be responsible by going hands-free -- is a major distraction.

The findings are published in the journal Frontiers in Human Neuroscience.

For the study, researchers had healthy volunteers operate a driving simulator that included a real working steering wheel and pedals, while in an MRI. That way, they were able to see which parts of their brains were activated in response to certain tasks.

The study participants were asked to "drive" in the simulator, and make six left turns against simulated oncoming traffic. While they were making these left turns, they were also asked several simple true-false questions.

Through the MRI brain imaging, researchers were able to see that when the study participants were making the left turn while having to also think and talk, the blood in their brain went from their visual cortex -- responsible for sight -- to the prefrontal cortex.

"This study provides real-time neuroimaging evidence supporting previous behavioural observations suggesting that multitasking while driving may compromise vision and alertness," study researcher Dr. Tom Schweizer, who is a a neuroscientist and director of the Neuroscience Research Program at St. Michael Hospital's Li Ka Shing Knowledge Institute, said in a statement. "'Hands free' [does not] mean 'brains free.'"

According to government statistics on distracted driving, cell phones are behind 18 percent of U.S. distraction-related deaths. According to the U.S. Department of Transportation:

So far, the research indicates that the cognitive distraction of having a hands-free phone conversation causes drivers to miss the important visual and audio cues that would ordinarily help you avoid a crash.