Using cell phones while driving has been a matter of controversy for some time, but this is the first study to look at listening alone as a distraction.
Just and colleagues found that listening alone reduced brain activity associated with driving by 37 per cent. Based on driving simulator results, this would be enough to cause a driver to weave out of their lane, said the researchers.
"Drivers need to keep not only their hands on the wheel; they also have to keep their brains on the road," said Just in a prepared statement.
Just and colleagues invited 29 volunteers to to use a driving simulator while inside an MRI brain scanner. The simulator gave them a winding road to drive on at a fixed but challenging speed. There were two conditions: undisturbed or while listening. While listening, the volunteers listened to statements and had to decide whether they were true or false, a similar level of cognitive processing as would be involved in a normal listening activity.
The researchers used the latest functional magnetic resonance imaging (fMRI) technology to measure second by second changes in brain activity in 20,000 places, each being about the size of a peppercorn, they said.
Compared to the undisturbed scenario, the listening while driving scenario showed a 37 per cent decrease in activity in the brain's parietal lobe, the part of the brain that is associated with driving and processes sensory inputs that are important for navigation and spatial awareness. The occipital lobe, which processes visual signals, also showed reduced activity, said the researchers.
Using measures of performance on the simulator, the researchers observed that the driving while listening scenarios resulted in much poorer quality of driving. When in listening while driving mode the volunteers made more errors in lane discipline, such as deviating from the middle and hitting a guardrail.
The study suggests that hands free and voice activated cell phones do not go far enough to ease safety concerns because the distraction of listening would still remain.
The researchers said that other distractions such as listening to the radio, eating or talking to a passenger can also divert a driver, and although there is no evidence of how these distractions compare to listening to a cell phone, they suggest cell phones are different because, as Just explained:
"Talking on a cell phone has a special social demand, such that not attending to the cell conversation can be interpreted as rude, insulting behavior."
A passenger, on the other hand, because he or she is physically in the car with the driver, can see if anything urgently needs the driver's attention and will stop talking, it is a situation that is less likely to put social pressure on the driver.