Simply listening to someone over a mobile phone, without dialing and holding it, while driving may distract the brain enough to cause an accident.
Previous studies have suggested that drivers who use cell phones run a greater risk of accidents, and that hands-free phones do not appreciably lower the odds, report.
The new findings cast further doubt on the idea that hands- free cell phones are safe for drivers. Just the act of listening appears to divert much of the brain resources that would normally go toward navigating the road.
American researchers studied 29 volunteers who used a driving simulator while inside an MRI brain scanner. Participants steered along a winding virtual road, once with no distractions and once while listening to various sentences and trying to decide whether they were true or false.
It was found that in the second scenario, the drivers' brain activity changed including a 37 percent drop in activity in the parietal lobe, a brain area involved in spatial sense and navigation.
Moreover, this shift in brain activity was accompanied by an increase in driving errors; drivers tended to drift more in their simulated lanes and were more likely to hit the virtual guardrail. Drivers need to keep not only their hands on the wheel; they also have to keep their brains on the road.
According to the researchers conversing on a cell phone may well be more distracting than listening to music or to someone in the passenger seat.
Listening to music does not require the cognitive processing necessary for having a conversation and can be more readily tuned out.
Because driving and listening rely on different brain networks, some scientists had speculated that the brain could handle both tasks at the same time.
But the above findings suggest that there is only so much the brain can accomplish simultaneously.