Don't feel so smug about how safety conscious you are by using a hands-free cell phone in the car: Carnegie Mellon University researchers say you're still likely going to be distracted.

The researchers used brain imaging to show that even just listening to a cell phone while driving cuts by more than a third of your attention to driving. Subjects inside an MRI brain scanner were tested on a driving simulator and were found to weave, similar to if they were under the influence of alcohol. The study showed lessened activity in the brain's parietal lobe, which is called upon for spatial sense and navigation, and occipital lobe, which handles visual information.

The findings by neuroscientist Marcel Just and colleagues Timothy Keller and Jacquelyn Cynkar, to be reported in an upcoming issue of the journal Brain Research, show that making cell phones hands-free or voice-activated is not sufficient in eliminating distractions to drivers. "Drivers need to keep not only their hands on the wheel; they also have to keep their brains on the road," said  Just, who is also director of the Center for Cognitive Brain Imaging., in a statement. 

It's unclear how much of a distraction talking or listening on a cell phone is vs. talking to a passenger or listening to a radio, Just said.

"Drivers' seats in many vehicles are becoming highly instrumented cockpits," Just said in a statement, "and during difficult driving situations, they require the undivided attention of the driver's brain."

It had been widely thought that driving could be made much safer by at least taking cell phones out of drivers' hands, and a number of states have enacted laws or discussed laws banning use of handheld phones while driving. 

Other research, from the University of Utah, has shown that cell phone wielding drivers actually tend to drive more slowly and can create traffic jams. 

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