PITTSBURGH, March 5
-- Using a cellphone while driving -- even a hands-free model --
sharply decreases activity in the brain regions used to control the
vehicle, researchers here said.
resonance imaging (fMRI) showed a 37% decrease in the brain activity
associated with driving when the task is complicated by listening to
speech, Marcel Just, D.O., of Carnegie Mellon University, and
colleagues reported in the journal Brain Research
Regulations that allow drivers to use hands-free or
voice-activated cellphones are missing the point, Dr. Just said in a
- Explain to interested patients that behavioral
studies have shown driving deteriorates when people use
cellphones, leading to suggestions that only hands-free models
should be allowed to be used in cars.
- Note that this study suggests that even hands-free
models are likely to cause significant distractions to drivers.
"Drivers need to keep not only their hands on the wheel," he
said. "They also have to keep their brains on the road."
In an experiment, 29 volunteers underwent fMRI scanning while
they guided a virtual vehicle down a winding road, either
undistracted or having to listen to recorded sentences and decide if
they were true or false.
In both cases, the researchers calculated how well the volunteers
kept their virtual cars on an ideal path and how often they had
"road maintenance errors" such as hitting a simulated guardrail.
The researchers also calculated what areas of the brain were
active when volunteers were just driving and when they also had to
The study found:
- On average, the root mean squared deviation from the ideal
path increased from 2.48 to 2.64 when the listening task was added
to driving. The change was significant at P<0.01.
- Mean road maintenance errors increased from 8.7 to 12.8, when
listening was added to driving. The change was significant at
- There were large decreases in activity in the areas of the
brain involved in the spatial processing associated with driving
when listening was added. In the parietal lobe the decrease was
37%, which was significant at P<0.0001.
Dr. Just and colleagues noted that the driving task did not
include having to react to potentially dangerous situations, so that
the finding probably underestimates the degree of distraction.
Equally, they said, the task didn't require participants to
speak, so that the listening task was probably less disruptive than
a true cellphone conversation.
"The clear implication is that engaging in a demanding
conversation could jeopardize judgment and reaction time if an
atypical or unusual driving situation arose," Dr. Just said.
"Heavy traffic is no place for an involved personal or business
discussion, let alone texting," he added.
The same considerations might apply to conversing with
passengers, the researchers said, although there is evidence that
passengers in a car are more likely to be aware of competing demands
on the driver's attention and stop talking when it's inappropriate.
The researchers noted that the "striking" decrease in brain
activity associated with driving while listening comes despite the
fact that driving and listening draw on two largely non-overlapping
One possible interpretation is that the brain has only a limited
amount of resources that can be devoted to paying attention, Dr.
Just and colleagues said.
|The study was supported by the Office of Naval Research.
Dr. Just reported no