The reason talking on a cell phone makes drivers less
safe may be that the brain can't simultaneously give full
attention to both the visual task of driving and the
auditory task of listening, a study by a Johns Hopkins
psychologist suggests.
The study, published in a recent issue of The
Journal of Neuroscience, reinforces earlier behavioral
research on the danger of mixing mobile phones and
motoring.
"Our research helps explain why talking on a cell
phone can impair driving performance, even when the driver
is using a hands-free device," said
Steven Yantis, a professor in the
Department of
Psychological and Brain Sciences in the Krieger School
of Arts and Sciences.
"The reason?" he asked. "Directing attention to
listening effectively 'turns down the volume' on input to
the visual parts of the brain. The evidence we have right
now strongly suggests that attention is strictly limited, a
zero-sum game. When attention is deployed to one modality
— say, in this case, talking on a cell phone —
it necessarily extracts a cost on another modality —
in this case, the visual task of driving."
Yantis' chief collaborator on this research project
was Sarah Shomstein, who was a doctoral candidate at Johns
Hopkins. Shomstein is now a postdoctoral fellow at Carnegie
Mellon University.
Though the results of Yantis' research can be applied
to the real-world problem of drivers and their cell phones,
that issue was not directly what the professor and his team
studied. Instead, healthy young adults ages 19 to 35 were
brought into a neuroimaging lab and asked to view a
computer display while listening to voices over headphones.
They watched a rapidly changing display of multiple letters
and digits while listening to three voices speaking letters
and digits at the same time. The purpose was to simulate
the cluttered visual and auditory input people deal with
every day.
Using functional magnetic resonance imaging, Yantis
and his team recorded brain activity during each of these
tasks. They found that when the subjects directed their
attention to visual tasks, the auditory parts of their
brain recorded decreased activity, and vice versa.
Yantis' team also examined the parts of the brain that
control shifts of attention. They discovered that when a
person was instructed to move his attention from vision to
hearing, for instance, the brain's parietal cortex and the
prefrontal cortex produced a burst of activity that the
researchers interpreted as a signal to initiate the shift
of attention. This surprised them, because it has
previously been thought that those parts of the brain were
involved only in visual functions.
"Ultimately, we want to understand the connection
between voluntary acts of the will (for instance, a choice
to shift attention from vision to hearing), changes in
brain activity (reflecting both the initiation of cognitive
control and the effects of that control) and resultant
changes in the performance of a task, such as driving,"
Yantis said. "By advancing our understanding of the
connection between mind, brain and behavior, this research
may help in the design of complex devices — such as
airliner cockpits — and may help in the diagnosis and
treatment of neurological disorders such as ADHD or
schizophrenia."
This type of work also informs debates about the
safety of mobile phone use while driving. It suggests that
when attention is focused on listening, vision is affected
even at very early stages of visual perception. A paper
describing the research appeared in the Nov. 24, 2004,
issue of the Journal of Neuroscience.
The National Institute on Drug Abuse funded this
research.