Research Reveals Cell Phone Hazards
Journalist: Ephraim Schwartz
August 6, 2001
of a study on the brain's ability to process two cognitive tasks
simultaneously appears to prove that hands-free use of cell phones while
driving impairs a driver's ability to perform at 100 percent.
Cognitive, as opposed to sensory, tasks are those that require high levels
The study, "Interdependence of Nonoverlapping Cortical Systems in Dual
Cognitive Tasks" conducted by researchers at the Center for Cognitive Brain
Imaging, at Carnegie Mellon University in Pittsburgh, was commissioned by
the Air Force Office of Scientific Research and published in the August
issue of NeuroImage, a scientific journal.
Research team lead, Dr. Marcel Just, believes the implications of the study
reach well beyond the laboratory.
"It should be part of the education of every driver and part of police
licensing procedures to make it clear that demanding driving can't be safely
time shared with other tasks," Just said.
Just included not only cell phone usage, with or without headsets, but also
conversations and the radio that should be stopped in tough driving
Just is the D.O. Hebb Professor of Psychology and co-director of the Center
for Cognitive Brain Imaging, Psychology
Department, at Carnegie Mellon University.
This is the first study of its kind that measures if a person can do two
high-level multi tasks at the same time, according to Just.
The tests used fMRI (functional magnetic resonance imaging) to measure brain
use during two "high-level cognitive" tasks that occur in two different,
unrelated parts of the brain.
The fMRI takes a three-dimensional image of the brain and dices it into
three-dimensional objects called voxels. The total number of voxels, about
the size of a peppercorn, measure the amount of brain power devoted to a
The researchers asked volunteers to listen to statements and say whether
they were true or false while simultaneously determining if two rotating,
three-dimensional objects were the same.
When each operation was done as a single task, the number of so-called
"activated" voxels was 37 for each task.
But when asked to do a dual task, the total number of voxels the brain could
devote was not the expected 74 voxels, the sum of the voxels when each task
was done alone, but rather a total of only 42 voxels were used. The signal
intensity of each voxel was also measured and proved to lower as well.
"People think of various parts of the brain as functioning autonomously.
Here you see this interdependence and resource dependence," Just said.
A very similar phenomenon occurred in the sensory, non-cognitive parts of
the brain. Both the primary auditory and primary visual parts of the brain
decreased their activation.
"This constraint on activation effects not just the conceptual area. It
effects the other areas as well. This is kind of surprising," said Just, who
commented he found it amazing that there is less brain activation when also
looking at something or listening to something at the same time.
The study also measured performance. Although the difference in accuracy of
the answers in the sentence comprehension portion of the test was negligible
when answering as a dual or single task, there was an increase in response
For the visual tasks, which would be similar to driving, there were an
increase in the rate of error when the volunteers performed dual versus
single tasks as well as an increase in response time.
The researchers offered three interpretations of their conclusions: There
may be a "biological mechanism that places an upper bound on the amount of
cortical tissue that can be activated at any give time," there is a "limit
on how much attention is available to distribute over more than one task,"
and there is a "limit on how well it is possible to perform concurrent