The results 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 of thinking.
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 situations.
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 taskThe 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 times.
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 tasks"