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Carnegie Mellon study provides conclusive evidence that cell phones distract drivers

Carnegie Mellon University

PITTSBURGH-By studying images of the brain at work, Carnegie Mellon University scientists have concluded that we cannot converse on cell phones without distracting our brains from the task of driving.

In findings reported in the journal NeuroImage, a team led by Carnegie Mellon Psychology Professor Marcel Just discovered that attending to a conversation significantly distracts the brain from processing complex visual information.

"This has direct implications for cell phone use during driving because it answers one of the classic questions about human thinking. We've demonstrated that the human brain has a limited ability to perform two cognitive tasks concurrently under demanding circumstances, such as simultaneously conversing and driving," said Just.

In a study using non-invasive techniques to see inside the brain, scientists read sentences to 18 people while they were doing a complex visual processing task. The researchers found that listening to someone speak consumes some of the resources that would otherwise be allocated to a complex visual information-processing task. In fact, the amount of brain activation allocated to the visual processing task decreased by 29% if participants were simultaneously listening to a sentence.

"The fundamental implication is that engaging in a demanding conversation could jeopardize judgment and reaction time if an atypical or unusual driving situation arose," Just said. Making cell phones "hands free" won't help. "Use of cell phones doesn't just distract the eyes. The conversation itself also distracts the brain. Making the cell phone hands-free will not help eliminate the brain distraction," Just added.

Driving isn't the only task that suffers during mobile conversation. Both conversation and driving skills take a hit. The research team found that doing a demanding visual task, such as driving, also distracts the brain from language processing.

The brain activation associated with language comprehension decreased by 53% if participants were simultaneously doing a complex visual processing task. Just commented that the worst possible situation would be to have an important difficult conversation while driving in heavy traffic.

Just's team used the most recent methods of functional magnetic resonance imaging (fMRI) to measure activity in tiny portions of the brain measuring a twentieth of a cubic centimeter; keeping track of how language-related activity affected the visual processing activity. The measurements were taken every three seconds while subjects listened to sentences and compared the structures of two complex three-dimensional objects.

These results show that activity in one system (such as the language processing network) affect the resource availability in another system (such as the spatial processing network). Specifically, the study shows the mutual interference between separate areas of the brain that are doing very different types of thinking.

Scientists thought that separate brain systems might be able to work independently of each other. But Just said this study demonstrates that there is only so much that the brain can do at one time.

"Practice can make one or both tasks more automated, but there is always a limit. Understanding spoken language is about the most automated cognitive task that exists, and driving can become fairly automated as well. But before driving is automated, in a novice driver, conversation can be extremely distracting," he noted.


The research is part of a project to develop imaging methods to measure brain workload in information-driven technology environments. The Air Force Office of Scientific Research (AFOSR) funded the research.

Other members of the research team included Carnegie Mellon Psychology Professor Patricia Carpenter, postdoctoral research associate Timothy Keller and research assistants Lisa Emery and Holly Zajac. Keith R. Thulborn, a professor of radiology at University of Chicago Medical Center, is a member of the research team. Just and Carpenter direct the Center for Cognitive Brain Imaging at Carnegie Mellon

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