The human brain struggles to simultaneuosly look and listen, a new study suggests.

The parts of the brain that handle visual input are less effective when the mind is also processing audio input, and vice versa.

"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 Johns Hopkins University psychologist. "Directing attention to listening effectively 'turns down the volume' on input to the visual parts of the brain."

In the study, people aged 19 to 35 watched a rapidly changing display of letters and numbers while listening to three voices speak other letters and numbers. If that sounds like the sort of clutter in your life, that was the researchers? goal.

The scientists recorded brain activity. When the test subjects paid attention to the screen, activity decreased in the parts of their brain responsible for listening.

The research yielded a surprise:

When a subject was told to shift attention from vision to hearing, the brain's parietal cortex and the prefrontal cortex produced a burst of activity. The scientists assume it was a signal to initiate the shift of attention. Experts had previously thought those parts of the brain were only involved in processing visual information.

"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," Yantis said.

The study, first published last year in the journal Neuroscience, was announced today.

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