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December 29, 2004

Blocking out background noises may facilitate hearing

From: Knoxville News Sentinel, TN - Dec 29, 2004

By LEE BOWMAN December 29, 2004

You're at a crowded, noisy holiday party, trying to tune into the conversation of someone standing right next to you, but he or she might as well be speaking another language. Don't blame your hearing, or even the champagne.

Researchers at the University of Florida in Gainesville have found that background noises don't just cover up conversation; they may actually scramble language-processing activity in the brain.

Their experiments with rats are beginning to unravel why even perfectly loud speech may be hard to understand in a noisy room, a finding that has applications for everything from hearing aids to MP3 players.

"Some people have a tremendously difficult time understanding speech in a noisy environment, and we've all had the experience of having someone tell us something, but we can't tell what it is that they are saying," said Purvis Bedenbaugh, an assistant professor of neuroscience at the university's medical college and the person who led the studies. "This research is the first step toward looking at why that would be." Their research was published earlier this year in The Proceedings of the National Academy of Sciences.

The scientists examined how brain cells in alert rats responded to specific sounds while one of three standardized noises played in the background. Implanted electrodes recorded the activity in the auditory thalamus of the rats.

Beeps and sharp shushing noises were the target sounds, intended to mimic words. The background noises were static, the conversational murmur at a busy restaurant and the disjointed whir of a rewinding tape recorder.

Scientists discovered that brain activity actually decreased in the presence of the background sounds. And the extra noise not only covered up the target sounds, it also interfered with the brain's ability to process or interpret information about sound, even though the sound was clearly heard by the ears.

This phenomenon may play a role in auditory processing disorder, a problem first noted in children in the 1970s, with a lack of coordination between the ear and the brain. Learning specialists have to help such children develop their own strategies for filtering out noise that affects their concentration and understanding.

Industrial safety experts have noted for years that many workers with normal hearing who start out wearing hearing protection are surprised to find that they actually hear speech from co-workers more clearly because background noise is reduced.

Noise specifically interferes with the way the brain processes information, said Michael Merzenich, a professor specializing in brain organization and speech and hearing at the Keck Center for Integrative Neuroscience at the University of California-San Francisco.

"Noise interference is a fundamental aspect of many impaired populations," Merzenich said.

"Children struggling with language and reading often have problems specifically in the presence of noise. Go to the other end of the age spectrum and again you find the loss of ability to operate effectively in noisy environments," he said. "Commonly, what older people want to do is turn up the volume when they have difficulty understanding, but it is important to know that noise interferes with the processing of speech, not just the reception."

Bedenbaugh and his colleagues are now trying to apply their findings to better designs for hearing aids, cochlear implants, and earphones that might filter out the growing cacophony of everyday life and allow the brain to hear the most important sounds.

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