WEST LAFAYETTE, Ind. - The world continues to be a noisy place, and Purdue University researchers have found that all that background chatter causes the ears of those with hearing impairments to work differently.
"When immersed in the noise, the neurons of the inner ear must work harder because they are spread too thin," said Kenneth S. Henry, a postdoctoral researcher in Purdue's Department of Speech, Language and Hearing Sciences. "It's comparable to turning on a dozen television screens and asking someone to focus on one program. The result can be fuzzy because these neurons get distracted by other information."
The findings, by Henry and Michael G. Heinz, an associate professor of speech, language and hearing sciences, are published as a Brief Communication in Nature Neuroscience. The work was funded by the National Institutes of Health and the National Institute on Deafness and Other Communication Disorders.
"Previous studies on how the inner ear processes sound have failed to find connections between hearing impairment and degraded temporal coding in auditory nerve fibers, which transmit messages from the inner ear to the brain," said Heinz, who studies auditory neuroscience. "The difference is that such earlier studies were done in quiet environments, but when the same tests are conducted in a noisy environment, there is a physical difference in how auditory nerve fibers respond to sound."
Hearing loss, suffered in varying degrees by 36 million American adults, means there is damage to sensory cells in the cochlea and to cochlear neurons as well. The cochlea is the part of the inner ear that transforms sound into electrical messages to the brain.
In this study, the researchers measured a variety of physiological markers in chinchillas, some with normal hearing and others with a cochlear hearing loss, as they listened to tones in quiet and noisy environments. Chinchillas are used because they have a
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