Background noise affects hearing impaired

Background noise causes ears of those with hearing impairments to work differently, U.S. researchers say. Kenneth S. Henry, a postdoctoral researcher, and Michael G. Heinz, an associate professor at Purdue University, said hearing loss, suffered in varying degrees by 36 million U.S. 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. "When immersed in the noise, the neurons of the inner ear must work harder because they are spread too thin," Henry said in a statement. "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." While previous hearing studies were done in quiet environments, these researchers measured a variety of physiological markers in chinchillas -- with a similar hearing range to humans -- in both quiet and noisy environments. Some of the chinchillas used in the study had normal hearing and others had a cochlear hearing loss. Chinchillas are used because they have a similar hearing range to humans, and background noise was used to simulate what people would hear in a crowded room. "The study confirmed that there is essentially no change, even for those with hearing loss, in terms of how the cochlear neurons are processing the tones in quiet, but once noise was added, we did observe a diminished coding of the temporal structure," Henry said. The findings were published as a Brief Communication in Nature Neuroscience.