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February 14, 2007

Two Cochlear Implants Better than One

We hear better with two ears, so maybe it's not so surprising that deaf children who receive cochlear implants hear better when they have them in both ears. That's the finding of University of Wisconsin researchers.

Led by Ruth Litovsky of UW-Madison's Waisman Center, scientists have found evidence that deaf children who have a cochlear implant in both ears locate sounds more accurately than those with only one. Children with two implants also become more skilled at localizing sound over time.

Information like this will be useful, says Litovsky, when doctors and parents have to decide if a child should get one or two of the electronic devices, which allow deaf people to hear by bypassing the damaged inner ear, or cochlea, to stimulate the auditory nerve directly.

This is not always an easy choice. A single implant and the associated surgery can cost $50,000. The device also permanently damages the cochlea, which might prevent recipients from taking advantage of any superior treatments for deafness that may be developed in the future.

Children never received more than one implant until about ten years ago. Then, doctors began to fit people with two, hoping this would assist them in understanding speech, especially in environments with lots of background noise. Still, only about three percent of the 100,000 people worldwide who currently wear implants have two.

The idea for this study, presented Feb. 13, 2007 at the Annual Midwinter Meeting of the Association for Research in Otolaryngology, was suggested by the fact that two normal ears make it easier to locate sounds. "If you close an ear, walk around and try to identify where sounds are coming from, it's very, very hard," Litovsky says.

To test whether a pair of cochlear implants also aids this ability, Litovsky's team studied 55 deaf children who received a second implant one to seven years after being fitted with their first.

When the research began, it appeared the group of 5- to 14-year-olds could not localize sounds at all, Litovsky says. Most, however, eventually did develop the ability to locate speech and other sounds more accurately when using two cochlear implants. This capability also increased with experience.

"We're now seeing that the ability to localize sounds takes time to emerge," says Litovsky. "What seems to get better is the integration of the information from the two ears in the brain."
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