Study Researches Bilateral Cochlear Implants NIDCD Demonstrates Bilateral Implants Benefit Children Who Are Deaf Research in Brief
Research in Brief  |   March 01, 2007
Study Researches Bilateral Cochlear Implants
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  • Dee Naquin Shafer, an assistant managing editor of The ASHA Leader, can be reached at
    Dee Naquin Shafer, an assistant managing editor of The ASHA Leader, can be reached at×
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Hearing Disorders / Hearing Aids, Cochlear Implants & Assistive Technology / Regulatory, Legislative & Advocacy / Research in Brief
Research in Brief   |   March 01, 2007
Study Researches Bilateral Cochlear Implants
The ASHA Leader, March 2007, Vol. 12, 5-19. doi:10.1044/leader.RIB.12042007.5
The ASHA Leader, March 2007, Vol. 12, 5-19. doi:10.1044/leader.RIB.12042007.5
Research funded by the National Institute on Deafness and other Communication Disorders (NIDCD) suggests that children who are deaf and have a cochlear implant in each ear more accurately locate sounds when they use both implants instead of one. Children with two implants also become more skilled at localizing sound over time.
For more than four years, Ruth Litovsky has been leading a team focusing on the research at the University of Wisconsin-Madison’s Waisman Center. Although the work has revolved around children, it has implications for adults, she said.
“Mainly, we are finding out that in adults, the issue of plasticity is also very important. Adults who were post-lingually deaf seem to have better outcomes with bilateral implants than adults who lost hearing during early childhood,” Litovsky said.
Patients did not receive more than one implant until about 10 years ago. Only about 3% of the 100,000 people worldwide who currently wear implants have received two, she said. Doctors began to fit people with two implants to assist in understanding speech, especially in environments with many competing sounds.
Litovsky’s team has studied 55 children who are deaf and who received a second implant one to seven years after being fitted with the first. When the research began, it appeared the group of 5- to 14-year-olds couldn’t localize sounds, Litovsky said. She began a longitudinal study designed to test their skills at this task and how those skills changed over time.
In a “listening game” devised by the team, children faced a semicircle of loudspeakers arranged at regular intervals, each with a picture attached. When a loudspeaker emitted speech or noise stimuli, the children were scored on their ability to identify the sound source by pointing to its location in the room.
In addition to completing the task while wearing both implants, the children are asked to complete the task again after removing the microphone and other external parts of one implant.
Although variability existed among the children, the study indicates that most develop the ability to locate speech and other sounds more accurately when using two cochlear implants than when using one implant. This capability also increased with experience.
The team worked with children who received their implants sequentially. It appeared that research subjects took a long time to combine the inputs from the two ears; the fact that they learned to do so indicates the brain’s plasticity. Litovsky elaborated, saying that mechanisms in the brainstem integrate inputs from the right and left.
“Those neurons have been deprived of binaural (left and right) inputs, and possibly never received them if the child was deaf from birth and only heard out of one implant initially,” she said.
“It appears that the binaural neural circuits have to be stimulated for some time before they can code for the information coming in. At cortical levels of stimulus processing, I believe that the child has to learn to map particular perceived locations in space with the auditory cues. There is likely to be a learned component that is central.”
Litovsky’s research results were presented at the Annual Midwinter Meeting of the Association for Research in Otolaryngology in Denver, held Feb. 10–15. “I am hopeful that the NIDCD-funded research will continue,” she said.
For more information, visit the Binaural Hearing & Speech Lab’s Web site or contact Ruth Litovsky at
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March 2007
Volume 12, Issue 4