Cochlear implants provide deaf people a bridge into the speaking world, but researchers are striving to make the devices do even more
April 24, 2007
Fine-tuning the instrument
Despite the seemingly miraculous out¬comes for implant users such as Linke-Ellis, the devices are fraught with limitations. They can't decipher music, and at best they provide only an approximation of human speech -- often described as a Donald Duck-like series of squawks. They are effective only in quiet environments. And perhaps most troublesome, there is no reliable predictor of how well an implant patient will perform with the device, since success depends on variable factors such as the degree of auditory nerve loss.
Nor can current models reliably process tonal languages, spoken by more than a quarter of the world's population. Tonal languages are typically more difficult to master than English because the pitch used to pronounce a word determines its meaning. So the same syllable can have different meanings, depending on how the speaker says it. The speech processors in the current generation of cochlear implants, though infinitely more advanced than those of 10 years ago, simply aren't capable of picking up such nuances.
That's where the pioneering research of a pair of Ohio University audiology professors comes in. Li Xu and Fuh-Cherng Jeng are hoping their work will help "teach" cochlear implants how to convey auditory details like the verve of a violin concerto and the tonal difference between "Ready?" and "Ready."
Xu is an associate professor in the College of Health and Human Services' School of Hearing, Speech and Language Sciences. Slightly built and soft-spoken in person, Xu's research on cochlear implantation is respect¬ed internationally. Much of his research been funded by a grant from the National Institute of Deafness and Communicative Disorders, part of the National Institutes of Health.
In the last few years, he's written extensively on tone recognition among implant users, and has been a featured speaker at international conferences in South Korea, Russia, Taiwan, France, Finland and the Netherlands. At the moment, he's collaborating on a study involving China's Beijing Tongren Hospital that focuses on tone perception and speech performance among children fitted with implants.
Hearing loss is particularly a problem in China, he said, due to the widespread use of an inexpensive antibiotic called gentamicin, which can damage the sound-sensing hair cells of the inner ear. Nearly 21 million Chi¬nese have at least some hearing loss, according to the advocacy group China Disabled Persons' Federation.
Xu focuses on finding the best methods for an implant's speech processor to divide sound into enough layers, or channels, so that the subtleties of the human voice aren't lost by the time they reach the brain.
Despite the limitations of today's cochlear implants and the years of research ahead to fine-tune them, Xu marvels at how empowering the devices can be for someone like Nanci Linke-Ellis.
"It is a miracle."
Complementing Xu's efforts is the work of his colleague, Jeng, an assistant professor who joined the university in fall 2006. Jeng works to map how and where the brain responds when it receives voice signals. He is setting up a lab in Grover Center for his testing, and he hopes to have the facility operating in early 2007.
Participants in his research will listen to speech while wearing an electrode-studded head covering that resembles a swimming cap. His equipment will scan the listener's brain for responses. On a nearby monitor, Jeng will study a three-dimensional image of the participant's brain as different areas light up, indicating a response. He speculates that there will be different responses to a speech sound whose tone is altered slightly. He offers an example.
"I love you."
"I love you."
Research is thin on how the brain reacts to such modulations, Jeng says, but it's this mapping that may hold the key to bringing music and tonal languages into the non-hearing world.
"The [cochlear implant] procedure itself is not the main issue," Jeng says. "The main issue is, 'Do you really understand how it works and how the auditory system works, and how do we mesh the two for maximum performance?' "
Coming to Ohio University has allowed him to fulfill his dream of continuing research in this area. When asked what drew him to study this field, the researcher's voice softens.
"Imagine one day when you find somebody you care for. You want to say something important. You want your information to be modulated with human speech, with music, with your emotion."
Big help for little voices
Cochlear implants have had a profound impact on many of the 20,000 or so deaf children who have received them. In 2002, the U.S. Food and Drug Administration approved the use of implants for children as young as a year old.
Pam Reese is a clinical supervisor at Ohio University Therapy Associates, the speech, hearing, language and physical therapy clinic in Grover Center. She has worked with young children after they received an implant, and she says watching a deaf child hear for the first time is unforgettable.
"You see a pause, a look in the eye, and the head turns and you realize, 'He heard it.' "
Maria Sentelik is founder and executive director of Ohio Valley Voices, a Cincinnati-area school that teaches deaf youngsters to talk and understand speech. The goal at Ohio Valley Voices, whose charges range from 18 months to second grade, is preparing deaf youngsters to attend school with their hearing peers.
Of the 40 currently enrolled, 38 have cochlear implants. Sentelik said the children blossom as they learn oral skills. Sign language, while helpful, she says, has limitations in the hearing world. Since most hearing people don't sign, she said, signing can be isolating if not combined with oral-aural communication.
"With the implants," Sentelik said, "we're able to have children who can com¬municate however they want. You give them a cochlear implant, you teach them to talk and the world is their oyster."
She has seen the successes. She describes a former female student who was fitted with an implant at 18 months is now in a public school gifted program.
Sentelik believes such success stories never would have been possible two decades ago. Before cochlear implants and their ability to help deaf children speak and engage in the hearing world, most were pushed to society's margins.
"You would have never recognized who they were or what they would be able to offer us," she said. "Now they can contribute to society and express their ideas and attain whatever they want."