The Mind Hears: Tuning In With a Cochlear Implant
"Can you hear what I'm saying?"
by Susan Boswell
These are often the first words spoken when a cochlear implant recipient's processor is turned on. And they have been a rite of passage for more than 36,000 people around the world who have received cochlear implants over the last two decades. Technological advances have brought dramatic changes in candidacy criteria, opening the door for more people with severe and profound hearing losses to choose this option.
When the U.S. Food and Drug Administration (FDA) first approved a cochlear implant with a single electrode for adults in 1985 and for children in 1990, only those who were almost completely deaf and could only perceive vibrations with a hearing aid could qualify.
Today, children and adults who were not candidates just two years ago may well be considered as candidates. The age of pediatric candidates has dropped from 2 years to as young as 12 months, and eligibility criteria for adults continue to expand.
A growing body of research has demonstrated that children who receive cochlear implants when they are very young make greater gains in acquiring age-appropriate language skills than children implanted when they are older. In response, the FDA recently approved cochlear implants for children as young as 12 months.
Changes in pediatric criteria have also resulted from changes in the adult criteria, said Carolyn Brown, associate professor at the University of Iowa. "We have seen adults with severe hearing losses do well with cochlear implants--better than they did with hearing aids. As the average performance levels with a cochlear implants increase, we have started implanting patients with more hearing."
Infants are candidates for cochlear implants only after it is determined that they are not making progress in acquiring language using powerful hearing aids. "For infants with severe-to-profound hearing loss, you have to teach them to understand the meaning of sound and then compare whether they function as well as a child with a cochlear implant. If they cannot function as well as children with implants, they are candidates." said Margo Skinner, director of the cochlear implant program at the Washington University School of Medicine in St. Louis.
Cochlear implants differ from hearing aids in bypassing the damaged hair cells in the cochlea and directly stimulating the auditory nerve, Skinner explained. Some speech sounds, such as "ed" or "s," are never heard by children with severe-to-profound hearing losses because hearing aids cannot make the sound loud enough, or because there are no longer cochlear hair cells left to transmit the sound.
"Often when kids get a cochlear implant, the first change you'll see is the ability to pick up the 's.' They hear these soft speech sounds--and it's so evident," Skinner said.
But cochlear implants do not hold a miracle cure for deafness. "There is a lot of variability in cochlear implant outcomes," emphasized Karen Iler Kirk, coordinator of the cochlear implant program at the Indiana University School of Medicine. "Some children may find that the sound provided by a cochlear implant enhances their speechreading ability or makes them more aware of environmental sounds, while others can understand a great deal of speech through listening alone."
Cochlear implants offer the opportunity for many young deaf children to acquire age-appropriate language skills, and they seem to acquire listening skills with less effort than do children who have profound hearing losses using hearing aids, Kirk said.
Adult Eligibility Expands
The success of cochlear implant technology has also enabled adults with greater residual hearing and speech recognition to qualify as cochlear implant candidates. According to the FDA, adults can now be considered candidates if they have severe-to-profound hearing loss and understand less than 50% of sentences spoken to them. They should also have realistic expectations, motivation to learn to hear again, and no medical contraindications to surgery.
Greater numbers of prelingually deaf adults, who lost their hearing before acquiring language, are now beginning to consider cochlear implants as a tool to enhance communication. "These are people who have developed fluent oral communication skills and are very dependent on whatever amount of sound they get through hearing aids--even if it's a tiny bit," said Diane Bracket, co-director of the New England Center for Hearing Rehabilitation.
They're looking for more sound than they can hear with hearing aids, Bracket said. "By using a cochlear implant, they're clearly able to hear more. They can hear at greater distances, and can even talk on the phone with familiar people by directly coupling the telephone to their processor or by holding the phone up to the implant microphone," she said.
The journey from silence to sound begins when the implant processor is activated four to six weeks after surgery. Hearing sound through a cochlear implant during those first months is often unstable as thresholds change and unpredictable as the quality of sounds change. The first sounds have been described as being "robotic," "like ducks quacking," or just plain "weird."
It all begins when the cochlear implant processor is programmed. Each electrode along the array is stimulated one at a time to find the lowest level of current needed to barely hear a sound to establish a threshold. The second step is to find the upper level of stimulation by stimulating each electrode individually and raising the current to find a level that is the comfortably loud, and balancing the level of current across all electrodes.
"We want to program sound in the outside world onto what they can hear," Skinner said. "We find that different people perform better with different rates of stimulation." Each implant manufacturer develops different strategies that determine the way that the electrodes are stimulated. Some strategies stimulate all electrodes at the same time, while other strategies stimulate the electrodes sequentially in pulses like playing a xylophone, or stimulate pairs of electrodes along the array.
"For small babies with limited language skills, the process of programming the processor can be challenging and time consuming," Brown said. To provide a starting point in programming the processor, small children can now be fit by neural response imaging which measures the response of the auditory nerve to electrical stimulation. The audiologist uses one electrode to stimulate the auditory nerve as the child hears pulsing beeps, and uses a nearby electrode to measures the response of the auditory nerve to the electrical stimulation. By sampling several electrodes throughout the array and watching to see if the baby turns his head in response to sound, the audiologist can determine the threshold where the sound is audible, but not too loud.
"With all these different options that we don't know how to predict, programming of the processor needs to last a month over weekly sessions to go through enough of the combinations to find out what works best," Skinner said.
Programming the cochlear implant processor is just the first step. Getting an implant is like being given the keys to a car but not knowing how to drive it. Aural rehabilitation is the key to helping children interpret interpret sound in their environment and use it in a meaningful way to acquire spoken language, Kirk said.
The aural rehabilitation process begins even before the child receives an implant to establish a readiness to listen. Through structured play, the child is taught to react to loud, low-frequency sounds from various locations within the room, and to understand that speech has a purpose and makes things happen, Kirk explained.
After implantation, aural rehabilitation serves a dual role in promoting the development of speaking and listening skills, and assessing those abilities to provide feedback to the audiologist about the cochlear implant speech processor settings.
"Parents play an important role in aural rehabilitation and they are the primary teacher for their child," Kirk said. "Whenever possible, parents should be active participants in therapy sessions, and try to weave listening and speech learning into activities throughout the day."
Coordination between schools and implant centers is also very helpful, Kirk said. "Many times, school personnel have little experience with children who use a cochlear implant." The implant center can assist by providing information about how an implant works, the auditory cues an implant provides, and the development of auditory skills with an implant. Schools, in turn, can assist the implant team by providing information about the child's development and language use in the classroom.
For adults, getting a cochlear implant brings changes in their communication abilities and their relationships, said Margo Skinner. "Some people have been dependent on a family member for part of their life with hearing loss and the cochlear implant changes their relationship." People have also learned communication strategies that aren't really effective--such as dominating the conversation to avoid the embarrassment of not understanding what was said--and they need to learn more effective strategies to promote communication.
Adults also need practice in listening without visual cues. Brackett suggested using both an analytic approach in which the listener deciphers the exact sounds of words, often using nonsense words, and a global approach, in which the listener uses familiar words and grammar to help them make sense of unfamiliar words within a paragraph.
"Aural rehabilitation provides a more directed approach in building on the auditory information they have already achieved through hearing aids," Brackett said "and it will help them learn to listen with the implant much quicker."
And with practice and patience, they'll be on the way to understanding what was said.