Study shows hearing devices open channels of communication for deaf people who lose vision
People who have lost both their vision and their hearing face a daunting challenge in our world of communication based on sight and sound. Without the ability to use visual or aural clues to help them comprehend text, images, or speech, they have few options.
But a new University of Michigan Health System study suggests that, contrary to expectations, the deaf-blind can indeed regain significant ability to recognize speech. The authors report significant improvement in eight deaf-blind patients who received a cochlear implant -- a device that translates sound into electrical impulses that are delivered directly to the inner ear.
While tens of thousands of deaf people have received cochlear implants, the devices haven't traditionally been seen as appropriate for deaf-blind patients. This is because significant numbers of deaf recipients still benefit from visual clues while using their implants to help them understand speech. But in fact, the group of deaf-blind UMHS patients did even better at speech perception after implantation than a comparison group of deaf patients, according to their case histories in a paper in the January Journal of Otology and Neurotology (formerly the American Journal of Otology.)
"These patients need every stimulus they can get, and cochlear implants seem to produce a significant impact on their ability to comprehend the world despite multiple sensory deficits," says lead author Hussam El-Kashlan, M.D., a UMHS cochlear implant surgeon and assistant professor of otolaryngology. "It also appears that the positive effect is greatest in those who receive their implants earliest."
The research finding comes from analysis of UMHS patients who had already lost most or all of their hearing, either before or after they learned spoken or sign language, and then began to lose their vision. All eight received a cochlear implant and substantial rehabilitation therapy at UMHS, and took tests before and afterward to measure their speech perception.
To date, the study is one of only two of its size to examine the effect of cochlear implants in people with multiple sensory deficits, as the condition is often called. The other looked at blind people who went deaf later in life.
In a comment published alongside the UMHS paper, British expert Richard Ramsden notes that the UMHS study "lends support to the increasing feeling that patients who suffer from...deafness and blindness may be very good candidates for cochlear implantation."
As many as 40,000 Americans are deaf-blind. Many still communicate via the same methods - finger spelling and Braille hand writing - as the most famous deaf-blind person in history, Helen Keller. And like Keller, many lose their senses either together or separately due to diseases in their genes, the womb or during childhood.
Two of the U-M patients in the study had Usher's syndrome, a common cause of deafness accompanied by a progressive vision loss due to retinitis pigmentosa. Two others had sensory loss thought to result from TORCH syndrome, which affects the babies of women who contract German measles, or rubella, while pregnant. Two others had genetic syndromes tied to problems in the mitochondria within their cells. The other two lost senses because of cancer or unknown factors tied to multiple medical problems.
Six of the U-M patients received the cochlear implant as adults, while the other two got theirs at the age of three and a half. All the adults except one had developed language skills before going deaf, and neither of the children had.
Before implantation, the adults who had language skills scored zero or extremely low on tests of their ability to hear and recognize sounds, words and sentences. After implantation, three of the five achieved good to excellent scores on tests of all sounds, the fourth has improved in use of selected sounds, and the last has not yet been totally evaluated but reports subjective improvement. The other adult, who never learned to speak or understand spoken language, is now aware of external sounds and is developing a limited understanding of spoken words.
One of the children, who started with a score of zero on pattern-recognition tests that don't rely on language skills, got a perfect score on the same test within one year after implantation, and is now scoring high on word, phrase and sentence tests and attending a mainstream school despite increasing visual impairment. The other child, who has numerous other medical problems that interfere with his development, has shown more alertness and awareness of sound.
El-Kashlan and his colleagues theorize that the cochlear implant acts as a "sensory substitute", allowing the patients to recognize speech by sound alone even though they cannot see someone's lips moving.
This theory goes along with observations and reports that people who have lost one sense have other senses that are much sharper - for instance, hearing in blind people. The brain's ability to learn this kind of compensation is thought to be greatest early in life, when all the senses are still feeding new data to the brain and it is "plastic" or able to acquire new knowledge easily.
The U-M team hopes to explore the phenomenon further using medical imaging techniques that will show which parts of the brain "light up" when the deaf-blind cochlear implant recipients are exposed to sounds. They will also continue to follow the seven of the eight patients who survive, and monitor their continuing progress with further tests.
The paper's other authors are audiologist Angelique Boerst, M.A., and Steven Telian, M.D., medical director of the UMHS Cochlear Implant Program, one of the largest and oldest in the nation.