Individuals who have lost both their vision and their hearing face a daunting challenge in our world of communication based on sight and sound.
But a new Health System study suggests that contrary to expectations, those who are both deaf and blind can regain significant ability to recognize speech through the use of a cochlear implanta 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 traditionally have not 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.
However, a group of eight deaf-blind U-M patients did even better at speech perception after implantation than did a comparison group of deaf patients, according to their case histories in a paper in the January issue of Otology and Neurotology.
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, a 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 U-M patients had lost most or all of their hearingeither before or after they learned spoken or sign languageand then began to lose their vision. All eight received a cochlear implant and substantial rehabilitation therapy at the Health System, and took tests before and after 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. The other study looked at blind people who became deaf later in life.
In a comment published alongside the U-M paper, British expert Richard Ramsden notes that the Health System 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 both deaf and blind, having lost their hearing and sight either together or separately due to diseases in their genes, the womb or during childhood. Many still communicate via the same methods as did Helen Kellerfinger spelling and Braille.
Two of the U-M patients in the study had Ushers syndrome, a common cause of deafness accompanied by a progressive vision loss due to retinitis pigmentosa. Two had sensory loss thought to result from TORCH syndrome, which affects the babies of women who contract German measles, or rubella, while pregnant. Two had genetic syndromes, and 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; the other two got theirs at age 3 1/2. Five of the adults 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 improved in use of selected sounds, and the other, though not yet totally evaluated, 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, got a perfect score on the same test within one year after implantation. The child is 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 patients to recognize speech by sound alone, even though they cannot see someones lips moving.
This theory goes along with observations and reports that people who have lost one sense have other senses that are much sharperfor instance, hearing in blind people. The brains 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 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.
The papers other authors are Angelique Boerst, clinical audiologist I, and Steven Telian, medical director of the Cochlear Implant Program, the John L. Kemink Professor of Neurotology and professor of otorhinolaryngology.