For People Who Cannot Benefit from Hearing Aids


Early Cochlear Implants Aid Deaf Children

Source: Press Release

January 3, 2001

Deaf and hearing-impaired children get more benefit from a cochlear implant the younger they are when they receive it, and will do better on speech recognition tests later on in life, according to a new study from the University of Michigan Health System.

Cochlear implants transform speech and other sounds into electrical impulses that stimulate auditory nerve terminals within the inner ear. Children and adults with severe to profound sensorineural hearing loss in both ears are able to have their hearing restored and improve their communication with the implants. Cochlear implants are for people who cannot benefit from hearing aids.

The report states that the positive effect of early implantation is noticeable even when comparing older and younger children who have had their implants for the same period of time, despite the older children's maturity advantage.

The report's findings, published in the January issue of the journal Otology and Neurotology (formerly the American Journal of Otology), add more evidence to the belief that hearing-impaired children should get cochlear implants as soon as possible if they are unable to gain any benefit from hearing aids.

"We found a significant difference in speech recognition between those who got their implants between the ages of two and four years, during the critical language development period, and those who received them later," Paul Kileny, Ph.D., lead author of the study and professor and head of audiology at UMHS explained. "We also found that the longer children had had their implants, the better they did, though the effect was still largest in those who were implanted earliest."

Test results were examined from 101 children between the ages of 2 and 14 years who received the same model of cochlear implant at UMHS. The study is more relevant than similar studies done in the past because of the size of the group and the identical management of the patients. The group of children represents a third of all pediatric patients treated in the history of the UMHS program, which is one of the oldest and largest in America.

The group was divided almost equally allowing for two analyses to isolate the effect age at implantation has on speech perception. A group of 48 children were tested on their speech-recognition skills once they turned 7, regardless of when they received their implants.

The other group of 53 children of various ages was tested three years after implantation. Each child was given six standard tests measuring their ability to recognize sounds, words, and sentences. The results showed a combined effect of age at implantation and the length of time children had their implants. The authors, Kileny, audiologists Teresa Zwolan, Ph.D., and Carissa Ashbaugh, M.A., collected the data used in the study over a period of several years from routine tests given to UMHS cochlear implant recipients. The children evaluated were between the ages of 5 and 17. The children in each part of the study were divided into four subgroups. Those tested at 3 years post-implant were divided according to their age at implantation and those at age 7 according to time since implantation.

The differences between the groups were most noticeable in the 7-year-olds who had their implants for four or more years, and the children whose implantation had occurred between the ages of 2 and 4. However, even the 7 year olds who had only had their implants for three years scored significantly better than those who had them one or two years. Children who were able to hear for the first time between the ages of 5 and 7 did better than children who did between the ages of 10 and 13.

While some speech perception test results didn't show clear differences among the groups, Kileny pointed out that some tests required sophisticated linguistic and vocabulary skills which the youngest patients might not have developed regardless of their age at implantation.

The reason for the better speech perception performance because of longer and earlier use of an implant is probably due to the effects cochlear implants have on developing auditory nerves, according to Kileny. Nerve cells used in the auditory system need early and constant stimulation to develop important connections and patterns of activation used in speech perception. Clinical studies have shown that both children and adults continue to improve their speech perception over time, although adults plateau eventually.

Because of this, Kileny says, the "wait and see" approach to newly diagnosed young children may do them more harm over time. "I have seen several youngsters whose parents have opted to wait for new technological developments, in some cases for two to four years. These patients, though they began with great potential, ended up deriving minimal benefit from their cochlear implant, having missed crucial speech and language development milestones."

Childhood development researchers consistently find that toddlers and young children reach important milestones in speech and language development early in life. The results of this study may indicate the risk of missing or delaying those milestones because of hearing impairment.

Long-term effects of cochlear implantation before the age of two are still being examined. The U.S. Food and Drug Administration has improved implants for children in as young as 12 months. Clinical trials involving 12 to 24 month old children are underway at UMHC among other places.

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