|Lisa Zastrow (left) watches as her 1 1/2-year-old daughter Riley undergoes a hearing test with Carissa Ashbaugh, clinical audiologist, at the Hearing Rehabilitation Centers Cochlear Implant Program. The test was done without Rileys cochlear implant in place. Photos by Marcia L. Ledford, U-M Photo Services|
In fact, Health System (UMHS) researchers report, the positive effect of early implantation is evident even in comparisons of children of various ages who have had their implants for the same length of time, despite the older childrens maturity advantage.
The study results are published in the January issue of the journal Otology and Neurotology (formerly the American Journal of Otology).
We found a significant difference in speech recognition between those who got their implants between the ages of 2 and 4 years, during the critical language development period, and those who received them later, says Paul Kileny, lead author, professor of otorhinolaryngology, and director of speech and audiology. 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.
The study looked at test results from 101 children who received the same model of cochlear implant between the ages of 2 and 14. The children represent one-third of all pediatric patients treated in the U-M program, one of the oldest and largest in the country.
The children were divided roughly in half, to allow for two analyses that could help isolate the effect of age at implantation on speech perception. One group of 48 children had their speech-recognition skills tested when they turned 7, regardless of when they got their implants. The other group of 53 children of various ages was tested three years after implantation, to isolate the effects of age at implantation. All children took a battery of six standard tests to measure their ability to recognize sounds, words and sentences.
|A cochlear implant|
Kileny and his co-authors, Teresa Zwolan, clinical associate professor of otorhinolaryngology, and Carissa Ashbaugh, clinical audiologist, collected the data over several years from routine tests taken by UMHS cochlear implant recipients at regular intervals. The children were between ages 5 and 17 when evaluated.
The researchers grouped the children in each arm of the study into four subgroups. Children tested at three years post-implant were divided according to age at implantation, and those tested at age 7 were grouped according to time since implantation.
The differences between the groups were clearestand most statistically significantin the 7-year-olds who had had their implant for four or more years and in children whose three years of implantation had begun between the ages of 2 and 4. But even those 7-year-olds who had only had their implants for three years scored significantly better than those who had had them one or two years. And children who first heard between the ages of 5 and 7 did better than those who got their implants between the ages of 10 and 13.
This effect of better speech perception performance from longer and earlier use of an implant is probably linked to the effect that cochlear implants have on the developing auditory nervous system, Kileny explains. Research has shown that the nerve cells involved in the auditory system require early and constant stimulation in order to develop important connections and patterns of activation necessary for speech perception. Clinical studies have shown that both children and adults keep improving their speech perception with time, though adults tend to plateau after a while and children continue to improve over a period of years.
Thus, according to Kileny, the wait-and-see approach in the case of newly diagnosed young children may be detrimental in the long run. 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.
Researchers in childhood development have consistently found that toddlers and young children reach crucial milestones in speech and language development early in life. The new studys result may clearly point to the risk of missing or delaying those milestones because of hearing impairment.
The team is still looking at the long-term effects of cochlear implantation before the age of 2. The U.S. Food and Drug Administration has approved implants for use in children as young as 1, and clinical trials in 12- to 24-month-olds are now under way at UMHS and elsewhere. Initial data on these youngest patients already shows a difference from those who got their implants later in life.