Cognitive skills, not just hearing devices, are key to children?s ability to hear

The key to whether cochlear implants work may lie in psychology, not in physiology.

By Beth Azar
Monitor staff

For the past decade, a handful of psychologists have been exploring why some deaf children with cochlear implants become proficient at spoken language while others don?t. They think they?re homing in on the answer: cognition.

They are collecting evidence to show that cognitive skills go hand-in-hand with hardware advances in the quest to teach profoundly deaf children oral language.

The hardware in question is the cochlear implant?a sophisticated electronic device with parts that are surgically implanted in the inner ear, or cochlea. Unlike hearing aids, which simply amplify sound waves, cochlear implants transform sounds into electrical impulses, which then stimulate the nerves connecting the ear to the brain, allowing a person to perceive sound. The sound coming from the implants is mechanical and somewhat impoverished but similar to normal speech, say researchers. Children must take this unnatural signal and extract information they can use to decipher and reproduce language.

Use of the devices in children is controversial. Opponents say that many children with implants never learn to understand spoken language and that the concentration on teaching them oral instead of signed language leaves many of them with no language at all. However, researchers working with the children say there?s plenty of evidence that cochlear implants provide many children with the ability to learn spoken language. But they admit that there are vast individual differences. Some children?those who researchers call the 'stars'?learn to speak on a par with hearing children and are even able to talk on the phone and play musical instruments. Others develop few oral language skills.

The goal is to figure out why some succeed and others fail to learn. Indiana University psychologist David Pisoni, PhD, is convinced that psychological and cognitive differences?more than difference in sound perception?hold the answer.

The research is just beginning, but he and a handful of others believe that they will decipher the cognitive reasons why some children have trouble translating the electrical stimulation into language and design interventions that help them do better. Much of their research is funded by the National Institute of Deafness and Other Communication Disorders (NIDCD) at the National Institutes of Health.

'The work is a very appropriate expansion of our research portfolio in the area of cochlear implants,' says Amy Donahue, PhD, chief of NIDCD?s Hearing and Balance Sciences Branch.

A language-specific lag

From early-stage studies of children with cochlear implants, researchers find that, although there?s little difference in the quality and quantity of the sounds reaching each implant recipients? brain, the earlier children receive implants, the more likely they are to develop spoken language. But early implantation doesn?t predict everything, say researchers.

'Most [of the children receiving implants] do better than they would with a hearing aid,' says developmental psychologist Suzanne Hasenstab, PhD, professor and director of audiology at the Medical College of Virginia Hospital. However, there are significant differences in language learning ability within that group, regardless of how early they receive the implant.

The goal of most psychological research is to understand the perceptual and cognitive reasons for these differences. Pisoni and his colleagues, for example, have begun to systematically compare the 'stars?' abilities with those of children with implants who score in the lowest 20th percentile on tests of spoken language perception and production. Preliminary findings indicate that the children don?t differ in IQ, visual motor ability, visual attention or their response to sounds. The difference appears to be specific to language?the ability to interpret spoken words and the acquisition and development of a lexicon.

'The stars are showing selective improvements and gains in areas related to the manipulation of words,' says Pisoni. 'This is critical. These children don?t differ on global measures of cognition' such as IQ and visual attention, just on language-related measures.

A double whammy

A language-specific problem could stem from several sources, says Pisoni. It could be that the children have trouble with language as a whole or with specific cognitive skills crucial to learning language.

In a recent study Pisoni and Ann Geers, PhD, professor of speech and hearing at the Central Institute for the Deaf at Washington University, tested how well children with cochlear implants remembered a list of numbers presented orally.

Short-term digit-span memory is a good test of working memory, and working memory is critical for understanding and producing language, says Pisoni. He and his colleagues found a strong correlation between digit-span memory and language-related measures, such as word recognition and comprehension with the children with the longest memories scoring the best.

It may be that a poor working memory is preventing some children with cochlear implants from learning oral language, says Pisoni. 'If [working memory] turns out to be a predictor of success, we can track it,' he says. 'And, because working memory is flexible, we can devise interventions that improve working memory in these children.'

But it?s too early to jump to any conclusions, says speech-language pathologist Bruce Tomblin, PhD, a member of a cochlear implant research team at the University of Iowa at Iowa City. We don?t know yet whether working memory influences children?s language development or whether a child?s language status affects working memory function, he says.

One thing that?s for sure: Some deaf children, like hearing children, have language disabilities above and beyond their hearing troubles, says Hasenstab. Problems with learning disabilities in the deaf community have only gained attention since the early 1980s. But it?s likely that some of the children with cochlear implants who have trouble learning oral language have a specific language learning disability.

'A cochlear implant will not fix a learning disability in a hearing impaired child with such a disorder,' says Hasenstab. Instead, such children will also need to be treated for the learning disability.

It takes work

Even for children without learning disabilities, learning spoken language with a cochlear implant is not magic, says John Knutson, PhD, of the University of Iowa at Iowa City. It takes a great deal of training, hard work, persistence and social support.

'The implant is like knee replacement surgery,' says Geers. 'Without proper postoperative therapy you won?t get much benefit.'

It?s even harder than recovering from a knee replacement, says Knutson. For a person with a new knee, walking is still second nature. But for children who have never heard sound, deciphering language is foreign. On average, children don?t begin to show clear signs of language improvement until about two years after implantation, says Tomblin. Interestingly, it also takes about two years for hearing children to begin using oral language skills.

'By two years post-implant we begin to see clear differences between children with cochlear implants versus deaf children without implants on English language production measures,' says Tomblin.

Geers and her colleagues are trying to determine the best strategies for teaching language to children with cochlear implants. They?re in the second year of a five-year project to evaluate the language abilities of long-time cochlear implant users?8- and 9-year-olds who have had implants since they were 2 or 3?exposed to a variety of learning environments.

The language abilities of the 50 children enrolled in the study so far run the gamut from unintelligible spoken language to perfect speech. And while some children read at the seventh-grade level, others are illiterate. Some children have been taught with what?s called total communication?a combination of talking and signing?and others are in oral-only programs. And even within each method, programs differ in their techniques: Some total communication programs emphasize signing, others equally emphasize signing and speech and others are mostly oral.

The jury is still out on what works best. But researchers agree that if children are to learn oral language, there must be a concerted effort by parents and educators to encourage them to use their cognitive skills to decipher the sounds coming in through the implant.