Earlier Age at CI is Associated with Better Communication Development

This finding is robust and has been verified in multiple studies by researchers using different assessment tools. The research literature suggests a substantial advantage for language acquisition in children receiving their CIs at young ages in comparison with older ages. Niparko and colleagues used a controlled prospective, longitudinal, multisite design to evaluate age at implantation in relation to spoken language development as part of the Childhood Development after Cochlear Implantation (CDaCI) study. Children implanted prior to18 months of age followed language development trajectories similar to hearing peers. Implantation after 18 months created less favorable trajectories.

These findings should compel us to examine just how early deaf children may need to receive a CI if language-learning gaps relative to hearing children are to be avoided. Even for children whose language-learning rate after implantation does not match that of normal-hearing (NH) peers, rates postimplantation have been shown to be consistently faster than those established preimplantation. In addition, higher increases in comprehension and expression were associated with greater residual hearing before implantation, higher parent-child interaction scores, and higher socioeconomic status.

Nicholas and Geers used spontaneous language samples and the Preschool Language Scale to evaluate 76 children whose age at cochlear implantation ranged from 12 to 36 months and who had used oral-only communication since implantation. Children implanted at the youngest ages, between 12 and 16 months, were more likely to achieve age-appropriate spoken language. By contrast, children implanted after 24 months of age did not catch up with NH peers when tested at age 4.5 years. The investigators concluded that children who receive a CI as late as age 3 years may experience great difficulty catching up with NH age mates.

Manrique and colleagues studied 130 CI children using the Peabody Picture Vocabulary Test and the Reynell Scales. Their findings suggested that children implanted before 2 years of age exhibited better language development than those implanted after age 2.

The effect of age at cochlear implantation was studied using scores from the Infant-Toddler Meaningful Auditory Integration Scale (IT-MAIS) in 3 groups of children who had received a CI at the age of 12 to 18 months, 19 to 23 months, or 24 to 36 months, respectively. Scores from each age group, obtained at pre-CI, then at 3, 6, and 12 months post-CI, were compared with IT-MAIS scores obtained from a large group of children with normal hearing. The results were consistent with those cited above: The most impressive scores were obtained from children in the youngest-implanted group, in which more than half of the subjects achieved scores after 6 months of CI use that matched the scores of NH peers. Although substantial gains in scores associated with CI use were also obtained from the two groups implanted at older ages, the trend was less dramatic for those implanted between ages 19 and 23 months, and still less dramatic for those implanted between ages 24 and 36 months. In addition, the scatter in scores was much wider for the oldest than the youngest group, indicating that it became harder to predict post-CI performance as children’s age at implantation increased.

The basis for improving the language-learning trajectory with young age at CI relates to sensitive periods and neural plasticity. Using the latency of the P1 cortical auditory evoked potential as a measure of central auditory pathway maturity, Sharma and colleagues found that children implanted at 3.5 years or younger showed age-appropriate latency responses by 6 months post-CI. These investigators concluded that in the absence of normal stimulation, a sensitive period persists for about 3.5 years during which the human central auditory system remains maximally plastic.

Other central nervous system factors play a role in language outcomes. For example, there is superior potential for younger children to learn language incidentally. Although children who are older at the time of CI may still benefit from incidental learning, it is likely that their rehabilitation and environment will need to address greater deficits.

Improved speech processing strategies provide more communication enhancement. The amount and quality of information provided by the speech processor has a measurable effect on language. Data from Geers and colleagues have shown that children whose CIs were upgraded on a regular basis with state-of-the-art speech-processing improvements outperformed children using older speech-processing technologies. A wide dynamic range and optimal growth of loudness characteristics contribute substantially to a child’s ability to hear speech. Accordingly, outdated processors should be revised in favor of technology that can enhance the child’s listening experience.

Children with CIs Outperform their Profoundly Deaf Peers Who Use Hearing Aids

Faster rates of language learning and higher overall language achievement levels are consistently documented in CI children relative to their unimplanted, deaf peers. The average profoundly deaf child with hearing aids learns language at about half the rate of NH children, acquiring 6 months of language in 1 year’s time. This trend for deaf children to acquire language, on average, at only about half the level of NH peers is found repeatedly in the literature, going back to such studies as those by Osberger. If the thresholds of hearing for a profoundly deaf child are improved to a level those similar to those experienced by a hard-of-hearing child, this conversion represents an enormous improvement in auditory learning potential, given the differences in performance that have been documented between children with profound versus aidable sensorineural hearing loss.

CIs Enable Some Children to Acquire Language at a Rate Similar to that of Normal-Hearing Children

The CI changes the trajectory of spoken language learning in most recipients, elevating the rate of learning relative to the pre-CI period. Several studies demonstrated that the average child who received a CI learned approximately 1 year of language in 1 year’s time. Blamey and colleagues documented a rate of language learning in a group of CI children that was considerably slower than that reported in other studies. However, some children in the Blamey and colleagues study had not received their CI until as late as age 8 years, a factor that likely contributed to the more modest improvements in language. As more data have been analyzed, especially from large-scale studies, it is clear that language outcomes are substantially more favorable if implantation occurs before a wide and persistent gap develops between chronologic and language age. In addition, it is estimated that 40% of deaf children have additional disabilities. An increasing number of children from that group, which makes up a substantial percentage of all deaf children, are receiving CIs. Among that group, a language-learning rate comparable to that of children with normal hearing would be the exception rather than the rule. This finding underscores the need to consider that certain conditions should prompt a thorough consideration.

Many Children Remain Delayed in their Language Skills Even After Implantation

In a nationwide sample of 8- to 9-year-olds who received a CI between 24 and 35 months of age, only 43% achieved combined speech and language skills within the average range, relative to NH peers. Recall that significant delays in language development already exist in most children by the time they receive their CI, even in those who are implanted early. As Tyszkiewicz and Stokes note, a 2-year-old hearing child has a highly tuned auditory system used since birth, generating a large auditory repertoire. The 2-year-old who is implanted has a very different starting position, with little of this knowledge in place. To prevent a continued delay, children must either learn language at a rate faster than normal after CI, or receive their CIs early enough to prevent an insurmountable chronologic language gap from forming in the first place. Unfortunately, language-learning rates that exceed those of hearing children are rare.

A Wide Range of Language Benefit is Observed Across Children

Studies of language ability in CI children consistently yield a wide range of performance outcomes. This wide range is found in virtually every study of CI users and requires that data be interpreted with caution, particularly when these data are presented as average performance. Large standard deviations in data limit the usefulness of looking at “average” scores. Regardless of the specific device used, some children do extremely well with their implants, performing at the upper end of the continuum, whereas a small number of children receive limited benefit from their implants. The attempt to identify the factors that might account for this variability requires a multivariate use.

Children Using both Oral and Total Communication Improve in their Language Skills After CI; but as a Group, Oral Communication Users Outperform Those Using Total Communication

This trend is robust, having been reported in a variety of observational studies using different assessment procedures. However, these studies are without controls, thus preventing analyses of covariates and confounders (eg, those related to specifics of the hearing history and the family environment). Underlying language skills are the domain in which total communication (TC) children with CIs have competed most favorably with oral communication (OC) children, when each group of children is tested in its preferred modality—that is, TC children tested in sign plus speech, OC children tested in oral-only mode. Under these conditions, Geers and colleagues found no significant differences in language comprehension or verbal reasoning between OC and TC children with CIs who were implanted by age 5 years. However, better performance of the OC children emerged when other aspects of language were assessed, including expressive vocabulary, morphosyntactic use, utterance length, and narrative form—all measured via spontaneous language samples. This advantage of the OC over the TC group was apparent even when the TC children were credited with signed as well as oral productions.

As mentioned, methodological challenges persist in this research related to confounding influences. TC and OC children may not be equal at the start of their intervention. It is not clear whether the mechanisms by which language is enhanced via a CI are the same for children using OC and TC. These studies almost all used subjects implanted before the age of 5 years. If children with long-standing profound deafness are implanted when they are older than 4 years, the likelihood that they will require sign to augment language learning is very high. This is especially true for language presented in academic settings where the pace of presentation is rapid and the amount of material introduced is voluminous. The advantages of the OC over the TC group have been even more striking in studies assessing speech perception and speech production in children with Cls.

Grammatical Development, Including Syntax and Morphology, is Mastered More Slowly than Other Language Skills in Children with CIs

Even in CI children who demonstrate language comprehension within the average range, expressive use of morphologic markers is often delayed. Deficits in this domain also persist longer than deficits in other language areas in NH children with specific language impairment, suggesting that morphosyntactic skills are a fragile aspect of language, vulnerable to delays. This vulnerability is compounded for children with hearing loss because morphologic markers are almost always in word-final position in English, and consist of high-frequency consonants such as s, z, and t that are often poorly audible, especially in conversation.

Cochlear implantation also affects the development of early communication skills such as eye contact and turn-taking. Tait and Lutman found that these skills begin to develop within 6 months of implantation.