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SIR–In children with profound bilateral deafness, the cochlear implant is the most suitable way of providing access to sound. This is a device equipped with electrodes which are surgically introduced into the inner ear. The implant receives sound information from the outside world, and the electrodes stimulate fibres of the auditory nerve. This surgical technique has been used since 1980 in adult patients and since 1990 in individuals aged 2 to 17 years (US Food and Drug Administration approval dates).1

A cochlear implant undoubtedly permits access to spoken language and facilitates integration into the social environment. As a result, the difficulties experienced by children with profound deafness in acquiring pragmatic skills and tacit knowledge relating to the social world2–5 should diminish after receiving an implant.

Similarly, studies of some aspects of cognitive capabilities comparing children with normal hearing and children with hearing impairment have revealed that the latter experience difficulties at the cognitive level. Whether at the spatial construction level, in categorization or in temporal structuring, some hearing impaired children exhibit developmental deficiencies.6 The mastery of a structured language, whether oral or signed, seems to be a key factor in knowledge structuring.

Few studies have investigated the social and cognitive development1,7–9 of children using cochlear implants. This is why we chose to monitor some aspects of cognitive and social abilities in pre-lingual, children with profound deafness who had received an implant over a period of 2 years. We investigated two hypotheses:

Hypothesis 1: Research into the development of communication abilities in children with severe and profound deafness children has revealed the difficulty they experience in acquiring language activities on the one hand and, on the other, the tacit knowledge which governs interactions in the social world. We therefore hypothesized that implantation, which gives these children access to sound information, would be accompanied by an increase in communication skills and an extension of tacit knowledge concerning the social world.

Hypothesis 2: Cognitive deficiencies observed in some children with hearing impairment compared with children with normal hearing allowed us to hypothesize that cochlear implantation, access to the sound environment and to verbal language would help implanted children perform better in some aspects of cognitive abilities.

The population consisted of 20 pre-lingual, participants with profound deafness (11 males and 9 females) who were aged between 2 years 6 months and 5 years 7 months at the time of surgery (mean age 3y 7mo). Participants were all children, without psychological disorders, who were candidates for receiving a cochlear implant. They were consecutively included from March 2000 to November 2002. All these children received the same cochlear implant (MED-EL Temp+). This study was accepted by the local ethics committee.

Three assessments were made: pre-implant evaluation (n=20), 1 year after activation of the implant (the implant was activated 1mo after surgery; n=20), and 2 years after activation (n=18).

In order to examine the impact of an implant on communication skills and acquisition of social rules, we used Doll’s Vineland Social Maturity Scale10 which has norms for populations with normal hearing and permits the evaluation of three domains of social development (Communication, Socialization, and Autonomy). We used the norms tables to convert gross scores into standardized scores and were able to monitor the participants’ scores in each of the above mentioned fields over a 2-year period.

To evaluate the children’s cognitive development, we used the Snijders-Oomen non-verbal intelligence scale for young children11 for two main reasons. First, the instructions relating to the tasks and the responses are not language-mediated, neither orally nor signed. Second, it provides standardized norms for the deaf population. We calculated an intelligence quotient on the basis of the standard scores. These quotients made it possible to monitor the changes in the participant's scores at the level of intellectual skills over a 2-year period.

Non-parametric tests (Friedman, Wilcoxon) were used for the analyses because the data were not normally distributed.

Analyses revealed a significant effect of the post-implantation experience on communication skills (Friedman, n=18, χ2=13.72, p=0.001; Fig. 1a). More specifically, communication abilities and lexical register increased significantly between the pre-implant interval and the first year after surgery (Wilcoxon, n=20, z=−2.80, p=0.005). Children scoring around 100 signifies that the developmental age corresponds to the chronological age. Although the scores increased again between year 1 and year 2, the difference was not significant.

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Figure 1. (a) Mean scores obtained on the Communication, Socialization, and Autonomy domains of the Vineland Social Maturity Scale10 at pre-implant, 1 year, and 2 years after implantation. (b) Mean scores of intelligence quotients with non-verbal intelligence scale of Snijders-Oomen11 at pre-implant, 1 year, and 2 years after implantation.

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The Socialization scale relates more specifically to the mastery of social conventions and the cultural codes which, to some extent at least, underpin social integration. The analyses revealed a significant effect of the post-implantation experience on the evolution of scores observed on this scale (Friedman, n=18, χ2=7.51, p=0.023). More specifically, while the results obtained increased significantly during the first year after implantation (Wilcoxon, n=20, z=−3.29, p=0.001), they then subsequently stabilized.

The Social Autonomy scale measures children’s ability to look after themselves during their everyday activities. It thus involves aspects such as getting dressed, washing, eating, participating in household chores, and going out. The results obtained indicated that the scores on this scale remained constant over the 2 years of observation.

The analyses revealed significant progress in the children’s intellectual skills after receiving an implant (Fig. 1b). There was a significant effect of the post-implantation experience on the evolution of scores obtained in this intellectual skills task (Friedman, n=18, χ2=10.46, p=0.005). More specifically, the mean intelligence quotient scores increased significantly from the pre-implant interval to the first year following implantation (Wilcoxon, n=20, z=−3,24, p=0.001). Children scoring around 100 signifies that the developmental age corresponds to the chronological age. The increase in the scores between 1 and 2 years following implantation was not significant.

The group of implanted children tended not only to exhibit a greater disposition to communicate but also possessed a greater lexical register as indicated by higher scores in these domains compared with those before implantation. They also had a greater mastery of the social rules which underpin their culture. These results are in line with the early studies conducted among populations of implanted children using another scale (Profil Socio-Affectif; PSA).7 However, our study also suggests that children who received implants did not progress in autonomy. Possibly because of their disability, these children have been particularly overprotected and provision of the implant does not greatly change this state of affairs. Similarly, we observed a significant improvement in performance in some aspects of cognitive abilities at 1 year after implantation. Our study supports preliminary results obtained for participants evaluated using the same task1 and results obtained for other participants evaluated using another task (Raven’s Matrices).9 It is possible that such improved performances are due, in part at least, to the enrichment of the perceptual stimulation which the children receive and their gradual access to language. We also noted that 1 year after implantation the children exhibited a more sustained level of attention. Indeed, prior to implantation, they had found it very difficult to concentrate. In fact, studies have revealed the role played by auditory information in the development and structuring of visual attention.9,12 Holt and Kirk13 showed a link between cognitive abilities and language gains. This study seems to suggest that access to sounds and language should improve some cognitive abilities. Implantation seemed to be accompanied by an increase in communication skills, an extension of tacit knowledge concerning the social role and children seemed to perform better in some aspects of cognitive abilities. An extended longitudinal study of matched profoundly-hearing impaired children with and without implants is needed to further evaluate the outcome of cochlear implantation.

References

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