Objectives: Intelligence as a construct of cognitive abilities is the basis of knowledge and skill acquisition and the main predictor of academic achievement. As a broad construct, it is usually divided into subdomains, such as nonverbal and verbal intelligence. Verbal intelligence is one domain of intelligence but is not synonymous with specific linguistic abilities like grammar proficiency. We aim to address the general expectation that early cochlear implantation enables children who are hard of hearing to develop comprehensively, including with respect to verbal intelligence. The primary purpose of this study is to trace the longitudinal development of verbal and nonverbal intelligence in children with cochlear implants (CIs).
Design: Sixteen children with congenital hearing loss who received unilateral or bilateral implants and completed at least two intelligence assessments around the age of school entrance were included in the study. The first assessment was performed around 3 years after CI fitting (chronological age range: 3.93 to 7.03 years). The second assessment was performed approximately 2 years after the first assessment. To analyze verbal and nonverbal IQ in conjunction and across children at different ages, we used corresponding standardized and normalized tests from the same test family (Wechsler Preschool and Primary Scale of Intelligence and/or Wechsler Intelligence Scale for Children).
Results: Regarding longitudinal development, both verbal and nonverbal IQ increased, but verbal IQ increased more substantially over time. At the time of the second measurement, verbal and nonverbal IQ were on a comparable level. Nevertheless, we also observed strong inter-individual differences. The duration between both assessments was significantly associated with verbal IQ at the second measurement time point and thus with verbal IQ gain over time. Education mode (regular vs. special kindergarten/school) was significantly correlated with nonverbal IQ at the second assessment time point.
Conclusions: The results, despite the small sample size, clearly suggest that children with CIs can achieve intellectual abilities comparable to those of their normal-hearing peers by around the third year after initial CI fitting, and they continue to improve over the following 2 years. We recommend further research focusing on verbal IQ assessed around the age of school entrance to be used as a predictor for further development and for the establishment of an individual educational program.
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