Estimating the influence of cochlear implantation on language development in children

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Abstract
Research studies reviewed here have identified a wide variety of factors that may influence a child's auditory, speech and language development following cochlear implantation. Intrinsic characteristics of the implanted child, including gender, family socioeconomic status, age at onset of hearing loss and pre-implant residual hearing may predispose a child to greater or lesser post-implant benefit. Intervention characteristics that may influence outcome include age of the child when deafness is identified and amplification and habilitation is initiated, the communication mode used with the child and the type of classroom/therapy employed. Characteristics of the implant itself include generation of technology used, the age of the child when implant stimulation is initiated, and the amount of time the child has used the implant. These factors interact in unpredictable ways, so that isolated correlations between predictor variables and outcome scores may be difficult to interpret. Results for two independent samples of children tested by different laboratories were compared using multiple regression analysis to take into account relationships among predictor variables. Implant age was a significant predictor, and children in both samples who received a cochlear implant sometime between their first and second birthday achieved oral receptive vocabulary levels within one standard deviation of hearing age-mates. Age at implant accounted for a similar proportion of variance in receptive vocabulary outcome scores in each sample. A unique predictor was then added to each analysis. The addition of pre-implant aided threshold not only increased the total predicted variance, but also increased the effect of implant age as a predictor variable. A different result was observed in the other sample, when the added predictor variable was non-verbal IQ, where the estimated contribution of implant age was reduced. Future studies are advised to control for independent contributions of implant age, non-verbal IQ, and pre-implant aided thresholds when examining expected outcomes.