Intellectual ability of Mandarin-speaking children using cochlear implants

The aim of this study was to assess the verbal and performance intelligence of young Mandarin-speaking cochlear implant users with the Wechsler Intelligence Scale for Children (WISC). We also analyzed whether related factors helped develop verbal and performance IQs. We studied 60 children implanted with Nucleus 24 devices; the children represented a consecutive sample of every implantee aged 6 or older from 2002 to 2006. All subjects had 1 year to 8 years and 7 months of implant experience. Five children with known neurological, developmental delay and multiple handicaps were excluded. Intellectual functions were evaluated using the Mandarin version of the WISC-III, which includes 5 subsets for verbal IQ (information, comprehension, similarities, arithmetic and vocabulary) and 5 subsets for performance IQ (picture completion, picture arrangement, block design, object assembly and coding). After conversion, we found that the mean verbal IQ was 85.1 +/- 19.9 (range 56-133), and the mean performance IQ was 99.2 +/- 15.9 (range 61-131). The distribution of verbal IQ was significantly different from that of the hearing population. A much larger proportion (32%) falls into the category of 'intellectual deficiency' and a relatively smaller proportion in the 'average' and 'above average' level. As for performance IQ, the distribution was not significantly different from the norms. Regarding the possibly related factors, univariate and multivariate linear regression showed that the verbal IQ was significantly affected by gender (female > male, p = 0.004), side of implantation (bilateral > left > right, p = 0.017) and two speech test scores (PB score, p = 0.036; sentence, p = 0.002), but not by age at implantation (p = 0.621) or length of implant usage (p = 0.480). Only a moderate correlation (r = 0. 49) was found between verbal and performance IQ. In conclusion, we have demonstrated that the performance IQ for the cochlear implant users is not different from their counterparts with normal hearing. However, the distribution of verbal IQ significantly shifts to the left. Our findings suggest that the verbal IQ test may just be another measurement of spoken language outcomes or learning skills and therefore may not represent the 'true intelligence' of these cochlear implant users.