Testing nonverbal IQ in children with Autism Spectrum Disorders

• We tested children with ASD and neurotypical controls on the nonverbal components of two different IQ tests, the KABC-II and WISC-IV.
• We examined the effects of selective timing criteria on performance.
• The ASD sample scored significantly worse on measures of processing speed.
• Only the ASD sample scored significantly higher on the KABC-II compared to the WISC-IV.
• The two tests appear to function differently in this clinical sample.

15 high-functioning school aged children with ASD and 15 neurotypically developing age matched controls were assessed using the WISC-IV and the KABC-II in order to assess whether the WISC-IV has rectified problems associated with the WISC-III's undue emphasis on timing measures. No significant group differences were found for the PRI sub-scale of the WISC-IV nor for the nonverbal scale of the KABC-II, but the ASD group scored significantly lower than controls on the Processing Speed Index of the WISC-IV. This supports the need to isolate of timing criteria when IQ testing in populations with ASD, as is now the case with the WISC-IV. However significantly higher scores were obtained for the KABC-II versus the PRI for children with ASD only. The reasons for this are discussed with regard to a possible cultural bias in the Picture Concepts subtest of the WISC-IV.