In think that advantage of Block Design above Picture Completion in Wechsler test appears to be autistic trait (which has not to be present in every autistic person, obviously). I saw interesting chart with average WISC-IV scores of children with autistic disorder, Asperger syndrome, NVLD and some other developmental disorders and average Block Design and Picture Completion scaled scores were about:
- for autistic disorder: Block Design 7,9, Picture Completion 6,5,
- for Asperger syndrome: Block Design 10,9, Picture Completion 11,5,
- for NVLD: Block Design 7,4, Picture Completion 9,6.
Nearly linear trend from autistic disorder by Asperger syndrome to NVLD: more autistic is Block Design dominance, more eneldic is Picture Completion dominance.
For autistic disorder BD - PC was about 1,4 scaled scores, for Asperger syndrome BD - PC was about -0,6 scaled score and for NVLD BD - PC was about -2,2 scaled scores.