The structures of the WISC-R subtests: a comparison of the IQ-profiles of reading impaired and autistic subjects.

The present paper is an analysis of the WISC-R test profiles of reading impaired subjects and autistic subjects. It is argued that well-known classification systems such as Bannatyne's categories (1974) and Kaufman's factors (1975) cannot explain differences in the peaks and troughs across the two populations. A new classification system is then developed. The 11 different WISC-R subtests are characterised in terms of a combination of three modes of cognitive functioning: a knowledge mode (declarative-procedural), a processing mode (transformation-preservation of information), and a verbal-nonverbal mode (verbal-nonverbal-processing). When reanalysed within this reference frame, the IQ profiles of reading impaired subjects (N = 114) and autistic subjects (data from 12 studies reviewed by Happé, 1994) were similar regarding differences in the verbal-nonverbal dimension. However, the IQ profiles showed an opposite pattern in the declarative-procedural dimension, and an opposite pattern in the preservation-transformation dimension. Thus, the new classification system allows one to interpret the IQ-profiles of both groups within a single and coherent reference frame.