Scheuffgen, Kristina; (1998) Domain-general and domain-specific deficits in autism and dyslexia. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The work presented in the thesis is based on the assumption that two types of cognitive processes can be differentiated, domain-specific (i.e. modular) and domain-general (i.e. central) processes. Autism and dyslexia are viewed as disorders with domain-specific deficits, while mental retardation is viewed as a disorder in central processing. Using Anderson's (1986) inspection time paradigm it was shown that central processing speed was intact in autism and dyslexia but impaired in mental retardation. The modularity status of phonological processing was investigated using the Phonological Assessment Battery. It was found that test performances did not only require intact phonological skills, but also intact domain-general functioning. The interaction between modular and central processes was studied by examining surface form retention levels for scrambled and ordered stories. The results showed that the autistic group had enhanced, the dyslexic and MLD groups suppressed surface form retention levels. It was further found that half of the subjects in the autistic group were hyperlexic, and that these subjects, in particular, represented enhanced levels of surface form. It was suggested that weak central coherence could explain this finding. Poor surface form retention in dyslexia was viewed as a secondary consequence of the phonological processing deficit. Representation of gist was examined for the same stories and in the same conditions, showing that enhanced piecemeal processing of text in the hyperlexic group was accompanied by poorer gist representation for ordered stories. The dyslexic and the MLD group were unimpaired in gist representation. These findings indicated that the abnormality in central processing in autism (i.e. weak central coherence) affected both low-level (surface form) and high-level (gist representation) central processes. In dyslexia gist representation was unaffected by modular, phonological processing deficits. The hyperlexic and non-hyperlexic subgroups were further investigated with respect to differences in the degree of weak central coherence, executive and Theory of Mind dysfunctioning. The results indicated that weak central coherence might be contributing factor in hyperlexic developments. There were no group differences in ToM, but some indication that hyperlexic subjects had greater executive function impairments.

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