Abstract

The extensive literature attests to the wide range of neuropsychological deficits to be found in children whose reading and writing achievement are substantially less than expected for their mental age (here referred to as dyslexic). Their performance on tests of oral language ability is often impaired (Lawson and Inglis 1985), and it is generally held that this is because dyslexia is a language-based disorder (Vellutino 1979), or because a language-based dyslexia subtype is the most prevalent (Kinsbourne and Warrington 1963). However, it is unclear which, if any, of these impaired test performances reflect the same impairment in mental operations as those underlying the difficulty in learning to read, and which are coincidental accompaniments (e.g. Fein et al. 1988). Light might be cast on this issue by studying a population that to date has not been documented neuropsychologically, namely dyslexic adults. Dyslexia often continues into the adult years, and numerous variables that characterize adults with dyslexia have been reported (see Aaron 1982, Miles 1986, Spreen 1989 for reviews). However, their undetermined neuropsychological status leaves scope for several contrasting predictions, depending on alternative models of the brain basis of dyslexia and of its response to remedial education. Neuropsychological predictions We organize our predictions around five hypothetical models. MODEL I. The problem in learning to read is specific and unrelated to the accompanying neuropsychological deficits. The latter might reflect more transitory, coincidental immaturities of brain development. If so, dyslexic adults should have few accompanying neuropsychological deficits and the degree of their reading retardation and neuropsychot-

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