Abstract
Investigation of a neurological patient (PT) who presents with a relatively pure disorder of reading was carried out. His performance on a number of oral reading tasks was very similar to that of the surface dyslexic patient (HTR) reported by Shallice, Warrington and McCarthy (1983). Both patients showed an effect of “degree” of regularity in terms of accuracy of reading response. PT did not, however, show an effect of “typicality of divergence”, which was considered by Shallice and his colleagues to be responsible for the former effect. The size of orthographic–phonological unit operational in PT's oral reading was experimentally determined. PT appeared to rely on grapheme–phoneme correspondences that were assigned in a probabilistic rather than an “all-or-none” manner. No evidence for the existence of the sub-syllable as an independent unit was found. In contrast, this unit apparently mediated the performance of skilled adult readers. Implications of these results for models of the phonological route are discussed.

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