Are There Orthographic Impairments in Phonological Dyslexia?

Two hypotheses have been advanced concerning the basis of acquired phonological dyslexia. According to the dual-route model, the pattern derives from impaired grapheme-phoneme conversion. According to the phonological impairment hypothesis, it derives from impaired representation and use of phonology. Effects of graphemic complexity and visual similarity observed in studies by Howard and Best (1996), orthographic effects on phoneme counting (Berndt, Haendiges, Mitchum, & Wayland, 1996), and data from patient LB (Derouesne & Beauvois, 1985) have been taken as evidence for an orthographic impairment in phonological dyslexia and therefore against the impaired phonology hypothesis (Coltheart, 1996). We present a computational simulation, results of two behavioral studies, and a critical analysis of the MJ and LB data, which suggest that the "orthographic" deficits in such patients arise from phonological impairments that interact with orthographic properties of stimuli.