Are there orthographic impairments in phonological dyslexia?

Two hypotheses have been advanced concerning the basis of acquired phonolog ical dyslexia. According to the dual-route model, the pattern derives from impaired grapheme-phoneme conversion. According to the phonological impairm ent hypothesis, it derives from impaired representation and use of phonolog y. Effects of graphemic complexity and visual similarity observed in studie s by Howard and Best (1996), orthographic effects on phoneme counting (Bern dt, Haendiges, Mitchum, & Wayland, 1996), and data from patient LB (Deroues ne & Beauvois, 1985) have been taken as evidence for an orthographic impair ment in phonological dyslexia and therefore against the impaired phonology hypothesis (Coltheart, 1996). We present a computational simulation, result s 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 sti muli.