Surface dyslexia without dysgraphia: a case report of a new dissociation

There is considerable debate on the extent to which reading and spelling rely on shared versus distinct cognitive processes (Tainturier & Rapp, 2001). Studies of brain-damaged individuals with impaired access to orthography have supported both views. Of particular interest are cases of "surface dyslexia," a disorder characterised by a dissociation between impaired reading of irregular words and relatively preserved reading of regular words and nonwords. Most errors are regularisations (e.g., CHEF--> "tchef"). Surface dyslexia is believed to result from a deficit at the level of the orthographic lexicon, a memory store of the spelling of familiar words. The accurate reading of regular words and nonwords is thought to reflect the use of a spared non-lexical route to reading. Attempting to read irregular words through this route will result in regularisation errors because the sublexical process maps graphemes to their most common pronunciation (i.e., CH pronounced "tch" rather than "sh"). Advocates of shared orthographic lexicons (e.g., Behrmann & Bub, 1992) have stressed the fact that patients with surface dyslexia usually also suffer from "surface dysgraphia," a disorder affecting words with ambiguous/irregular spellings and manifesting itself by the production of phonologically plausible errors such as "knowledge" --> NOLIGE. However, advocates of distinct reading/spelling lexicons (e.g., Caramazza, 1988) have pointed out that some patients have surface dysgraphia without surface dyslexia. This might suggest impaired access to an orthographic output lexicon used in spelling with preserved access to an orthographic input lexicon used in reading and written word recognition. We report the first case of a patient who presents with the opposite dissociation, that is, prototypical surface dyslexia with entirely preserved spelling. (C) 2002 Elsevier Science (USA). All rights reserved.