CANADIAN JOURNAL OF PSYCHOLOGY, 1983,37(4), 565-571 Deep Dyslexia and the Right Hemisphere Hypothesis: Evidence from the U.S.A. and the U.S.S.R.* Derek Besner University of Waterloo ABSTRACT One account of the residual reading abilities seen in deep dyslexia asserts that they entirely reflect the operation of an intact right hemnisphere reading system rather than a partially disabled left hemisphere reading system. Evidence from an experiment with normal subjects suggests that the right hemisphere contains no lexical entries for abbreviations that can be accessed by visual presentation. Examination of three deep dyslexic's understanding of printed abbreviations reveals considerable sparing. This contrast suggests that the current right hemisphere account of the residual reading abilities seen in deep dyslexia is not a sufficient one. RESUME Une des explications des capacites residuelles de lecture qui se retrouvent dans les cas de dyslexie profonde affirme qu'elles refletent le fonctionnement d'un systeme de lecture intact situe dans I'hemisphere droit, plutot que celui d'un systeme partiellement detruit situe dans I'hemisphere gauche. Les resultats d'une experience avec des sujets normaux laissent supposer que I'hemisphere droit ne contient pas d'entrees lexicales pour les abreviations, entries qui pourraient etre accessibles par presentation visuelle. Un examen de la comprehension des abreviations imprimees, chez trois dyslexiques profonds revele cependant beaucoup d'economie. Ce contraste suggere que I'explication courante, en terme d'hemisphere droit, des capacites residuelles de lecture observees dans la dyslexie profonde n'est pas suffisante. In recent years considerable effort has been expended in investigating the deficits seen in "deep" or "phonemic" dyslexia, a form of acquired dyslexia resulting from left-hemisphere damage (e.g., Andreewsky & Seron, 1975; Kapur & Perl, 1978; Marin, Saffran, & Schwartz, 1975; Marshall & Newcombe, 1966; Morton & Patterson, 1980a; Newcombe & Marshall, 1980a, b; Patterson, 1978, 1979, 1980; Patterson & Marcel, 1977; Saffran, Boygo, Schwartz, & Marin, 1980; Saffran & Marin, 1977; Saffran, Schwartz, & Marin, 1976; Sasanuma, 1980; Shallice & Coughlan, 1980; Shallice & Warrington, 1975). Briefly, these patients show the following deficits when asked to read single words (or nonwords) aloud, without time pressure: (1) semantic errors (e.g., tulip-> crocus), (2) visual errors (e.g., scandal - > sandal), (3) derivational errors (e.g., wrestle -> wrestler), (4) almost total "Supported in part by grant U0051 from the Natural Sciences and Engineering Research Council of Canada. I am grateful to Ian Dennis for encouragement. Address reprint requests to the author, Department of Psychology, University of Waterloo, Waterloo, Ontario, Canada, N2L3G1. 565