context-sensitive grapheme-phoneme conversion rules impairment in the semantic variant of primary progressive aphasia.

Introduction. The semantic variant of primary progressive aphasia (svPPA) is characterized by a progressive deterioration of semantic memory, associated with word comprehension and naming deficits (Gorno-Tempini et al., 2011). Patients with svPPA also show acquired surface dyslexia and dysgraphia. According to the 'dual-route' model, reading aloud (Coltheart, 1978) and spelling (Ellis, 1982) of nonwords are achieved by resorting to a nonlexical and non semantic route, through the application of grapheme-phoneme conversion (GPC) rules. The aim of the present study was to examine the performance of two individuals with svPPA in tasks tapping consistent GPC rules of two types: a) non-contextual GPC rules (n-cGPC) in which each grapheme has only one unequivocal phonemic correspondence; 2) context-sensitive GPC rules (c-sGPC) in which the pronunciation or spelling is determined by the preceding or following letters (e.g. C and G, which are consistently pronounced /k/ and /g/, change to /s/ and /ʒ/ before the letters E and I). Method. Participants. We report the performance of two French-speaking patients (NG and ND) that fulfilled clinical and imaging-supported criteria for svPPA. Both presented with surface dyslexia and dysgraphia. Each of them was matched by age, gender and education to three normal controls. Tasks and procedure. NG and ND were administered the following experimental tasks comprising bisyllabic and trisyllabic words and nonwords with n-cGPC and c-sGPC rules, placed at the beginning, the middle or the end of the stimulus: 1) regular word and nonword reading; 2) adding a missing letter in words and nonwords: the patients were asked to complete stimuli by a letter to make them correspond to the word or nonword pronounced by the experimenter (for n-cGPC rules, the missing letter was randomly chosen; for c-sGPC rules, one of the letters of the context was missing); 3) rhyme judgement of nonwords: stimuli were auditorily presented and the patients had to indicate if they rhymed or not (for c-sGPC stimuli, in non-rhyming pairs, the difference between nonwords implied one of the context letters). Results. As shown in Table 1, NG and ND's performance was well preserved in tasks with words and nonwords with n-cGPC rules. However, ND was impaired in all tasks with c-sGPC rules, whilst NG's performance was affected for c-sGPC stimuli only in the rhyming task. Discussion. The processing of regular words and nonwords is assumed to be unimpaired in svPPA since their production do not necessary rely on the lexical-semantic route of reading and spelling. In the present study, this hypothesis was confirmed for n-cGPC rules only. However, both patients presented with difficulty in c-sGPC stimuli. This pattern of performance, never reported before in svPPA, questions the possible role of semantic memory in the reading and spelling of stimuli comprising consistent but contextual GPC rules.