Varieties of Pure Alexia: the Case of Failure to Access Graphemic Representations.

We document the case of a patient (GV) w ho, following a left posterior brain lesion, showed a selective and severe deficit in naming visual objects and in reading letters, words, and numerals. Three sets of findings are critical for the interpretation of the patient's alexia. First, despite intact visual processing abilities and preserved ability to recognise the shape and orientation of letters, GV could not determ ine whether a pair of letters had the same name. Second, she should not access the orthographic structure and meaning of visually presented words, although she could access meaning from orally spelled words and she could access orthographic structure from m eaning in w ritten words. Third, GV could access partial semantic information from pictures and Arabic num erals. Based on this pattern of results, we conclude that the form of alexia manifested by our patient results from failure to access the graphemic representations of letters and w ords from normally processed visual input. The findings further suggest that access to letter forms and grapheme representations are sequentially ordered stages of processing in word recognition. The results also suggest that graphemic processing may be a distinct property of the left hemisphere.