Evidence for lexicographic processing in a patient with preserved written over oral single word naming.

A number of studies have shown superior written over oral performance in fluent aphasia. One reasonable explanation for this result is that writing in these cases takes place through a different set of output mechanisms than oral naming. Specifically, conversion of lexical information directly into graphemic code can occur for writing whereas output requires access to underlying phonology. If phonological processing is impaired, it is possible that written performance can still be sustained via lexicographic retrieval of information. A case study is described supporting this account of incongruous written over oral naming. Written naming for single words was markedly superior to spoken naming. Performance in rhyme matching tasks disclosed impaired retrieval of the underlying sound component of words and nonlexical phonological processing was severely impaired in writing to dictation. This suggests that written naming was mediated entirely by nonphological processes. In addition, recovery of function indicated considerable independence of phonological processing between reading and writing. While grapheme-phoneme conversion improved substantially six months post-onset, phoneme-grapheme transcoding remained severely impaired. This suggests that different neural mechanisms mediate access to phonology for reading and writing systems.