Confrontation of PDP models and dual-route models through the analysis of a case of deep dysphasia

Abstract

A case study is presented of a patient, EA, who demonstrated all the defining features of deep dysphasia. His repetition disorder was associated with surface dyslexia and deep dysgraphia. EA also showed a severely restricted phonological STM. His performance in both picture confrontation naming and writing-to-dictation paralleled his performance in repetition, whereas reading aloud and oral lexical decision were not influenced by the imageability of the word input. Further testing indicated that EA did not have difficulty in either perceiving or semantically processing spoken words. An exhaustive investigation of EA's cognitive functioning was first conducted by reference to Patterson and Shewell's model (1987). Such a triple-route model can account for EA's overall performance by postulating multiple functional lesions. We alternatively show that EA's language profile could be accounted for within a highly interactive model of language processing incorporating most basic principles of connectionist-PDP models. Within this latter framework, deep dysphasia, surface dyslexia, and deep dysgraphia could be interpreted as originating from a single functional deficit. Our analysis further suggests an impact of semantic and orthographic knowledge on phonological processing.