Independent Access to Phonological and Orthographic Lexical Representations: A Replication Study

Abstract

Traditionally, it has been assumed that written abilities are completely dependent on phonology (the so-called phonological mediation theory). In this view, the semantic system activates the phonological form of a word, which then activates the corresponding orthographic representation. This hypothesis predicts that in double naming tasks (two temporally close responses to the same picture in the two output modalities), the word selected for a written response will always correspond to the one selected for a spoken output. On the contrary, the orthographic autonomy theory hypothesises the independence of the written output lexicon, which, in the presence of severe damage to conversion procedures, could be directly activated from the semantic system. In this case, the theory predicts that double naming tasks give rise to lexically inconsistent responses. We describe a non-fluent aphasic patient, RA, with agrammatic speech and severe word- finding difficulties. He also presented with severe damage to the phonology-to-orthography and orthography-to-phonology conversion procedures. His performance on picture naming tasks was significantly worse in the spoken than in the written output modality. Errors were predominantly omissions. Few semantic paraphasias were present. Semantic errors did not arise from a deficit in the semantic system since the patient performed flawlessly on a semantic questionnaire and a word picture matching task and gave correct definitions of the items. Although not predicted by the phonological mediation theory, on double naming tasks the patient gave inconsistent responses (i.e. he correctly wrote the stimulus “z-e-b-r-a” but he orally produced “giraffe”). Taken together, these results further confirm the hypothesis that access to the orthographic form of words can be accomplished independently, without the mediation of phonology (the orthographic autonomy hypothesis).