Jargon dyslexia in an individual with semantic dementia: further evidence for task-specificity in phonological output.

We report a patient with semantic dementia who demonstrated a very unusual dyslexia. He had a global loss of conceptual knowledge in the context of a fluent dysphasia and intact syntax. However, he did not have the surface dyslexia which is typical of semantic dementia; rather his reading impairment was characterized by speech production errors resulting in multiple neologisms. In a series of experiments it was established that input phonological and input orthographical processing were intact as was output phonology for naming and propositional speech. We demonstrate that our patient has a task-specific phonological deficit and we argue that reading and propositional speech rely upon dissociable phonological output systems. Thus we corroborate our earlier evidence of task-specific phonological output stores (Crutch and Warrington, 2001). We also document a greater difficulty with comprehending the written than the spoken word. We account for this pattern of performance in terms of our patient's attempting to read by the indirect phonological route, as with other semantic dementia patients, but suggest that this process is overridden by the task-specific speech production deficit.