Preservation of Propositional Speech in a Pure Anomic: The Importance of an Abstract Vocabulary

Abstract

We describe a detailed quantitative analysis of the propositional speech of a patient, FAV, who became severely anomic following a left occipito-temporal infarction. FAV showed a selective noun retrieval deficit in naming to confrontation and from verbal description. Nonetheless, his propositional speech was fluent and content-rich. To quantify this observation, three picture description-based tasks were designed to elicit spontaneous speech. These were pictures of professional occupations, real world scenes and stylised object scenes. FAV’s performance was compared and contrasted with that of 5 age- and sex-matched control subjects on a number of variables including speech production rate, volume of output, pause frequency and duration, word frequency, word concreteness and diversity of vocabulary used. FAV’s propositional speech fell within the range of normal control performance on the majority of measurements of quality, quantity and fluency. Only in the narrative tasks which relied more heavily upon a concrete vocabulary, did FAV become less voluble and resort to summarising the scenes in an manner. This dissociation between virtually intact propositional speech and a severe naming deficit represents the purest case of anomia currently on record. We attribute this dissociation in part to the preservation of his ability to retrieve his abstract word vocabulary. Our account demonstrates that poor performance on standard naming tasks may be indicative of only a narrowly defined word retrieval deficit. However, we also propose the existence of a feedback circuit which guides sentence construction by providing information regarding lexical availability.