NOUNS AND VERBS ARE RETRIEVED WITH DIFFERENTLY DISTRIBUTED NEURAL SYSTEMS

In a task designed to elicit the production of verbs, the patients kno wn as AN-1033 and Boswell consistently produced the correct target wor ds, performing no differently from normal controls. However, in a simi lar task designed to elicit the production of nouns, both patients per formed quite defectively, and their scores were many SDs below those o f controls. Language processing was otherwise normal-i.e., there were no impairments in grammar, morphology, phonetic implementation, or pro sody; reading and writing were normal. In a third patient (KJ-1360), w e obtained the reverse outcome-i.e., retrieval of common and proper no uns was preserved, but verb retrieval was defective. Together, the fin dings in the three patients constitute a double dissociation between n oun and verb retrieval. In AN-1033 and Boswell, the lesions are locate d outside the so-called language areas (left frontoparietal operculum, posterior temporal region, inferior parietal lobule), where damage is associated with aphasia. The region of damage shared by the two patie nts is in left anterior and middle temporal lobe. This sector of left hemisphere contains systems for the retrieval of nouns that denote con crete entities. We propose that those systems are not essential for th e retrieval of verbs and are not involved in the vocal implementation of word forms. Those systems perform a two-way lexical-mediation role for concrete nouns and promote the reconstruction of a word form after the processing of sensory-motor characteristics of the entity denoted by that word. The findings in patient KJ-1360, whose lesion is in lef t premotor cortex, suggest that equivalent mediation systems for verbs are located in the left frontal region.