Noun-verb dissociation in aphasic patients' spontaneous speech

Bastiaanse and Jonkers (1998) found that in verb-impaired aphasic patients verb retrieval in picture naming tasks and in spontaneous speech do not always correlate. This study aims at (i) further investigating the relationship between verb production in formal tasks and spontaneous speech, (ii) extending this analysis to noun-specific impairments and (iii) using this evidence to clarify the cognitive damage underlying noun-verb dissociation. Seven Italian aphasic patients (three noun-impaired fluent, two verb-impaired fluent and two verb-impaired non-fluent patients) participated in the study. For each patient a three-hundred-word sample of spontaneous speech was analyzed. The number of tokens, types and roots was then calculated for any of these five categories: open-class words, closed-class words, nouns, open-class verbs and closed-class verbs. These variables were analyzed using the modified t-test described by Sokal and Rohlf (1995) and the norms reported in Semenza et al. (1989). Verb-impaired patients split according to the type of aphasia they suffer from; non-fluent patients have a poor verb-type production in spontaneous speech, while fluent patients produce a normal amount of verbs. Also noun-impaired fluent patients have a reduced noun production in spontaneous speech. We argue that this different behaviour depends on the different cognitive damages underlying the dissociations and on the different impact of the frame context characterizing spontaneous speech on noun and verb retrieval. The consequence of these results on the different hypotheses on noun-verb dichotomy mental representation will be also discussed.