Selective impairments of nouns and verbs in aphasia: a word retrieval task in sentence context

INTRODUCTION Several authors described cases of dissociated impairment in naming nouns and verbs. There are four accounts of this dissociation: (i) patients may have purely lexical damage, which selectively affects verbs or nouns at a late stage of the linguistic processing (phonological or orthographic lexicons) (Rapp & Caramazza, 2002); (ii) the damage affects a lexical device, either at an ortographic-phonological modality-specific level (the lexeme; Levelt et al., 1999) or at a unitary lexical-syntactic level (the lemma) (Berndt et al., 1997); (iii) N-V dissociation arises from a semantic damage (Bird, Howard & Franklin, 2000); (iv) N-V dissociation is due to syntactic damage (Friedmann & Grodzinsky, 2000). To disentangle imageability and grammatical class effects, a new task was developed allowing to elicit nouns and verbs with identical imageability ratings in a sentence context. The results obtained will permit to address the following three questions: Does imageability play a role in determining N-V dissociation? If so, is imageability the unique cause of dissociation? If there is additional damage, at which level of linguistic processing does it take place? METHODS Twelve Italian aphasic patients and 11 normal controls participated in the study. Nouns and Verbs Retrieval in a Sentence Context (NVR-SC). Forty-five pairs of sentences denoting the same event, either using a noun or the corresponding verb (e.g. the evasion/to evade) were used. The first sentence was presented in complete form, while a gap was left in the second sentence, to be completed with the target word. For each pair of sentences two different conditions were employed, one triggering a verb and one triggering a noun. E.g. V-N: The prisoner was dreaming to evade The prisoner was dreaming the ......... N-V: The prisoner was dreaming the evasion The prisoner was dreaming to ......... The performance in the NVR-SC task was compared to that obtained on a classic picture naming task