On nouns, verbs, lexemes, and lemmas: Evidence from the spontaneous speech of seven aphasic patients

Background: Although disproportionate impairment of noun or verb retrieval has been described on the basis of the evidence from several aphasic cases since the mid 1980s, with different theoretical frames being proposed to account for noun-verb dissociation, very few studies have dealt with this dissociation in spontaneous speech. Aims: The objectives of this study were to investigate (i) whether the dissociation also emerged in connected speech, and (ii) whether the analysis of patients' narratives could shed light on the functional damage underlying their grammatical-class-specific impairment. Methods Procedures: Two non-fluent verb-impaired patients, two fluent verb-impaired patients, and three fluent noun-impaired patients participated in this study. Their noun-verb dissociation was preliminarily assessed through a picture-naming task, following which their spontaneous speech was collected and analysed using a single-case approach, taking into consideration both lexical productivity (as indicated by the number of different tokens produced by the patients) and lexical diversity (as indicated by the number of different types and stems used by the patients). Outcomes Results: Non-fluent verb-impaired patients tended to produce a lower proportion of verb types than unimpaired control participants, as opposed to fluent verb-impaired patients, who produced a normal verb rate in their spontaneous speech on all counting procedures. One out of three fluent noun-impaired patients produced a lower proportion of noun tokens, types, and stems compared to normal speakers. Conclusions: The data presented in this paper indicate that noun-verb dissociation as assessed in picture-naming tasks might not emerge in spontaneous speech and indicates the need for the inclusion of a lemma level in models of word production that aims at explaining grammatical-class-specific impairments in people with aphasia.