Towards theory-driven therapies for aphasic verb impairments: A review of current theory and practice

Background: This review is intended for both theoretically and clinically motivated audiences with an interest in aphasic verb impairments. Aims: Building from previous reviews, our aim is to provide a concise summary of the relevant theoretical research and perspectives on verbs, and from this theoretical foundation to explore which aspects have been incorporated and tested in therapy studies. Main Contribution: In the theoretical domain, the review first considers the patterns of verb and noun impairments in aphasic syndromes. Second, an overview of the linguistic differences between verbs and nouns is provided, differences that occur at various levels of linguistic analysis: phonological, morphological, semantic, and syntactic. This is followed by a detailed account of the psycholinguistic perspective on verb-noun differences. Specifically, this section examines the role of variables such as imageability and frequency, and the issue of depiction of actions in static picture versus dynamic video format. Evidence from neuroimaging studies as well as neurodegenerative conditions such as semantic dementia is also reviewed. Finally, the psycholinguistic account further discusses the question of whether verbs ( and nouns) serve as primary ordering principles in the cognitive architecture of language processing or whether they should be more accurately viewed as points on an overarching psycholinguistic continuum. Also within the psycholinguistic discussion, event perception is described as a theoretical account with implications for verb processing. Despite the importance of verbs in their pivotal role in connected speech, there is a very limited body of literature on verb therapies and only a small number of the theoretical issues/perspectives have penetrated approaches to treating verb impairments. Ten published papers are described. Two of these directly compare verb and noun therapies, reflecting the many comparisons of noun vs verb impairments in the theoretical literature. The remaining eight consist of purely verb-focused therapies, which also examined the effects of increased verb retrieval skills on related sentence production (reflecting the pivotal role of verbs in connected speech). These eight studies are subdivided between four that targeted verb retrieval only and four that also investigated aspects of verb argument structure and sentence production. Conclusions: The general discussion notes possible new approaches to the treatment of verb deficits that arise from the many factors noted in the theoretical literature which are yet to be fully explored in therapy studies.