Semantic representations of English verbs and their influence on psycholinguistic performance in healthy and language-impaired speakers

Abstract

Background – English verbs are linguistically more complex than nouns and this has contributed to the dearth of in-depth investigation into similarities and differences between their representations within semantic memory and subsequent implications for language processing. However, recent theoretical accounts have argued that verbs and nouns are represented within a unitary semantic system. Aims – This thesis investigates the semantic representations of English verbs with particular attention to how verbs are inter-related as a consequence of semantic similarity. This is achieved through a series of psycholinguistic experiments with healthy adult speakers and an intervention study with adults with aphasia (i.e. acquired communication impairment). Throughout the thesis, comparisons are made to the semantic representations of nouns either directly (i.e. through parallel experimentation) or indirectly (i.e. through the existing literature). Methods – The experiments conducted with healthy adult speakers included: (1) category listing of verbs; (2) typicality rating of verbs within categories; (3) similarity rating of verb pairs; (4) an analysis of verbs’ semantic features; (5) category verification of verbs; and (6) semantically primed picture naming of actions. The intervention study carried out with adults with aphasia compared patterns of improvement in verb and noun retrieval following a semantically-based therapy task. Results and discussion – The results of the experiments shed light on the nature of semantic representations of verbs, in particular, in relation to the similarity between the semantic representations of verbs and those of nouns and also where they differ. These insights are considered in terms of how they provide evidence for or against a unitary semantic system for verbs’ and nouns’ semantic representations and parallel mechanisms for accessing these representations. Two themes emerged in terms of future research potential: (1) the influence of polysemy on speaker’s performance in psycholinguistic tasks; and (2) the nature and influence of typicality within categories/cluster of verbs.