Abstract/Summary

Word production is an essential feature for successful communication where semantic information of a word is activated first, followed by the activation of the targeted words’ phonological form, finalized by word articulation. Existing research has largely concentrated on the lexical-semantic processes of word retrieval in speech production, however, the interaction of word production processes- linguistic and speech motor - and the influence they have on one another during word production in the healthy older population and people with aphasia has been rarely addressed. Moreover, beyond language, there is increasing agreement that the broader cognitive profile of aphasia can influence the manifestation of linguistic impairment. Furthermore, the nature of linguistic deficits in people with aphasia and their relationship to speech motor and executive control mechanisms is not established in the literature. This thesis aimed at exploring the relationship between linguistic, speech motor, and executive control processes on healthy younger adults, healthy older adults, and people with aphasia. The exploration of the research aim followed in a systematic and stepwise structure in two phases. Phase one, measured the influence of linguistic and speech motor process on word production during a picture naming task on healthy younger and healthy older adults (Chapter 2) and participants with aphasia (Chapter 3). Phase two investigated the relationship amongst linguistic, speech motor, and executive control processes on healthy younger and healthy older adults (Chapter 4) and in the participants with aphasia (Chapter 5) where the participants completed one linguistic task (picture naming) and six executive control tasks (inhibitory measures: Word colour and spatial Stroop, Updating measure: N-back and digit span, Switching measure: Same different and Trail Making Test). In Chapter 2, compared to healthy younger adults, the healthy older adults performed significantly poorer on all the word production measures (Accuracy, RT, WD). No interactions between linguistic and speech motor processes was indicated in this chapter, however, linguistic and speech motor processes influenced one another on word production measures. Findings for Chapter 3 revealed that people with aphasia demonstrated significantly poorer on all word production measures as compared to the healthy controls. The influence of linguistic and speech motor processes on one another was indicated on word production measures. Additionally, significant associations amongst linguistic, speech motor, and executive control abilities was found. Chapter 4 indicated no significant correlations between the word production measure and the executive control measures on the healthy younger adults. The healthy older adults demonstrated significant correlations amongst executive control measures and measures of word production. Both groups of participants in Chapter 5 demonstrated significant correlations between the measures of executive control and word production. Taken together, findings revealed important insight into the broader linguistic-speech motor- executive control profile for the healthy older adults and participants with aphasia and the theoretical and therapeutic implications.