Conceptualisation difficulties in stroke-induced and primary progressive aphasia

In order to speak we have to transform our thinking into a form that can be verbally expressed– so called conceptualisation. Conceptualisation processes, including the selection and ordering of important information, perspective taking and topic maintenance, can be particularly difficult for individuals with acquired language impairments. This thesis aimed to identify symptoms of conceptualisation deficits in people with neurological language impairments (stroke aphasia, Primary Progressive Aphasia [PPA]) using a speech production task that is commonly used in clinical assessment (i.e., picture description) This research applied a modification of an established connected speech analysis -concept analysis - to investigate the number, quality and order of the information produced in picture description. The results showed that some individuals with stroke-aphasia (Chapter 2) and PPA (Chapter 3) omitted essential information and/or showed difficulties producing it in an appropriate temporal order. These impairments were hypothesised to be associated with either linguistic or cognitive impairments (e.g., working memory, attention). Chapter 4 investigated how far discourse macrostructure was influenced by impaired word availability. The ‘Taboo paradigm’ was used to induce lexical access difficulties in unimpaired speakers and their performance compared to speakers with aphasia. The results suggested that impaired word availability can account for a reduced amount of essential information. However, omissions of the most central concepts and temporal order violations, observed in some speakers with aphasia, cannot be explained by linguistic impairment alone. Chapter 5 reports a pilot investigation of the eye movements made during complex picture description. This pioneering study revealed clearly different gaze patterns (e.g., timing of fixations to critical areas) between a man with aphasia and unimpaired controls. This motivates the use of eye tracking for further research on conceptualisation difficulties. In summary, the results of this thesis provide evidence for the possible symptoms of conceptualisation difficulties in individuals with stroke-induced and primary progressive aphasia and have clinical application for enhancing the effectiveness of aphasia diagnosis and treatment.