Khuu, SieuAlnawmasi, Mohammed2023-06-012023-06-012023-05-30https://hdl.handle.net/20.500.14154/68248Purpose: Traumatic Brain Injury (TBI) is a major worldwide public health concern, with approximately 69 million individuals sustaining some form of brain injury annually. Though this figure is likely to be underreported as many do not seek medical treatment. Long-term changes in cognition and memory are sequelae of all brain injury severities and, most commonly as deficits in attention. Attentional processes are heterogenous and have been proposed to comprise different functional aspects or components that operate to deploy attention in different ways. For example, attention can be selective, divided, sustained and spatially allocated. However, it remains to be established whether TBI leads to a general deficit in attention or whether certain components are more affected. The thesis addresses this research question by focusing on visual attention using two approaches. First, behaviourally using two novel tasks (Motion tracking and a variant of Posner cueing) in which their stimulus conditions (such as duration and search efficiency) were systematically varied to assess different components of attention. And secondly, by observing changes in the allocation of visual attention through eye movement measurements and pupil responses (which are effective markers of attention) while performing these attentional tasks. Method: A systematic review and meta-analysis was initially conducted (Chapter 2) to provide an indication of the impact of TBI on visual attention and its components from the published literature. Drawing on the limitations and gaps in knowledge observed from this review, a series of cross-sectional studies were conducted that compared the performance of patients with mild TBI and normal participants on multiple conditions in which each task condition was used to assess a specific component of visual attention. Particularly, in Chapters 3 and 4, selective, divided and sustained attention was investigated using a multiple object tracking (MOT) task and varying stimulus parameters such as the number of targets to be tracked, the number of distractors and tracking duration. In Chapters 5 and 6, we investigated the allocation of attention using a modified Posner cueing task for conditions in which search efficiency and cue validity were systematically varied. Behavioural measures include sensitivity and reaction time and response-independent measures, including the pupillary response and eye movements. Results: Meta-analysis of previous works showed that the combined effect size of an attentional deficit following TBI is large but characterised by high heterogeneity. The latter finding highlights the potential impact of different dependent and independent variables on study outcomes. Additionally, there was a paucity of knowledge in understanding changes in divided and sustained visual attention following TBI. Chapters 3 and 5 contribute to knowledge by showing that patients with mild TBI exhibit a poor ability to orient visual attention (endogenously and exogenously) and in tracking multiple targets, particularly when the tracking duration was long and the number of to-be-tracked targets and the number of distractors was high. Chapters 4 and 6 showed that deficits in attention following mild TBI are also associated with deficits in eye movement measures (number of fixation and duration and tracking strategy) and pupillometry measures (latency and pupil amplitude), which is broadly indicative of a lack of attentional resources. Conclusion: Collectively, the results of this thesis showed a generalised visual attention deficit after TBI, which was not selective to a specific component of visual attention. Deficits in visual attention manifested in all outcome measures (including performance accuracy and reaction time), which suggests the importance of considering them in the assessment of visual attention. The cognitively driven pupillary response and eye movement patterns differentiated patients with mild TBI and might be considered an alternative measure of visual attention, particularly in the clinical population.378enTraumatic brain injuryvisual attentioncomponents of visual attentioncognitively driven pupillary responseeye movemen.Thesis