| Summary: | It has been suggested that control over saccadic eye movements represents cognitive proficiency. but the precise cognitive mechanisms underpinning saccades are unclear. This thesis aims to elucidate the mechanisms controlling the accuracy, validity and latencies of prosaccades and antisaccades. Experiment I assessed the role of working memory in determining antisaccade latencies and errors, by measuring the impact of imposing a task-relevant, concurrent load. It was found that reducing available working memory for saccades comparably impeded prosaccade and antisaccade performance. This suggests that, contrary to earlier indications, working memory capacity is not a specific determinant of antisaccade latencies or errors. Experiment 2 systematically varied concurrent working memory load in prosaccade and antisaccade tasks, whilst eliminating potentially confounding attentional factors. The results confirmed the minor role played by working memory in the control of antisaccades: when attentional factors were eliminated, the effects previously misattributed to working memory were abolished. Experiment 3 assessed the relative contributions of working memory and inhibitory control, and revealed that antisaccades are more reliant upon an inhibitory mechanism, particularly in older adults. In Experiment 4, the previously documented decline in this inhibitory mechanism with age was unpacked. Inhibitory control was temporally segregated into covert inhibition of attention and overt inhibition of saccades. The results suggested that it is only when covert and overt inhibition are required simultaneously, as in the standard antisaccade task, that older adults exhibit notably poorer performance, since older adults demonstrated a selective decline in overt inhibitory control. Finally, Experiment 5 tested competitive programming models of antisaccades, which predict that performance is largely determined by the relative programming speed of prosaccades, but found no support for such models. Taken together, these results suggest that visual attention, covert and overt inhibition, and working memory capacity all contribute to the cognitive control of saccadic eye movements.
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