Executive processes in visual and spatial working memory tasks
The main aim of the thesis was to investigate the nature of the cognitive mechanisms which underlie performance on specific visuo-spatial working memory tasks, with the emphasis on exploring the extent of central executive involvement. This research began with an attempt to investigate performance on two standard visual and spatial tasks in a small sample of mild-to-moderate AD patients, and compare this with performance on two adapted versions of the tasks (Experiments 1 & 2). The tasks were adapted to increase the ecological validity, but this adaptation appeared to alter the demands of the tasks, which prevented their further investigation as useful alternatives. The following experiments concentrated on investigating visual and spatial working memory in healthy populations. Experiments 3, 4, 5 and 6 employed a dual-task paradigm, whereby specific visual and spatial working memory tasks were combined with tasks assumed to involve executive processes. Experiments 3, 4 and 5 employed oral random digit generation as an executive task. The results of Experiments 3 and 5 indicated that visuo-spatial tasks which involve sequential processing show more interference with random digit generation than visuo-spatial tasks which involve simultaneous processing. The findings of Experiment 4 suggested that, when both item and order information are presented (i.e. with sequential presentation), subsequent recall or visuo-spatial material is attention demanding regardless of whether item only, order only, or both item and order information are required in response. These findings appear to indicate that visuo-spatial tasks which involve sequential processing require executive resources to a greater extent than visuo-spatial tasks which involve simultaneous processing. However, oral random generation is a sequential task, and requires the maintenance of serial order (in order to produce a random sequence). Therefore an alternative interpretation could be that the sequential nature of the oral random generation task gave rise to the pattern of selective impairment on sequential visuo-spatial tasks, rather than more general executive load.