Selective attentional processes in mild Parkinson's disease and mild Alzheimer's disease

On tasks of visual selective attention, both patients with mild Parkinson's disease (PD) and mild Alzheimer's disease (AD) show patterns of performance that differ from those observed in healthy controls. Typically in research, selective attention is treated as a unitary concept and altered performance explained in terms of a broad inhibitory deficit, i.e. problems ignoring extraneous stimuli. This thesis sought to clarify whether the performance of these patients reflected mechanisms that impact on different stages of attentional processing. The goal of the series of studies reported was not to compare the performance of patients with PD (n=20 throughout) and AD (n=16 to 20), rather it was to examine within each patient group (and healthy controls) similarities or differences in patterns of performance across tasks. In each study, targets and distractors were presented simultaneously and the characteristics of the distractors and/or their relationship to the target stimuli were manipulated in terms of visual characteristics, location or meaning. The performance of patients with mild PD improved when distractors were semantically related to the target. It was suggested that this was due to a priming mechanism that aided stimulus identification, and so these patients tended to rely on the meaning of items within the visual array. In contrast, the performance of patients with mild AD did not benefit from semantic similarity and was impaired by visual similarity. It was suggested that these patients tended to rely on the visual characteristics of items, and so the distraction from extraneous visual information interfered with stimulus selection. A framework was suggested that articulated how the properties of visual stimuli interact with processing mechanisms that impact on different stages of selective attention. The impairment of different visual attentional processes in patients with mild PD and mild AD could have implications for the cognitive support provided to them.EThOS - Electronic Theses Online ServiceGBUnited Kingdo