The cognitive and motor deficits of Parkinson's disease.
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Deficits of attentional and motor set that are seen in patients with PD were investigated in the research reported in this thesis. A deficit of attentional set is a failure of selective attention to one aspect of a complex stimulus. Deficits of motor set manifest as an inability to form a state of motor 'readiness' that can speed movement initiation. Attentional set was investigated with tasks that require patients to shift attention between perceptual dimensions (extradimensional - ED - shifting tasks), and motor set was studied using reaction time (RT) tasks. Study 1 rejected the hypothesis that the mechanism of 'learned irrelevance' causes ED shift deficits in patients with PD. Studies 2 and 3 confirmed that learned irrelevance also plays no role in determining the difficulty of ED shifts in healthy subjects. The experimental manipulation used in Study 4 succeeded in creating changes in scores that resembled those seen in patients with PD. Thus, it appears that patients with PD may have a deficit similar to that induced by the experimental manipulation - that is, an inability to attend to all dimensions present when hypothesis testing after an ED shift. A quantitative analysis of past RT studies of PD showed that the ability to speed movement initiation when given advance information about an upcoming movement - a form of motor set - is intact in patients with PD. In contrast, the motor set that underlies rapid simple RT performance is consistently dysfunctional in patients with PD. Study 5 investigated temporal and spatial motor set in PD, finding that these two mechanisms are functionally separate and that temporal motor set is intact in PD. A final study (Study 6) investigated the cognitive consequences of a novel neurosurgical treatment for PD, finding it to be largely a neuropsychologically 'safe' procedure.
Thesis, PhD Doctor of Philosophy
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