This thesis investigated the role of the supplementary motor area (SMA) in visuospatial processing using Parkinson’s disease (PD) patients as a model of pre-supplementary motor area (pre-SMA) dysfunction. The vector transformation hypothesis assumes that visuospatial transformation deficits in PD are a result of impairments in calculating vectors or co-ordinate remapping with a reference frame. These vector transformation processes were investigated in spatial normalisation during mental rotation and showed that PD patients demonstrate slower image normalisation rates indicative of a deficit compares with controls. It was then investigated how far these deficits extend to other vector transformation tasks such as abstract grid navigation. PD patients were less accurate than controls and these deficits were independent of spatial short term memory and serial processing suggesting that PD is associated with spatial transformation deficits. Comparisons of visual vector transformation and auditory vector transformation showed that PD patients were less accurate at visual vector transformation than auditory vector transformation suggesting that vector transformation processes may be more sensitive to the visual domain. The final study was a pilot study to investigate the feasibility of using a cognitive vector transformation task to remediate symptoms of bradykinesia in PD. Modest improvements in movement velocity following the vector transformation task but no significant change in movement velocity following a control task suggests that vector transformation can be used for therapeutic gain.