Item

Abstract

Lesions of the posterior parietal cortex (PPC) in humans cause severe visuomotor decits. These patients demonstrate large deviations of pointing and reaching movements to peripheral targets and an inability to adjust their grip aperture to different object sizes. In addition, a decit to adjust movements to perturbations of target positions during movement execution has been recently shown. However, it is unclear whether such a decit of an on-line correction mechanism also affects the distal component of grasping movements, i.e. whether patients with lesions of the PPC can adjust their grip aperture to perturbations of object size during movement execution. We compared the performance of a patient with bilateral lesions of the PPC with the performance of healthy controls in a virtual grasping task. A virtual disc (36 or 44 mm in diameter) was rendered using stereo computer graphics. Virtual, haptic feedback was given using two robot arms (PHANToM TM). In half of the trials, the virtual disc either increased to a size of 52 mm or decreased to a size of 28 mm. Otherwise the objects size was stable during the trial. The patient's performance towards the unperturbed discs was not impaired compared to the grasping kinematics of the healthy controls. In contrast, her grasping movements towards the perturbed objects seemed to be more prone to error than the movements of the healthy controls. This nding supports the previously suggested crucial role of the PPC in the online control of visuomotor actions and suggests that the PPC is also involved in the online control of the distal component of grasping movements.