Showing papers by "Jose L. Contreras-Vidal published in 2003"

Visuomotor adaptation in normal aging.

Abstract: Visuomotor adaptation to a gradual or sudden screen cursor rotation was investigated in healthy young and elderly subjects Both age groups were equally divided into two subgroups; one subgroup was exposed to 1125° step increments of visual feedback rotation, every 45 trials (up to a total of 90°), whereas a second subgroup was subjected to 90° rotation from the onset of exposure Participants performed discrete, horizontal hand movements to virtual targets in four randomized directions Targets appeared on a computer screen in front of them, and a board prevented vision of the hand at all times Differential effects of aging on visuomotor adaptation were found, depending on the time course of the visual distortion In both age groups, early exposure to the sudden visual feedback distortion resulted in typical spiral-like trajectories, which became straighter by late exposure However, the final adaptation level was reduced in the aged group, although the aftereffects were similar When subjects were exposed to the gradual distortion, no statistically significant differences in measures of adaptation with advancing age were found In this case, both age groups appeared to adapt equally However, after removal of the distortion, elderly subjects showed reduced aftereffects as compared with the young group These findings suggest differential effects of aging on adaptation to gradual versus sudden visual feedback distortions, and may help to explain the conflicting results obtained in previous visuomotor adaptation studies

Effects of Parkinson's disease on visuomotor adaptation.

Abstract: Visuomotor adaptation to a kinematic distortion was investigated in Parkinson's disease (PD) patients and age-matched controls. Participants performed pointing movements in which the visual feedback of hand movement, displayed as a screen cursor, was normal (pre-exposure condition) or rotated by 90° counterclockwise (exposure condition). Aftereffects were assessed in a post-exposure condition in which the visual feedback of hand movement was set back to normal. In pre- and early-exposure trials, both groups showed similar initial directional error (IDE) and movement straightness (RMSE, root mean square error), but the PD group showed reduced movement smoothness (normalized jerk, NJ) and primary submovement to total movement distance ratios (PTR). During late-exposure the PD subjects, compared with controls, showed larger IDE, RMSE, NJ, and smaller PTR scores. Moreover, PD patients showed smaller aftereffects than the controls during the post-exposure condition. Overall, the PD group showed both slower and reduced adaptation compared with the control group. These results are discussed in terms of reduced signal-to-noise ratio in feedback signals related to increased movement variability and/or disordered kinesthesia, deficits in movement initiation, impaired selection of initial movement direction, and deficits in internal model formation in PD patients. We conclude that Parkinson's disease impairs visuomotor adaptation.