Assessment of Three-dimensional Vision Alteration in Parkinson Disease

3D psychophysical performances using a categorization tasks and their underlying mechanisms measured with visual evoked potentials will be assessed in a randomized and comparative study. The order of psychophysical and visual evoked potentials experiments will be randomized between the L Dopa ON and OFF conditions. The randomization will be done by the clinical investigational center. The comparisons will be made between parkinsonian patient and control subjects, and between parkinsonian patients in L Dopa ON and OFF conditions.