The purpose of this prospective, within-subject randomized cross-over design study is to determine if a computer training program (Speed of Processing Training - SOPT) improves safe pedestrian behavior in patients with Parkinson's disease and in healthy older adults in a virtual reality pedestrian environment. Pedestrian injury poses significant risk to healthy older adults and patients with Parkinson's disease. Several age-related changes, including slowing of visual processing speed, increase risky pedestrian behavior. This study will determine if SOPT improves pedestrian behavior in patients with Parkinson's disease and healthy older adults and evaluate the persistence of the SOPT training effects.