Additional Study Information: This study seeks to understand which areas of the brain play a role in cognitive processes such as memory, attention, and motivation. We hope to learn how these processes work together and the extent to which Parkinson's disease and the dopaminergic medications prescribed to treat the disease can affect the interplay between them. We are seeking men and women volunteers who have been diagnosed with Parkinson's disease and are 30-90 years old. To participate, you will first go through a phone screening to ensure eligibility and learn about the study. Then you will be asked to visit our facility at the Morningside Campus of Columbia University, where you will complete a few short questionnaires and take part in a computer-based task. The study requires two visits and each visit takes between one and two hours. You will be asked to abstain from taking any dopaminergic medication for at least 12 hours prior to one of the study visits. You will be compensated $12/hour for your participation, including travel time. As part of this study, you may have to allow us to access some of your medical history, such as any brain scans that were taken, medications you are on, and/or information about your diagnosis.