The investigators will recruit 10 PSP, 10 PD and 10 healthy controls for the study. All subjects will be asked to come to the OHSU clinic at the Center for Health and Healing for an initial screening visit. They will meet with the primary investigator to conduct a brief interview and physical examination. In addition, they will be asked to answer questions regarding current and past medical illness, how often they fall and what kinds of medications they are on.