Inclusion Criteria:  Patients assigned to PD or non-PD group based on medical records Control participants will be without previous diagnosis of a movement disorder Experimental groups and normal controls matched by age and gender  Exclusion Criteria:  Severe drug/alcohol use Severe medical problems (e.g. terminal cancer) Macular degeneration Inability to consent Patients at 4 or more on the Hoehn-Yahr scale Inability to complete experimental protocol