The Effects of Auditory Cues on Gait Mechanics in Parkinson's Disease

10 unimpaired controls and 30 subjects with Parkinson's Disease (described in detail below - see inclusion/exclusion criteria). The 30 subjects with Parkinson's Disease will be assigned into 3 groups (10 with H\&Y Stage 1, 10 with H\&Y Stage 2, and 10 with H\&Y Stage 3). Inclusion Criteria: * Individuals with a diagnosis of Parkinson's Disease (made by movement disorders specialist) will be included in this study. Additional inclusion criteria include: self-reported ability to walk \>10 m overground as well as walk on a treadmill for a total of 14 minutes with rest breaks as needed, and be classified as Stage 1, 2, or 3 on the Hoehn and Yahr Scale since these stages have the most independence with mobility (Goetz et. al, 2004). Exclusion Criteria: * Exclusion criteria include Hoehn and Yahr Stage 4 and 5, uncontrolled cardiorespiratory/metabolic disease (e.g., cardiac arrhythmia, uncontrolled hypertension or diabetes, orthostatic hypertension, chronic emphysema), or other neurological or orthopedic disorders that may affect walking. The investigators will also exclude participants with severe communication impairments, which could impede understanding of the purpose or procedures of the study or an inability to comply with experimental procedures.