Inclusion Criteria:

• Parkinson's subjects will have received physician verified diagnosis of the disease and be on a dopaminergic medication for at least 3 months

Exclusion Criteria:

• Any movement, strength, or balance assessments that may pose a potential risk for injury
• Individuals with a history of photosensitive epilepsy or seizure activity triggered by visual stimuli
• Current use of antipsychotics, stimulants, or other medications known to affect central dopaminergic transmission
• Pregnancy
• Recent ocular surgery
• Phenylketonuria
• (PD participants) not cognitively intact and not able to consent for themselves
• (non-PD subjects) a pre-screening survey will assess medication use and neurological history
• Ophthalmologic or visual system conditions that may interfere with stimulus delivery or retinal function. These include significant cataract (defined as LOCS III ≥ NC2/NO2 or any media opacity that precludes adequate delivery of visual stimuli to the retina), active retinal or macular pathology (including age-related macular degeneration with significant drusen or geographic atrophy, diabetic retinopathy, retinal vein occlusion, or epiretinal membrane with foveal involvement), glaucoma, or any optic neuropathy.
• Individuals with congenital color vision deficiencies, particularly tritan-spectrum defects
• Ocular surgery within the past three months
• Use of medications known to affect retinal electrophysiology (e.g., chronic hydroxychloroquine, vigabatrin, deferoxamine, or isotretinoin)
• History of photosensitive epilepsy or visually triggered seizures (especially relevant given the use of bright visual stimuli and potential flicker paradigms)