**Online Motor Control in People With Parkinson's Disease** *Parkinson's disease (PD)* is a brain disorder that affects movement, causing symptoms like slow movements and difficulty starting movements. This study explores how people with PD adjust their movements to changes, like if something suddenly moves in front of them. *Online movement corrections* mean changing your movement while it's happening, like shifting your hand to catch a flying butterfly. The study uses *virtual reality* to see how people with PD handle these changes. Participants will be tested on how they move when faced with visual changes (seeing something move) and force changes (feeling a push or pull). This information may help improve PD treatment. The study involves reaching activities with different levels of challenges, comparing responses between people with PD and healthy individuals of similar age. **Key Points:** - **Participation requires**: Age 18-85, ability to make reaching movements of about 20 cm, willingness to attend all sessions. - **PD group needs**: Diagnosis of PD and taking specific medication. - **Excludes**: Those with other neurological disorders or recent arm injuries. This study will help us understand and potentially improve movement for people with PD.