Participants complete the testing for this study in four main sessions scheduled at least a week apart and five short follow-up sessions. At each main session, participants take either a carbidopa-levodopa tablet or a placebo (a look-alike inactive substance). Stroke patients have their arm and hand function assessed using two tests. One requires them to insert pegs into holes; the other includes writing, lifting various objects, and performing activities like turning pages, feeding or stacking checkers.