The purpose of this study is to characterize specific brain signals elicited by motor disturbances and errors in stroke patients. The patients will perform a motor task using both their affected and unaffected hands. There are two types of errors: low level errors and high level errors. While disturbances (low level errors) have been shown to elicit P300, uncorrectable actions (high level errors) have been shown to elicit ERN. These event related potentials (ERP) have been extensively studied in healthy subjects including a recent paper from our Lab.