Subject demographics and rejected trials and subjects in the analyses comparing PD patients on and off DBS.

Trials were rejected due to the criteria for button press and eye movements (Table 1) that were explained in Methods. Subjects were rejected if more than half of trials in either of their on or off sessions was rejected. In total we rejected 10 subjects; 3 were rejected in both sessions, while the other 7 were rejected in one session (6 in the off-session and 1 in the on-session). MDS-UPDRS score are the mean of 6 patients, because we could not obtain MDP-UPDRS in the on-DBS session.