Fig. 1.

Antisaccade paradigm. Schematic and timeline of the three trial types: Easy, Hard and Fake-Hard. Each trial lasted for 4 s and began with a cue informing the participant of either an Easy or Hard trial. The cue was either a blue or a yellow “X” and the mapping of cue color to trial type was counterbalanced across participants. The cue was flanked horizontally by two small white squares with a width of 0.4° that marked the potential locations of stimulus appearance: 10° left and right of center. These squares remained visible for the duration of each run. At 300 ms, the instructional cue was replaced by a white fixation ring at the center of the screen, with a diameter of 1.3°. At 1800 ms, the central fixation ring disappeared (200 ms gap), and at 2000 ms, it reappeared on either the right or left side as the imperative stimulus to which participants were required to respond. Hard trials were distinguished by an increase in luminance of both the peripheral squares that mark the potential locations of stimulus appearance during the gap and the imperative stimulus. Except for the hard cue, Fake-Hard trials were identical to Easy trials. In the trials depicted, the correct response was a saccade away from the stimulus on the left side of the display. An error would involve a saccade toward the stimulus. After 1 s, the fixation ring returned to the center. Participants were instructed to return their gaze to the center and fixate until another trial began. Fixation intervals, which lasted 2, 4, or 6 s, were simply a continuation of the fixation display that constitutes the final second of the previous saccadic trial.