Figure 1.

The arm countermanding task. Each trial begins when the cursor is positioned inside the center box. After a delay, the target box appears to one side of the screen and the center box disappears, instructing the monkey to move the cursor into the target box. On stop signal trials, the center box reappears after the SSD signaling that the monkey should cancel the planned movement. On the variable-reward version of the paradigm, the color of the center box indicates whether the trial will result in a high or low reward if performed correctly.