Figure 2.

The conditional stop-signal paradigm. A, Critical and noncritical Stop trials. On Go trials, the subject has 1 s (the hold period) to press a left or right button in response to a stimulus, using the index or middle finger of the right hand. On a Stop trial, a tone is played at some delay (SSD) after the arrow stimulus. The SSD changes dynamically throughout the experiment. Subjects are instructed in advance whether the critical finger is the index or middle one. If the arrow stimulus is in the critical direction and a tone occurs, then the subject must try to inhibit, but if the arrow is in the noncritical direction and a tone occurs, then the subject must respond anyway. B, The different trial types with descriptions. L, Left; R, right.