Fig. 1: Schematic representation of the Stop-Signal Task.

Each trial starts with a fixation point (+) (jittered duration between 0.3 and 0–8 s) followed by a neutral or cocaine-related cue (jittered duration between 0.5 and 0–8 s). In a Go Trial (a) the participant must press a button with the index or the middle finger of the right hand as quickly as possible after the presentation of an arrow pointing left or right, respectively (the maximum RT is 1.2 s). The arrow is superimposed on a cue which can be either neutral or cocaine related. Conversely, in a Stop trial (b), after the arrow and cue presentation, a sound (stop signal) occurs after a variable stop-signal delay (SSD) indicating the participants to withhold their response. Each trial ends with a feedback screen indicating the accuracy of the participant’s response.