In the stop signal task, participants watched a series (300 trials) of Ls and Rs appear on the screen, and were asked to press the F key in response to Ls and the J key in response to Rs. In 75 trials, however, a red stop sign appeared and participants were instructed to withhold responses on trials when this happened. This left 225 trials where responses were required. The stop sign was presented 150 ms post-stimulus on the first stop trial, and this latency was increased by 25 ms every time the participant successfully withheld their response and was decreased by 25 ms every time they responded.
In all tasks the participants were asked to respond as quickly and accurately as possible to every letter.