Trial types and regressors for isolating preparatory activity in the SST.

<p><b>Trials began with a fixation dot (warning stimulus) in the middle of the screen for 500 ms followed by a response stimulus for 1 s.</b> The response stimulus was either an “X”, indicating that the subject should press a button with their left thumb (a), or an “O”, indicating that the subject should press a button with their right thumb (b). On one third of trials (c), the response stimulus was followed by a stop signal (screen colour change from black to red), indicating that the subject should not respond on that trial. The box at the top right of the figure describes the stimuli that are used to estimate warning and response phase activities.