presented at time zero for 200 ms. A centrally located fixation cross was presented after the cue for a random length of time between 400 and 800 ms. The imperative stimuli were composed of a centrally presented fixation stimulus and two letters, one letter on each side of the fixation, one colored red and the other green The target letter was identified by the color cue. The subjects had as long as 1,000 ms to identify the target letter and respond. Subjects responded by pressing a left button with their left index finger when the target letter was an H or a right button press with their right index finger when the target letter was an S. Trials in which the target and flanker letter were the same were considered low-conflict stimuli (Ls). Trials in which the target letter was different from the flanker letter were considered high-conflict stimuli (Hs). Trials in which the target letter was presented on the same side of the screen as the required response hand were considered low-conflict response (Lr). Trials in which the target letter appeared on the opposite side of the screen as the required response hand were considered high-conflict response (Hr) trials.
