The experimental paradigm, a flanker letter discrimination task (Gehring and Knight 2000), was programmed using E-Prime 2 software. Responses were collected on a Psychology Software Tools serial response box. Stimuli were presented on a 16 in. Dell UltraSharp monitor via an NVIDIA GeForce FX 5200 video card. Subjects were instructed to respond as quickly and accurately as possible. They were told not to dwell on their mistakes but rather maintain pace with the experiment. After achieving the performance criteria above 60% accuracy, the subjects completed five blocks of 96 trials each with rest periods in between the blocks. A trial was composed of a cue, fixation stimulus, imperative stimulus, and response (Fig. 1). A random inter trial interval between 400 and 800 ms was used. The cue, either the word “green” or “red” printed in black on white background, was 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
