Fig. 1. Schematic representation of the MID-paradigm depicting screen sequence, contrast used, and key performance variable intervals.

The sequence presented screens including an anticipatory cue, inter-stimulus (IS) interval, target stimulus, feedback, and fixation cross. The neutral cue (no reward) was represented by an empty circle, the small gain (10 pence) cue was represented by a circle transected by a single horizontal line, and the large gain (50 pence) cue was represented by a circle transected by two horizontal lines. Successful feedback was depicted by an image of a 10p or 50p coin with the words “you’ve won 10p!” and “you’ve won 50p!” respectively (depending on the magnitude of the previous anticipation cue). Unsuccessful feedback (too late or too early) and successful neutral reward feedback, was depicted as an empty circle with the words “you’ve won 0p!”