Figure 1. Monetary Incentive Delay Task.
Example trials of the monetary incentive delay (MID) task depict both gain and loss, and anticipation and outcome phases. Trial periods were TR-locked so that for each trial TR 1 = Cue (Anticipation), TR 2 = Fixation (Anticipation), TR 3 = Target, TR 4 = Feedback (Outcome), TR(s) 5~7 = Variable Duration Inter-trial Interval. Cues (2 s duration) were circles (potential gains) or squares (potential losses) with monetary values under the shape images. Each fixation period (2 s duration) was followed by a target period (2 s duration) during which a triangle was presented for variable duration (~250 ms) depending on prior accuracy of responses to obtain an average 66% hit rate. Monetary gain or loss values were presented as win/loss feedback (2 s duration) at the end of each trial. Trials were separated by a black screen for a pseudo-randomized inter-trial interval period (2, 4, or 6 s durations).