Figure 1.

Reward reversal learning task: subjects select an image (right/left) by pressing the corresponding button (right/left). If is the choice is correct/incorrect, positive/negative feedback is given. Once the subject has made 4–6 correct responses, the stimulus-reward contingency is reversed. PETs, where incorrect feedback is given for a correct response, are included to prevent subjects from predicting an upcoming reversal trial. The task contains on average 20 reversal trials with 20 interspersed PET trials.