 During all four conditioning sessions, subjects perform a series of computer tasks. Depending on group assignment, subjects are able to earn high PairHi, UnpHi or low monetary reward PairLo, UnpLo, but this is not contingent on subjects performance. Each run for each game begins with a credit to prevent a negative outcome early in the run. The PairNone group play the same games without monetary reward. The order of the three games and the background images used are randomized across subjects, but remain constant within subjects. 