From an associative perspective the acquisition of new goal-directed actions requires the encoding of specific action-outcome (AO) associations and, therefore, sensitivity to the validity of an action as a predictor of a specific outcome relative to other events. Although competitive architectures have been proposed within associative learning theory to achieve this kind of identity-based selection, whether and how these architectures are implemented by the brain is still a matter of conjecture. To investigate this issue, we trained human participants to encode various AO associations while undergoing functional neuroimaging (fMRI). We then degraded one AO contingency by increasing the probability of the outcome in the absence of its associated action while keeping other AO contingencies intact. We found that this treatment selectively reduced performance of the degraded action. Furthermore, when a signal predicted the unpaired outcome, performance of the action was restored, suggesting that the degradatio...