P300, not feedback error-related negativity, manifests the waiting cost of receiving reward information.

Previous studies have investigated how temporal discounting influences reward processing in the human brain; however, it remains unclear whether a short delay in presenting an outcome affects brain activity related to reward processing that is indexed by the two event-related potential components: the feedback error-related negativity (fERN) and P300 components. The present study used a revised simple gambling task and manipulated the waiting time before reward presentation. Behavioral data showed that participants did not respond differently between conditions; however, they reported more negative emotion under long-waiting conditions than under short-waiting conditions. Event-related potential results showed that fERN was not significantly different between the two conditions, whereas the short-waiting feedback elicited a notably larger P300 amplitude than the long-waiting feedback, particularly in frontal-central regions. The present study shows that P300, not fERN, reflects high-level motivated evaluation of waiting cost in such a decision-making task.