Electrophysiological reward signals predict episodic memory for immediate and delayed positive feedback events

Previous research has shown that in reinforcement learning, the hippocampus is involved in the processing of feedback when it is delayed for several seconds. Also, better recognition memory has been reported for temporally delayed than for immediately presented feedback pictures. Event-related potential (ERP) studies have found that feedback delay affects the amplitude of the feedback-related negativity (FRN), and there is evidence suggesting that the FRN is modulated by declarative learning. In the present study, a subsequent memory paradigm was used to investigate the effects of feedback delay on the incidental encoding and subsequent retrieval of feedback events. Participants used immediate or delayed feedback to learn associations between Chinese characters and reactions. Unrelated pictures were presented simultaneously with positive or negative feedback, and recognition memory for the pictures was tested in a surprise memory test. Behaviorally, memory was better for positive than negative feedback pictures, but there was no effect of feedback delay on memory performance. Electrophysiological activity during the FRN time window was found to predict subsequent memory for positive, but not negative feedback pictures, suggesting that positive reward prediction errors as reflected in the FRN contribute to successful memory encoding. Consistent with previous studies, the FRN was reduced for delayed feedback, but only in a condition in which feedback was useful for learning. Behavioral and ERP estimates of familiarity and recollection support the view that positive feedback enhanced memory mainly by boosting familiarity-based recognition.