Stimulus Novelty Inhibits Reward Evaluation: EEG Evidence

Rewards frequently occur in novel contexts, yet whether novelty facilitates or inhibits reward evaluation remains unclear. Using EEG, we investigated how stimulus novelty affects reward evaluation across two experiments. Participants performed a monetary guessing task where gains and losses were delivered in either novel or familiar forms. In experiment 1 (N = 49), stimulus novelty was integrated into feedback valence as a feedback attribute; in experiment 2 (N = 50), it was separated from feedback valence as a contextual modulator. Time and time-frequency domain results revealed that stimulus novelty reduced reward-related signals when embedded in feedback (experiment 1), regardless of feedback valence. When stimulus novelty acted as a contextual modulator (experiment 2), it selectively attenuated neural responses to gains but not losses. Critically, this gain-specific inhibition diminished as stimulus novelty habituated with task exposure, regardless of novelty's role. Our findings elucidate how stimulus novelty constrains reward evaluation, supporting the novelty inhibition hypothesis.