Sleep deprivation disrupts the gatekeeping role of confidence in belief updating.

Belief updating in response to social feedback is essential for adaptive decision making but may be sensitive to sleep deprivation. Across two preregistered within-subjects studies (N = 36, conducted in 2023, and N = 49, conducted in 2024), we examined how 24 hr of total sleep deprivation affects belief change and confidence updating after agreeing or disagreeing with peer feedback. Sleep deprivation consistently increased belief change, regardless of feedback type, and disrupted the stabilizing role of initial confidence. High-confidence beliefs, typically more resistant to revision, were more often changed when participants were sleep deprived. To examine confidence dynamics, Study 2 added a no-change block, where participants could adjust confidence, but not change beliefs. Here, sleep-deprived participants showed larger confidence drops, especially at high initial confidence. Moreover, stronger confidence drops in the no-change block predicted more frequent belief change when change was allowed. In sleep-deprived states, higher initial confidence no longer protected against strong confidence updating in response to peer feedback. Rather than simply increasing suggestibility, sleep deprivation undermines confidence-based mechanisms that normally regulate belief change. (PsycInfo Database Record (c) 2026 APA, all rights reserved).