Public communication alters private confidence

We use private feelings of confidence to coordinate our public, social lives. When making joint decisions we can share uncertainty honestly to reach an accurate consensus, or exaggerate our confidence to increase our influence1. Some theories suggest that we can strategically distort the confidence we express to others while leaving our private feelings unchanged2, but recently we hypothesised that our interactions with others may be a key source of beliefs about uncertainty in our own minds3. Consistent with this idea, we show that changes in how we publicly communicate our confidence to others can lead to changes in private confidence when we're alone. Our experiments and modelling reveal how social interaction can shape our sense of confidence - which could explain how confidence biases emerge and persist in interacting groups.