Public communication alters private confidence

We use our private feelings of confidence to coordinate our public, social lives. For example, when making joint decisions we can share our uncertainty honestly to reach an accurate consensus, or exaggerate our confidence to exaggerate our influence on the group. Some theories in cognitive neuroscience suggest that we can strategically distort the confidence we express to others while leaving our private feelings unchanged. But other theories suppose that our interactions with others may be a key source of beliefs about uncertainty in our own minds. If the latter is true, communicating about confidence with others could alter introspection on ourselves. We tested this idea in a novel decision-making task, where participants made perceptual choices and gave confidence ratings alone, together with a partner and then alone again. Across studies, participants showed ‘confidence matching’, with the confidence they expressed gravitating towards the confidence of their partners. Most importantly, these shifts in reported confidence persisted even after the interaction terminated, and participants made decisions alone again. These effects can be captured by a new predictive learning model, which assumes that agents use the confidence expressed by themselves and others to predict the confidence they ought to feel. These results reveal how the dynamics of social interaction can shape our sense of confidence and point to a mechanism that explains how communication with others can change our private states of mind.