Flexible mechanisms underlie the evaluation of visual confidence.

Visual processing is fraught with uncertainty: The visual system must attempt to estimate physical properties despite missing information and noisy mechanisms. Sometimes high visual uncertainty translates into lack of confidence in our visual perception: We are aware of not seeing well. The mechanism by which we achieve this awareness--how we assess our own visual uncertainty--is unknown, but its investigation is critical to our understanding of visual decision mechanisms. The simplest possibility is that the visual system relies on cues to uncertainty, stimulus features usually associated with visual uncertainty, like blurriness. Probabilistic models of the brain suggest a more sophisticated mechanism, in which visual uncertainty is explicitly represented as probability distributions. In two separate experiments, observers performed a visual discrimination task in which confidence could be determined by the cues available (contrast and crowding or eccentricity and masking) or by their actual performance, the latter requiring a more sophisticated mechanism than cue monitoring. Results show that observers' confidence followed performance rather than cues, indicating that the mechanisms underlying the evaluation of visual confidence are relatively complex. This result supports probabilistic models, which imply the existence of sophisticated mechanisms for evaluating uncertainty.