Individual consistency in the accuracy and distribution of confidence judgments.

We examine which aspects of the confidence distributions - its shape, its bias toward higher or lower values, and its ability to distinguish correct from erred trials - are idiosyncratic of the who (individual specificity), the when (variability across days) and the what (task specificity). Measuring confidence across different sessions of four different perceptual tasks we show that: (1) Confidence distributions are virtually identical when measured in different days for the same subject and the same task, constituting a subjective fingerprint, (2) The capacity of confidence reports to distinguish correct from incorrect responses is only modestly (but significantly) correlated when compared across tasks, (3) Confidence distributions are very similar for tasks that involve different sensory modalities but have similar structure, (4) Confidence accuracy is independent of the mean and width of the confidence distribution, (5) The mean of the confidence distribution (an individual's confidence bias) constitutes the most efficient indicator to infer a subject's identity from confidence reports and (6) Confidence bias measured in simple perceptual decisions correlates with an individual's optimism bias measured with standard questionnaire.