Confidence judgments interfere with perceptual decision making

Determining one’s confidence in a decision is a vital part of decision-making. Traditionally, psychological experiments have assessed a person’s confidence by eliciting confidence judgments. The notion that such judgments can be elicited without impacting the accuracy of the decision has recently been challenged by several studies which have shown reactivity effects—either an increase or decrease in decision accuracy when confidence judgments are elicited. Evidence for the direction of reactivity effects has, however, been decidedly mixed. Here, we report three studies designed to specifically make reactivity effects more prominent by eliciting confidence judgment contemporaneously with perceptual decisions. We show that confidence judgments elicited contemporaneously produce an impairment in decision accuracy, this suggests that confidence judgments may rely on a partially distinct set of cues/evidence than the primary perceptual decision and, additionally, challenges the continued use of confidence ratings as an unobtrusive measure of metacognition.