Frontal scalp potentials foretell perceptual choice confidence.

When making decisions, people naturally ask two implicit questions: how soon can I make a decision, and how certain am I? In perception, people's confidence (how certain?) shows a nonmonotonic relationship with response time (how soon?), such that choice confidence can either increase or decrease with response time. Although a frontoparietal network has been implicated as a neural substrate that binds choice confidence and action (e.g., response time), the dynamic interplay between choice behaviors within such a network has not been clarified. Here, we show that frontal event-related potentials (ERPs) reflect choice confidence before a decision. Specifically, we report a second positive peak of the stimulus-locked frontal ERP at ~500 ms that scales with confidence but not stimulus level, whereas the centroparietal ERP amplitude covaries inversely with response time. This frontal ERP component occurs before the response, which helps explain the inverse relationship between choice confidence and response time (i.e., higher confidence for shorter response time) when choice accuracy is emphasized over speed. Our findings provide the first early neural representation of confidence, consistent with the temporal precedence for its causal role in the current decision-making task: "I decided earlier because I am confident."