Human VMPFC encodes early signatures of confidence in perceptual decisions

Abstract

Choice confidence, an individuals internal estimate of judgment accuracy, plays a critical role in adaptive behaviour. Despite its importance, the early (decisional) stages of confidence processing remain underexplored. Here, we recorded simultaneous EEG/fMRI while participants performed a direction discrimination task and rated their confidence on each trial. Using multivariate single-trial discriminant analysis of the EEG, we identified a stimulus- and accuracy-independent component encoding confidence, appearing prior to subjects choice and explicit confidence report. The trial-to-trial variability in this EEG-derived confidence signal was uniquely associated with fMRI responses in the ventromedial prefrontal cortex (VMPFC), a region not typically associated with confidence for perceptual decisions. Furthermore, we showed that the VMPFC was functionally coupled with regions of the prefrontal cortex that support neural representations of confidence during explicit metacognitive report. Our results suggest that the VMPFC encodes an early confidence readout, preceding and potentially informing metacognitive evaluation and learning, by acting as an implicit value/reward signal.