Abstract
Feelings of confidence in our perceptual decisions allow us to learn from and communicate the validity of our choices. Confidence should reflect the quantity and quality of evidence used to make perceptual decisions. However, confidence can also benefit from additional information not used by the perceptual system, or can suffer from additional noise. Here we sought to examine the neural computations associated with confidence evaluation and contrast them to those for the processing of the perceptual decision. We used a paradigm in which observers naturally tend to commit to perceptual decisions early, whilst continuing to monitor additional evidence for evaluating their confidence (Balsdon, Wyart, and Mamassian, 2020, Nat Commun). On each trial, observers were presented with a sequence of Gabor patterns and had to choose which orientation category they belonged to. The two categories were defined by overlapping circular Gaussian distributions centred on orthogonal orientations, such that observers must accumulate evidence over multiple uncertain stimuli to make accurate decisions. We traced the neural representation of accumulated evidence for decisions and confidence based on dynamic patterns of electrical brain activity using EEG. While the orientation of each Gabor pattern produced a transient occipital response, the informativeness of each Gabor and the accumulated perceptual evidence were associated to more sustained responses in parietal and frontal regions. The distribution of spectral power overlying motor cortex betrayed early commitments to perceptual decisions, and the neural representation of accumulated evidence used to make decisions was attenuated following these early commitments. However, observers continued to monitor the evidence for making confidence judgments after committing to the perceptual decision. We isolated spatiotemporal clusters of neural activity reflecting accurate confidence evaluation, in particular, in orbitofrontal and superior parietal cortices. Together, these results provide direct empirical evidence of the theoretical dissociation between the computations of perception and confidence.