Human VMPFC encodes early signatures of confidence in perceptual decisions

Choice confidence, an individual’s internal estimate of judgment accuracy, plays a critical role in adaptive behaviour, yet its neural representations during decision formation 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-independent component encoding confidence, which appeared prior to subjects’ explicit choice and confidence report, and was consistent with a confidence measure predicted by an accumulation-to-bound model of decisionmaking. Importantly, trial-to-trial variability in this electrophysiologically-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, activity in the VMPFC was functionally coupled with regions of the frontal cortex linked to perceptual decision-making and metacognition. Our results suggest that the VMPFC holds an early confidence representation arising from decision dynamics, preceding and potentially informing metacognitive evaluation

Spatiotemporal neural correlates of confidence in perceptual decision making

In our interactions with the environment, we often make inferences based on noisy or incomplete perceptual information - for example, judging whether the person waving their hand in the distance is someone we know (as opposed to a stranger, greeting the person behind us). Such judgments are accompanied by a sense of confidence, that is, a degree of belief that we are correct, which ultimately determines how we act, adjust our subsequent decisions, or learn from errors. Neuroscience has only recently begun to characterise the representations of confidence in the animal and human brain, however the neural mechanisms and network dynamics supporting these representations are still unclear. The current thesis presents empirical findings from three studies that sought to provide a more complete characterisation of confidence during perceptual decision making, using a combination of electrophysiological and neuroimaging methods. Specifically, Study 1 (Chapter 2) investigated the temporal characteristics of confidence in relation to the perceptual decision. We recorded EEG measurements from human subjects during performance of a face vs. car categorisation task. On some trials, subjects were offered the possibility to opt out of the choice in exchange for a smaller but certain reward (relative to the reward obtained for correct choices), and the choice to use or decline this option reflected subjects’ confidence in their perceptual judgment. Neural activity discriminating between high vs. low confidence trials could be observed peaking approximately 600 ms after stimulus onset. Importantly, the temporal profile of this activity resembled a ramp-like process of evidence accumulation towards a decision, with confidence being reflected in the rate of the accumulation. Our results are in line with the notion that neural representations of confidence may arise from the same process that supports decision formation. Extending on these findings, in Study 2 (Chapter 3) we asked whether rhythmic patterns within the EEG signals may offer additional insights into the neural representations of confidence. Using an exploratory analysis of data from Study 1, we identified confidence-discriminating oscillatory activity in the alpha and beta frequency bands. This was most prominent over the sensorimotor electrodes contralateral to the motor effector that subjects used to indicate choice (i.e., right hand), consistent with a motor preparatory signal. Importantly however, the effect was transient in nature, peaking long before subjects could execute a response, and thus ruling out a direct link with overt motor behaviour. More intriguingly, the observed confidence effect appeared to overlap in time with the non-oscillatory representation of confidence identified in Study 1. In line with the view that motor systems track the evolution of the perceptual decision in preparation for impending action, results from Studies 1 and 2 open the possibility that confidence-related information may also be contained within these signals. Finally, following on from our work in the first study, we next aimed to capitalise on the single-trial neural representations of confidence obtained with EEG, in order to identify potentially correlated activity with high spatial resolution. To this end, in Study 3 (Chapter 4) we recorded simultaneous EEG and fMRI data while subjects performed a speeded motion discrimination task and rated their confidence on a trial-by-trial basis. Analysis of the EEG revealed a confidence-discriminating neural component which appeared prior to participants’ overt choice and was spatiotemporally consistent with our results from the first study. Crucially, we showed that haemodynamic responses in the ventromedial prefrontal cortex (VMPFC) were uniquely explained by trial-to-trial fluctuations in these early confidence-related neural signals. Notably, this activation was additional to what could be explained by subjects’ confidence ratings alone. We speculated that the VMPFC may support an early and/or automatic readout of perceptual confidence, potentially preceding explicit metacognitive appraisal. Together, our results reveal novel insights into the neural representations of perceptual confidence in the human brain, and point to new research directions that may help further disentangle the neural dynamics supporting confidence and metacognition

The Confidence Database

Understanding how people rate their confidence is critical for the characterization of a wide range of perceptual, memory, motor and cognitive processes. To enable the continued exploration of these processes, we created a large database of confidence studies spanning a broad set of paradigms, participant populations and fields of study. The data from each study are structured in a common, easy-to-use format that can be easily imported and analysed using multiple software packages. Each dataset is accompanied by an explanation regarding the nature of the collected data. At the time of publication, the Confidence Database (which is available at https://osf.io/s46pr/) contained 145 datasets with data from more than 8,700 participants and almost 4 million trials. The database will remain open for new submissions indefinitely and is expected to continue to grow. Here we show the usefulness of this large collection of datasets in four different analyses that provide precise estimations of several foundational confidence-related effects

Neural representations of confidence emerge from the process of decision formation during perceptual choices

Choice confidence represents the degree of belief that one's actions are likely to be correct or rewarding and plays a critical role in optimizing our decisions. Despite progress in understanding the neurobiology of human perceptual decision-making, little is known about the representation of confidence. Importantly, it remains unclear whether confidence forms an integral part of the decision process itself or represents a purely post-decisional signal. To address this issue we employed a paradigm whereby on some trials, prior to indicating their decision, participants could opt-out of the task for a small but certain reward. This manipulation captured participants' confidence on individual trials and allowed us to discriminate between electroencephalographic signals associated with certain-vs.-uncertain trials. Discrimination increased gradually and peaked well before participants indicated their choice. These signals exhibited a temporal profile consistent with a process of evidence accumulation, culminating at time of peak discrimination. Moreover, trial-by-trial fluctuations in the accumulation rate of nominally identical stimuli were predictive of participants' likelihood to opt-out of the task, suggesting that confidence emerges from the decision process itself and is computed continuously as the process unfolds. Correspondingly, source reconstruction placed these signals in regions previously implicated in decision making, within the prefrontal and parietal cortices. Crucially, control analyses ensured that these results could not be explained by stimulus difficulty, lapses in attention or decision accuracy

Data from: Human VMPFC encodes early signatures of confidence in perceptual decisions

Choice confidence, an individual's internal estimate of judgment accuracy, plays a critical role in adaptive behaviour, yet its neural representations during decision formation 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-independent component encoding confidence, which appeared prior to subjects' choice and explicit confidence report and was consistent with a confidence measure predicted by an accumulation-to-bound model of decision-making. Importantly, trial-to-trial variability in this electrophysiologically-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, activity in the VMPFC was functionally coupled with regions of the frontal cortex linked to perceptual decision-making and metacognition. Our results suggest the VMPFC holds an early confidence representation arising from decision dynamics, preceding and potentially informing metacognitive evaluation

Data and code

EEG data (in DATA.mat) and nifti fMRI activations maps (unthresholded). Matlab function plot_code_Sep2018.m for reproducing all main and supplementary figures in the paper. Readme details in the plot_code_Sep2018.m

The Confidence Database.

Understanding how people rate their confidence is critical for the characterization of a wide range of perceptual, memory, motor and cognitive processes. To enable the continued exploration of these processes, we created a large database of confidence studies spanning a broad set of paradigms, participant populations and fields of study. The data from each study are structured in a common, easy-to-use format that can be easily imported and analysed using multiple software packages. Each dataset is accompanied by an explanation regarding the nature of the collected data. At the time of publication, the Confidence Database (which is available at https://osf.io/s46pr/) contained 145 datasets with data from more than 8,700 participants and almost 4 million trials. The database will remain open for new submissions indefinitely and is expected to continue to grow. Here we show the usefulness of this large collection of datasets in four different analyses that provide precise estimations of several foundational confidence-related effects