Disentangling the origins of confidence in speeded perceptual judgments through multimodal imaging

Our everyday life is full of rapid decisions such as a driver having to choose which exit to take on the highway. These rapid decisions often come with a certain level of subjective confidence ranging from certainty of having made the right choice to certainty of having chosen wrong and passing through various levels of uncertainty. Since our sense of confidence stems from the monitoring of the decision it relates to, its underlying brain mechanisms have been difficult to study in isolation of the accompanying decisions. We have published a study in which we isolate confidence from decisional processes by comparing confidence related to our own decisions with confidence related to other people’s decisions (e.g. the confidence of the passenger in the car). In our study, decisions were taken about which stimulus contained the highest number of dots. These decisions could be taken either by the study participants by pressing a button, or by the computer by showing a hand on the chosen side. In both cases, participants had to rate their confidence in the previous decision. We found that confidence ratings tracked the correctness of decisions better when those decisions were taken by the participants. Since we recorded electroencephalography while the participants were in a functional magnetic resonance imaging scanner, we were able to precisely locate the brain regions associated to confidence both in time and space. We found only one brain region that was still associated with confidence when participants rated the computer’s decisions: the inferior frontal cortex. One other brain region, the anterior prefrontal cortex, that is well known to relate to confidence was only associated to confidence in participants’ own decisions. Our study thus sheds light on the underlying mechanisms of confidence, highlighting the role of the inferior frontal cortex as a key region for confidence independently from decisions and constraining the role of the anterior prefrontal cortex to self-related monitoring.