The existence of animal models of metacognition opens the door to an examination of its neural mechanisms. Indeed, metacognitive protocols that assess the animal's degree of confidence in its own responses have become simple enough to lead to neurophysiological experimentation. Kiani and Shadlen (2009) used J. David Smith's "escape key" paradigm in a statistical decision-making lecture. The animal is asked to make a binary decision about the direction of movement. On some trials, even before this decision is made, a third response possibility appears ("escape" response). Choosing this target leads to a fixed but smaller reward. This choice can therefore be interpreted as a refusal to respond to the main task, which could indicate that the animal is uncertain and lacks self-confidence. Indeed, behavioral observations indicate that objective performance is better when the animal has the option of refusing to respond than when it does not. This means that, given the same stimulus, the animal correctly discarded trials where it felt unable to respond.
What signals enable the animal to calculate its level of confidence in its responses? Neuronal discharges in the lateral intraparietal area (LIP) reflect not only the upcoming decision, but also the animal's confidence in this response, even before the animal knows whether or not the escape option will be offered. In addition, trial-to-trial fluctuations in neuronal discharges, measured just before the option of refusing to respond is presented, predict the choice of this option: the animal selectively chooses to avoid responding, precisely on trials where its parietal neurons do not sufficiently discriminate between the two responses of the primary task. The rate of increase of discharges during stimulus presentation also contributes independently to the choice of the option to refuse to respond. Taken together, these results are well described by a simple mathematical model that reduces metacognition to the level of a simple higher-level decision.
