Type-1 and type-2 decisions feature computational noise of similar magnitude.

Mounting evidence supports the existence of Type-2, metacognitive noise that affects human confidence judgments. The existence of this noise has led to the hypothesis that metacognitive judgments arise from a metacognitive system that is separate from the decision-making system responsible for Type-1 decisions. However, Type-2 decisions are different than standard Type-1 decisions in that they require evaluating the strength of sensory evidence rather than just making a simple categorical judgment. Here, we investigated whether Type-2 computational noise still exceeds Type-1 computational noise when both judgments require evaluation of the strength of sensory evidence. Participants (N = 319) performed a perceptual discrimination task and in different conditions provided Type-2 confidence judgments or Type-1 judgments based on biased expectations or unequal rewards. All these judgments require a similar fine-grained evaluation of the strength of sensory evidence (e.g., is the evidence high enough to justify a high-confidence rating or choosing the alternative with smaller probability or reward). We first confirmed that the confidence and expectation conditions resulted in similarly biased criteria and perceptual sensitivity drop, whereas the reward conditions exhibited less biased criteria and smaller perceptual sensitivity drop. Critically, formal computational modeling demonstrated that all conditions exhibited comparable levels of computational noise. These findings demonstrate that Type-1 and Type-2 decisions exhibit computational noise of similar magnitude when they require similar fine-grained evaluation of sensory evidence strength. More generally, our results have implications for the debate on whether Type-1 and Type-2 decisions are made by separate systems.