Sensory noise increases metacognitive efficiency

Metacognitive efficiency quantifies people’s ability to introspect into their own decision making relative to their ability to perform the primary task. Despite years of research, it is still unclear how visual metacognitive efficiency can be manipulated. Here, we show that a hierarchical model of confidence generation makes a counterintuitive prediction: Higher sensory noise should increase metacognitive efficiency. The reason for this is that hierarchical models assume that although the primary decision is corrupted only by sensory noise, the confidence judgment is corrupted by both sensory and metacognitive noise. Therefore, increasing sensory noise has a smaller negative influence on the confidence judgment than on the perceptual decision, resulting in increased metacognitive efficiency. To test this prediction, we used a perceptual learning paradigm to decrease sensory noise. In Experiment 1, 7 days of training led to a significant decrease in sensory noise and a corresponding decrease in metacognitive efficiency. Experiment 2 showed the same effect in a brief 97-trial learning for each of 2 different tasks. Finally, in Experiment 3, we combined increasingly dissimilar stimulus contrasts to create conditions with higher sensory noise and observed a corresponding increase in metacognitive efficiency. Our findings demonstrate the existence of a robust positive relationship between across-trial sensory noise and metacognitive efficiency. These results could not be captured by a standard model in which decision and confidence judgments are made based on the same underlying information. Thus, our study provides direct evidence for the existence of metacognitive noise that corrupts confidence but not the perceptual decision.