Product, not process: Metacognitive monitoring of visual performance during sustained attention.

The performance of the human visual system exhibits moment-to-moment fluctuations influenced by multiple neurocognitive factors. To deal with this instability of the visual system, introspective awareness of current visual performance (metacognitive monitoring) may be crucial. In this study, we investigate whether and how people can monitor their own visual performance during sustained attention by adopting confidence judgments as indicators of metacognitive monitoring - assuming that if participants can monitor visual performance, confidence judgments will accurately track performance fluctuations. In two experiments (N $=$ 40), we found that participants were able to monitor fluctuations in visual performance during sustained attention. Importantly, metacognitive monitoring largely relied on the quality of target perception, a product of visual processing ("I lack confidence in my performance because I only caught a glimpse of the target"), rather than the states of the visual system during visual processing ("I lack confidence because I was not focusing on the task").