Action planning modulates perceptual confidence through action monitoring processes.

Dominant models of metacognition suggest that sensory information quality determines perceptual confidence, but recent accounts propose that motor signals also affect confidence judgments. In this study, we investigated the impact of motor planning of perceptual responses on decision confidence, testing two hypotheses. The "fluency hypothesis" suggests that ease of motor response selection and preparation enhances confidence. In contrast, the "monitoring hypothesis" posits that increased action monitoring during response selection boosts confidence, potentially counteracting response fluency. In three preregistered experiments, participants reported the orientation of a stimulus and indicated their confidence in their response. A cue-induced action planning that was either congruent or incongruent with the response side used to report the stimulus orientation. Across experiments, we consistently observed higher confidence when participants prepared spatially incongruent actions compared with congruent ones, regardless of response accuracy. In the third experiment, electroencephalography revealed an increased frontocentral P2 amplitude for incongruent actions, suggesting that incongruent action planning heightened early attentional resources needed to resolve response conflict. Incongruent action plans also modulated postresponse event related potentials at centro-parietal channels (e.g., Pz), typically linked to confidence and error monitoring. These findings align with the "monitoring hypothesis" suggesting that the degree of action monitoring during response selection modulates retrospective decision confidence. (PsycInfo Database Record (c) 2025 APA, all rights reserved).