Dynamic facial movements shape how confident speakers appear

Human communication is inherently multimodal, relying on signals conveyed through speech, vocal tone and facial movements. While gestures and vocal cues are known to influence how speech is understood, the role of facial movements remains poorly specified. Here, we test whether dynamic facial movements shape how spoken responses are interpreted by systematically modulating listener inferences of speaker confidence and doubt. Using a data-driven reverse-correlation approach and a generative model of facial behaviour, we manipulated speakers' upper-face movements while holding verbal content constant. On each trial, participants (n = 44; UK English and Mandarin Chinese speakers) rated the confidence of speakers responding to questions (e.g. 'Would they make a good leader?') on a five-point scale across 1800 trials. We find that opposing facial movements bias these inferences: eye closure and brow raising are associated with confidence, whereas brow lowering and eye tightening are associated with doubt. Signal amplitude further shapes these inferences, primarily by intensifying perceived doubt for doubt-associated movements. These mappings are largely shared between the two cultural groups, indicating common signal-inference relationships alongside differences in the weighting of specific cues. Together, these findings show that facial movements provide graded social signals that systematically shape how spoken responses are interpreted.