Metacognition Indexes Causal Inference in Audiovisual Speech

In multisensory environments, our brains perform causal inference to estimate which sources produce specific sensory signals. While these inferences are often accurate, they sometimes create multisensory illusions. Here, we ask two questions about multisensory causal inference: can our brains index the causal structures that underlie sensory experience? And can they do so when perceived content is identical across illusory and non-illusory scenarios? To answer these questions, 122 online participants viewed videos with congruent, McGurk, and rarely integrated audiovisual speech. On each trial, participants reported which syllable theyperceived, and rated confidence in their judgment. Across four experiments, results showed that confidence was highest for congruent speech and lower for McGurk and rarely integrated speech. Critically, when the perceived syllable for congruent and McGurk videos was matched, confidence scores differed between congruent and McGurk stimuli. Together, these results demonstrate how higher-order metacognitive systems index the causal structure of audiovisual speech.