Supramodal Coding of Detection and Confidence in the Human Cortex
Perception is inherently multisensory, yet it remains unclear whether the brain detects stimuli and evaluates confidence in these detections using circuits shared across senses or circuits specific to each modality. Prior evidence is limited: scalp electrophysiology cannot localize where a shared code operates, whereas functional imaging cannot resolve its timing. We recorded intracranial activity (stereoelectroencephalography) in eight patients with epilepsy who performed a near-threshold audiovisual detection task in which they reported, on each trial, whether a visual, auditory, or audiovisual stimulus was present and rated their confidence, both overall and separately for each modality. Analyzing high-gamma activity at the single-channel and region-of-interest levels, we found that stimulus detection involved a broadly distributed, largely supramodal set of cortical regions responding regardless of modality, including the insula, dorsomedial prefrontal cortex, and superior temporal gyrus. Multivariate decoders trained to distinguish detected from undetected stimuli in one modality generalized to the other modality, indicating a shared detection code within these regions. Confidence relied on a more mixed architecture but was also substantially supramodal. Finally, the auditory cortex encoded confidence information about its non-preferred (visual) modality, with a similar effect in the visual cortex for auditory confidence, suggesting that the involvement of sensory cortices in confidence is not confined to its preferred input.