Late Cross-Modal Biases in Neural Spatial Representations Revealed by EEG Decoding.

During audiovisual perception, spatial information from vision and audition is combined, often producing biases such as the ventriloquist effect. While these interactions are well documented behaviorally, it remains unclear when cross-modal information begins to alter modality-specific spatial representations in the brain. Here we used cross-generalized inverted encoding modeling of electroencephalography (EEG) data to track the temporal evolution of spatial representations during a spatial ventriloquist task. Human participants (both sexes) localized audiovisual stimuli with horizontally offset auditory and visual components. Decoders trained on unisensory EEG responses were applied to audiovisual trials to estimate whether and when spatial representations of one modality were biased toward the other. Behaviorally, participants integrated cues but showed slight visual overweighting. Neural decoding revealed robust spatial representations for both modalities, with early unisensory encoding remaining unaffected by cross-modal input. Cross-modal biases emerged only later (from ∼200 ms onward), within a generalized representational window, and occurred sequentially: auditory representations were biased earlier than visual. These findings indicate that multisensory spatial integration arises via recurrent feedback during later processing stages, while early sensory-specific representations remain independent, providing a neural basis for the temporal dynamics underlying the ventriloquist effect.