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The paper introduces MIRAGE, a novel brain encoding framework that predicts whole-brain fMRI responses to audiovisual stimuli using a natively multimodal backbone with adaptive feature gating. MIRAGE outperforms unimodal approaches by adaptively integrating visual, auditory, and linguistic information across network layers. Analysis of the learned attention weights reveals distinct anatomical patterns for each modality, offering insights into modality-specific processing in the brain.
Multimodal AI isn't just about better predictions; MIRAGE reveals how different modalities carve out distinct territories in the brain.
Recent progress in task-optimized neural networks has established encoding models as a powerful tool for predicting brain responses to naturalistic stimuli, yet most existing approaches rely on unimodal representations. The emergence of omni-modal foundation models and rich multimodal neural datasets enables encoding models that jointly integrate visual, auditory, and linguistic information across subjects. We introduce MIRAGE, a brain encoding framework for predicting whole-brain fMRI responses to naturalistic audiovisual stimuli. MIRAGE achieves state-of-the-art performance via a native multimodal backbone and adaptive feature gating across layers. These representations are then combined with a transformer-based brain encoder and a subject-specific linear head over the cortical parcels. Controlled comparisons show that natively multimodal features consistently outperform post-hoc aggregation of independent unimodal features, across architectural levels and backbones. Beyond predictive accuracy, the learned attention weights are directly inspectable to interpret the modality-specific gating profile over the backbone, and each modality traces a distinct anatomical pattern across cortex. Together, these results propose adaptive layer-wise aggregation of natively multimodal features as a generalizable, interpretable, and accurate approach for whole-brain encoding.