Multimodal RL rewards models for shortcutting, so a new method trains them against their own language-prior failures
AspireAI community · arXiv (NeurIPS 2026)
Standard outcome supervision in multimodal RLVR suffers credit assignment ambiguity: a model can earn positive reward by exploiting language priors or dataset shortcuts instead of grounding its reasoning in visual evidence. EVAN first finds the examples where the visual evidence matters most, using a scaled image information gain metric with a mixed-ranking strategy to preserve data diversity, then masks the most discriminative image patches to elicit plausible but visually ungrounded responses from the current policy. Those responses become bounded auxiliary signals under the clean image, penalising shortcut learning without destabilising RL. The code is published.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.