A unified model's own image generator turned out to help it reason about space
AspireAI community · arXiv
Unified multimodal models support both visual understanding and image generation, but information mostly flows one way - understanding representations condition generation, while the generative branch is rarely reused for reasoning. DiFuse asks whether the native diffusion branch can supply complementary spatial cues, and the answer is yes, under conditions. Layer-wise analysis identifies which diffusion representations carry usable spatial signal and where they can be injected into the understanding pathway with minimal interference, after which the features are spatially aligned with visual tokens and fused residually into selected multimodal decoder layers. On UniWorld-V1 the method consistently improves spatial reasoning over a matched SFT baseline while keeping general multimodal performance broadly comparable, and results on OmniGen2 suggest the approach transfers across unified architectures. The gains depend critically on the choice of representations, injection position and preservation of spatial correspondence.
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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.