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Training a handful of attention heads to look at the right pixels lifted a 4B thinking VLM from 74.1 to 76.6 percent on high-resolution benchmarks

AspireAI community · arXiv
Thinking vision-language models reason for thousands of tokens and still miss small details in high-resolution images, while zoom-in methods pay for extra inference passes. The authors locate the bottleneck in selection rather than perception: in Qwen3.5-4B a few attention heads, which they call localization heads, pick the evidence out of thousands of visual tokens, and ablating four of them costs 13.2 points more than ablating four random heads. Localization-Head Alignment makes attention a training signal, adding an auxiliary loss so that when the reasoning states a visual fact, those heads look at the focal region; on V*, HR-Bench 4K and TreeBench it lifted Qwen3.5-4B from 74.1% to 76.6%, with alignment alone adding 1.8 points over otherwise identical training while shortening reasoning by 20%. The gains carried over to Qwen2.5-VL-3B, but the evidence rests on one 4B model family and three benchmarks.
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One distance function matched sparse-autoencoder features across layers and compressed feature circuits into supernodes
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.
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