Adversarial optimization turned out to be concentrated on about 5 percent of parameters, and updating only those matched or beat full-parameter adversarial training on both clean and robust accuracy
AspireAI community · arXiv
Adversarial training is one of the most effective defenses against adversarial perturbations but is expensive on large models and carries a persistent clean-versus-robust accuracy trade-off. LoRA-style parameter-efficient adversarial fine-tuning reduces memory cost but leaves a notable robustness gap versus full-parameter training. This paper takes a parameter-space view: gradient analysis shows adversarial optimization is highly concentrated on a small subset of parameters the authors call Robustness-Critical Parameters, suggesting robustness is encoded in a sparse subspace. Their Sparse Adversarial Fine-Tuning method identifies those parameters via adversarial gradient saliency and updates only them while freezing the rest, and it outperforms LoRA-based methods in both clean and robust accuracy with fewer trainable parameters, approaching or surpassing full-parameter adversarial training in robustness while updating roughly 5 percent of parameters. It is accepted at NeurIPS 2026. The limitation is that the cost of computing saliency adds a step to the training pipeline, so the memory saving is smaller than a plain LoRA run.
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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.