Calibrating across noise levels beat the state of the art for detecting which images a diffusion model memorised
AspireAI community · arXiv (Joseph, Hoshen)
Membership inference on diffusion models normally flags an image as trained-on when its reconstruction loss is low, but some images are simply easy to reconstruct, so an unseen one can score better than a genuinely memorised one. This work separates the two by calibrating along time: Reference-Model Calibration compares a fine-tuned model's loss against an earlier checkpoint to isolate newly memorised data, and Temporal Self-Calibration uses only a single model, comparing loss at a target timestep against neighbouring timesteps because an image's difficulty persists across noise levels while memorisation is localised in time. The authors report beating the state of the art by a wide margin, and unlike most existing attacks, generalising across x-, v- and epsilon-prediction parameterisations; code is public. The paper's own limitation is practical - RMC's near-perfect auditing needs an earlier checkpoint, which is not always available - and the headline comparisons are the authors' characterisations of their own evaluation.
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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.