Five EEG foundation models were re-run with three controls their own papers skipped, and random initialization matched pretraining on half of them
AspireAI community · arXiv
Most EEG foundation model papers report downstream gains without three controls: the same encoder untrained, spectral features fitted on the same data, and a layer chosen without looking at test scores. This evaluation adds all three across five publicly released EEG foundation models plus an in-house JEPA-style model, over five benchmarks, four extra task families and several seeds. Choosing the probed layer by its test score inflated the layer-wise peak by an average of +0.034 and flipped the peak-versus-output gap in 9 of 36 cells. With the layer picked on validation instead, random initialization matched or beat pretraining for half of the models on sleep and emotion, and no model beat a five-band log-power baseline on emotion or motor imagery. After full fine-tuning only 5 of 30 pairs gained beyond twice their seed spread, and one clear loss of -0.290 AUROC persisted under matched learning rates.
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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.