DiscoverLessWrong (30+ Karma)“Finding Features in Neural Networks with the Empirical NTK” by jylin04
“Finding Features in Neural Networks with the Empirical NTK” by jylin04

“Finding Features in Neural Networks with the Empirical NTK” by jylin04

Update: 2025-10-17
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Description

Audio note: this article contains 63 uses of latex notation, so the narration may be difficult to follow. There's a link to the original text in the episode description.

Summary

Kernel regression with the empirical neural tangent kernel (eNTK) gives a closed-form approximation to the function learned by a neural network in parts of the model space. We provide evidence that the eNTK can be used to find features in toy models for interpretability. We show that in Toy Models of Superposition and a MLP trained on modular arithmetic, the eNTK eigenspectrum exhibits sharp cliffs whose top eigenspaces align with the ground-truth features. Moreover, in the modular arithmetic experiment, the evolution of the eNTK spectrum can be used to track the grokking phase transition. These results suggest that eNTK analysis may provide a new practical handle for feature discovery and for detecting phase changes in small models.

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Outline:

(00:23 ) Summary

(01:25 ) Background

(04:57 ) Results

(05:10 ) Toy models of Superposition

(06:34 ) Modular arithmetic

(10:00 ) Next steps

The original text contained 9 footnotes which were omitted from this narration.

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First published:

October 16th, 2025



Source:

https://www.lesswrong.com/posts/cpFqDDjhvhbaoyHnd/finding-features-in-neural-networks-with-the-empirical-ntk-1


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Narrated by TYPE III AUDIO.


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Images from the article:

For TMS, the eigenspectrum of the flattened eNTK exhibits cliffs that track the number of features the model is able to reconstruct and the total number of ground-truth features.
Heatmaps depicting cosine similarity between flattened, importance-rescaled eNTK eigenvectors and ground-truth feature vectors, for the same three sets of <span>__T3A_INLINE_LATEX_PLACEHOLDER___(n,m,S,I)___T3A_INLINE_LATEX_END_PLACEHOLDER__</span> hyperparameters as above.
Evolution of the full eNTK spectrum across the grokking phase transition. Left panel: The model with the hyperparameters p = 29, n = 512 undergoes grokking around epoch 90. Right panel: At the same time, the eNTK spectrum develops the second cliff.
Heatmaps depicting cosine similarity between eNTK eigenvectors in the second cliff and 'sum' and 'difference' Fourier feature vectors in the modular arithmetic problem at different epochs. Grokking happens around epoch 90 with our hyperparameters, but alignment of eNTK eigenvectors with the Fourier features seems to happen continuously to either side of it.
Graph showing

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“Finding Features in Neural Networks with the Empirical NTK” by jylin04

“Finding Features in Neural Networks with the Empirical NTK” by jylin04