Sparse Prototype Code Underlies Classification and Prediction Across Modalities
Organizations: The Racah Institute of Physics, Hebrew University · Edmond and Lily Safra Center for Brain Sciences, Hebrew University · Department of Electrical and Computer Engineering, Cornell Tech, Cornell University · Center for Brain Science, Harvard University
Abstract
Neural representations have become a central tool for studying the internal mechanisms of modern AI models, yet their complex high-dimensional structure makes them difficult to interpret. We show that classification tasks give rise to a universal representational geometry, shared across state-of-the-art models in vision, audio, and language processing. The key structure is that within-class variability is not random in representation space. Instead, its classifier-relevant component has strong and structured correlations with the class's own centroid and with the centroids of its competing classes. Building on this observation, we derive an analytical mean-field theory governed mainly by the variability along true-class and rival-class centroid coordinates, together with a global renormalization of the class radius that compensates for the non-Gaussian statistics of real representations. The theory accurately predicts classification accuracy across architectures and modalities. The relevant geometric quantities improve systematically with model scale, mirroring the observed gains in accuracy. A striking feature of the theory is its sparsity: accurate prediction requires only a small set of centroid coordinates associated with the true class and its strongest rivals - connecting our framework to sparse-feature extraction approaches such as sparse autoencoders. Together, these results provide a parsimonious predictive theory of neural representations and suggest that classification in deep networks is governed by a sparse, centroid-aligned structure embedded within the full high-dimensional representation space.
Figures & tables
| model | class | top-5 rivals (by ) |
|---|---|---|
| Qwen3-32B | happy | excite, proud, glad, surprised, curious |
| bad | sad, sorry, scare, angry, tired | |
| voice | loud, noise, sound, big, funny | |
| smile | reply, nod, say, think, tell | |
| cake | delicious, cookie, food, ice, big | |
| forest | park, garden, grass, world, sky |
| Notation | Name | Definition |
|---|---|---|
| Centroid | ||
| Unit centroid | ||
| Residual | ||
| Radius 2 | ||
| Variance fraction | ||
| Std. projection |
| Backbone | range | Fixed fluctuations | -rot | ||||||
| Vision – ImageNet-1K | |||||||||
| DINOv3 ViT-7B/16 | 1000 | 4096 | [0.4, 4.3] | 0.855 | 0.099 | 1.000 | 0.392 | 14.4 | 4.5 |
| DINOv3 ConvNeXt-L | 1000 | 1536 | [0.2, 3.1] | 0.814 | 0.100 | 1.000 | 0.312 | 14.2 | 4.4 |
| CLIP ViT-L/14 | 1000 | 768 | [0.6, 2.7] | 0.792 | 0.124 | 0.999 | 0.077 | 13.9 | 16.4 |
| ViT-B/16 (IN21K) | 1000 | 768 | [0.5, 2.7] | 0.853 | 0.088 | 1.000 | 0.265 | 14.1 | 4.1 |
| Audio – VGGSound | |||||||||
| Model | Acc | ||||||
|---|---|---|---|---|---|---|---|
| DINOv3 ViT-S | 1.68 | 1.06 | 0.172 | 0.574 | 0.558 | 19.3 | 0.706 |
| DINOv3 ViT-S | 1.60 | 1.09 | 0.172 | 0.555 | 0.535 | 14.4 | 0.738 |
| DINOv3 ViT-B | 1.52 | 1.19 | 0.163 | 0.542 | 0.529 | 9.0 | 0.794 |
| DINOv3 ViT-L | 1.39 | 1.36 | 0.147 | 0.447 | 0.322 | 7.0 | 0.845 |
| DINOv3 ViT-H | 1.29 | 1.59 | 0.164 | 0.236 | -0.011 | 5.3 | 0.855 |
| DINOv3 ViT-7B | 1.50 | 2.01 | 0.120 | 0.289 | 0.038 | 4.5 | 0.855 |
Appendix figures & tables19 assets
Supplementary material from the paper’s appendix.
Appendix
| Backbone | Acc | |
|---|---|---|
| Vision (ImageNet-1K) | ||
| ViT-B/16 (IN21K) | ||
| ConvNeXt-B (IN1K) | ||
| DINOv3 ViT-L/16 | ||
| DINOv3 ViT-H + /16 | ||
| DINOv3 ConvNeXt-S | ||
| Family | Model | Data / task | Objective | ||
| Vision — ImageNet-1K | |||||
| Vision | DINOv3 ViT-S/16 | ImageNet-1K | Self-supervised | ||
| Vision | DINOv3 ViT-S+/16 | ImageNet-1K | Self-supervised | ||
| Vision | DINOv3 ViT-B/16 | ImageNet-1K | Self-supervised | ||
| Vision | DINOv3 ViT-L/16 | ImageNet-1K | Self-supervised | ||
| Vision | DINOv3 ViT-H+/16 | ImageNet-1K | Self-supervised | ||
| Selector | within | within | within | within |
|---|---|---|---|---|
| Centroid correlations ( ) | 14 | 24 | 36 | 87 |
| Projection variance ( ) | 14 | 20 | 30 | 54 |
| Theory margin | 11 | 18 | 25 | 49 |
| Gaussian margin | 10 | 19 | 28 | 73 |
| Modality | Centroids corr. | Proj. variance | Theory margin | Gaussian margin | |
|---|---|---|---|---|---|
| Vision | 15 | 76 | 47 | 45 | 56 |
| Autoregressive LM | 14 | 102 | 89 | 82 | 108 |
| Masked LM | 4 | 48 | 42 | 35 | 43 |
| Audio | 3 | 60 | 39 | 37 | 49 |
| Modality | RMSE | RMSE | floor | within by | |
|---|---|---|---|---|---|
| Vision | 15 | 0.049 | 0.047 | 0.045 | 13/15 |
| Audio | 3 | 0.081 | 0.076 | 0.064 | 0/3 |
| Masked LM | 4 | 0.064 | 0.062 | 0.061 | 4/4 |
| Autoregressive LM | 14 | 0.080 | 0.075 | 0.075 | 14/14 |
| All | 36 | 0.065 | 0.062 | 0.060 | 31/36 |
| fitted | |||||||
|---|---|---|---|---|---|---|---|
| Modality | RMSE | RMSE | |||||
| Vision | 15 | 0.812 | 0.876 | 0.080 | 0.819 | 0.047 | 1.228 |
| Audio | 3 | 0.613 | 0.657 | 0.087 | 0.617 | 0.076 | 1.084 |
| Masked LM | 4 | 0.715 | 0.785 | 0.090 | 0.724 | 0.062 | 1.131 |
| Autoregressive LM | 14 | 0.522 | 0.583 | 0.096 | 0.524 | 0.075 | 1.111 |
| All | 36 | 0.672 | 0.734 | 0.088 | 0.677 | 0.062 | 1.160 |
| Backbone | ||
|---|---|---|
| Vision (ImageNet-1K) | ||
| DINOv2 ViT-g | ||
| ConvNeXt-B | ||
| ViT-B | ||
| DINOv3 CNX-L | ||
| DINOv3 ViT-7B | ||
| Backbone | Acc | Acc th | RMSE | ||||
|---|---|---|---|---|---|---|---|
| Vision (ImageNet-1K) | |||||||
| ConvNeXt-B | 1000 | 1024 | |||||
| ResNet50 | 1000 | 2048 | |||||
| DINOv3 ViT-H + | 1000 | 1280 | |||||
| DINOv3 ViT-7B | 1000 | 4096 | |||||
| ViT-B | 1000 | 768 | |||||
| Layer | Acc | ||||||
|---|---|---|---|---|---|---|---|
| L58 (0.91) | 2.40 | 0.993 | 0.172 | 0.514 | 0.496 | 10.9 | 0.521 |
| L59 (0.92) | 2.32 | 0.996 | 0.175 | 0.511 | 0.502 | 11.0 | 0.542 |
| L60 (0.94) | 2.24 | 0.999 | 0.175 | 0.510 | 0.474 | 10.9 | 0.557 |
| L61 (0.95) | 2.20 | 1.007 | 0.175 | 0.503 | 0.451 | 11.4 | 0.566 |
| L62 (0.97) | 2.17 | 0.957 | 0.181 | 0.517 | 0.463 | 13.7 | 0.553 |
| L63 (0.98) | 2.16 | 0.894 | 0.191 | 0.521 | 0.448 | 18.1 | 0.528 |
| Uncorrelated | Main theory | Cluster expansion | ||||
| Backbone | RMSE | RMSE | RMSE | |||
| Vision (ImageNet-1K) | ||||||
| ConvNeXt-B | ||||||
| ResNet50 | ||||||
| DINOv3 ViT-H + | ||||||
| DINOv3 ViT-7B | ||||||
Neural Representation Geometry
Neural representation geometry studies how learned features are arranged and how that structure relates to model behavior and performance.
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