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Unleashing the Power of Meta-tuning for Few-shot Generalization Through Sparse Interpolated Experts
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Proposes SMAT, a meta-tuning method that learns sparse interpolated experts (shared dense update masked per expert, merged by a hypernetwork) on a pre-trained ViT to improve both ID and OOD few-shot generalization.
Problem
Meta-tuning of vision foundation models for few-shot learning tends to underperform on out-of-distribution tasks due to meta-overfitting and task interference when all parameters are updated.
Approach
Meta-tune a frozen pre-trained ViT with a set of learned sparse binary masks over a shared dense update, combined per task by hypernetwork-predicted Gumbel-sigmoid expert weights, with a task-specific dense teacher distillation loss and a Lagrangian-constrained target sparsity level; each expert is a sparse interpolation between pre-trained and meta-tuned weights.
Key results
- Without fine-tuning, SMAT reaches 85.36% ID and 67.65% OOD average accuracy vs. 84.23% and 64.10% for PMF on DINO-ViT-Small.
- With LoRA fine-tuning, SMAT+LoRA reaches 85.88% ID and 75.02% OOD average, versus 85.59% and 72.91% for PMF+LoRA.
- With Sup21k ViT-Small, SMAT+full achieves 87.11% ID and 88.05% OOD average, the best among compared methods.
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use SMAT instead of PMF without fine-tuning | DINO-ViT-Small · Meta-Dataset ID Avg | accuracy: 0.91% | Helped |
| Use SMAT instead of PMF without fine-tuning | DINO-ViT-Small · Meta-Dataset OOD Avg | accuracy: 3.17% | Helped |
| Use SMAT as initialization for full fine-tuning instead of PMF | DINO-ViT-Small · Meta-Dataset ID Avg | accuracy: 0.82% | Helped |
| Use SMAT as initialization for full fine-tuning instead of PMF | DINO-ViT-Small · Meta-Dataset OOD Avg | accuracy: 2.48% | Helped |
| Remove dense teachers (ablation) | SMAT · Meta-Dataset ID Avg | accuracy: 85.14 -> 85.07 | Hurt |
| Remove dense teachers (ablation) | SMAT · Meta-Dataset OOD Avg | accuracy: 67.27 -> 66.44 | Hurt |
| Remove interpolated experts (ablation) | SMAT · Meta-Dataset ID Avg | accuracy: 85.14 -> 84.77 | Hurt |
| Remove interpolated experts (ablation) | SMAT · Meta-Dataset OOD Avg | accuracy: 67.27 -> 67.02 | Hurt |
| Remove the support/query split during meta-training (ablation) | SMAT · Meta-Dataset ID Avg | accuracy: 85.14 -> 82.35 | Hurt |
| Remove the support/query split during meta-training (ablation) | SMAT · Meta-Dataset OOD Avg | accuracy: 67.27 -> 63.64 | Hurt |
| Replace meta-learned sparsity with predetermined sparsity patterns and remove interpolation (ablation) | SMAT · Meta-Dataset ID Avg | accuracy: 85.14 -> 85.21 | Mixed |
| Replace meta-learned sparsity with predetermined sparsity patterns and remove interpolation (ablation) | SMAT · Meta-Dataset OOD Avg | accuracy: 67.27 -> 66.21 | Hurt |
Surprising findings
- Higher expert sparsity improves OOD accuracy at the cost of ID accuracy, revealing a controllable ID-OOD tradeoff.
- PMF meta-tuning with a DINO backbone can underperform simple pre-trained plus fine-tuned baselines on OOD tasks.
Limitations
- Gradient-free expert selection is limited on OOD tasks with large distribution shift such as TrafficSign.
- Gradient-based fine-tuning requires about 4x the GPU memory of gradient-free and about 2x the time of gradient-free adaptation.
- Sparse parameter savings rely on a naive (value, position) storage scheme and are not optimized in memory.
Experimental setup
Datasets: Meta-Dataset ImageNet Omniglot Aircraft CUB DTD Quickdraw Fungi VGG Flower
Benchmarks: Meta-Dataset TrafficSign MSCOCO CIFAR-10 CIFAR-100 MNIST
Metrics: few-shot classification accuracy
Baselines: Pre-trained DINO-ViT-Small PMF SoftMerge (SMEAR) Pre+full PMF+full Pre+LoRA PMF+LoRA SoftMoE
Builds on: PMF SMEAR Prototypical Networks stretched hard concrete distribution LoRA
Closest papers by meaning
- Provable Meta-Learning with Low-Rank Adaptations (NeurIPS 2025 · similarity 0.87)
- Data-Centric Meta-Learning for Robust Few-Shot Generalization (CVPR 2026 · similarity 0.87)
- Learning where to learn: Gradient sparsity in meta and continual learning (NeurIPS 2021 · similarity 0.87)
- Expanding Sparse Tuning for Low Memory Usage (NeurIPS 2024 · similarity 0.87)
- Pushing the Limit of Fine-Tuning for Few-Shot Learning: Where Feature Reusing Meets Cross-Scale Attention (AAAI 2024 · similarity 0.86)
- Patch Rebirth: Fast and Transferable Model Inversion of Vision Transformers (NeurIPS 2026 · similarity 0.86)
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