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Expandable Subspace Ensemble for Pre-Trained Model-Based Class-Incremental Learning
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Proposes EASE, an exemplar-free pre-trained-model class-incremental learning method that adds a lightweight adapter per task to form expandable subspaces, and synthesizes old-class prototypes in new subspaces via semantic similarity.
Problem
Class-incremental learning with pre-trained models suffers from forgetting when updating, and expandable-backbone methods are too costly and need exemplars; exemplar-free PTM-based CIL needs a way to add task-specific capacity without conflict and to map expanding features to old classes.
Approach
Freeze the pre-trained ViT and train one bottleneck adapter per incremental task to create task-specific subspaces; concatenate features from all adapters, synthesize missing old-class prototypes in the newest subspace via class-similarity recombination from the co-occurrence subspace, and reweight the matching subspace's logits at inference.
Key results
- On ImageNet-R B0 Inc5 (ViT-B/16-IN21K) EASE attains the best results among seven benchmarks in Table 1, e.g., 78.31 average and 70.58 last on ImageNet-R... (reported as IN-R column)
- On VTAB B0 Inc10 EASE reaches 93.61 average and 93.55 last accuracy, versus 87.47 for the runner-up ADAM+Finetune-type baselines.
- EASE outperforms exemplar-based methods such as FOSTER and DER on CIFAR and ImageNet-R B0 settings while using zero exemplars (e.g., 92.35 vs 89.87 average on CIFAR B0 Inc10 for FOSTER).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Use EASE instead of ADAM + Adapter | PTM-based class-incremental learning · ImageNet-R B0 Inc5 | average accuracy: 72.35 -> 78.31 | Helped |
| Use EASE instead of ADAM + VPT-S | PTM-based class-incremental learning · VTAB B0 Inc10 | last accuracy: 85.36 -> 93.55 | Helped |
| Use EASE instead of FOSTER with 20 exemplars per class | Pre-trained-model CIL · CIFAR B0 Inc10 | last accuracy: 84.91 -> 87.76 | Helped |
| Add task-specific adapters to the pre-trained model (ablation) | EASE · ImageNet-R B0 Inc20 | accuracy | Helped |
| Add semantic-guided prototype complement rather than using only diagonal classifier components (ablation) | EASE with task-specific adapters · ImageNet-R B0 Inc20 | accuracy | Helped |
| Add subspace reweighting to the prototype-complement model (ablation) | EASE with prototype complement · ImageNet-R B0 Inc20 | accuracy | Helped |
| Use similarity-based prototype complement instead of linear regression or optimal transport (ablation) | EASE · ImageNet-R, ImageNet-A, and ObjectNet | last accuracy | Helped |
Surprising findings
- EASE without any exemplars is competitive with or better than exemplar-based CIL methods such as iCaRL, DER, FOSTER and MEMO when all use the same PTM.
Limitations
- Adapters still add model storage that grows linearly with the number of tasks.
- Compression of adapters is left as future work.
Experimental setup
Datasets: CIFAR100 CUB200 ImageNet-R ImageNet-A ObjectNet OmniBenchmark VTAB
Benchmarks: CIFAR100 CUB200 ImageNet-R ImageNet-A ObjectNet OmniBenchmark VTAB
Metrics: average incremental accuracy last-stage accuracy
Baselines: L2P DualPrompt CODA-Prompt SimpleCIL ADAM LwF SDC iCaRL DER FOSTER MEMO
Builds on: Adapter tuning ADAM expandable networks (DER/FOSTER) prototype classifier
Closest papers by meaning
- Adapter Merging with Centroid Prototype Mapping for Scalable Class-Incremental Learning (CVPR 2025 · similarity 0.87)
- Harnessing Neural Unit Dynamics for Effective and Scalable Class-Incremental Learning (ICML 2024 · similarity 0.87)
- Tripartite Weight-Space Ensemble for Few-Shot Class-Incremental Learning (CVPR 2025 · similarity 0.87)
- Knowledge Memorization and Rumination for Pre-trained Model-based Class-Incremental Learning (CVPR 2025 · similarity 0.86)
- Reducing Class-wise Confusion for Incremental Learning with Disentangled Manifolds (CVPR 2025 · similarity 0.86)
- Compress to One Point: Neural Collapse for Pre-Trained Model-Based Class-Incremental Learning (AAAI 2025 · similarity 0.86)
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