Can Spectral-Clipping Enable Better Learning While Forgetting Less for Low-Rank Adaptation?
Paper · 2026 · Hyowon Wi and Noseong Park
Summary
This paper asks why LoRA fine-tuning erodes what a pre-trained model already knows, and how to prevent that while still learning the new task. The authors use SVD to analyze pre-trained weights. They measure Fisher overlap between the pre-training data (BookCorpus) and downstream tasks for groups of singular components. Components with large singular values turn out to be largely transferable, while those with small singular values need the most task-specific change. They also prove (Theorem 3.1) that rising adapter singular values weaken the pre-trained prior, which links unchecked spectral growth to catastrophic forgetting. Their method, SCLoRA, builds adapters as a parameterized SVD with orthogonality regularization. It caps the learned singular values with a bound set by a quantile q of the pre-trained spectrum, which steers updates toward the minor part of the spectrum. Experiments cover GLUE tasks with RoBERTa base and other model scales. Against LoRA, PiSSA, MiLoRA and related variants, SCLoRA improves downstream scores and keeps far more pre-training accuracy. This makes PEFT more reliable when the general knowledge of the base model must survive adaptation.
Key points
- Fisher overlap analysis: Overlap on BookCorpus vs. MRPC falls steadily as one moves from principal to minor singular-component groups. This supports focusing adaptation on minor components.
- Ablation on MRPC (Table 5):
- Plain LoRA drops pre-training (BookCorpus) accuracy from 61.64 to 3.77, with 89.05 fine-tuning accuracy.
- SCLoRA reaches 90.32 fine-tuning accuracy and retains 32.00 pre-training accuracy.
- Ablation on SST-2 (Table 5): SCLoRA scores 95.37 fine-tuning and 51.29 pre-training accuracy, versus 94.81 and 32.35 for LoRA.
- Component ablation: Variants were tested with fixed singular values, learnable singular values, and clipping without orthogonality (LoRA U V⊤, LoRA SVD, LoRA γ=0). Each performed worse than the full SCLoRA on both measures.
- Sensitivity to q: Very small values such as q = 0.1 hurt retention of pre-trained knowledge. Results stay stable for q ≥ 0.3. The authors suggest extending the approach to MoE architectures as future work.
Institutions
Fields, topics and concepts
📚 Shelves 5The field of science this work belongs to (OpenAlex fields).Computer Science · 18,614 worksArtificial Intelligence · 17,965 worksArts and Humanities · 17,450 worksLanguage and Linguistics · 17,296 worksComputer Vision and Pattern Recognition · 3,486 works
🧭 Topics 2Research subjects and languages the work is about.Language models & pretraining · 3,894 worksEfficient models & compression · 297 works
💡 Concepts 1Key ideas and methods explained on our concept pages.Latent semantic indexing · 29 works
Cite
Cite as Hyowon Wi and Noseong Park. 2026. Can Spectral-Clipping Enable Better Learning While Forgetting Less for Low-Rank Adaptation?. Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers).
@inproceedings{wi2026can,
title = {{Can Spectral-Clipping Enable Better Learning While Forgetting Less for Low-Rank Adaptation?}},
author = {Hyowon Wi and Noseong Park},
booktitle = {Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2026},
doi = {10.18653/v1/2026.acl-long.1179},
url = {https://doi.org/10.18653/v1/2026.acl-long.1179}
}References
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