A common approach to transfer learning under distribution shift is to fine-tune the last few layers of a pre-trained model, preserving learned features while also adapting to the new task. This paper shows that in such settings, selectively fine-tuning a subset of layers (which we term surgical fine-tuning) matches or outperforms commonly used fine-tuning approaches. Moreover, the type of distribution shift influences which subset is more effective to tune: for example, for image corruptions, fine-tuning only the first few layers works best. We validate our findings systematically across seven real-world data tasks spanning three types of distribution shifts. Theoretically, we prove that for two-layer neural networks in an idealized setting, first-layer tuning can outperform fine-tuning all layers. Intuitively, fine-tuning more parameters on a small target dataset can cause information learned during pre-training to be forgotten, and the relevant information depends on the type of shift.
@article{arxiv.2210.11466,
title = {Surgical Fine-Tuning Improves Adaptation to Distribution Shifts},
author = {Yoonho Lee and Annie S. Chen and Fahim Tajwar and Ananya Kumar and Huaxiu Yao and Percy Liang and Chelsea Finn},
journal= {arXiv preprint arXiv:2210.11466},
year = {2023}
}