分析视觉Transformer对抗性微调的机制,发现泛化能力有限。
A Mechanistic Analysis of Adversarial Fine-tuning of Vision Transformers

- 通过对抗性微调增强模型对特定图像扰动的鲁棒性。
- 在训练中看到的扰动类型外,性能提升无法迁移。
- 注意力机制与内部表示虽有变化,但稀疏特征学习未根本改变。
图像分类模型在高风险现实场景中的广泛应用,要求其具备对输入图像轻微扰动(如模糊或锐化)的鲁棒性。尽管视觉变换器(ViTs)在多模态模型(如视觉-语言模型VLMs和视觉-语言-动作模型VLAs)中扮演关键角色,但在鲁棒性方面的研究仍不足。本文从机制角度分析对抗性微调对ViT在扰动与常规图像上性能的影响。我们在低频和高频图像损坏数据上对抗性微调了一个ViT,通过考察其注意力机制、内部表示及知识演化,解释下游性能变化。结果表明:尽管在常见损坏类型上微调能提升模型在新损坏实例上的表现和置信度,但这种提升无法推广至训练中未见的其他类型损坏;虽然各层的视觉注意力和知识演化有所变化,但对抗性训练并未导致ViT学习到的根本性稀疏表示发生变化。
原文摘要 · Abstract (English)
The widespread use of image classification models in high-risk, real-world situations necessitates making these models robust to slight disturbances or perturbations, such as blurring or sharpening, in the input images. While vision transformers (ViTs) play an integral role in many modern-day multi-modal models like Vision-Language-Models (VLMs) and Vision-Language-Action (VLA) models, they have received a lack of attention in the setting of robustness. In this work, we analyze the effects of adversarial fine-tuning, a popular method for improving model robustness to image perturbations, on a ViT's performance on perturbed and regular images through a mechanistic lens. We adversarially train a ViT on low-frequency and high-frequency image corruptions, and attempt to explain changes in downstream model performance through an examination of the model's attention mechanisms, internal representations, and knowledge evolution. Overall, our results suggest that, while fine-tuning on inputs with common corruptions improves model performance and certainty on new instances of corrupted data, these improvements do not transfer to other classes of corruptions not seen in the training. Additionally, despite observing changes in visual attention and knowledge evolution across layers, we found that adversarial training did not lead to fundamental changes in the sparse representations learned by ViTs.
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