arXiv:2509.15272cs.CV2025-09被引 1

分析视觉Transformer未加工特征在下游任务中的表示能力,指导模型选择与决策方式。

Which Direction to Choose? An Analysis on the Representation Power of Self-Supervised ViTs in Downstream Tasks

  • 对比不同注意力头和前馈层特征,评估原始输出的表达能力。
  • 在标准与少样本场景下,分类与分割任务表现差异显著。
  • 揭示预训练目标影响特征方向性,为任务适配提供依据。

自监督学习(SSL)在视觉Transformer(ViT)中展现出巨大潜力,适用于图像分类与分割等任务,涵盖标准与少样本场景。当前主流方法依赖对比学习与掩码图像建模两种预训练目标。通常从Transformer最后一层的键、查询、值或前馈层输出提取特征,并通过轻量级头或蒸馏进一步处理以提升性能。然而,现有研究尚未系统评估未经修改的原始特征的内在表示能力。本研究针对图像分类与分割任务,在标准与少样本设置下,基于超平面或余弦相似度规则,系统评估不同特征类型、预训练模型及任务间的表现。结果揭示了最优特征类型与决策规则的选择策略,结合两个广泛使用的数据集,提供了任务与预训练目标相关的深层洞察。

原文摘要 · Abstract (English)

Self-Supervised Learning (SSL) for Vision Transformers (ViTs) has recently demonstrated considerable potential as a pre-training strategy for a variety of computer vision tasks, including image classification and segmentation, both in standard and few-shot downstream contexts. Two pre-training objectives dominate the landscape of SSL techniques: Contrastive Learning and Masked Image Modeling. Features (or tokens) extracted from the final transformer attention block -- specifically, the keys, queries, and values -- as well as features obtained after the final block's feed-forward layer, have become a common foundation for addressing downstream tasks. However, in many existing approaches, these pre-trained ViT features are further processed through additional transformation layers, often involving lightweight heads or combined with distillation, to achieve superior task performance. Although such methods can improve task outcomes, to the best of our knowledge, a comprehensive analysis of the intrinsic representation capabilities of unaltered ViT features has yet to be conducted. This study aims to bridge this gap by systematically evaluating the use of these unmodified features across image classification and segmentation tasks, in both standard and few-shot contexts. The classification and segmentation rules that we use are either hyperplane based (as in logistic regression) or cosine-similarity based, both of which rely on the presence of interpretable directions in the ViT's latent space. Based on the previous rules and without the use of additional feature transformations, we conduct an analysis across token types, tasks, and pre-trained ViT models. This study provides insights into the optimal choice for token type and decision rule based on the task, context, and the pre-training objective, while reporting detailed findings on two widely-used datasets.

视觉Transformer自监督学习特征表示少样本学习

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