APT: 行動エキスパートの事前学習による視覚-言語-行動ポリシーの指示汎化の改善
APT: Action Expert Pretraining Improves Instruction Generalization of Vision-Language-Action Policies
視覚-言語-行動モデルにおいて、言語データの不均衡が原因で未見の指示への汎化が悪い問題を、行動エキスパートを事前学習する二段階手法APTで解決した。
詳しい要約
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著者: Kechun Xu, Zhenjie Zhu, Anzhe Chen, Rong Xiong, Yue Wang
分類: cs.RO
原文アブストラクト
Vision-Language-Action (VLA) models that couple pretrained Vision-Language Models (VLMs) with continuous action experts have achieved strong manipulation performance, yet generalization to out-of-distribution (OOD) language instructions remains poor. A known challenge is the structural imbalance in VLA data, where language is far less diverse than visual and action content, making policies prone to visual shortcuts. While discrete-action methods mitigate this through vision-language co-training, continuous action experts lack such protection: they start from random initialization and learn entirely from imbalanced data, producing noisy gradients that corrupt the VLM and fail to exploit its language capability. We address this from a Bayesian perspective, factorizing the policy into a language-agnostic Vision-Action (VA) prior and a language-conditioned VLA likelihood, and propose APT, a two-stage training method emphasizing Action expert PreTraining. In Stage 1, the action expert is pretrained as a VA prior on vision-action pairs from a frozen VLM, bypassing the language imbalance. In Stage 2, language tokens are injected through a gated fusion mechanism that integrates VLM features while preserving the learned visuomotor prior. APT applies to mainstream VLA architectures, including the $\pi$ and GR00T-style architectures. Comprehensive experiments validate that APT achieves consistent gains on unseen instructions and compositional tasks. Project Page: https://xukechun.github.io/papers/APT/
