Prefix Conditioning Unifies Language and Label Supervision

Kavli Affiliate: Xiang Zhang

| First 5 Authors: Kuniaki Saito, Kihyuk Sohn, Xiang Zhang, Chun-Liang Li, Chen-Yu Lee

| Summary:

Vision-language contrastive learning suggests a new learning paradigm by
leveraging a large amount of image-caption-pair data. The caption supervision
excels at providing wide coverage in vocabulary that enables strong zero-shot
image recognition performance. On the other hand, label supervision offers to
learn more targeted visual representations that are label-oriented and can
cover rare categories. To gain the complementary advantages of both kinds of
supervision for contrastive image-caption pre-training, recent works have
proposed to convert class labels into a sentence with pre-defined templates
called prompts. However, a naive unification of the real caption and the prompt
sentences could lead to a complication in learning, as the distribution shift
in text may not be handled properly in the language encoder. In this work, we
propose a simple yet effective approach to unify these two types of supervision
using prefix tokens that inform a language encoder of the type of the input
sentence (e.g., caption or prompt) at training time. Our method is generic and
can be easily integrated into existing VL pre-training objectives such as CLIP
or UniCL. In experiments, we show that this simple technique dramatically
improves the performance in zero-shot image recognition accuracy of the
pre-trained model.

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