Progressive Visual Prompt Learning with Contrastive Feature Re-formation

Prompt learning has recently emerged as a compelling alternative to the traditional fine-tuning paradigm for adapting the pre-trained Vision-Language (V-L) models to downstream tasks. Drawing inspiration from the success of prompt learning in Natural Language Processing, pioneering research efforts have been predominantly concentrated on text-based prompting strategies. By contrast, the visual prompting within V-L models remains underexploited. The straightforward transposition of existing visual prompt methods, tailored for Vision Transformers (ViT), into the V-L models often leads to suboptimal performance or training instability. To mitigate these challenges, in this paper, we propose a novel structure called Progressive Visual Prompt (ProVP). This design aims to strengthen the interaction among prompts from adjacent layers, thereby enabling more effective propagation of image embeddings to deeper layers in a manner akin to an instance-specific manner. Additionally, to address the common issue of generalization deterioration in the training period of learnable prompts, we further introduce a contrastive feature re-formation technique for visual prompt learning. This method prevents significant deviations of prompted visual features from the fixed CLIP visual feature distribution, ensuring its better generalization capability. Combining the ProVP and the contrastive feature re-formation technique, our proposed method, ProVP-Ref, significantly stabilizes the training process and enhances both the adaptation and generalization capabilities of visual prompt learning in V-L models. To demonstrate the efficacy of our approach, we evaluate ProVP-Ref across 11 image datasets, achieving the state-of-the-art results on 7 of these datasets in both few-shot learning and base-to-new generalization settings. To the best of our knowledge, this is the first study to showcase the exceptional performance of visual prompts in V-L models compared to previous text prompting methods in this area.