Abstract
Prompt tuning methods use learnable tokens for parameter-efficient downstream adaptation on large pre-trained models. However, for dual-modal visual-language pre-trained models (VLPMs), existing prompt tuning methods overlook the preservation of pre-trained text-image alignment during fine-tuning. To address this issue, we propose Synchronous Dual Prompt Tuning (SDPT). SDPT initializes a single set of learnable unified prototype tokens in the established modal aligning space to represent the aligned semantics of text and image modalities for downstream tasks. Furthermore, SDPT establishes inverse linear projections, whose projection matrices need no training, to embed the information of learnable unified prototype tokens into the input space of different modalities. The inverse linear projections allow the unified prototype token to synchronously represent the two modalities and enable SDPT to share the unified semantics of text and image for downstream tasks across different modal prompts. Experimental results demonstrate that SDPT assists VLPMs to achieve superior outcomes with only 0.04% of model parameters for training across various scenarios, outperforming other single- or dual-modal methods. github/SDPT.