  Prompt tuning, a recently emerging paradigm, enables the powerful
vision-language pre-training models to adapt to downstream tasks in a parameter
-- and data -- efficient way, by learning the ``soft prompts'' to condition
frozen pre-training models. Though effective, it is particularly problematic in
the few-shot scenario, where prompt tuning performance is sensitive to the
initialization and requires a time-consuming process to find a good
initialization, thus restricting the fast adaptation ability of the
pre-training models. In addition, prompt tuning could undermine the
generalizability of the pre-training models, because the learnable prompt
tokens are easy to overfit to the limited training samples. To address these
issues, we introduce a novel Gradient-RegulAted Meta-prompt learning (GRAM)
framework that jointly meta-learns an efficient soft prompt initialization for
better adaptation and a lightweight gradient regulating function for strong
cross-domain generalizability in a meta-learning paradigm using only the
unlabeled image-text pre-training data. Rather than designing a specific prompt
tuning method, our GRAM can be easily incorporated into various prompt tuning
methods in a model-agnostic way, and comprehensive experiments show that GRAM
brings about consistent improvement for them in several settings (i.e.,
few-shot learning, cross-domain generalization, cross-dataset generalization,
etc.) over 11 datasets. Further, experiments show that GRAM enables the
orthogonal methods of textual and visual prompt tuning to work in a
mutually-enhanced way, offering better generalizability beyond the uni-modal
prompt tuning methods.
