TreePrompt: Learning to Compose Tree Prompts for Explainable Visual Grounding

TreePrompt: Learning to Compose Tree Prompts for Explainable Visual Grounding
Prompt tuning has achieved great success in transferring the knowledge from large pretrained vision-language models into downstream tasks, and has dominated the performance on visual grounding (VG). However, almost all existing prompt tuning paradigms suffer from poor interpretability. In this paper, we argue that their poor interpretability is attributed to the holistic prompt generation and inference process. By "holistic", we mean that they usually directly learn a set of vectors as the prompt (i.e., prompt generation), and use the learned global prompt to augment the textual input for the VG model (i.e., prompt inference). To this end, we propose a new prompt construction paradigm with explicit explainable ability, named TreePrompt. Specifically, we first deconstruct a complex sentence into a tree, that is consistent with human reasoning. Then, following the syntax tree, we compose a structured prompt in a bottom-up manner. Thanks to this step-by-step prompt construction process, each intermediate prompt (i.e., tree node) permits us to understand the reasoning process. Extensive ablations on various backbones and benchmarks consistently demonstrate the effectiveness and interpretability of our TreePrompt.

Summary Notes

TreePrompt: Advancing Explainable AI in Visual Grounding

The field of artificial intelligence (AI) is constantly advancing, with a growing emphasis on creating models that are not just high-performing but also understandable in their operations.
This is particularly important in visual grounding, which plays a crucial role in applications like autonomous driving and interactive AI.
Traditional techniques rely on pretraining and finetuning large models, which is not only costly but also prone to overfitting.
Prompt tuning offers a more efficient alternative, though it has lacked in interpretability—until the introduction of TreePrompt.

Understanding TreePrompt

TreePrompt innovates prompt tuning by generating structured prompts that mirror human thought processes, improving both model performance and interpretability.
By converting complex sentences into a tree structure for prompt creation, TreePrompt provides a clear, step-by-step insight into the model's decisions, similar to human reasoning.

How It Works

TreePrompt's methodology is straightforward yet impactful, consisting of three main phases:
  • Tree Structure Generation: It starts by breaking down the query sentence into a tree structure using dependency parsing, setting the stage for prompt creation.
  • Modular Network: This network, with its Leaf, Rel, and Enti modules, turns each tree node into intermediate prompts, creating a context-rich and hierarchically organized prompt output.
  • Integration with Global Prompt: To grasp broader context, structured prompts are combined with a global prompt, refining the model's reaction to the query.
This approach not only reflects human cognitive processes but also tailors dynamic prompts to the input's syntactic structure, marking a significant progress in the field.

Performance Insights

TreePrompt has shown superior performance on several datasets like RefCOCO, RefCOCO+, and RefCOCOg, outpacing traditional prompt tuning and full model finetuning methods.
This highlights its adaptability and the effectiveness of its structured prompt generation approach.

Implications and Insights

TreePrompt's approach to creating structured prompts provides a new level of understanding of the model's reasoning, establishing a benchmark for interpretability in visual grounding.
Its compatibility with various vision-language models enhances its versatility.
TreePrompt carefully balances structured and global prompts, optimizing performance while deepening our understanding.

Challenges and Next Steps

Though TreePrompt is a breakthrough, its dependency on the underlying pre-trained models and the accuracy of the parsing steps pose challenges that warrant further investigation.
Despite these issues, TreePrompt paves the way for future research and applications, especially in extending its methodology to other multimodal tasks and refining the structured-global prompt dynamic.


TreePrompt marks a significant advancement in developing explainable, efficient, and adaptable visual grounding models.
By integrating the syntactic structure of language with the model's processing abilities, it offers an interpretable, human-like method for processing complex queries. Looking ahead,
TreePrompt's foundational principles could revolutionize AI, making systems not only more intelligent but also more transparent and reliable.

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