BRIDGE: Multimodal-to-Text Retrieval via Reinforcement-Learned Query Alignment

TL;DR

BRIDGE is a system that improves multimodal-to-text retrieval by aligning queries through reinforcement learning and reasoning-enhanced retrieval, outperforming existing methods.

Contribution

The paper introduces FORGE and LENS components that address query mismatch without multimodal encoders, significantly boosting retrieval performance.

Findings

BRIDGE surpasses all multimodal encoder baselines on MM-BRIGHT.

Applying FORGE as a plug-and-play aligner improves retrieval beyond text-only baselines.

Query alignment is identified as the key bottleneck in multimodal-to-text retrieval.

Abstract

Multimodal retrieval systems struggle to resolve image-text queries against text-only corpora: the best vision-language encoder achieves only 27.6 nDCG@10 on MM-BRIGHT, underperforming strong text-only retrievers. We argue the bottleneck is not the retriever but the query -- raw multimodal queries entangle visual descriptions, conversational noise, and retrieval intent in ways that systematically degrade embedding similarity. We present \textbf{BRIDGE}, a two-component system that resolves this mismatch without multimodal encoders. \textbf{FORGE} (\textbf{F}ocused Retrieval Query Generato\textbf{r}) is a query alignment model trained via reinforcement learning, which distills noisy multimodal queries into compact, retrieval-optimized search strings. \textbf{LENS} (\textbf{L}anguage-\textbf{E}nhanced \textbf{N}eural \textbf{S}earch) is a reasoning-enhanced dense retriever fine-tuned on reasoning-intensive retrieval data to handle the intent-rich queries FORGE produces. Evaluated on MM-BRIGHT (2,803 queries, 29 domains), BRIDGE achieves \textbf{29.7} nDCG@10, surpassing all multimodal encoder baselines including Nomic-Vision (27.6). When FORGE is applied as a plug-and-play aligner on top of Nomic-Vision, the combined system reaches \textbf{33.3} nDCG@10 -- exceeding the best text-only retriever (32.2) -- demonstrating that \textit{query alignment} is the key bottleneck in multimodal-to-text retrieval. https://github.com/mm-bright/multimodal-reasoning-retrieval