MedLVR: Latent Visual Reasoning for Reliable Medical Visual Question Answering

TL;DR

MedLVR introduces an explicit visual evidence reasoning process within medical VQA models, enhancing the preservation of subtle visual clues and improving answer accuracy in clinical scenarios.

Contribution

It proposes a latent visual reasoning framework with a two-stage training strategy, enabling iterative visual evidence refinement for more reliable medical VQA.

Findings

Outperforms recent reasoning baselines on multiple benchmarks.

Improves average VQA score from 48.3% to 53.4%.

Demonstrates effective preservation of visual evidence.

Abstract

Medical vision--language models (VLMs) have shown strong potential for medical visual question answering (VQA), yet their reasoning remains largely text-centric: images are encoded once as static context, and subsequent inference is dominated by language. This paradigm is fundamentally limited in clinical scenarios, where accurate answers often depend on subtle, localized visual evidence that cannot be reliably preserved in static embeddings. We propose \textsc{MedLVR}, a latent visual reasoning framework that introduces an explicit visual evidence state into autoregressive decoding. Instead of relying solely on text-based intermediate reasoning, \textsc{MedLVR} interleaves a short latent reasoning segment within the decoder by reusing hidden states as continuous latent steps, enabling iterative preservation and refinement of query-relevant visual evidence before answer generation. To support effective visual supervision, we adopt a two-stage training strategy: region of interest (ROI)-supervised fine-tuning aligns latent states with clinically relevant image evidence, and Visual-Latent Policy Optimization (VLPO) further optimizes latent reasoning and answer generation under outcome-level rewards. Experiments on OmniMedVQA and five external medical VQA benchmarks show that \textsc{MedLVR} consistently outperforms recent reasoning baselines and improves the average score over the Qwen2.5-VL-7B backbone from 48.3\% to 53.4\%. These results show that latent visual reasoning provides an effective mechanism for preserving diagnostically relevant visual evidence and improving the reliability of medical VQA.