[Submitted on 15 Oct 2026]
Abstract:Medical vision-language models (VLMs) for visual question answering (VQA) often pass long visual-token sequences to the language model, making visual-token pruning attractive but risky for medical images, where answers may depend on localized boundary and texture evidence. We study training free pre-decoding pruning and treat pruning as a subspace stable evidence preservation problem. The retained tokens should remain close to the dominant visual evidence subspace induced by the full token set. To this end, we propose emph{Subspace-Transition Token Pruning} (method{}), which estimates each token’s spectral support from principal component space and constructs a compact representation subspace. To better reflect medical image structure, method{} further uses a bounded token-grid transition prior to promote boundary and texture sensitive tokens. We evaluate method{} on the closed-ended SLAKE and OmniMedVQA benchmarks and on RadImageNet-VQA, which provides both closed-ended and open-ended evaluations, using Lingshu-7B and Qwen3-VL-8B backbones. method{} delivers consistently strong performance on both the closed-ended and open-ended RadImageNet-VQA evaluations. These results show that method{} is an effective training free pruning framework for medical domain VQA.
Submission history
From: Mengchen Fan [view email]
[v1] Thu, 15 Oct 2026 23:38:57 UTC (39,625 KB)
