Tiny Evidence Region Localization with Selective Contrastive On-Policy Self-Distillation

Yujuan Pang, Wenhao Xu, Yinglei Teng

Multimodal large language models have made progress in general visual tasks. However, limitations remain in fine-grained visual tasks requiring evidence from minute image regions. Existing methods primarily train models using evidence-related regions while overlooking the influence of extensive background regions, resulting in a limited ability to resist interference from irrelevant regions. We propose selective positive-negative on-policy self-distillation (SPN-OPSD), which considers both evidence and background regions. Supervision from both views improves the model's ability to resist interference from irrelevant regions. Furthermore, selective token-level distillation provides more informative supervision, improving the model's ability to attend to evidence regions in Fine-Grained Visual Tasks. On Qwen3.5-2B, SPN-OPSD improves accuracy on V* Bench, ZoomBench, and MME-RealWorld-Lite from 76.44%, 45.92%, and 57.43% to 84.82%, 54.56%, and 59.56%, respectively. Similar gains are also observed on Qwen3.5-0.8B.