Beyond Dominant Patches: Spatial Credit Redistribution For Grounded Vision-Language Models
About
Vision-Language Models (VLMs) often hallucinate objects that are not present in the input image. We identify a contributing cause of this behavior, which we term spatial credit collapse: in early transformer layers, hidden-state activation concentrates on a small number of visual patches, suppressing surrounding contextual evidence and increasing reliance on language priors. Across seven models we observe a strong correlation between visual attention entropy and hallucination rate (r = -0.65, p < 0.001), suggesting that reduced spatial credit diversity contributes to hallucination. To address this issue we propose Spatial Credit Redistribution (SCR), a training-free inference-time method. SCR uses a lightweight two-pass procedure. A diagnostic pass identifies the top-K high-attention source patches and their spatial neighbors. A redistribution pass then scales each source by 1/lambda (~0.91) and injects a (lambda - 1) weighted copy of its hidden state into neighboring patches, restoring suppressed visual context without modifying model weights. Because the diagnostic pass is performed once per image and reused across the output sequence, the added latency is negligible (<0.5 ms per token for 100-token responses). We evaluate SCR across seven model configurations from four VLM families (Chameleon, LLaVA-1.5, Qwen-VL/Qwen2-VL, and InternVL2) on five benchmarks: POPE, CHAIR, MME, HallusionBench, and AMBER. SCR reduces POPE-Adversarial hallucination by 4.6-6.0 percentage points and CHAIR-s by 41-51 percent while preserving caption quality (CIDEr drop <=0.8). Compared with prior inference-time methods including OPERA, VCD, OA-VCD, DoLa, VLI, SID, and CRoPS, SCR achieves a better trade-off between hallucination reduction, generation quality, and latency.