通过分析注意力头定位幻觉根源,精准干预降低视觉语言模型的虚构物体生成。
Targeting the Attention Heads Behind Object Hallucination in LLaVA

- 按幻觉词附近图像注意力下降程度筛选出32个关键注意力头。
- 联合使用适配器与推理时控制器,幻觉率从37%降至23%,提及率从15.6%降至9.6%。
- 方法可解释且可复现,适合关注模型可信度与可控生成的研究者。
如LLaVA-1.5-7B等视觉语言模型在生成描述时常虚构图像中不存在的物体。本文探究可解释性诊断能否指导针对性修复,并测量该修复的实际影响。通过评估幻觉词附近图像注意力的下降程度,筛选出32个候选注意力头;再通过消融实验和对幻觉标记对数概率的测量验证其有效性。针对这些头引入两种干预:头切片LoRA适配器与推理时接地控制器。在400张独立COCO图像上,联合方法使幻觉比例(CHAIR)从0.370降至0.230,幻觉提及比例(CHAIRi)从0.156降至0.096(p < 0.001,配对符号翻转检验)。两个对照组进一步验证了方法的有效性:随机头LoRA控制组在200张独立图像上表现与基线无异,证明头选择的关键作用;在固定解码预算下,幻觉减少效果随预算增加而增强(64词时23%,128词时58%),排除了单纯截断或最大词数的假象。尽管对象召回率由0.78降至0.70,但未支持的物体提及显著减少。本研究提出从诊断到干预的完整流程,并提供行为层面的实证反馈,而非单一指标,揭示干预位置具有真实非随机影响力。
原文摘要 · Abstract (English)
Vision-language models such as LLaVA-1.5-7B often hallucinate objects absent from the image when generating captions. We ask whether an interpretability diagnosis of this failure can guide a targeted fix, and we measure what that fix actually changes. We rank attention heads by how much their image attention drops around hallucinated object words, then screen the shortlist by ablating candidate heads and measuring the change in hallucination-token log probability, yielding a 32-head set. We restrict two interventions to these heads: a head-sliced LoRA adapter and an inference-time grounding controller. On 400 held-out COCO images, the combined method lowers CHAIRs (the fraction of captions with a hallucinated object) from 0.370 to 0.230 and CHAIRi (the fraction of hallucinated object mentions) from 0.156 to 0.096 (p < 0.001, paired sign-flip tests). Two controls sharpen attribution. A random-head LoRA control, matched layer-for-layer and trained identically, performs no better than the matched baseline on a separate 200-image control split, supporting the role of head selection rather than LoRA capacity. Under fixed decoding budgets, the CHAIR reduction persists and grows with budget (23% at 64 tokens to 58% at 128), arguing against a pure max-token or truncation artifact, although the method remains shorter and more conservative. The resulting behavior reduces unsupported object mentions while also lowering object recall (0.78 to 0.70). We present a diagnosis-to-intervention pipeline for object hallucination, and, more importantly, a controlled account of what acting on the diagnostic signal actually does: it localizes intervention sites with real, non-random leverage, reported as a behavioral profile rather than a single score.
Thank you to arXiv for use of its open access interoperability. PaperDance 不是 arXiv 官方产品;中文卡片由大模型生成,请以原文为准。