detecting-hallucinated-text-spans-vision-language-model-outputs-span-localization CLM-0041For detecting hallucinated text spans in vision-language model outputs, span localization and confidence calibration come from different architectures: a fine-tuned generative VLM proposes better span boundaries but scores them poorly, while a discriminative token tagger trained with a direct regression loss on human-consensus confidence gives better-correlated probabilities but conservative spans, so using the generative spans as proposals and the tagger's probabilities as scores beats either alone.
Capability: Stating false facts confidently
Observed on
Character-level hallucination span detection on the SHROOM-Visions dataset (EN, FR, IT, ZH), responses under 512 tokens; tuning done on the English split..
Sources
- Measured on the English validation split (N=379): tagger Pearson 0.369 vs generative 0.285; generative hallucinated IoU 0.182 vs tagger 0.155; fusion 0.413 Pearson and 0.391 IoU. Ablation shows removing the MSE calibration loss costs the most (-0.095 Pearson). Single task, single team, fusion weights tuned on the same validation split used to report the main number; hallucinated-span IoU stays low (0.196) throughout.
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Related claims
- In 7-8B vision-language models, fine-tuning visual and text embeddings toward perturbation-averaged and ground-truth anchors before cross-modal contrastive alignment lowers object and attribute hallucination rates on captioning and existence benchmarks without reducing object coverage or general VQA accuracy.Grounding answers in the image · reviewed by AI
- On adversarial video hallucination pairs scored only when a method both accepts the factual statement and rejects the counterfactual one, purpose-built video hallucination detectors (embedding-similarity, learned-entailment, atomic-fact and attention-based) top out around 34.63% overall accuracy, well below a general frontier video-language model prompted to judge the same items (about 83.63%).Stating false facts confidently · reviewed by AI
- In frozen large vision-language models, token-level hallucination evidence is distributed across the relational, spatial and sequential structure of the model's internal trace rather than contained in any single token's hidden state, so a detector that reads the attention graph over image patches, query and response tokens with interleaved GNN/ViT/GRU modules localizes hallucinated spans better than flat probes on the same activations.Grounding answers in the image · reviewed by AI
- For training-free inference-time hallucination mitigation in 7B vision- language models, reported gains on object-hallucination benchmarks are largely inseparable from reduced informativeness: hallucination rate and object recall/coverage move together, so a lower score can mean the model mentioned fewer visual entities rather than grounded better.Whether the measurement made the finding · reviewed by AI
- In diffusion vision-language models generating free-form captions, object tokens that are hallucinated commit at later denoising steps and with lower per-token confidence than grounded object tokens, so the commit-step trajectory is an available internal hallucination signal that has no counterpart in autoregressive decoding.Grounding answers in the image · reviewed by AI
Notes
Drafted from the paper by a model and filed unreviewed. Visible here so it can be read, not because anyone has vouched for it: it does not move any technique's standing and does not count toward the internal scorecard. Drafted confidence: low. Falsifier as drafted: A fine-tuned generative VLM whose own token probabilities match or beat a dedicated regression-head tagger on calibration correlation, or a fusion that fails to improve on both subsystems on a held-out split. Proposed technique, not catalogued: union-calibrated fusion of a generative span proposer with a calibrated tagger.