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VLN-NF: Feasibility-Aware Vision-and-Language Navigation with False-Premise Instructions

Paper · 2026 · Hung-Ting Su, Ting-Jun Wang, Jia-Fong Yeh et al.

Summary

Standard Vision-and-Language Navigation benchmarks assume every instruction is feasible, so agents are never asked to admit that a requested object is missing. This paper addresses false-premise instructions, where the named target does not exist in the indicated room. The authors build VLN-NF on top of REVERIE in Matterport3D. An LLM swaps the original target for a plausible but absent object, and a VLM confirms the object is not there. Agents must reach the room, search it, and then declare NOT-FOUND when the target is absent. Ordinary SPL rewards stopping early, so the authors introduce REV-SPL. It scores room reaching, exploration coverage against a reference search protocol, and decision correctness across mixed feasible and infeasible episodes. They also propose ROAM, a two-stage hybrid. A weakly supervised model first finds the target room. LLM/VLM-driven exploration, guided by a free-space clearance prior, then searches the room and verifies the target. ROAM scores best among the compared methods, while baselines tend to under-explore and give up too soon. This makes the work a step toward robots that handle mistaken human requests safely.

Key points

  • Dataset size: VLN-NF pairs each original REVERIE instruction (FOUND) with a generated infeasible counterpart (NF), sharing the same start point and target room.
    • Train: 55 scans, 2,362 pairs, 4,724 instructions.
    • Val-seen: 38 scans, 234 pairs.
    • Val-unseen: 10 scans, 718 pairs, 1,436 instructions.
  • Label quality: Human checks of a sample found NOT-FOUND labels about 98% correct (under 2% errors). Strict filtering keeps only 45% of REVERIE episodes.
  • Main results (REV-SPL): ROAM reaches 6.1. The supervised DUET-style baseline (Chen et al., 2022) gets 4.2, and two LLM-based agents get 1.0 and 1.5. ROAM's gain over the supervised baseline is about 45%, and it needs only room-level annotations.
  • Failure mode identified: Simply adding a NOT-FOUND action and training by imitation leads to premature abstention, because there is no clear signal for when a search is finished.
  • Limitations:
    • ROAM depends on a fixed Grounding-DINO confidence threshold.
    • Only the "object absent from the specified room" type of false premise is covered.
    • The system has no recovery behavior, such as asking the user for clarification.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Hung-Ting Su, Ting-Jun Wang, Jia-Fong Yeh, Min Sun and Winston H. Hsu. 2026. VLN-NF: Feasibility-Aware Vision-and-Language Navigation with False-Premise Instructions. Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers).

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.acl-long.1152

@inproceedings{su2026vln,
  title = {{VLN-NF: Feasibility-Aware Vision-and-Language Navigation with False-Premise Instructions}},
  author = {Hung-Ting Su, Ting-Jun Wang, Jia-Fong Yeh, Min Sun and Winston H. Hsu},
  booktitle = {Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
  year = {2026},
  doi = {10.18653/v1/2026.acl-long.1152},
  url = {https://doi.org/10.18653/v1/2026.acl-long.1152}
}

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