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Beyond Cross-Modal Alignment: Measuring and Leveraging Modality Gap in Vision-Language Models

Paper · 2026 · Hanqi Yan, Xiangxiang Cui, Lu Yin et al.

Summary

Vision-language models are usually judged by how well they align images and text. Most prior work treats the remaining modality gap as a defect. This paper argues instead that the gap is common and can be useful. It introduces the Modality Dominance Score (MDS), which compares how strongly each final-layer feature of a CLIP model responds to image versus text inputs, averaged over more than 10k image-text pairs. Based on this score, features are sorted into image-dominant (ImgD), text-dominant (TextD) and cross-modal (CrossD) groups.

The grouping is checked in three ways:

  • ablation probes on COCO;
  • inspection of the images and texts that most activate each feature;
  • new embedding-based metrics for monosemanticity and cross-modal fidelity, which scale better than LLM-based judging.

ImgD features tend to encode low-level visual cues such as patterns and colours. TextD features capture abstract notions such as emotions and atmosphere. The groups also support training-free editing for:

  • reducing gender bias;
  • defending against cross-modal adversarial attacks;
  • steering text-to-image generation.

This suggests that modality-specific components are practical handles for interpreting and lightly editing multimodal models.

Key points

  • Ablation results (CLIP ViT-H/14, LAION-2B; logistic-regression probes on COCO):
    • Zeroing ImgD features (426 removed) lowered image classification accuracy from 0.776 to 0.750 (−2.6%), versus −2.1% for random removal.
    • Zeroing TextD features (554 removed) lowered text classification accuracy from 0.713 to 0.683 (−3.0%), versus −2.0% for random removal.
    • Removing CrossD features had little effect on either task.
  • Feature groups: a feature is labelled TextD or ImgD when its MDS lies more than one standard deviation below or above the mean. Features in between are CrossD.
  • Jailbreak defense: alignment training restricted to TextD features defended best against adversarial samples, followed by CrossD and then ImgD. The setup used 50 adversarial samples, each attacked 100 times.
  • Generation control (Stable Diffusion v2): the authors blended the prompt embedding with a reference-image embedding at α values from 0 to 0.7, but only on the indices of one feature group.
    • Blending on TextD transferred the main subject (a horse) without the reference background.
    • Blending on ImgD carried over background texture and caused distortions at larger α.
  • Limitations: the interpretability metrics were not validated with human studies, and experiments cover only CLIP-family models.

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 Hanqi Yan, Xiangxiang Cui, Lu Yin, Jindong Gu, Paul Pu Liang, Yulan He and Yifei Wang. 2026. Beyond Cross-Modal Alignment: Measuring and Leveraging Modality Gap in Vision-Language Models. Findings of the Association for Computational Linguistics: ACL 2026.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.findings-acl.588

@inproceedings{yan2026beyond,
  title = {{Beyond Cross-Modal Alignment: Measuring and Leveraging Modality Gap in Vision-Language Models}},
  author = {Hanqi Yan, Xiangxiang Cui, Lu Yin, Jindong Gu, Paul Pu Liang, Yulan He and Yifei Wang},
  booktitle = {Findings of the Association for Computational Linguistics: ACL 2026},
  year = {2026},
  doi = {10.18653/v1/2026.findings-acl.588},
  url = {https://doi.org/10.18653/v1/2026.findings-acl.588}
}

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