Improving Multimodal Contrastive Learning of Sentence Embeddings with Object-Phrase Alignment

Kaiyan Zhao, Zhongtao Miao, Yoshimasa Tsuruoka


Abstract
Multimodal sentence embedding models typically leverage image-caption pairs in addition to textual data during training. However, such pairs often contain noise, including redundant or irrelevant information on either the image or caption side. To mitigate this issue, we propose MCSEO, a method that enhances multimodal sentence embeddings by incorporating fine-grained object-phrase alignment alongside traditional image-caption alignment. Specifically, MCSEO utilizes existing detection and segmentation models to extract accurate object-phrase pairs, which are then used to optimize a proposed contrastive learning objective tailored to object-phrase correspondence. Experimental results on semantic textual similarity (STS) tasks across different backbone models demonstrate that MCSEO outperforms image-caption-only baselines on average, and that it is complementary to existing methods: combining MCSEO with KDMCSE yields further gains. A random-pairing control and a manual evaluation of the extracted pairs additionally indicate that the improvements stem from correct object-phrase alignment.
Anthology ID:
2026.findings-aacl.22
Volume:
Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venue:
Findings
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
397–404
Language:
URL:
https://aclanthology.org/2026.findings-aacl.22/
DOI:
Bibkey:
Cite (ACL):
Kaiyan Zhao, Zhongtao Miao, and Yoshimasa Tsuruoka. 2026. Improving Multimodal Contrastive Learning of Sentence Embeddings with Object-Phrase Alignment. In Findings of the Association for Computational Linguistics: IJCNLP-AACL 2026, pages 397–404, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Improving Multimodal Contrastive Learning of Sentence Embeddings with Object-Phrase Alignment (Zhao et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-aacl.22.pdf