mDPO: Conditional Preference Optimization for Multimodal Large Language Models

Fei Wang, Wenxuan Zhou, James Y. Huang, Nan Xu, Sheng Zhang, Hoifung Poon, Muhao Chen


Abstract
Direct preference optimization (DPO) has shown to be an effective method for large language model (LLM) alignment. Recent works have attempted to apply DPO to multimodal scenarios but have found it challenging to achieve consistent improvement. Through a comparative experiment, we identify the unconditional preference problem in multimodal preference optimization, where the model overlooks the image condition. To address this problem, we propose mDPO, a multimodal DPO objective that prevents the over-prioritization of language-only preferences by also optimizing image preference. Moreover, we introduce a reward anchor that forces the reward to be positive for chosen responses, thereby avoiding the decrease in their likelihood—an intrinsic problem of relative preference optimization. Experiments on two multimodal LLMs of different sizes and three widely used benchmarks demonstrate that mDPO effectively addresses the unconditional preference problem in multimodal preference optimization and significantly improves model performance, particularly in reducing hallucination.
Anthology ID:
2024.emnlp-main.460
Volume:
Proceedings of the 2024 Conference on Empirical Methods in Natural Language Processing
Month:
November
Year:
2024
Address:
Miami, Florida, USA
Editors:
Yaser Al-Onaizan, Mohit Bansal, Yun-Nung Chen
Venue:
EMNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
8078–8088
Language:
URL:
https://aclanthology.org/2024.emnlp-main.460/
DOI:
10.18653/v1/2024.emnlp-main.460
Bibkey:
Cite (ACL):
Fei Wang, Wenxuan Zhou, James Y. Huang, Nan Xu, Sheng Zhang, Hoifung Poon, and Muhao Chen. 2024. mDPO: Conditional Preference Optimization for Multimodal Large Language Models. In Proceedings of the 2024 Conference on Empirical Methods in Natural Language Processing, pages 8078–8088, Miami, Florida, USA. Association for Computational Linguistics.
Cite (Informal):
mDPO: Conditional Preference Optimization for Multimodal Large Language Models (Wang et al., EMNLP 2024)
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PDF:
https://aclanthology.org/2024.emnlp-main.460.pdf