James Y. Huang, Sailik Sengupta, Daniele Bonadiman, Yi-An Lai, Arshit Gupta, Nikolaos Pappas, Saab Mansour, Katrin Kirchhoff, Dan Roth. Proceedings of the 63rd Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers). 2025.

We introduce MuirBench, a comprehensive benchmark that focuses on robust multi-image understanding capabilities of multimodal LLMs. MuirBench consists of 12 diverse multi-image tasks (e.g., scene understanding, ordering) that involve 10 categories of multi-image relations (e.g., multiview, temporal relations). Comprising 11,264 images and 2,600 multiple-choice questions, MuirBench is created in a pairwise manner, where each standard instance is paired with an unanswerable variant that has minimal semantic differences, in order for a reliable assessment. Evaluated upon 20 recent multi-modal LLMs, our results reveal that even the best-performing models like GPT-4o and Gemini Pro find it challenging to solve MuirBench, achieving 68.0% and 49.3% in accuracy. Open-source multimodal LLMs trained on single images can hardly generalize to multi-image questions, hovering below 33.3% in accuracy. These results highlight the importance of MuirBench in encouraging the community to develop multimodal LLMs that can look beyond a single image, suggesting potential pathways for future improvements.

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.

Parameter-efficient tuning aims at updating only a small subset of parameters when adapting a pretrained model to downstream tasks.In this work, we introduce PASTA, in which we only modify the special token representations (e.g., [SEP] and [CLS] in BERT) before the self-attention module at each layer in Transformer-based models.PASTA achieves comparable performance to full finetuning in natural language understanding tasks including text classification and NER with up to only 0.029% of total parameters trained.Our work not only provides a simple yet effective way of parameter-efficient tuning, which has a wide range of practical applications when deploying finetuned models for multiple tasks, but also demonstrates the pivotal role of special tokens in pretrained language models. 1

Traditional sentence embedding models encode sentences into vector representations to capture useful properties such as the semantic similarity between sentences.However, in addition to similarity, sentence semantics can also be interpreted via compositional operations such as sentence fusion or difference.It is unclear whether the compositional semantics of sentences can be directly reflected as compositional operations in the embedding space.To more effectively bridge the continuous embedding and discrete text spaces, we explore the plausibility of incorporating various compositional properties into the sentence embedding space that allows us to interpret embedding transformations as compositional sentence operations.We propose INTERSENT, an end-toend framework for learning interpretable sentence embeddings that supports compositional sentence operations in the embedding space.Our method optimizes operator networks and a bottleneck encoder-decoder model to produce meaningful and interpretable sentence embeddings.Experimental results demonstrate that our method significantly improves the interpretability of sentence embeddings on four textual generation tasks over existing approaches while maintaining strong performance on traditional semantic similarity tasks. 1 .

James Y. Huang, Bangzheng Li, Jiashu Xu, Muhao Chen. Proceedings of the 2022 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies. 2022.

Pre-trained language models have achieved huge success on a wide range of NLP tasks.However, contextual representations from pretrained models contain entangled semantic and syntactic information, and therefore cannot be directly used to derive useful semantic sentence embeddings for some tasks.Paraphrase pairs offer an effective way of learning the distinction between semantics and syntax, as they naturally share semantics and often vary in syntax.In this work, we present ParaBART, a semantic sentence embedding model that learns to disentangle semantics and syntax in sentence embeddings obtained by pre-trained language models.ParaBART is trained to perform syntax-guided paraphrasing, based on a source sentence that shares semantics with the target paraphrase, and a parse tree that specifies the target syntax.In this way, ParaBART learns disentangled semantic and syntactic representations from their respective inputs with separate encoders.Experiments in English show that ParaBART outperforms state-of-theart sentence embedding models on unsupervised semantic similarity tasks.Additionally, we show that our approach can effectively remove syntactic information from semantic sentence embeddings, leading to better robustness against syntactic variation on downstream semantic tasks.