While pretrained large language models (LLMs) excel in understanding linguistic contexts, it is still an open question: Can LLMs extend their capabilities beyond linguistic contexts to non-linguistic information? This paper introduces VLAP, a novel approach that bridges vision encoders and language models through assignment prediction. Since the LLMs interpret and reason linguistic information from correlations between word embeddings, we harness the well-established word embeddings to map visual representations into language space. Specifically, we simultaneously assign the visual and text representations to a set of word embeddings within LLMs. We propose a new training objective, optimal transport-based assignment prediction, to enforce the consistency of word assignments for paired multimodal data. This allows frozen LLMs to ground their word embedding space in visual data and use their robust semantic taxonomy visually. Moreover, VLAP is memory- and parameter-efficient in that it trains only a single linear layer, and works without extra embedding space (e.g. learnable prototypes) for the assignment prediction. Experimental results show that VLAP achieves substantial improvements over the previous linear transformation-based methods across a range of vision-language tasks, including image captioning, visual question answering, and cross-modal retrieval. We also demonstrate the learned visual representations hold a semantic taxonomy of LLMs, making visual semantic arithmetic possible.
Bridging Vision and Language Spaces with Assignment Prediction
Jungin Park Jiyoung Lee Kwanghoon Sohn