Do Multimodal Large Language Models Truly See What We Point At? Investigating Indexical, Iconic, and Symbolic Gesture Comprehension

Understanding hand gestures is essential for human communication, yet it remains unclear how well multimodal large language models (MLLMs) comprehend them.In this paper, we examine MLLMs' ability to interpret indexical gestures, which require external referential grounding, in comparison to iconic gestures, which depict imagery, and symbolic gestures, which are conventionally defined.We hypothesize that MLLMs, lacking real-world referential understanding, will struggle significantly with indexical gestures.To test this, we manually annotated five gesture type labels to 925 gesture instances from the Miraikan SC Corpus and analyzed gesture descriptions generated by state-of-the-art MLLMs, including GPT-4o.Our findings reveal a consistent weakness across models in interpreting indexical gestures, suggesting that MLLMs rely heavily on linguistic priors or commonsense knowledge rather than grounding their interpretations in visual or contextual cues.