这篇论文系统测了多模态思维链到底行不行，发现它在视觉定位上帮倒忙，但对数学推理很管用，还揭示了视觉瓶颈。做多模态的值得看。
该研究系统评估12项多模态任务，涵盖感知与推理两类，使用14个非推理模型和8个推理模型。结果显示，CoT在视觉定位、目标计数等感知任务中会导致性能下降，但在数学、科学和多图推理中有效。开源多模态推理模型整体提升有限，可能因过度侧重数学。当前多模态CoT存在'轻看，重思'模式，视觉反省持续减弱，而口头反思相对保持。视觉推理仍是主要瓶颈。
Look Light, Think Heavy: What Multimodal Chain-of-Thought Reasoning Can and Cannot Do
Chain-of-Thought (CoT) has become a standard method for improving reasoning capabilities in large language models (LLMs) by eliciting step-by-step thinking, but its effectiveness in multimodal tasks remains unclear. In this paper, we aim to systematically investigate the key question: What can multimodal Chain-of-Thought reasoning do, and where and why does it fall short? To this end, we evaluate 12 multimodal tasks across perception and reasoning categories using both 14 non-reasoning models and 8 reasoning models. Our analysis reveals several important findings: (1) CoT is not a free lunch and should be used selectively depending on the specific requirements of each task. For perception tasks, CoT can lead to undesirable side effects, such as reduced performance in visual grounding and object counting. In contrast, it proves effective for reasoning tasks involving mathematical, scientific, and multi-image reasoning; (2) Compared to original models, existing open-source multimodal reasoning models often yield only marginal overall improvements, possibly due to an overemphasis on mathematical reasoning at the expense of broader capabilities; (3) Visual reasoning remains a key bottleneck for current multimodal CoT, as models exhibit a Look Light, Think Heavy pattern where verbal reflection rises and falls during reasoning, whereas visual reflection consistently diminishes. These findings suggest that while multimodal CoT handles verbal reflection relatively well, it lacks the ability to maintain deep visual introspection throughout the reasoning process.