As multimodal large language models (MLLMs) are increasingly integrated into early-stage design tools, it is important to understand how designers collaborate with AI during ideation. In a user study with 12 participants, we analysed sketch-based design interactions with an MLLM-powered system using automatically recorded interaction logs and post-task interviews. Based on how creative responsibility was allocated between humans and the AI, we predefined four interaction modes: Human-Only, Human-Lead, AI-Lead, and Co-Evolution, and analysed how these modes manifested during sketch-based design ideation. Our results show that designers rarely rely on a single mode; instead, human-led and AI-led roles are frequently interwoven and shift across ideation instances. These findings provide an empirical basis for future work to investigate why designers shift roles with AI and how interactive systems can better support such dynamic collaboration.

翻译：随着多模态大语言模型（MLLMs）日益融入早期设计工具，理解设计师在构思阶段如何与人工智能协作变得至关重要。在一项包含12名参与者的用户研究中，我们通过自动记录的交互日志与任务后访谈，分析了设计师与一个基于MLLM的系统在草图设计中的交互行为。依据创意责任在人与AI之间的分配方式，我们预先定义了四种交互模式：纯人工主导、人主导、AI主导与协同演化，并分析了这些模式在草图设计构思过程中的具体表现。研究结果表明，设计师很少依赖单一模式；相反，人主导与AI主导的角色频繁交织，并在不同的构思实例中动态转换。这些发现为未来研究提供了实证基础，以深入探究设计师为何与AI转换角色，以及交互系统如何更好地支持此类动态协作。