Asking the Right Question

Abstract

Social robots can shape group interaction, but robot facilitation is often studied at the level of the robot as a whole rather than at the level of the specific utterances through which the robot intervenes. This paper investigates how three spoken elicitation strategies delivered by a social robot -generative, elaborative, and perspective-shifting prompts- shape participant engagement and contribution substantiveness in a two-person creative ideation task about improving the TU Delft campus experience. The study used a within-subjects design in which each of the 20 groups received one prompt from each strategy during divergence and one during convergence, while the task, robot, scheduling rule, and technical setup were kept constant. Engagement was measured using self-reports, response delay, speaking time, vocal activation, and connection cues; contribution substantiveness was measured using manually coded idea count, elaboration units, and consecutive same-subject turns. The descriptive results suggest that convergence produced higher self-reported engagement than divergence, generative prompts were most associated with idea breadth, and elaborative prompts were most associated with developed and sustained discussion. Perspective-shifting prompts appeared more useful once participants already had ideas to evaluate. The findings do not establish a universally superior strategy, but they show that robot facilitation should be designed as phase-sensitive prompt behaviour rather than treated as a general effect of robot presence.