Nudging Without Words: Movement-Only Cues from a Robot Manipulator Influence Human Decisions

Abstract

Robots are increasingly present in our everyday environments, offering services and products. But can they influence our choices through movement alone? This paper investigates whether a robot manipulator can nudge user decisions using only its arm movements, without speech, facial expressions, or physical contact. We first identified plausible nudging motions through a bodystorming session, then designed and implemented three composite nudges (positive, neutral, and negative) using a UR5 robot arm. In a video-based online study (N=35), participants more often chose positively nudged items and avoided negatively nudged ones. A small in-person study (N=9) confirmed the effect. These results demonstrate that movement-only nudges can influence decision-making and highlight the potential of subtle physical behaviors for nonverbal persuasion.