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The external aspects of a robot affect how people behave and perceive it while interacting. In this paper, we study the importance of the mouth displayed by a social robot and explore how different designs of an artificial LED-based mouths alter the participants' judgments of a robot's attributes and their attention to the robot's message. We evaluated participants' judgments of a speaking robot under four conditions: 1) without a mouth; 2) with a static smile; 3) with a vibrating, wave-shaped mouth; and 4) with a moving, human-like mouth. A total of 79 participants evaluated their perceptions of an on-video robot showing one of the four conditions. The results show that the presence of a mouth, as well as its design, alters the perception of the robot. In particular, the presence of a mouth makes the robot to be perceived more lifelike and less sad. The human-like mouth was the one participants liked the most and, along with the smile, they were the friendliest ones. On the contrary, participants rated the mouthless robot and the one with the wave-like mouth as the most dangerous ones.
Evaluation; human factors; human-robot interaction (HRI); LED-based mouth; mouth; robot mouth; social robot