Do Your Expectations Match? A Mixed-Methods Study on the Association Between a Robot's Voice and Appearance

Both physical appearance and voice can elicit mental images of what someone and/or something should sound and look like. This is particularly relevant for human-robot interaction design and research since any voice can be added to a robot. Therefore, it is important to give robots voices that match users' expectations. In this paper, we examined the voice-appearance association by asking participants to match a robot image with a voice (Experiment 1, N = 24), and vice versa, a voice with a robot image (Experiment 2, N = 24), in two mixed-methods studies. We looked at participants' differences that could influence the voice-robot association (gender and nationality) and at voice and robot features that could influence participants' voice preferences (voice gender, pitch and robot's appearance). Results show that nationality influenced participants' association with a robot image after hearing its voice. Furthermore, a content analysis identified that when creating a voice mental image, participants looked at robots' gendered characteristics and height and they paid special attention to human-like and gender-specific cues in a voice when forming a mental image of a robot. Sociological differences also emerged, with Swedish participants suggesting the use of gender-neutral voices to avoid strengthening existing stereotypes, and Italians saying the opposite. Our work highlights the importance of individual differences in the robot voice-appearance association and the importance of involving the end user in designing the voice.