The Uncanny Valley Effect in Zoomorphic Robots: The U-Shaped Relation Between Animal Likeness and Likeability

The uncanny valley effect denotes a dip in the positive relation between a robot's human likeness and likeability. This paper provides first evidence that this design-guiding effect is not limited to humanoids, but extends to zoomorphic robots. In a first online survey, a diverse group of 235 participants rated the animal likeness of 140 robots. Three predictors for high or low animal likeness emerged: surface properties, such as joint visibility; facial properties, such as presence of a pupil; animal-specific properties, such as presence of snout. In a second online survey, 187 participants rated the likeability of 53 robots of varying degrees of animal likeness drawn from the first study. The relation between animal likeness and likeability followed a U-shaped function and showed an uncanny valley effect: robots high and low in animal likeness were preferred over those mixing realistic and unrealistic features. Besides theoretical implications tentative guidelines for the design of zoomorphic robots are discussed.