  Communicating the robot state is vital to creating an efficient and
trustworthy collaboration between humans and collaborative robots (cobots).
Standard approaches for Robot-to-human communication face difficulties in
industry settings, e.g., because of high noise levels or certain visibility
requirements. Therefore, this paper presents zoomorphic gestures based on dog
body language as a possible alternative for communicating the state of
appearance-constrained cobots. For this purpose, we conduct a visual
communication benchmark comparing zoomorphic gestures, abstract gestures, and
light displays. We investigate the modalities regarding intuitive
understanding, user experience, and user preference. In a first user study (n =
93), we evaluate our proposed design guidelines for all visual modalities. A
second user study (n = 214) constituting the benchmark indicates that intuitive
understanding and user experience are highest for both gesture-based
modalities. Furthermore, zoomorphic gestures are considerably preferred over
other modalities. These findings indicate that zoomorphic gestures with their
playful nature are especially suitable for novel users and may decrease initial
inhibitions.
