  Mobile robots have recently been deployed in public spaces such as shopping
malls, airports, and urban sidewalks. Most of these robots are designed with
human-aware motion planning capabilities but are not designed to communicate
with pedestrians. Pedestrians that encounter these robots without prior
understanding of the robots' behaviour can experience discomfort, confusion,
and delayed social acceptance. In this work we designed and evaluated nonverbal
robot motion legibility cues, which communicate a mobile robot's motion
intention to pedestrians. We compared a motion legibility cue using Projected
Arrows to one using Flashing Lights. We designed the cues to communicate path
information, goal information, or both, and explored different Robot Movement
Scenarios. We conducted an online user study with 229 participants using videos
of the motion legibility cues. Our results show that the absence of cues was
not socially acceptable, and that Projected Arrows were the more socially
acceptable cue in most experimental conditions. We conclude that the presence
and choice of motion legibility cues can positively influence robots'
acceptance and successful deployment in public spaces.
