Biological Motion in Robots and Users’ Action Understanding

When a robot’s motion is more predictable, users experience lower stress and perceive the robot as more competent. The present study examined previously unexplored relationships between robot motion, anthropomorphic forms, and human action understanding. In an online experiment, we tracked participants’ (n = 62) gaze as they watched a robotic arm, humanoid, and human pouring coffee, either in biological (smooth, curvilinear) or nonbiological (segmented, sudden) motion. Additionally, the action outcome was either correct (filling a cup) or erroneous (spilling); participants gave key-press responses to predict which outcome. Motion had significant main effects on both predictive gaze and error detection response times. However, while predictive gaze was statistically equivalent when observing the robotic arm and humanoid in biological motion, it was counterintuitively lower when observing humans. Taken together, our findings contribute evidence to support an expanded role of predictable motion in robot design.