At first sight: Robots' subtle eye movement parameters affect human attentional engagement, spontaneous attunement and perceived human-likeness

Human-robot interaction research could benefit from knowing how various parameters of robotic eye movement control affect specific cognitive mechanisms of the user, such as attention or perception. In the present study, we systematically teased apart control parameters of Trajectory Time of robot eye movements (rTT) between two joint positions and Fixation Duration (rFD) on each of these positions of the iCub robot. We showed recordings of these behaviors to participants and asked them to rate each video on how human-like the robot's behavior appeared. Additionally, we recorded participants' eye movements to examine whether the different control parameters evoked different effects on cognition and attention. We found that slow but variable robot eye movements yielded relatively higher human-likeness ratings. On the other hand, the eye-tracking data suggest that the human range of rTT is most engaging and evoked spontaneous involvement in joint attention. The pattern observed in subjective ratings was paralleled only by one measure in the implicit objective metrics, namely the frequency of spontaneous attentional following. These findings provide significant clues for controller design to improve the interaction between humans and artificial agents.