Unintentional entrainment effect in a context of Human Robot Interaction: An experimental study

Modelling nonverbal communication in robotics is a crucial issue to improve Human Robot interactions (HRI). Among several nonverbal behaviours we focus in this article on unintentional rhythmic entrainment and synchronization which has been proven to be highly important in intuitive and natural Human Human communication. Hence, the rising question is whether or no this phenomenon can be reproduced in a context of HRI and what are the prerequisites to ensure its emergence. In this paper, we study rhythmical interactions during imitation games between a NAO robot and naive subjects. We analysed two main types of interactions, a first where NAO performs movements at a fixed rhythm (unidirectional) and a second one where the robot is able to adopt the human motion dynamic (bidirectional) using a neural modelling of the entrainment effect based on dynamical systems. We show that using such model allows us to reach synchronization during the interactions and that both partners (robot and human) adapt their frequency as observed in natural HHI. This puts forward the importance of bidirectionality for HRI. Moreover, the participants shifted their motion dynamics during the interaction without noticing it, proving the presence of such unintentional rhythmic entrainment in HRI.