1. Social Robotics Laboratory, Interactive Digital Media Institute and NUS Graduate School for Integrative Sciences and Engineering, National University of SingaporeSingapore119613Singapore
2. Robotics Institute and School of Computer Science and Engineering, University of Electronic Science and Technology of ChinaChengdu610054People's Republic of China
3. Department of Electrical and Computer EngineeringNational University of SingaporeSingapore119077Singapore