1. a Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
2. b Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
3. c Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany
4. d Institute for Robotics and Cognitive Systems, University of Lübeck, Ratzeburger Allee 160, 23538 Lübeck, Germany