“…NUI design promises an intuitive interaction that is easy to learn. Monitoring of users can be found in recent concepts, namely, eye, head and body tracking [ 10 ], recognition and identification of facial expressions [ 11 ] and poses [ 12 ], gesture-based interaction on multi-touch devices [ 13 ] and in particular mobile devices [ 14 ], as well as voice-based interaction [ 15 ]. Therefore, it is likely to further differentiate the concept of NUI into the characteristic of Vision User Interface (VUI), Touch User Interface (TUI) and Audio User Interface (AUI) [ 16 ].…”