I. Introduction
Human-computer interaction techniques for computer games are one of the hottest topics in terms of research and development. Although a lot of different interaction approaches exist (e.g. mouse, keyboard, joystic, Nintento Wii controller, Microsoft Kinect, Guitar Hero, etc) they require a lot of physical effort. This restricts user's expressive capabilities as well as the information transfered from the user to the computer [1]. During the past few years, non-invasive brain-computer interfaces (BCIs) seem to be getting a lot of attention as alternative human-computer interaction devices for games and virtual environments [2], [3].