1. Toward a Definition of ‘Virtual Worlds;Bell;Journal of Virtual Worlds Research,2008
2. Engeström , J. 2005 Why some social network services work and others don't-or: the case for object-centered sociality http://zengestrom.com/blog/2005/04/why_some_social.html
3. Garau , M. Slater , M. Bee , S. Sasse , M. A. 2001 The impact of eye gaze on communication using humanoid avatars