Frank Steinicke Gerd Bruder Klaus Hinrichs Anthony Steed Alexander L. Gerlach Does a Gradual Transition to the Virtual World increase Presence? 203-210 2009 VR http://dx.doi.org/10.1109/VR.2009.4811024 conf/vr/2009 db/conf/vr/vr2009.html#SteinickeBHSG09