In addition, the user is free to move {HEAD ~ his/her eyes} around {TAIL ~ rolling centers} 215 and 216 while continuing to see computer generated imagery 
In addition , the user is free to move { HEAD ~ his / her eyes } around { TAIL ~ rolling centers } 215 and 216 while continuing to see computer generated imagery
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH