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