Primary position is generally close to center , but it may be rotated slightly up or down , left or right .
Direct measurements show that the location of primary position ( and thus the orientation of Listing 's plane ) varies between subjects .
Primary position is generally close to center , but position may be rotated slightly up or down , left or right .
Direct measurements show that the location of primary position ( and thus the orientation of Listing 's plane ) varies between subjects .