This is for internal use only. Use opiSetup() with
these Arguments and you will get the Value back.
A list containing err which is NULL for success, or some string description for fail.
is a list that could contain:
fixation c(x,y,t) where
x is one of -20, -6, -3, 0, 3, 6, 20 degrees.
y is 0 degrees.
t is 0 for a spot fixation marker at c(x,y), or 1 for a
square centred on one of (-3,0), (0,0), (+3,0).
tracking_on TRUE for tracking on, FALSE for off
Note: tracking will be relative to the PRL established with the fixation marker used at setup (call to OPI-OPEN), so when tracking is on you should use the same fixation location as in the setup.