THE IDIOT'S GUIDE TO EYETRACKING
WARNING #1: Turn Servo switch (on back panel Gen. V, front panel Gen. 6) OFF before
turning Power OFF!
WARNING #2: The Eyetracker includes front-surfaced mirrors and coated lenses. You should
never attempt to clean these with anything but special pressurized air made for cleaning optical
equipment. Lens paper will damage mirrors, but is okay for lenses.
1. BEFORE TURNING ON DPI TRACKER CHECK THE FOLLOWING:
1.1
Turn Master Servo switch OFF (down position).
1.2 Setup/Track switch should be in Setup Position (red light). This puts device in standby
mode so that it can warm up without having the moving parts search for a 1st and 4th reflection.
1.3 Auto Stage switch should be OFF (red light). We will turn this on later after your subject
is properly positioned and her/his nose is out of the way.
1.4 Set Focus Lock switch to OFF (down) position.
2. WARM UP EQUIPMENT:
2.1 Turn Power on. This switch is located in lower-left front panel. It should never be
accidentally turned off while the device is in use. If all is well the Setup/Track light should blink
red.
2.2 Turn Master Servo switch on. The Setup/Track light is now red. Don't panic, the servos
won't come on for a while until device is warmed up a bit. You come to recognize their familiar
whine.
2.3 Wait for approximately 5 minute warm-up period. I have noted DC drift during the
warm up period.
3. POSITION SUBJECT IN DEVICE:
3.1 Position the bite bar, the subject and the display device. Move the bite bar until your
subject indicates that she/he is comfortable and yet his/her eye is positioned directly in line with
the zero position of your display device. If comfort and alignment cannot be achieved
simultaneously, move your display device. If the display device is not positioned properly it will
be impossible to get symmetrical, nearly linear recordings. It may also prevent getting subject
locks in lower fields where eye lashes may block the 4th LL reflection, or when display is placed
too far temporally where pupil margin effects are possible.
3.2 Adjust the staging using the Left-Right, Up-Down, In-Out switches.
Now that subject and display are positioned, move the optical stage of the eyetracker using the
positioning controls located in the upper left of the front of the box marked L/R, U/D, I/O. Move
the IN/OUT switches until the cornea is on the cornea mark. The UP/DOWN and LEFT/RIGHT
until the beam covers the pupil, offset to the right side to avoid a pupil margin.
3.3 Turn ON Setup-Track switch (green light). Did you lock? Oops, too bad!
TO ACHIEVE EYETRACKER LOCK:
4.1 Turn Auto-Stage switch ON (green light). Instruct subject to look around +/- 1 to 2
degrees until the Auto Stage mechanism stops hunting and remains stable.
4.2 Voided
4.3 Voided
4.4 Turn Auto-Stage OFF (Red light).
4.5 Check the 1st LL. Using the front panel meter, measure the 1st Light Level Detector
voltage. It should be -3.5 to -6.0 volts during lock.
4.6 Fine adjust 1st Purkinje images. With subject fixating, set front panel switches to H1 and
then V1 and check that the meter reads close to zero. If not zero, fine adjust position of tracker
by using the toggles labeled L/R for H1, and U/D for V1, in the upper right center of the front
panel. Just flick the switches as the staging moves fast. ALWAYS START WITH FOCUS
AND IN/OUT.
4.7 Zero 4th Detector. Subject should fixate eye at calibrate zero. At the time of fixation,
activate (push) the 4th Detector Auto Position Switch (on front panel. If offset with 4th Detector
Switch is not good enough, it can be improved by manipulating the H & V switches next to the
4th Autoposition switch. Good enough is a matter of personal needs. If your program can not
deal with offsets then you must be particular. Examine Theta-H and Theta-V to determine the
offset while subject fixates center of display.
4.8 Check the 4th LL. Using the front panel meter, measure 4th Light Level Detector voltage.
It will probably read -6 volts. Adjust it to -5.00 volts using the 4th LL adjust pot on the front left
side of the box.
WRITE SOME THINGS DOWN:
5.1 Write down 4th LL Value. This will force you to remember to adjust it to -5.00. (This
applies to Gen 5.X only).
6. RUN TESTS:
7. TO END TESTS TEMPORARILY: Put Setup/Track switch in Setup position (red light)
and leave system on.
NOTE: Since certain functions are manipulated by electronics box front panel, optics unit
switches, or remote switches, only the color of the light over the switch will tell the true status of
the eyetracker.
8. TO STOP OPERATION:
8.1 Put Setup/Track switch in Setup Position.
8.2 Turn Master Servo switch OFF.
8.3 Turn Power OFF.
WARNING: Turn Master Servo switch OFF before turning Power ON or OFF!
9. WHEN YOU HAVE PROBLEMS:
9.0 Pray
9.1 Output of tracker is slow to follow the eye. Check that the subject is properly and securely
positioned relative to the display device. See item #9.0 and #3.1 above.
9.2 Calibration data reveals very nonlinear measures. Check that the subject is properly and
securely positioned relative to the display device. See item #9.0 and #3.1 above.
9.3 Track-loss occurs when ss looks to far upper temporal quadrant. This has usually
revealed that the tracker is locked on a pupil margin. Start again at item #3.2 above. You can
verify this hypothesis by removing the 4th detector and positioning the IR scope and the
crosshairs to examine the position of the pupil margin and the 4th reflection relative to the
detector. Someone will have to show you this at least once. If you still have no success turn
down room lights to dilate subject's pupil as much as possible and start at #3.2 again. If there is
still no reliable 4th lock then you will have to call Fourward Technologies. In the past, this has
meant that something is out of alignment (steering mirrors or phase of the moon, something like
that).
9.4 Track-loss/signal error occurs when SS looks to far medial lower quadrant. I associate
this with an error in the position of the tracker angle relative to the subject. From my
measurements the tracker needs to be positioned somewhere at about 7 degrees from the
frontoparallel plane of the subject to give the most linear recording on the medial side.
9.5 Dynamics are not the same temporal-nasal and nasal-temporal. So far the answer to this
is "That's the way it is due to asymmetries in the 4th reflection."
9.6 Apparent dynamic overshoot at the end of the saccade. This is an artifact resulting from
the inertial movement of the lens of the eye. This should be noticeable at the end of rapid eye
movements in both directions, but not at the beginning of eye movements or only on some eye
movements. If not, have the tracker adjusted. The magnitude of the lens artifact can be modified
by an adjustment to the damping circuit of the motors. Overdamping can extend and thereby
severely distort the duration of rapid eye movements.
NOTE: If you find a student with big pupils, never let her graduate, as good subjects are hard to
find.