Adjust Image Thresholds And Focus The Lens - SR Research EyeLink 1000 Installation Manual

sight to both the Illuminator and the Camera Head when the mirror is tilted at an angle
yielding a good view of the entire area where the stimulus is to be displayed.
Adjust the focus of the lens by turning the lens barrel to roughly focus the lens so that at least
what you are looking at is clear. Use any landmarks of the head coil (such as writing) to orient
your pointing of the camera; having the volunteer make recognizable movements such as
winking might help. The threshold coloring of the Host computer may assist in finding the eye,
but keep in mind that if you would rather see the image uncolored, you can turn the coloring
off and on by toggling the "Threshold Coloring" button of the Camera Setup screen.
Adjust the Mounting Bar of the eye tracker to change the Camera Head's view. The eye needs to
be clearly visible in the camera's global view and ideally, not too close to the edges of the
camera's view. If operating in monocular mode, be sure only one eye is present in the global
image. When the system is capable of tracking the eye, crosshairs will appear on the pupil and
corneal reflection indicating that the system is capable of picking up the eye.
If the observer can clearly see the infrared points of the illuminator (890 nm - the 940 nm
Illuminator may be invisible) as well as having line of sight down the barrel of the lens, then
the camera and illuminator are close to the correct position. Have the volunteer report on how
the camera should be adjusted to achieve their ability in seeing down the camera barrel. Note
that this is an alternative method to aligning the Camera Head and Illuminator – after finding
the eye in the center of the global camera image, adjust the illuminator angle so that the eye(s)
and its(their) surround are well lit.
7.9.7

Adjust Image Thresholds and Focus the Lens

This section assumes some familiarity with the basics of using the EyeLink 1000. For a
thorough introduction to a tracking session, please consult the tutorial in Section 3 of the
EyeLink 1000 User Manual. Some of the essential steps are recapped here, but for an overview
of the procedure and the reasoning behind the different steps, please consult the tutorial.
Once the eye is in view of the camera and the crosshairs are present, with threshold coloring
turned on, switch to the zoomed in thumbnail view of the eye. The thumbnail that is selected
and transferred to the Display PC can be toggled by pressing the left or right arrow/cursor keys
on either keyboard.
Focus the lens. The goal is to minimize the size of the corneal reflection, resulting a good focus
overall. Simply turn the barrel of the lens while monitoring the size of the corneal reflection to
minimize it. If threshold coloring is preventing a clear view of the eye, try 'A' for autothreshold
to set the thresholds in reasonable range.
Once the image is in focus, press 'A' on the Host or Display PC keyboard to perform an
'autothreshold' or use the mouse to click on the pupil of the eye, which will typically perform
an autothreshold procedure. Autothreshold simply guesses at some appropriate threshold
levels to use in determining which parts of the image belong to the pupil and the corneal
reflection. Pupil threshold levels should be above 60 (presented below the thumbnail image)
otherwise this indicates that the illumination is not good. Below a level of about 60 will
Long Range Mount Installation 61
2005-2010 SR Research Ltd.