EyeLink II User Manual version 2.12
(07/02/2006)
©
2002-2006 SR Research Ltd.
39
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Figure
3-3: Horizontal Adjustments of Eye Camera
Finally, the height of the eye camera below the eye may need to be adjusted, as
in the middle row of Figure 11. If the camera is too high, the subject's view of
the bottom of the display may be blocked. If the camera is too low, the pupil
may be hidden if the subject smiles or squints, and the calibration will be poor.
The camera height is set by swinging the camera rod in and out.
The proper height may be set by the curvature of the lower eyelid in the image,
or by observing the position of the corneal reflections in the camera image. If
the lower eyelid curves up at the edges (smile shape) the camera should be
lowered. If the lower eyelid curves up in the middle (frown shape) the camera
should be raised. The position of the two eye illuminator corneal reflections (the
2 white circles) should be at the bottom of the pupil: lower the camera if they
are too high.
Note: The corneal reflections mentioned here are not the corneal reflections
used by the system for headband movement compensation and are white with a
position that should be at the bottom of the pupil. The corneal reflection used in
the Pupil-CR mode is a single circle and is yellow in colour, located near the top
of the pupil.
The pupil of the eye must now be centred in the camera image. Two methods
can be used, depending on the operator’s preference and camera clamp
mechanics. The camera may be loosened and slid left or right to centre the
pupil. Squeeze the spring clamp handle to loosen and move the camera.
The second method is to move the nose end of the camera rod towards and
away from the face, twisting the rod though the rod clamp. This may cause the
eye image to tilt as well, which is not a problem. This may require some
practice: try setting up the headband on yourself, while watching the display on
the operator monitor.
