EyeLink II User Manual version 2.12
(07/02/2006)
©
2002-2006 SR Research Ltd.
44
The proper timing is best learned by watching the gaze cursor during validation
(discussed later).
The EyeLink II system helps prevent improper triggering by locking out the
↵
key if the eye is moving. Sometimes the
↵
key will be locked out because of poor
eye-camera setup, with the pupil noisy or undetected in some positions. You
can use the
⇐
or
⇒
keys on the operator keyboard to select the eye camera
image to view on-screen and the
⇑
and
⇓
keys to change the threshold if
required. If this fails, or the eye camera needs repositioning, press the ‘ESC’
key to exit back to the Camera Setup menu.
After the first fixation has been accepted, several more calibration targets are
displayed in sequence and fixations for collected each. The EyeLink II
calibration system presents these targets in a random order, which discourages
subjects from making saccades away from the current target before it
disappears.
If automatic sequencing has been enabled, targets will be presented and
fixations collected without further intervention. Each time a new target is
displayed, the subject quickly makes a saccade to it. The EyeLink II system
detects these saccades and the fixation following, producing an automated
sequencing system.
NOTE: Sequencing may halt if the setup of one or both eyes causes pupil loss or
noise at the target position. If this happens, adjust the threshold and restart
the calibration by pressing the ‘ESC’ key. Press it twice (once to restart and
again to exit) to return to the Setup menu.
Even though the calibration is automatic, watch the operator PC’s display
carefully. Note the position of the cross-shaped pupil position markers: these
should form a grid shape for the 9-point calibration (i.e., they form three
parallel horizontal or close-to-horizontal lines and three parallel vertical or
close-to-vertical lines; see Figure 3-7). Lapses of subject attention will be clearly
visible in the movements of this cursor. Also visible will be any difficulties the
subject has in fixating targets, and most eye camera setup problems.
