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An EyeLink Portable Duo Tutorial: Running an Experiment
©
2016-2017 SR Research Ltd.
If automatic sequencing has been enabled, targets will be presented and
fixations collected without further intervention. Each time a new target is
displayed, the participant should quickly make a saccade to it. The EyeLink
system detects these saccades and the fixation following, producing an
automated sequencing system.
NOTE: Sequencing may halt if the improper setup of the eye causes pupil loss
or noise at the target position. If this happens, press the ‘ESC’ key twice to exit
the calibration, adjust the threshold and/or the participant setup, and then
restart the calibration. Pressing the ‘ESC’ key once will restart the calibration
whereas pressing it twice will exit calibration and return to the Setup menu.
Even though the calibration is automatic, watch the Host 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. Lapses of participant attention will be
clearly visible in the movements of this cursor. Also visible will be any
difficulties the participant has in fixating targets, and most camera setup
problems. The following figure illustrates a good calibration (left panel) and a
poor calibration (right panel).
Good Calibration
Poor Calibration
Figure 3-10: Calibration Grid
For some participants (especially those with neurological conditions) short
fixations or lapses of attention can make the automated procedure unusable. A
manual calibration mode can be used for these participants, where the ENTER
key or spacebar must be pressed to collect each fixation. Pressing the ‘M’ key
switches automatic calibration off. It may be switched back on by pressing the
‘A’ key.
One useful key in the middle of a calibration sequence is the Backspace key (or
the “Undo Last Point” button), which can undo recent calibration targets. With
each press of this key, data collected for the last point in the calibration
sequence is erased and new calibration data can then be collected. This can be
used to improve calibration accuracy for one or a few selected points without
having to restart the calibration procedure. This is especially helpful for those
participants whose calibration data is hard to get.
