SR Research EyeLink Portable Duo User Manual page 75

method does however have to be arranged whereby the experimenter knows
that the participant is looking at a particular aspect of the stimulus at a
particular point in time, so that the drift correction fixation sample at that
known location can be acquired. Pre-arranging that the participant look at a
particular aspect of the stimulus display that will act as a fixation target (e.g., a
fixation cross) allows the experimenter to perform such drift corrections during
the actual recording.
Using Online Drift Correct to a fixed location requires that the coordinate that
the participant should fixate is set using an EyeLink command (or predefined in
the software). When a drift correction is to be applied the experimenter initiates
the correction by clicking the "Drift Correct" button on the Recording Screen of
the Host PC or by pressing a prearranged key that will initiate the drift
correction.
If the participant regularly fixates some known entity in the displayed image
then this could be used to perform the drift correction. When the participant is
known to be looking at a fixation cross for instance, simply click the "Online
Drift Correct" button (or press the assigned key – F9 by default) to execute the
drift correction. If the attempted correction is above an acceptable distance then
the drift correction will fail and a message will appear in the text box reporting
the size of the attempted drift correction and noting it failed such as
FAILED: offset of 14.6 degrees rejected".
To enable online drift correcting to a fixed location, the Host PC needs to be
configured manually by adding some commands to the FINAL.INI file or it can
be configured through software sending the commands across the link. The
commands required are:
driftcorrect_cr_disable = OFF
online_dcorr_refposn 512,384
online_dcorr_button = ON
normal_click_dcorr = OFF
After enabling drift correction, these commands set the reference position to
which the drift correction will take place (in this example, at the coordinate 512,
384 on the Display PC screen). Next the "Drift Correct" button is enabled on the
Recording Screen by turning it on. Finally, the drift correction will be executed
by clicking the button.
The drift correction can also be executed when an assigned key is pressed. To
do this the following command defines the F9 key to be used to trigger the drift
correction action.
key_function F9 "online_dcorr_trigger"
An EyeLink Portable Duo Tutorial: Running an Experiment
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