SR Research EyeLink Portable Duo User Manual page 61

The Remote Mode exclusively uses Pupil-CR tracking mode. The CR is identified
by a filled (turquoise) circle marked by a crosshair. The CR threshold value is
displayed under the zoomed camera view. The CR threshold is updated
automatically and CR bias can be manually adjusted using buttons, or with the
+ and – keys. Pressing the AUTO button resets the CR threshold bias. Once the
CR threshold bias is adjusted, have the participant slowly look along the edges
of the display surface and ensure that the CR signal is consistently detected
and tracked. If the CR is not consistently detected or lost entirely, a red warning
message will appear below the small camera image for the eye indicating "CR
MISSING" on the Host PC.
The EyeLink Portable Duo Host software also implements exposure control,
which is used to adjust the brightness of the camera image when the eye-to-
camera distance changes and to improve the dynamic range of the camera.
Unlike the head-stabilized tracking mode, the distance between the participant
and the eye tracker and the position of the tracked eyes in the camera image
can vary quite a bit during recording in the Remote Mode. Since the effective
brightness of the illuminator output changes as a function of distance squared,
this means that the brightness of the camera image and thus the pupil and
target thresholds can vary a lot if the viewing distance and image position
changes. Exposure control in the EyeLink Host software is used to adjust the
exposure duration of each camera frame to avoid getting overexposed or
underexposed camera images. In the Remote Mode, an automatic exposure
control is implemented using the brightness of the target sticker as a reference.
This adjustment in the exposure duration is primarily based on the target-
camera distance but can also be influenced by other factors (e.g., position in the
camera sensor, eye rotation angle, etc).
The auto exposure control can be enabled or disabled by pressing CTRL + E
(auto exposure is turned off if "AUTO" is missing from the exposure control
text). When operating in the Remote Mode, it is recommended that the default
settings are used (i.e., auto exposure enabled) so that the eye tracker
automatically adjusts the exposure duration of the camera image frames to
keep the threshold of the target and pupil relatively constant. CTRL and
UP/DOWN arrow keys adjust the bias value (multiplier) of the auto exposure
control. Pressing the CTRL and UP arrow keys may help if the pupil threshold is
too low because of a dark camera image; pressing the CTRL and DOWN keys
will help if you are getting an overexposed camera image. It is recommended
that the default bias value of 1.0 be kept. The current auto exposure settings
can be read from the lower right corner of the "Advanced Settings" box in the
Setup screen.
The Remote Mode draws a red search limit ellipse which is automatically
updated and moves along with the eye(s). This search limit area is used to
An EyeLink Portable Duo Tutorial: Running an Experiment 51
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