User manual

The pupil status error message “MISSING” highlighted in red, indicates that the

pupil is missing from the camera view. This could be that the participant is

blinking. It could also be that there is a problem with camera setup. Please

adjust as needed.

Indicates Status of Corneal

OK = Corneal is visible

MISSING = Corneal is missing

The corneal status error message “MISSING”, highlighted in red, indicates that

the corneal reflection is not visible to the camera. See section 3.4 for details on

how to set up corneal reflection properly.

All status flags remain on for a minimum of 200 msec, even if the condition that

caused the warning or error to be raised lasted for less than 200 msec.

3.8 Validation

It is important that problems with the calibration be identified and corrected

before eye-movement recordings are ruined. By running a validation

immediately after each calibration, the accuracy of the system in predicting

gaze position from pupil position is scored. If performance is poor, the

calibration should be immediately repeated.

In a validation, targets are presented on the subject display in a random order,

similar to the calibration procedure. When the subject fixates these, the

calibration is used to estimate the gaze position of the subject, and the error

(difference between target position and computed gaze position) is estimated.

Note: a scaling factor is built in for automatically generated validation points to

pull in the corner positions (see the

‘validation_corner_scaling’ command

setting in the CALIBR.INI file). This is used to limit validation to the useful part

of the display.

The gaze-position error comes largely from errors in fixation data gathered

during the calibration, which come from two sources: the eye-tracking system

and physiological eye-movement control. The EyeLink system has extremely low

pupil-position noise and very high resolution. These common sources of error in

the eye-tracking system are virtually eliminated. One physiological source of

calibration inaccuracy is the natural variability in fixation position on targets.

Vergence eye movements also contribute.

For calibrations with 9 targets, it is highly likely that one or more targets will be

fixated with an error of 1° or greater. Poor eye/camera setup can cause a highly

distorted calibration pattern. Some subjects may show substantial drifts in gaze

position during fixations or may not fixate carefully, adding to the errors.

An EyeLink 1000 Tutorial: Running an Experiment