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Video Eyetracker Toolbox
Eye tracking appears inaccurate
Occasionally, there may be consistent errors between where the
subject is looking and where the system thinks the subject is
looking. This may be solved by checking the following:
•
The eye may be slightly out of focus due to head
movement away from the infrared mirror. Ensure that the
subject maintains contact with the headrest at all times
and refocus if necessary.
•
The eyelid may be obscuring the pupil slightly, which
would reduce the accuracy of finding the pupil centre.
•
The system may have been poorly calibrated or lost
calibration due to movement of one of the headrest
components. Ensure that all headrest adjustments are
correctly and securely set and then recalibrate.
Eye tracking appears noisy, erratic or intermittent
In normal use, the Toolbox will track the subject’s point of fixation
with angular noise of between one quarter and one half of a
degree (which is approximately 2.5 – 5mm positional error at a
viewing distance of 500mm). These specifications can be
achieved by ensuring that:
•
The radial lines on the iris are clearly visible (i.e. the
pupil / iris is in focus -- not the eyelashes)
•
There are no bright spurious glints close to the pupil
•
The pupil is in the centre of the image and not occluded
by the eyelid in any way
These are illustrated in Fig 80:
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