Tobii X1 Light User Manual
45
Time to tracking
recovery after lost
tracking
An eye tracker working in a natural user environment may
occasionally lose track of the subject’s eyes, e.g., when the
subject completely turns away from the tracker. If a period
of a few hundred milliseconds elapses during which the eye
tracker is unable to detect the eyes in close proximity to where
they were last detected, the eye tracker will start searching
for the eyes within the entire head movement box. The stated
measurement is the typical time to tracking recovery in such a
situation. If the eye tracker is unable to detect the eyes of the
subject even after about one minute, the system will enter a
“slow search” mode, leading to larger recovery times.
Freedom of head
movement
Describes an area (height × width in cm) where at least one
eye is within the eye tracker’s field of view.
Operating distance
Describes the minimum and maximum distances between
the subject’s eyes and the surface covering the eye tracker
sensors at which eye tracking can be done while maintaining
robust tracking.
Recommended
largest gaze angle
The largest recommended gaze angle for which the eye
tracker can perform robust and accurate tracking on both
eyes. The gaze angle is the angle ABC with A = center of the
eye tracker (midpoint between the two eye tracking sensors),
B = eye position (midpoint between the left and the right eye)
and C = stimuli point.
Eye tracking
technique
Tobii Eye Trackers use two different techniques to determine
eye position: 1. Bright pupil eye tracking, where an illuminator
is placed close to the optical axis of the imaging device,
causing the pupil to appear lit up (the same phenomenon that
causes red eyes in photos). 2. Dark pupil eye tracking where
the illuminator is placed away from the optical axis, causing the
pupil to appear black.
Eye tracking
processing unit
Gaze data calculations are performed by firmware embedded
in the eye tracker.
Chapter 7
Appendices
