EYE TRACKING

It has a long history, originating in in medicine (differential diagnosis of neurological diseases).
-- Today, it is used in Virtual Reality research.
-- Combining eye-tracking with head-motion devices in visualization would be a realization of Sutherland's dream, the ``ultimate display'' [Sutherland'65].

There are three basic approaches.

1. Electro-oculography (EOG) Methods.
   -- This is the oldest.
   -- It measures the voltage difference between the cornea and the retina.
2. Scleral Search Coil Methods. [Robinson'63]
   -- This is the standard approach today.
   -- It requires the subject to wear contact lenses wound with coils.
3. Video Oculography (VOG) methods. [Nakayama'74].
   -- This is an emerging "non-invasive approach".
   -- The subject wears a goggle with an attached miniature CCD camera.
   -- Frame rates are about 30 fps. Issues include occlusion of iris and pupil and compensation for head motion.

OTHER METHODS
-- Corneal reflection methods. But this is restricted to 2-D measurements of movement (not torsional movement).
-- At NYU, some work based on Spherical Pointing Motor (SPM) Technology has been done by Perlin and Hansen.
-- Joel Kollin (University of Washington) has developed the virtual retina display. This creates a high resolution color virtual image display by scanning an image directly onto the retina of the eye. This technique affords a panaromic display.