HUMAN EYE MOVEMENTS

A variety of {\bf visual tasks} depend on this eye movement capability:
-- (i) searching for some feature in a scene,
-- (ii) saccades to compare two features in a scene,
-- (iii) tracking a moving target in a scene,
-- (iv) fixating on a spot while the head moves.

There are four principal eye movements:

1. saccades (discrete rapid movements between fixation points),
2. pursuit eye movements (tracking to keep a moving target foveated),
3. vestibular systems (maintains the gaze by counteracting head movements), and
4. vergence (controls the depth that the two eyes fixate together)

-- Vergence is useful for stereo version.
-- A fifth movement physiological nystagmus is not important for us.

REFERENCE: [Robinson'68]