2. Visual Tracking
• Why Visual Tracking ?
– To keep the image in the Fovea which is less than 1mm size and
detect visual field of less than diameter of full moon.
– It keeps the eye still when the image is still and stabilizes the
image when the object moves in the world or when the head itself
moves.
• How Visual Tracking?
– Oculomotor system: moves the eye in the orbit
– Head movement which moves the orbit in the space
– Information of head motion processed by the vestibular system
3. Three Axes of Eye Rotations
1. Ductions refer to monocular movements of each eye
2. Versions refer to binocular conjugate movements of both eyes
3. Vergences refer to binocular disjunctive movements
10. Up and to the Left Indicates: Visually Constructed Images (Vc)
If you asked someone to "Imagine a purple buffalo", this would be the
direction their eyes moved in while thinking about the question as they
"Visually Constructed" a purple buffalo in their mind.
11. Up and to the Right indicates: Visually Remembered Images (Vr)
If you asked someone to "What color was the first house you lived in?",
this would be the direction their eyes moved in while thinking about the
question as they "Visually Remembered" the color of their childhood
home.
12. To the Left Indicates: Auditory Constructed (Ac)
If you asked someone to "Try and create the highest the sound of the pitch
possible in your head", this would be the direction their eyes moved in
while thinking about the question as they "Auditorily Constructed" this
this sound that they have never heard of.
13. To the Right Indicates: Auditory Remembered (Ar)
If you asked someone to "Remember what their mother's voice
sounds like ", this would be the direction their eyes moved
in while thinking about the question as they "Auditorily
Remembered " this sound.
14. Down and to the Left Indicates: Feeling / Kinesthetic (F)
If you asked someone to "Can you remember the smell of a
campfire? ", this would be the direction their eyes moved in
while thinking about the question as they used recalled a
smell, feeling, or taste.
15. Down and To the Right Indicates: Internal Dialog (Ai)
This is the direction of someone eyes as they "talk to
themselves".
16. Brain area participate in Visual Fixation
The cerebral structures involved in
fixation are:
Parietal eye field (lateral
interparietal area and area 7a in
monkeys)
V5 and V5A (MT and MST in
monkeys)
Supplementary eye field
Dorsolateral prefrontal cortex
The brainstem structures involved
in fixation are:
Substantia nigra pars reticulata in
the basal ganglia
Rostral pole of the superior
colliculus
18. The Visual Fixation System
•The fixation system holds the image of a stationary object on the fovea
when the head is immobile.
•Steady fixation is actually an illusion.
•Normal fixation consists of three distinct types of physiological miniature
movements that are not detectable by the naked eye
19. Eye Movement
Function of Eye Type of Eye Movement
Movement
"Version" (Conjugate) "Vergence" (Disjunctive)
"Holding" (slow)
•Smooth Pursuit
•Optokinetic Nystagmus •Convergence
(slow phase) •Divergence
•Vestibular Nystagmus •Accommodative Vergence
"Catching" (fast)
•Saccades
•Optokinetic Nystagmus
(quick phase)
"Sustaining"
(miniature) •Microsaccades •Tremor
•Drift
voluntary eye movement; involuntary eye movement
20. The Vestibular and Optokinetic Systems
• The vestibulo-ocular and optokinetic reflexes are the
earliest eye movements to appear phylogenetically
• The vestibulo-ocular reflex (VOR) stabilizes retinal
images during head motion by counter-rotating the eyes at
the same speed as the head but in the opposite direction
• Optokinetic eye movements stabilize the eyes during
tracking of a large moving visual scene, which causes an
illusionary sensation of self rotation (circularvection) in the
opposite direction
21. Types of Head Motion
1. Rotation : A change in orientation
2. Translation: A change in position
22. Characteristics of the VOR
The VOR stabilizes retinal images during brief head movements by
counter-rotating the eyes at the same speed as the head but in the
opposite direction
27. The Optokinetic System
•Optokinetic nystagmus is induced
reflexively by motion of a large
visual scene, which causes an
illusionary sensation of self-
rotation (circularvection) in the
opposite direction
•Whereas the angular VOR
responds best to brief, high-
frequency head rotation, the
optokinetic system maintains
retinal image stability during
sustained, low-frequency rotation
