10d eye movement control

Visual Tracking and Fixing

Visual Tracking

bull Why Visual Tracking

ndash To keep the image in the Fovea which is less than 1mm size and

detect visual field of less than diameter of full moon

ndash 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

bull How Visual Trackingndash Oculomotor system moves the eye in the orbit

ndash Head movement which moves the orbit in the space

ndash Information of head motion processed by the vestibular system

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

Extra Ocular Muscles

Extra-ocular muscles nerve supply

Actions of Extra-ocular muscles

Laws of Ocular Motor Control

1 Sherringtons law of reciprocal innervation

2 Herings law of equal innervation

Six Cardinal Position

Visual Accessing Cues

Richard Bandler and John Grinder Frogs into Princes Neuro Linguistic Programming (NLP)

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

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

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

To the Right Indicates Auditory Remembered (Ar)

If you asked someone to Remember what their mothers voice sounds like this would be the direction their eyes moved in while thinking about the question as they Auditorily Remembered this sound

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

Down and To the Right Indicates Internal Dialog (Ai)

This is the direction of someone eyes as they talk to themselves

Brain area participate in Visual Fixation

The cerebral structures involved in fixation are

1048708 Parietal eye field (lateral interparietal area and area 7a in monkeys)

1048708 V5 and V5A (MT and MST in monkeys)

1048708 Supplementary eye field

1048708 Dorsolateral prefrontal cortex

The brainstem structures involved in fixation are

1048708 Substantia nigra pars reticulata in the basal ganglia

1048708 Rostral pole of the superior colliculus

An Active Fixation System Keeps the Eyes on a Stationary Target

The Visual Fixation System

bullThe fixation system holds the image of a stationary object on the fovea when the head is immobile

bullSteady fixation is actually an illusion

bullNormal fixation consists of three distinct types of physiological miniature movements that are not detectable by the naked eye

Function of Eye Movement

Type of Eye Movement

Version (Conjugate) Vergence (Disjunctive)

Holding (slow)bullSmooth Pursuit bullOptokinetic Nystagmus (slow phase) bullVestibular Nystagmus

bullConvergence bullDivergence bullAccommodative Vergence

Catching (fast)bullSaccades bullOptokinetic Nystagmus (quick phase)

Sustaining (miniature) bullMicrosaccades bullTremor

bullDrift

voluntary eye movement involuntary eye movement

Eye Movement

The Vestibular and Optokinetic Systems

bull The vestibulo-ocular and optokinetic reflexes are the earliest

eye movements to appear phylogenetically

bull 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

bull 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

Types of Head Motion

1 Rotation A change in orientation

2 Translation A change in position

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

The Horizontal VOR Pathway

The Vertical and Torsional VOR Pathway

The Otolith-Ocular Pathway

VOR Adaptation and the Cerebellum

The Optokinetic System

bullOptokinetic nystagmus is induced

reflexively by motion of a large

visual scene which causes an

illusionary sensation of self-

rotation (circularvection) in the

opposite direction

bullWhereas the angular VOR

responds best to brief high-

frequency head rotation the

optokinetic system maintains

retinal image stability during

sustained low-frequency rotation

The Saccadic System Points the Fovea Toward Objects of Interest

Saccads during reading

Pulse-Step of Innervation for Saccadic Eye Movement

Extraocular Motor Signal Eye Position and Velocity

Central control of Horizontal Saccad

Brainstem Generation of Vertical and Torsional Saccades

Cortical Pathway for Saccades

Summary of Central Control of Saccades

The Smooth Pursuit System Keeps Moving Targets on the Fovea

Gaze Involves Combined Head and Eye Movements

Cortical control of Pursuit Eye movement

Summary of Central Control of Pursuit Eye Movement

Vergence Eye movment

Neural Substrate of Vergence Eye Movements

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