8. Eye Movements 1 & 2 Flashcards
Eye movement is the movement of?
Movement of the brain itself because the eye is not a peripheral organ.
Retina is what type of tissue?
Brain tissue
Do eye muscles have monosynaptic strech reflex?
No
What does each movement have in unique?
Each EM has its own function, stimulus, anatomic & physiological pathway.
Also, this movements can occur simultaneously at the same time.
What is saccade?
The fastest eye movement that can be made. Hence, to record saccades a high sampling rate is required.
Eyes have how many muscles?
6 muscles that exists in pairs.
How many axis for eye movements?
3 axes
1. Vertical axis- movement of eyes horizontally.
2. Horizontal axis- movement of eyes vertically.
3. Visual axis- along the fovea at the centre of the pupil, controls torsion of the eye.
2 overall functions of eye movements?
- Maintain a stable view of the world
- Redirect the line of sight
What are the 2 compensatory (Reflective eye movements)? And the role of this movements?
VOK & OKN
Role: correct eye movements to keep the view stable
Saccades meaning?
Change in gaze independent to head orientation.
Smooth pursuit movement?
Follow a (Slowly) moving target.
Vergence meaning?
Enlarge binocular field/ reduce disparity.
3 eye movements that redirect line of sight (Fovea)
Saccades, smooth pursuit & vergence
Vergence is said to be the only disjunctive eye movement, what does this mean?
eyes move in opposite directions
Effect of inertial mass on eye movements humans vs birds
Humans have a smaller inertial mass of eyes compared to birds. Hence, in birds the head moves to create movements whereas in humans eyes move.
Primates have frontally faced eyes but animals have laterally orientated eye, hence they require a special system to main stable gaze. what is the special system for birds?
Head bobbing in birds
Influence of eye movements?
Disturbance to the stable view of the world
Land’s observation?
All animals have the same five visuomotor movements.
Mittelstaedt’s hypothesis?
Saccadic systems are designed to localize objects in space.
Most eye movements are conjugate- what does this mean?
Eyes moves together
What is the relationship between head movements?
Gaze
Stability of vision is the same as stability of gaze- what does this mean?
This is the stability gaze that is stability of retinal image on the fovea
3 Classifications of eye movements?
- Compensatory/ stabilizing OR targeting.
- Conjugate or disjunctive
- Visual vs non- visual stimulus (VOR)
2 Compensating eye movements?
VOR - Vestibulo-ocular reflex
OKN- Optokinetic Nystagmus
3 Targeting movements?
Saccades, Smooth Pursuit and Vergence
Which eye movement has no visual stimulus?
VOR
Role of VOR
Stabilises gaze ensuring clear vision during head movements. It is non-visual stimulus
Non-visual stimulus is driven by?
Afferent signals from the inner ear canals.
VOR compensates for?
fast, transient head movements
VOR takes place in what light conditions?
Dark and light
Which system kicks in when trying to maintain a stable gaze?
VOR
VOR is unconscious or conscious?
Unconscious
VOR driven by which system?
Vestibulo system
VOR nystagmus meaning
The eyes are trying to maintain stable gaze for as long as possible THEN it snaps- this is called slow & fast phase.
What is the fastest movement made in terms of latency?
VOR
Implications of large head movements and fast movements?
Large head movements, beyond limit leads to fast phase correction.
Fast movements cause retinal slip- Because VOR IS not compensating for complete head movements.
Slow vs fast phase eye movements in relation to head movements?
Slow phase: opposite direction to head movement.
Fast phase: same direction to head movements.
OKN Role?
Stabilizes gaze ensuring clear vision during movements of the visual field (world).
Visual stimulus of OKN?
Retinal slip or Optic flow
OKN compensates for?
Fat and transient movements
OKN has a speed limit?
Yes
OKN can not compensate for very very fast motion
OKN generates slow phase movements in which direction?
Slow phase movements generated in the same direction and velocity as perceived retinal slip.
When OKN reaches its maximum limit it produces?
Quick “reset” phase called saccade
Saccades or Pursuits - which movement needs a stimulus?
Saccades do not require a stimulus. They can also be made from memory. Pursuit needs a stimulus.
Ballistic movement?
React to 1 stimulus at a time, then a refractive period (i.e., latency period).
Main sequence?
Correlation between amplitude, duration and velocity. This sequence is used to compare normal Px’s with abnormal Px’s.
Saccadic suppression?
Inability to see anything during a saccade.
When a saccade is executed there is suppression of?
Conscious vision in V1
Relation between duration and amplitude of saccade?
Linear relationship
Relationship between peak velocity and saccadic amplitude exists because?
Because of action potential of motor neurons driving the muscles making the saccade.
Duration and velocity of a saccade is driven by?
Duration- bust of firing in the motor neuron
Velocity- by the frequency of action potential
Saccadic suppression is suppression of?
Low spatial frequency
Saccadic suppression involves which pathway?
Magnocellular at LGN
Which system is suppressed in smooth pursuit?
OKN
Smooth pursuit is driven by?
vestibular NUCLEUS
Slowest eye movement is?
Vergence
How can the speed of vergence be increased
If combined with saccades
Stimuli for vergence?
-Blur = accommodative vergence (provoked by changing lens)
-Disparity = fusional vergence (provoked by changing prism)
Retinal ques that provoke accommodative response?
Objects temporal to the fovea- interpreted as closer, nasal to the fovea- interpreted as far.
Parallax is?
Non-retinal que on distance of objects
Visuomotor control is restricted by how many axes?
3
How does the brain identify if change in retinal image is due to objective motion or subjective motion?
Brain has a system called efference control center. The brain gets a copy of efference output which is compared against retinal shift.
