Eye Movement and Sensorimotor Integration Flashcards
Why do we move our eyes?
High visual acuity restricted to a small area (the fovea)
Eye movement direct the phobia to objects of interest, or ‘foveate’
You can learn a whole lot about how people are acquiring information by examining their eye movements
Also incredibly important as a clinical assessment tool
“foveate”
keeping our fovea on the object of interest to gain information about features of the object
How do we move our eyes?
Three antagonistic pairs of muscles control eye movements
- Lateral and medial rectus
- Superior and inferior rectus
- Superior and inferior oblique
We have three axes of eye movements
- Horizontal, adduction and abduction (towards or away from the nose)
- Vertical, elevation or depression (up or town)
- Torsional, intorsion or extorsion (towards or away from the nose)
Extraocular muscle innervation
Extraocular muscles
Innervated by lower motor neurons in cranial nerves
- Abducens (VI): Lateral rectus
- Trochlear (IV): Superior oblique
- Oculomotor (III): All the rest, plus eyelid, pupillary construction (medial rectus, superior, inferior rectus, and inferior obliques)
Name the 5 basic types of eye movements
Gaze
Stabilize
Saccades
Smooth Pursuit
Vergence
Gaze
moving eyes to an object of interest
via saccades, smooth pursuit, vergence
stabilizing eye movements
keeps eyes on object of interest
vestibuloocular or optokinetic movement
Describe saccades
- Rapid
- Ballistic (…well not really, but we can pretend)
- Change the direction of fixation
- Can be small (like when reading) or large while searching a visual scene
- Can be voluntary or reflexive
- Occur during REM sleep
How long does a saccade take?
200 ms to process, 80 ms to actually move eyes
Describe smooth pursuit eye movements.
Slower tracking movements
Used to keep fovea on target
sort of voluntary
- we can choose whether to track an object, but require training to smooth pursuit without a target.
Describe smooth pursuit’s speed limit.
We have catch-up saccades to get to where the object is if it’s moving faster than we can smooth pursuit.
Once they’re oriented, and if the object is moving slowish, we can smooth pursuit right along with the object movement.
Describe vergence eye movements
Align the fovea of each eye with targets located at different distances
Most common when shifting gaze between objects of different depths
Disconjugate movements
Describe VOR/ OKN types of movements
Operate together
Move the eyes to stabilize gaze relative to the external world
Compensate for head movements
Prevent retinal slipping (object getting outside of foveal vision)
VOR is based on sensory information from the semicircular canals
OKN is based on large portions of the visual field moving
Looking out a car window (optokinetic nystagmus): typewriter example
VOR is a reflection of ____ movement, while OKN is a reflection of _____ movement.
self; world
or
fast; slow
The brain controls what two aspects of a saccade? What allows the brain to know the amplitude of the saccade?
Brain needs to accomplish two tasks
- Control direction of saccade
- Control amplitude of saccade
Amplitude is coded by the duration of neuronal activity within the oculomotor nuclei
Neural control of saccades: how is direction of eye movement determined?
Direction is determined by which eye movements are active
Controlled by local neuron circuits in two gaze centers
- Paramedian pontine reticular formation (PPRF or horizontal gaze center)
- Rostral interstitial nucleus (vertical gaze center)
Activating each system separately results in uni-axis movements
PPRF also sends axons to medullary reticular formation, to inhibit contralateral muscles
“etch-i-sketch”
neuron control of saccades: how is the location of the stimuli transformed to appropriate activity in gaze center?
Our old friend the superior colliculus
Several frontal and parietal lobe regions
FEF, MEF, SEF, DMFC (Frontal)
LIP, MT, MST (Parietal
Superior colliculus and FEF contain topographical maps
How does the cerebral cortex play a role in neural control of saccades?
Cerebral cortex regions concerned with eye movements collaborate with superior colliculus in controlling saccades
- FEF, for example, can control eye movements by activating selected populations of SC neurons
Cerebral cortex regions also can control eye movements directly
- FEF –> Contralateral gaze centers
Allows for some sparing of eye movements following damage!
- To either cerebral cortex or brainstem
Describe the neural contro of smooth pursuit eye movements.
We have it easy
Once thought to be mediated by different structures (more to know!)
Now, it is believed that smooth pursuit is controlled by many of the same structures as saccades
- Gaze centers, SC, Frontal and Parietal eye movement regions
Neurons in striate and extrastriate cortex provide sensory information necessary to guide smooth pursuit
Damage to occipital and parietal lobes can result in abnormalities in smooth pursuits (sobriety test)
Neural control of vergence.
We know very little about how these movements are performed
Information about location of retinal activity is relayed through the LGN to cortex, where information from the two eyes is integrated
Amount of binocular disparity is used by extrastriate regions to determine whether eyes should diverge or converge
Information sent to vergence centers in the brain stem
- Some populations of neurons command convergence movements, others divergence movements
Describe sensorimotor integration within the superior colliculus
Superior Colliculus
Superficial visual layer and deeper motor layer
Visual and motor maps were are in register
- Visual cells that respond to a certain region of space are connected to deep layer that controls eye movements to the same region
