VF - Eye Movements 1 - What & Why? - Week 5 Flashcards
What are the advantages and disadvantages of having frontal eyes?
Advantages
Facilitates stereoscopic vision, precise estimates of depth can be obtained.
Disadvantages
- Limited visual field, allowing for vulnerability to rear/side attacks.
- Any slight misalignment of the eyes will affect vision.
What are the advantages and disadvantages of having lateral facing eyes?
Advantages
Extremely wide visual field.
Disadvantages
-Little binocular overlap, visual acuity is generally poor.
What perfentage of the retina does the fovea make up, and how much of the optic nerve does it contribute to?
5% of the retina
50% of the optic nerve
How can fixation patterns be important clinically?
Fixations on faces normally follow stereotyped patterns. Deviations can sometimes indicate a disorder.
Define saccadic suppression.
Our brain receives a sequence of clear images (where the fovea is focusing) surrounded by blurriness.
Instead we perceive a single, clear, sharp image.
The brain selectively blocks visual processing during eye movements in such a way that large changes in object location in the visual scene during a saccade or blink are not detected.
Describe the reflexive saccade, the part of the eye that is involved, the features of the cells involved, and whether or not high visual acuity is needed.
High visual acuity is not needed, only need to detect a change.
The peripheral retina is involved, via fast-acting, change-sensitive cells.
Describe the dorsal and ventral stream hypothesis for primate visual systems. Mention what each pathway is responsible for, and what input it is dominated by.
Dorsal - Works out where something is, dominated by magnocellular inputs.
Ventral - Works out what something is, dominated by parvocellular inputs.
Describe an instance of optokinetic nystagmus.
Looking out a train, and watching the moving scenery, and your eyes make quick saccades as you reach the limit of the field.
Describe the vestibulo-ocular reflex. Give two examples that demonstrates it, and the sensory stimulus in both cases.
A rotation of the head is detected, which triggers an inhibitory signal to the extraocular muscles on one side and an excitatory signal to the muscles on the other side. The result is a compensatory movement of the eyes.
1. Youre moving and your fixation target is stationary.
2. Youre moving, and your fixation target is moving with you.
The sensory stimulus is the same in both cases.
What is the vestibulo-ocular reflex driven by?
Head motion.
Where does the sensory organ for the vestibulo-occular reflex lie, and what do they most directly respond to?
They lie in the inner ear, and respond most directly to acceleration, including gravity, making this crucial for balance.
Give evidence of the vestibulo-ocular reflex using trains departing as an example.
Consider sitting in a stationary train besides another stationary train.
The train youre sitting in begins to move, but after a while you realise it wasnt your train moving, but the train beside you that was leaving, giving the impression your train was moving.
Can humans move their eyes in different directions?
No, unless they suffer from unusual pathology.
The only exception is vergence, crucial for maintaining binocular vision.
