CHAPTER 6 –LECTURE NOTES
We can make torsional head movts but can’t do torsion eye movements voluntarily.
Not good sign if you can do torsional eye movements voluntarily
You cannot fixate completely steadily when u rotate your head because your eyes make counter rotations
Superior and inferior make torsional movements
Axons radiate out and form the cranial numbers. The cranial nerves are named after the nuclei out of which the axons grow.
The occulomotor neurons send out axons which form the cranial nerve 3, called occulomotor nerve.
4 of the 6 muscles are innervated by the occulomotor nerve.
The trochlear nerve si innervating muscle f the eye on opposite side :superior oblique
Abducens innervate the lateral rectus
Basic level of control __^
More higher control level:
Some structure in cortex innervate Superior colliculus- in midbrain.on the brain stem.also has more than one map. topographical
Visual pathways go directly to superior colliculus besides going directly to cerebral cortex.
Quick movts are controlled by sup.colliculus.
Type of eye movements
Smooth pursuit: following an object with your eyes as the object moves
- Quick test
- When you are following an object, the rest of the world stays stable.
- There is no movt of the finger/object relative to your eye yet we get the perception that the finger is moving
- The moving object stays fixated on the retina, no movt of the finger relative to your eye yet you perceive the finger to be as
- ~~when movt on the retina you perceive it as moving
- When you tap eye, it appears as if the world is moving.misperception of the movt.
- So if there is movt on the retina, u attribute to the outside world and some movts on the retina and u dismiss it.
- Purpose of smooth pursuit is to keep something out in the world that you are fixating stable on the retina. Advantage :
everything that is stable on the retina is better perceived.
Saccades: jerky movements. seen when someone is reading. when jump from one word to next. Rapid eye movts. dispersed with
Fixation- when you try to keep your eye movements stable.
Tiny little saccades called microsaccades. Eyes are moving all the time even when you aer trying to keep them stable.
Vergence – the two eyes can converge or diverge when you fixate something farther away.
- Are performed by both eyes together
Tapping the eye : appears world moving
And can create condn where misperceptions of world as moving
~Perceptual Problem that needs to be distinguished by our nervous system: movement by the eye or motion caused by something
Similar effects can be observed with saccadic eye movts.
Saccadic eye movts: false motion, u see false motion.
Retinal smear are caused by photoreceptors being slow, so the afterimages of lights etc, little streask of light after images.
Yarbus: scanpaths are depended on cognitive things. Can reveal intentions. Scanpaths change depending on the intentions. If she
speaking, focus on mouth. If checking out her eye colour, scanpaths shifts to eye.
10,0000 of saccades every single day. Ppl don’t perceive that they are making saccadic eye movts.
How come we don’t perceive eye movts?
-our ability compensate for problems/errors such as movt of retian causing world to move around caused by saccade movts.
Why does this happen?
Mechanism: saccadic suppression During saccade eye movt, vision is reduced in certain way, reduced contrast and motion perception.
Helps us ignore retinal image smear.
Motor commands are also called efference copies.
Efference copy – a motor command of the brain. send to sup. colliculus then to eye muscles but also send to back to brain. Brain
uses efference copy to ignore uninteresting sensory information.
- Are simiilaetd sensory signals and informs the brain what the eye muscles are more likely will be doing
- The brain is telling itself that it just send out this command
- It can predict within few msec eye muscles will contract
- Efference copies is used everywhere not just for saccadic eyemovts.
Example : Why does it tickle when friend tickles but not when you do it yourself, same sensation, no?
-b/c your brain knows exactly whats the fingers doing. b/c the brain is sending out commands and the efference copy si telling your
brain that I am doing tickling.
Efference copy also called corollary discharge
Neurosn through superior colliculus control eye muscles
Corollary discharge Is fed back into the cerebral cortex to the comparator.
Visual input is also going directly to the comparator.
you wouldn’t see any movt if the comparator sees that the two signals are exactly the opposite!
Limits of compensation theory:
Perisaccadic misperception: is the following experiment.
- A participant told to make eye movement to a target, you make the eyemovt
- New stimulus is briefly flashed on the computer screen
- Then the stimuli disappears
- Make yee movt
- Asked where did u see that stimulus flash
- Results: p’s often see the stimulus flash shifted toward the saccade
- You see stimulus shifted in the direction of the saccade. Is a misconception. Not caused by the eye movts themselves
because the stimuli is flashed before making the eyemovt.
- Befor e making the eye movt, the world is shifting slightly in the direction of the saccade movt
~our ability to compensate for eye movt is limited. There ARE brief moments of time where the world shifts.
Euclidean geometry: no matter where u stand, the roof of the house and the ground would always be parallel.
Only one sense that is governed by Euclidean geometry: touch.
Euclidean geometry works for touch but not for vision!
Why it doesn’t work for vision because lights from 3D are projected on 2D surface of our retina. Change in
geometry when going from 3D to 2D.the geometry is not the same anymore.
Parallel line receding in depth would converge.
Parallel lines would stay the same if they are planar.
We have distortions because of change of geometry can be used to reconstruct 3d world from 2D images projected on
to our retina.
The 2 retinal images are not the same because they are spaced apart and not in same location.
Parallax- To the right eye, the image is to the left and vice versa for left eye.> depends on which eye yo