PSYB51H3 Lecture Notes - Lecture 6: Superior Colliculus, Efference Copy, Smooth Pursuit

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Published on 19 Apr 2013
School
UTSC
Department
Psychology
Course
PSYB51H3
PSYB51
October 22nd, 2010
Lecture 6:
- we need exactly 6 muscles to control eye
movement
- So there are 3 dimensions to locate an
object in space
- Also the orientation of the object in
space (3 possible axis for orientation = x-,y-,z-axis)
[So axis on which an object could rotate 3 possible axis]
So an object can be described in terms of 6 dimensions: 3 for location & 3 for
orientation/rotation
- So why 6 muscles?
You need 2 muscles: 1 for pulling back while another for the pulling in
opposite direction (to rotate on one axis)
REMEMBER: MUSCLES ONLY CONTRACT OR RELAX (2
MOVEMENTS!)
So we have 3 rotation dimensions & therefore 6 muscles!
So for every rotation dimension > we have 2 muscles!
- Muscles controlled by the brain indirectly
Eye movements by itself isn’t perception but they are very significant
FOR perception
- These cranial nerves are named after the nuclei out of which the axons grow
e.g. Ocumotor nucleus [in the brain stem] fans out axons that form the cranial nerve # 3 (also called the
ocumotor nerve)
- 4 out of 6 muscles are innervated by THE OCULOMOTOR NERVE while the TROCHLEAR NERVE
(CRANIAL #4) innervates the muscle of the eye on the opposite side (superior oblique) & the ABDUCENS
NERVE innervates the (lateral rectus) muscle.
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PSYB51
October 22nd, 2010
Superior colliculus: eye movements can be controlled
through this short-cut
So visual input not only going through the primary
pathway we talked about in previous lectures but also
directly going into the Superior colliculus and from
there directly into motor control regions within the
Superior colliculus and down to the muscles = this way
you can make very quick eye movements
How does a smooth pursuit
eye movement help us
perceive moving objects?
In smooth pursuit eye
movements, the eyes
smoothly track a moving
object, allowing better
extraction of visual detail from
the object as well as providing
an estimate of the object’s
velocity.
- Saccades: performed when reading for example
- Fixational eye movements: what you show when you try to keep your eyes
stable
- Micro saccades: eye shifts a little all the time even though you try and keep
the eye stable
- What is the role of the vergence eye movements?
Vergence eye movements are helpful when one is focussing on a near or far
object. In this type of eye movement the two eyes move in opposite
directions: they either diverge outward, or converge inward. [they do the
movements together = both the eyes move together not independently]
Superior colliculus: A structure in the
midbrain that is important in initiating
and guiding eye movements.
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PSYB51
October 22nd, 2010
Function of smooth eye...: B/c
something that is stable on the
retina will be perceived better as
the photoreceptor are SLOW in
the retina = it takes a certain
amount of light stimulating
them
So keep the eyes stable
for some time to “catch” enough photons
So why don’t we notice making eye movements?
Why don’t we don’t really perceive these eye
movements?
Why is saccadic suppression
important in motion
perception?
Saccadic suppression is important
in motion perception because it
eliminates the smear from retinal
image motion during an eye
movement. Saccadic suppression
results in a brief reduction of
visual sensitivity while the eye
makes a saccadic eye movement.
What kind of problem does the
comparator solve?
During the saccadic eye movement we
have reduced contrast perception and
reduced motion perception
This helps us avoid/ignore retinal
image smear
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Document Summary

We need exactly 6 muscles to control eye movement. So there are 3 dimensions to locate an object in space. Also the orientation of the object in space (3 possible axis for orientation = x-,y-,z-axis) [so axis on which an object could rotate 3 possible axis] So an object can be described in terms of 6 dimensions: 3 for location & 3 for orientation/rotation. Eye movements by itself isn"t perception but they are very significant. You need 2 muscles: 1 for pulling back while another for the pulling in opposite direction (to rotate on one axis) So we have 3 rotation dimensions & therefore 6 muscles! So for every rotation dimension > we have 2 muscles! These cranial nerves are named after the nuclei out of which the axons grow e. g. ocumotor nucleus [in the brain stem] fans out axons that form the cranial nerve # 3 (also called the ocumotor nerve)

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