NROC64: Lec 9: Gaze Control and Spatial Constancy (nearly word-for-word what was said in lec)

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29 Mar 2012
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Lec 9: Gaze Control and Spatial Constancy
-usually eye movements correspond with attention
-eye movements are motor control that are fairly simple; 3 pairs of agonist/antagonist
muscles only = more simpler than having multiple joints and arm movement etc;
-how motor control works specifically; oculomotor control is quite simple topic
-eye movements special in another way; eye mvts are almost exclusively meant to adjust
your sensation (for perception), meant to change vision = very impt for vision = will move
your fovea to regions where you want to look at
-not necessarily the same as hand mvts; you may use your hands to touch
something (sensation) but then you would also use it for other things = open door
etc;
Short Answer Question:
Why is motor control considered to be redundant? Give an example.
Answer:
Example with Duchenne (genuine assoc w/ emotions) smile and fake smile. 2 patients that
had difficulties with facial muscles; one patient could do Duchenne smile but not the
voluntary smile while the other patient could do fake smile but not the Duchenne smile. It’s
redundant because both are similar functions and it’s innervating for the same facial
muscles for the mouth.
Slide 6: Six kinds of eye movements
Bring fovea to the target and keep it there
oEx) reading and want to look at a word
Saccades & fixations (2 eye mvts that go together)
oMove fovea to target
oUp to 900 deg/s
oSaccade amplitude under voluntary control, not velocity
picture diagram used as a stimulus for research
oMirrors on side of eyes with light shined onto light; movement of eye would
be detected by crystal surface which would be superimposed onto the image
itself
oPicture of little girl and superimposed are traces of eye mvts
oSeen are saccadic eye mvts = lines that connect the knots (the knots are
fixations)
oFixation = very little eye mvt because the eye never stands still; form thick
knots on pictures because eyes aren’t completely stable, they’re moving a
little bit
oGraph: right eye movement as a fxn of time; smooth transition from some
position relatively to the left to some position relatively to the right
This phase here, in terms of ms is pretty quick = less than 50 ms
Saccadic mvts can be btn 2ms – 20 ms; depending on how large the
eye mvts are
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Graph shows that most of the time, eye isn’t moving = fixation time
period; this is so we get the best possible vision
Saccades are meant to move the eye as quickly as possible but
during this phase vision is blurred (this time period is very short)
Normally head movements are smooth but in ppl who have problems with eye
muscles, their head mvts are jerky (b/c lack of eye mvt control)
oNormal ppl do these jerky mvts if they have a tube thru which eye is
looking thru; since only looking thru small aperture, must make jerky head
mvts (eye mvts don’t really help anymore) these are like saccades
Saccades can be voluntary or spontaneous
You cannot determine how fast the saccade will be; there’s not quite a linear
relationship between saccade amplitude and velocity
That’s what’s plotted here: during the saccade, there’s a spike of velocity
Slide 7: Six kinds of eye movements
Eye mvt #3 (smooth pursuit) is also meant to have the fovea on a target of interest
that is moving (ex: reading the letters of a truck that’s going by) have to follow
the letters on the truck with your eyes
Dashed line: is the stimulus that the participant is supposed to fixate on, right where
the eye is looking at; then stepping to 10 degrees to the right side and then slowly
moving to the left side
There’s a little delay, the computer will measure rxn time
The saccade catches up with the stimulus and then pretty much matches the position
and velocity of the stimulus
One of the things that neurologist would test in a patient because normally able to
do that unless you’re older (aging effect) or have some neurological deficit
Slide 8: Six kinds of eye movements
#4: Vesibulo-ocular reflex
Brings fovea to the target outside in the world and keeps it there; compensates for
the head movements
Holding camera, sitting on chair and turning himself around; notice that the eyes
are continuously moving as he’s turning b/c it’s trying to focus on something
Graph: sawtooth pattern
oPlotted as fxn of time; vertical is horizontal eye position
oThere are periods where the eye is moving slowly and there’s a quick phase
(saccade) back to some other position, and then slow phase and another
quick phase and so on = sawtooth pattern
oKind of combo of smooth pursuit and saccade
Driven by the vestibular system
So, trying to keep your eyes stable; your trying to look straight ahead but since your
head moves to one side when you’re spinning, the vestibular system causes your
eyes to counter-rotate this is the slow phase, the velocity during this time would
try to match the velocity of your head rotations but in exact opposite direction
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Why are there quick phases?
oWe can’t infinitely rotate our eyes in our head of course; the limit is reached
at this point and then you just quickly make a saccadic eye mvt to allow that
position to stay there
Slide 9: Six kinds of eye movements
Bring fovea to the target and keeps it there
oOptokinetic nystagmus
Video of eyes looking out the moving train
Looks somewhat similar to the vestibular-ocular reflex except its not driven by the
vestibular system but rather, it’s driven by the optic flow outside the train’s window
So, you have slow phase where you try to follow the stimuli (ex: tree outside) to the
point when it’s not convenient anymore to look at it and then you snap to some
other point, quick saccadic phase somewhere else
This eye mvt is meant to keep the fovea stable on an object
Slide 10: Six kinds of eye movements
6th eye mvt: vergence movement
Stereovision
Brings fovea to the target and keeps it there
Linked with accommodation = naturally accommodating the lens to have sharp
images; near response
Whatever you want to fixate on, you do it in such a way so that you are matching
pieces of the retina; have both retinas look at the same object
Looking at an object at further away, retinas are rotated away from the nose; when
finger closer to the nose, crossing eyes
Slide 12: Six eye muscles because we live in 3D world, therefore 3 dimensions of
translation
For 3D: 3 axes of rotation (L/R, U/D and torsional eye mvts) and 3 dimensions of
translation
Since 3 types of rotations, you need 3 muscle pairs
Each eye has 3 agonist/antagonist muscle pairs
This allows rotations about any axis in 3 dimensions; turning the eye right or left,
up or down, clockwise or CCW
Slide 13: Six eye muscles
Have 4 rectus muscles = run straight
oLateral rectus = one on the side away from your nose on both sides
oMedial rectus = closer to the nose
oSuperior rectus
oInferior rectus
Have also:
oInferior oblique = near lateral rectus and runs under belly of the eye
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