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34. Eye Movements
Degree: NEUR 3002
V 1.0 Haydn Allbutt (18/6/2015)
Notes:
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The Optokinetic tank and Bárány chair activity were filmed in 2014, and this
video was shown instead of the demonstration described here.
The Bárány chair was moved to the CPC for both the MED and the
NEUR3002 version of this class. In 2015 the NEUR3002 class is in week 12,
while the Med class is 3 weeks before semester starts. The Bárány chair
needs to be moved to the CPC by removalists, so will need to be stored
during the semester.
Not clear yet (as of 30/1/2015) what the course coordinators will do for this
class this year.
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34. Eye Movements
Degree:
NEUR 3002
Convener:
Dario Protti
Date and time of Classes (for 2014):
 Mon 30/3/15
2pm – 6pm
 Wed 29/4/15:
2pm – 6pm
No. of Classes:
Micro 1 & 2
FDS 1 & 2
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No of students per class: ~100
Students working in groups of: N/A
Class Summary
In this class various mechanisms and reflexes that control eye movement are
demonstrated to the students using a volunteer subject. Electrodes are placed on
the outside of the eyes to measure EMG of the ocular muscles which can then be
displayed to demonstrate the eye movements using LabChart.
Saccadic eye movement – looking at marks on wall (Bárány chair)
Small saccades – reading passage of text (Bárány chair)
Smooth trace – following ping pong ball (Bárány chair)
Optokinetic Tank – effect of fixation on eye movements
Vestibulo-ocular movement – Eye movements when blindfolded (Bárány
chair)
6. Fine motor control when dizzy – touching finger when dizzy (Bárány chair)
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Special Notes for class
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This class needs to use the Bárány chair from the Anderson Stuart Building –
prior to the class the chair will need to be brought down to the CPC by
removalists
In 2015 we have organized to keep the chair in the Basement Store room
(the dark room) until it is used in the Neuro Classes later in the semester.
Will move the chair back up to the Anderson Stuart Building once the Neuro
Classes have finished
The optokinetic tank that use to attach to the Bárány chair was too big to
bring down to the CPC so this activity is potentially not going to be used in
this class.
Before this class you have use a string and protractor to place 3 x sticky tape
strips on the wall 20° apart (outer 2 will be 40° apart)
Equipment Setup
Students are given an introductory talk on eye movements and the reflexes that are
in place in order to move the eyes and keep them fixated on objects. This prac is
performed as a demonstration on a volunteer student.
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Equipment
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Bárány chair
Human Bioamp
Set of electrodes to attach to ECG electrodes
Ping pong ball
ping pong ball track on a pole
Vestibular apparatus model
Powerlab
Laptop
Scope program
Consumables
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3 x ECG electrodes – two of them cut to go on lateral aspect of eyes
The Activities Performed
There are a series of different demonstrations performed in this class to
demonstrate different aspects of the reflexes necessary for various eye tracking
movements. All exercises have the electrodes attached.
Cutaneous electrode dots are attached on the temples (ECG electrodes), in line
with the eyes.
Third (earth) electrode goes on the left ankle.
Electrodes attached by alligator clips, then attached to the human bioamp, which
sits behind the Bárány chair. Always zero the amp before any recording. The zero
button is located on the amp (red button).
1st exercise – Saccadic eye movement
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Record using chart, Need to set a high sample rate so that you can measure
the time taken for the very quick saccades
Get subject (sitting on chair) to look at the back of the room and move their
eye between three marks (piece of black gaf tape on the wall that are set 40°
apart.
Instruct students to look at particular points marked with tape (ie, left, middle,
right)
Tell subject to not move head, move eyes only.
From left to middle bottle = 40°
From left bottle to far right bottle = 80°
You can figure out the average degrees per second
Rate of saccade from zero to 80° should be double that from 0 to 40°
degrees
Can’t control rates of saccades
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Trace on chart will look something like the following
2nd exercise- small saccades
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Get the student to silently read a passage of text
Use chart to record a trace while student is reading
After reading, zoom up on a step, make sure it’s a smoothish one, it should
look something like the pattern below
Each vertical step in the trace is an eye movement as the eyes move to a new set
of words, each horizontal step is the amount of time the student paused to
comprehend the words. Less able readers will take in fewer words at a time and so
there will be a greater number of steps per line of text. A good reader will take in a
number of words at once and so there will be fewer saccades per line of text.
You can count the number of steps, and count how many words are in the line to
see if they read each word individually or group words together.
If the subject re-reads a word or skips back the trace will have a dip in it.
3rd exercise – smooth trace
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Get subject to follow ping pong ball as it rolls across the rail.
When recording, overlap the traces
Remind the subject to use their eyes only, do not move head
Record as subject follows ball movement
Next get the subject to repeat the eye movement but without using the ball,
get them to pretend they are following the ball with their eyes
Results
You will notice that the trace is smooth when the subject is tracking a ball but when
there is no ball their eyes will move in small steps.
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The trace should look similar to the image below:
The blue line is the smooth pursuit when following ping pong ball. The black line is
when there is no visual stimuli to follow.
4th exercise – Optokinetic Tank
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Student sits in chair, drum gets lowered
Get subject to slightly tilt head down, have eyes open facing forward, keeping
head still.
The visual stimulus is presented by spinning the drum
The eye movements produced by the moving visual stimulus are recorded.
When the tank is rotating anticlockwise the trace should look something like the
image below:
When the tank is rotating clockwise the trace should look something like the image
below:
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Next, repeat the activity and get subject to try their absolute hardest to look
straight ahead and not move their eyes
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Result
The student will find they can’t since it’s a natural reflex for the eye to fixate on a
moving pattern of high contrast and follow it to the periphery of the visual field and
flick back. This is referred to as the optokinetic reflex.
5th exercise – vestibulo-ocular movement
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This exercise uses the Bárány chair
You need to unplug the output of amp and plug in the BNC cable that is
attached to the chair, the other end of this cable is stowed away under the
platform, plug this into the output on powerlab
NB: since the chair spins you can’t have cables running from the subject to any
external devices. The chair has its own connection for this activity which transmits
via contacts in the pivot supporting the chair.
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Get subject to sit in chair, blindfolded with seat belt on.
Subject should tilt their head forward slightly to put their horizontal
semicircular canals on a properly horizontal plane
Spin chair (chair moves clockwise) and record the effect on the eye
movements of the subject
Spin long enough for trace to flatten out a little, then stop, but continue to
record.
Result
Initially the subject will have the sensation of spinning. As they continue to spin at
the same rate they will get use to the movement and the sensation of spinning will
become less pronounced. When the chair stops the subject should get the
sensation that they are spinning in the opposite direction as the fluid in their
vestibular apparatus will continue to move though their body has now stopped.
The eyes of the subject will track when they are spun in order to keep their visual
field stationary even though they are now moving. As the fluid in the vestibular
apparatus speeds up to move at the same rate as the body of the subject the hair
cells in the apparatus are deflected less and so the eye movements will be less
pronounced. When the rotation is stopped the fluid in the vestibular apparatus will
keep moving even though the body has stopped so now the hair cells are deflected
in the opposite direction. Thus when the subject stops the eyes will begin moving in
the opposite direction.
This is referred to as the vestibulo-ocular reflex.
The trace from this will look similar to the image below:
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To demonstrate what the hair cells are doing in the vestibular apparatus, the clear
plastic tube with the red disks suspended in it, which is a model of the vestibular
apparatus, is used.
The model is placed onto the Bárány chair and the chair is turned on. When the
model spins the water inside is initially stationary and so the red valves are
deflected as the tube and the valves slide by it. After a while the water begins to
rotate with the tubing and so is now flowing at a similar pace to the tubing and so
the red valves are not deflected as much. When the chair is stopped the water
keeps moving inside the tubing and so the red valves are deflected in the opposite
direction as the water moves through the now stationary tubing and valves.
6th exercise
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Spin the student again on the chair blindfolded.
As soon as chair has stopped spinning get subject to take blindfold off, and
get them to touch the demonstrators finger.
Definitions
Eye saccades are quick, simultaneous movements of both eyes in the same
direction. Initiated by eye fields in the frontal and parietal lobes of the brain,
saccades serve as a mechanism for fixation, rapid eye movement and the fast
phase of optokinetic nystagmus. The fovea shifts to a visual target in the periphery.
Smooth pursuit is the ability of the eyes to smoothly follow a moving object. It is
one of two ways that visual animals can voluntarily shift gaze, the other being
saccadic eye movements. Pursuit differs from the vestibulo-ocular reflex, which only
occurs during movements of the head and serves to stabilize gaze on a stationary
object.
Vergence is the simultaneous movement of both eyes in opposite directions to
obtain or maintain single binocular vision. Vergence movements are closely
connected to accommodation of the eye. Under normal conditions, changing the
focus of the eyes to look at an object at a different distance will automatically cause
vergence and accommodation.
The vestibulo-ocular reflex (VOR) or oculovestibular reflex is a reflex eye
movement that stabilizes images on the retina during head movement by producing
an eye movement in the direction opposite to head movement, thus preserving the
image on the center of the visual field. For example, when the head moves to the
right, the eyes move to the left, and vice versa. Since slight head movements are
present all the time, the VOR is very important for stabilizing vision
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The optokinetic reflex allows the eye to follow objects in motion when the head
remains stationary (e.g. observing individual telephone poles on the side of the road
as one travels by them in a car).
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