YILDIZ TECHNICAL UNIVERSITY
DEPARTMENT OF B IOMEDICAL
E NGINEERING
EXPERIMENT 6
ELECTROOCULOGRAM I
(EOG I)
Author:
MARWA
ABOUARRA
17.May.2023
1.
OBJECTIVE
The objective of the EOG 1 experiment is to:
1) compare eye movements made when tracking an object in the vertical plane, and while
tracking a pendulum, both in real life and in a simulation by looking at the readings of the EOG.
2) When reading in three distinct ways: quietly (easy), silently and aloud (difficult) records and
compare the "saccadic" eye movements.
2.
THEORY
Figure 1. Cross-section of the eye [1].
The cornea and lens work like a camera's lens when combined. When light enters the
eye, it is bent and concentrated on the retina [2]. The distance between the lens and the film
shifts when focusing a camera. By shifting the lens's shape, our eyes are able to do this. When
focusing on surrounding objects, the ciliary muscle, a circular muscle connected to the lens by a
suspensory ligament, contracts, releasing tension from the suspensory ligament and allowing the
lens to thicken. To concentrate on distant objects, the ciliary muscle relaxes, thinning the lens.
Cones and rods, two different types of light-sensitive photoreceptors, are found in the retina. For
color vision and day vision, cones are utilized. In the fovea, where focused light creates the
sharpest image, they are most concentrated [3]. Rods are used to detect movement in the visual
field and to see in low light. Because rods are concentrated on the retina's periphery, people
prefer to glance away from the fovea when it's dark [4]. Regardless of whether the object is
stationary (still) or moving, the eye's muscular control helps to maintain the image on the fovea.
Visual fixation is the term for this action. To fixate on things in the visual field, which is the
field of vision without moving your head, there are two main techniques used:
1. Voluntary fixation, and
2. Involuntary fixation.
Voluntary fixation involves performing a deliberate attempt to focus your attention on a
particular item in your field of vision and "lock on" to it. This method is used to choose the first
items in your area of vision. Unconscious processes that hold the chosen object in your field of
vision after you've locked on to it are known as involuntary fixation. Your eyes continue to
move in repetitive, unconscious, minute, jerky motions after they have locked onto an object,
known as microsaccades [5]. By slightly moving the position of the retinal picture within the
fovea, these motions prevent perceptual fading, which is a result of the retinal receptor systems'
quick adaptation to steady input. Additionally, microsaccades improve visual acuity. Six tiny
voluntary muscles linked to the surface of the eyeballs contract individually to move each
eyeball in its orbit as shown in figure2. The superior, inferior, medial, and lateral recti
muscles are four of the six muscles that run straight from their origin to insertion and are referred
to as recti muscles (rectus, straight). The inferior oblique and superior oblique are the two
remaining muscles, which are obliquely linked to the surface of the eyeball. Extrinsic eye
muscles refer to the two oblique muscles and the four recti muscles taken together [6].
Figure 2. Extrinsic eye muscles for the right eye. The numbers in mm show the distance maximum values from Limbus to
Insertion. As Insertion distances vary in individuals [6].
Three pairs -one right, one left- of cranial nerves and motor pathways in the brain work together
to govern the extrinsic muscles' ability to contract. All extrinsic eye muscles, with the exception
of the superior oblique and the lateral rectus, are supplied by Cranial Nerve III, the
oculomotor nerve. The superior oblique is supplied by trochlear nerve, or cranial nerve IV.
The lateral rectus is innervated by Cranial Nerve VI, or the abducens nerve [7]. The fixation
point of the gaze is transferred onto comparable sensory areas in the retinal foveas when a typical
person looks at an appropriately lit object. The sensory data from each retina is combined by the
occipital lobe brain to create a typical, single, sharp image of the object. A loss of retinal
correspondence leads to a disturbance in the alignment of the eyes, which can result in diplopia
or double vision. This can happen, for example, when one or more extraocular muscles are weak
[8]. While the pendulum swings, the brain uses visual sensory information about the change in
position of the moving pendulum to grade the extraocular muscle contractions in order to
maintain the visual fixation point. The eyes' involuntary oscillating or back-and-forth movements
are a type of tracking movement in which the eyes keep a fix on a moving object in the visual
field. Motor centers in the frontal lobe cortex and the motor centers of cranial nerves III, IV, and
VI in the brainstem regulate coordinated voluntary and involuntary eye movements. Using
traditional EEG techniques, cortical activity related to the regulation of the extraocular muscles
can be found and recorded. The cornea serves as the positive terminal of the human eye's
electrical dipole, and the retina serves as the negative terminal. The corneal-retinal potential
(CRP), which ranges from 0.4 to 1.0 mV and is predominantly caused by the hyperpolarization
and depolarizations of retinal nerve cells, is the potential between the front and back of the
eyeball [9]. A method for capturing voltage variations while the eyes move within their orbits is
called electrooculography. The electrooculogram (EOG), a record of the voltage variations
obtained as the individual moves their eyes from one fixation point to another within the visual
field without moving their head, is an electroencephalographic technique. When a person is
instructed to read a brief passage silently, pause, and then repeat the passage aloud, additional
variations in the EOG may be noticed. The eyes jump from one fixation point -here it is a wordto another swiftly and jerkily as the words in each phrase are read. Eye movements that are
quick, jerky, and voluntary are referred to as saccades (saccade-jerky) [10]. The amount of time
spent reading a word is the amount of time between saccades. When reading aloud in silence, the
eyes scan a line swiftly from word to word, and the space between saccades is small. The
interval between saccades is longer when the lines are read aloud because the auditory
information slows eye movement to give each viewed word time to be uttered [10]. When
reading a tough chapter compared to an easy passage, the gap between saccades is typically
larger because the brain needs more time to digest the information. When evaluating visual
problems involving neuromuscular control of the eyes, such as in the diagnosis and prognosis of
sixth nerve palsy (lateral rectus paralysis), electrooculography is frequently utilized [11].
3.
DATA and CALCULATIONS
1. Pendulum Tracking
Table 1. Pendulum Tracking vs. Simulation Tracking (using Horizontal data).
Pendulum
Simulation
Cycle
(sec)
(mv)
(sec)
(mv)
1
1.82
0.789
2.22
0.902
2
1.55
0.807
2.06
0.837
3
1.6
0.775
2.11
0.731
4
1.5
0.767
2.25
0.662
5
1.52
0.719
1.98
0.575
6
1.49
0.666
1.94
0.574
7
1.62
0.544
1.93
0.514
8
1.48
0.441
1.84
0.389
9
1.6
0.342
1.76
0.354
10
1.69
0.267
2.29
0.266
2. Vertical Tracking
Table 2. Vertical Tracking vs. Simulation.
Real Object
Simulation
Cycle
(sec)
(mv)
(sec)
(mv)
1
3.85
1.033
2.07
1.074
2
3.33
1.005
2.31
1.068
3
3.5
1.0012
2.33
1.075
4
3.75
1.0037
2.58
1.009
5
3
0.969
1.9
0.985
3. Saccades
Table 3. Saccades.
Read Silently 1
Read Silently 2
st
2 line
st
Number of words
9
Number of
saccades
9
Measurement
Time interval
between saccades
(sec)
1 line
nd
Read Aloud
nd
1 line
2 line
8
7
7
8
7
9
st
1 line
2nd line
9
8
0.16
0.19
0.
1
9
0.
2
4
0.
1
6
0.
20
#2
0.18
0.15
0.
3
2
0.
2
9
0.
2
2
0.
16
#3
0.23
0.15
0.
2
8
0.
2
1
0.
2
4
0.
20
#4
0.17
0.13
0.
2
5
0.
1
7
0.
2
1
0.
21
#5
0.27
0.14
0.
2
1
0.
2
4
0.
2
8
0.
12
#1
#6
0.27
0.26
0.
2
3
0.
2
6
0.
2
7
0.
18
#7
0.15
0.16
0.
2
3
0.
2
0
0.
2
6
0.
29
#8
0.14
0.18
0.
1
4
0.
2
4
0.
22
#9
0.23
0.
1
9
0.
1
8
Average time
interval between
saccades (sec)
0.2
0.
2
0.
2
2
4.
0.17
0.
2
4
DISCUSSION
Figure 3. Selection of the first Horizontal tracking cycle.
0.
19
Figure 4. Selection of the second Horizontal tracking cycle.
Figure 5. Selection of the first Horizontal cycle.
Figure 6. Selection of the second Horizontal cycle.
Figure 7.Selection of the first Vertical tracking cycle.
Figure 8. Selection of the second Vertical tracking cycle.
Figure 9. Selection of the first Vertical cycle.
Figure 10. Selection of the second Vertical cycle.
Figure 11. Selection of interval between saccades.
For Table1.Pendulum Tracking vs. Simulation Tracking (using Horizontal data)
Using the Electrooculography technique, we measured the eye movements. The objective of this
experiment was to compare the eye movements made when tracking a pendulum in real life with
the eye movements made when tracking a simulated pendulum. The table contains data for each
cycle of the experiment, including the time taken to track the pendulum or simulation in seconds
and the corresponding EOG readings in millivolts. Looking at the data in Table 1, we can
observe the following:
i.
ii.
The average time taken to track the pendulum in the real-life scenario ranges from
approximately 1.48 to 1.82 seconds, with some fluctuations between cycles.
In contrast, the average time taken to track the simulated pendulum ranges from
approximately 1.84 to 2.29 seconds, also with some variations across cycles.
Concluding that the subject maybe took slightly longer to track the simulated pendulum
compared to the real-life pendulum. This could be attributed to the differences in the visual cues
and depth perception provided by the real-life pendulum compared to the simulated one. As for
the EOG readings, we observe that real-life pendulum tracking is slightly higher compared to
simulated pendulum tracking. We also notice that the readings range from approximately 0.267
to 0.807 mv for the real-life pendulum tracking and from 0.266 to 0.902 mv for the simulated
pendulum tracking. It is important to keep in mind that the EOG readings for both tracking
situations vary slightly between cycles. The slight variations in tracking time between cycles for
both scenarios may tell us the influence of factors such as fatigue, attention, or learning effects.
The higher EOG readings during the real-life pendulum tracking could indicate greater eye
movement activity or increased effort in visually tracking the pendulum. The slightly lower EOG
readings during the simulated pendulum tracking on the other hand, may suggest reduced eye
movement activity or decreased effort, possibly due to the lack of physical presence and realism
associated with the simulated pendulum.
For Table 2. Vertical Tracking vs. Simulation
It presents the results obtained from the conducted EOG 1 experiment, which aimed to compare
eye movements during vertical object tracking this time, in real life versus a simulated
environment. The data in the table includes the time taken to complete a cycle of tracking an
object vertically, as well as the corresponding millivolt (mv) readings obtained from the EOG.
Comparing the real object tracking to the simulation, it is evident that the time taken to complete
a cycle differs between the two conditions. On average, the subject took approximately 3.69
seconds (sec) to track the real object, while it took them around 2.26 seconds to track the object
in the simulation. This indicates that the subject was able to track the object more quickly in the
simulated environment compared to real life. In both conditions, the EOG readings fluctuated
throughout the cycles, suggesting variations in eye movement patterns. EOG readings between
the real object tracking and simulation are relatively small as in Table1. In terms of the specific
values, the EOG readings for the real object tracking ranged from approximately 0.969 mv to
1.033 mv, while for the simulation, they varied between 0.985 mv and 1.075 mv, indicating the
small variations in the electrical activity of the eye muscles during tracking. it can be concluded
from this table’s results that the subject may have exhibited faster eye movements in the
simulation due to factors such as reduced cognitive load, lack of real-world distractions, or
increased familiarity with the simulated environment. The shorter time taken to complete the
tracking task in the simulation suggests that subject was able to process and respond to visual
stimuli more efficiently. These findings have can be used for understanding human visual
perception and the potential benefits of utilizing simulations in eye tracking research. Simulated
environments provide controlled settings that allow researchers to isolate and examine specific
variables, leading to a better understanding of eye movements. The faster tracking times
observed in the simulation suggest that it could be a valuable tool for training and skill
development in tasks that involve visual tracking.
For Table 3. Saccades.
The fact that the number of saccades aligns with the number of words suggests that the subject
that the experiment was conducted on was fixating on each word individually. This indicates a
typical reading behavior where each word is processed sequentially, leading to a separate eye
movement for each word. As for the time intervals between saccades, we know that it reflects the
speed at which the subject moved their eyes from one word to the following word. Shorter
intervals indicate faster eye movements, while longer intervals suggest slower eye movements.
Noting that the variations observed in the time intervals between saccades can also be attributed
to individual differences in reading speed, comprehension, and cognitive processing. Some
subjects may have a faster reading pace, leading to shorter intervals, whilst others may take more
time in comparison, thus resulting in longer intervals. The average time intervals between
saccades provide an overall measure of the subjects' reading speed. It is crucial to remember that
these values are particular to the study's subjects and the lines utilized, and they might not be
indicative of readers' behavior generally. Finally, we come to the fact that the results suggests
that the subject engaged in typical eye movement patterns during silent reading, with each word
triggering a saccadic eye movement.
5.
QUESTIONS
1. Focusing a camera changes the distance between the lens and the film. Does the eye focus by
changing the distance between the lens and the retina? Explain your answer.
It is intriguing how the eye concentrates light because most of the refraction is performed not
by the lens but rather by the aqueous humor, a liquid that sits on top of the lens. This fluid
bends light as it enters the eye, then the lens bends it slightly more, and finally the jelly-like
vitreous humor, which fills the gap between the lens and the retina, bends light even more.
The lens is essential for creating a sharp image, but one of the most astounding things about
the human eye is how rapidly it can focus on objects that are closer or farther away. The
word "accommodation" refers to this process of adjustment. The lens of a camera has a set
focal length. When the object distance changes, the lens must be moved to modify the image
distance, which is the distance between the lens and the film. The image distance, or the
distance between the lens and the retina, is fixed in the human eye, making this impossible.
This is accomplished by altering the lens's shape; the ciliary muscle performs this.
2. Define the following terms:
a. Cone: They are most concentrated in the fovea, where focused light produces the
sharpest image and are used for day vision and color vision.
b. Rods: they are concentrated in the periphery of the retina, therefore the tendency to
focus away from the fovea (“look to the side of the eye") in darkness. They are used for
vision in dim light and for the detection of movement in the visual field.
c. Fovea: is a small depression within the neurosensory retina where visual acuity is the
highest.
d. Visual Field: the field of vision without moving your head, in other words, when you
focus your eyes on a central point, the visual field is the overall area in which items can
be viewed in the periphery (side) vision.
e. Visual Fixation: Muscular control of the eye works to keep the image on the fovea,
regardless of whether the object is stationary or moving.
f. Saccade/ Micro-saccade: Eye movements that are quick, jerky, and voluntary are
referred to as saccades. Your eyes continue to move in repetitive, unconscious, minute,
jerky motions after they have locked onto an object, known as microsaccades.
3. Why is vision in darkness more effective when focusing away from the fovea rather than
focusing directly on the fovea?
Rods are used to detect movement in the visual field and to see in low light. Because rods are
concentrated on the retina's periphery, people prefer to glance away from the fovea when it's
dark. Regardless of whether the object is stationary (still) or moving, the eye's muscular
control helps to maintain the image on the fovea.
4. Explain the difference between “voluntary fixation” and “involuntary fixation”:
Voluntary fixation involves performing a deliberate attempt to focus your attention on a
particular item in your field of vision and "lock on" to it, in other words, conscious effort.
Unconscious processes that hold the chosen object in your field of vision after you've locked
on to it are known as involuntary fixation.
5. Examine the data in Table 1 and answer the following questions:
a. Did the amplitude continue to decrease with each successive swing cycle during
pendulum tracking? Explain.
Yes. As the pendulum slows, less eye movement is needed in order to observe it.
b. Did the amplitude continue to decrease with each successive swing cycle during
simulated pendulum tracking? Explain.
Yes, it decreased but the pattern was more chaotic. The neuromuscular control of the
eyes deteriorates due to a lack of visual sensory information, which results in jerky
movement.
c. Did the time interval (period) of each successive swing cycle increase, decrease, or
remain constant during pendulum movement? Explain.
It does not show a consistent pattern of increase or decrease, however, constant periods
in the data indicate a relatively steady and consistent behavior for the pendulum, with
tiny oscillations most likely resulting from experimental conditions.
d. Did the time interval (period) of each successive swing cycle increase, decrease, or
remain constant during simulated movement? Explain.
It does not show a consistent pattern of increase or decrease. However, we can notice
that the periods remain fairly constant with slight variations. It could be due to the
control system or algorithm used for simulation.
e. Are the waveform shapes different between tracking and simulated tracking data?
Explain.
Yes, the tracking was sinusoidal and smooth. The activated monitored data moved in a
jerky way.
6.
Examine the data in Table 2 and answer the following questions:
a. Do the cycle amplitudes increase, decrease, or remain constant during vertical
tracking? Explain.
Decreased, because the subject was following the pen movement.
b. Do the cycle amplitudes increase, decrease, or remain constant during simulated
vertical tracking? Explain.
Generally, it was decreasing, it might be due to the subject getting used to the
object's motion in the vertical plane, they may also adjust their eye movements to
minimize unnecessary movements and conserve energy.
c. Do the cycle periods increase, decrease, or remain constant during vertical
tracking? Explain.
Generally, it was decreasing, which suggests that the subject became more
efficient and skilled in tracking the object as they gained experience with the task.
d. Do the cycle periods increase, decrease, or remain constant during simulated
vertical tracking? Explain.
They are not constant; the varying cycle periods suggest that the subject’s ability
to track the object in the simulation has fluctuated throughout the experiment.
e. Are the waveform shapes different between vertical tracking and simulated
vertical tracking data? Explain.
Yes, because the eye was jerking while trying to maintain a steady cycle without
the actual pendulum during stimulated tracking.
7.
Examine the data in Table 3 and answer the following questions:
a. Did the number of saccades match the number of words for each line? Explain
any differences.
In general, there are more words because humans’ group together simpler, shorter
terms. However, with challenging reading, saccades may become more frequent
as the mind scans the words more slowly or even analyzes some words twice.
b. Is the average time interval between saccades different when reading an easy
passage vs. a challenging passage? Explain.
When reading an easy passage compared to a difficult one, the average time was
marginally different. When reading aloud, the average time interval should lengthen. Due
to the additional cognitive and physical functions required to vocalize the text, reading
aloud tends to lengthen the average time interval.
c. Is the average time interval between saccades different when reading the same
passage silently vs. aloud?
Due to the additional cognitive and physical functions required to vocalize the
text, reading aloud tends to lengthen the average time interval.
d. Are the waveform shapes different between Read Silently 2 and Read Aloud data?
Explain.
Yes, because when reading out loud we’ll get a wider waveform thus a longer one
than if we read in silence.
e. Name the cranial nerves tested, and the extraocular muscles tested when the
subject is asked to follow the eraser on a pencil when moved in a one-foot circle,
two feet from face.
Cranial Nerves
Extraocular Muscles
abducens nerve
four rectus muscles (superior, inferior,
lateral, medial)
oculomotor nerve
two obliques (superior and inferior)
trochlear nerve
8.
Define corneal–retinal potential (CRP) and explain its relation to electrooculography and
the electrooculogram.
The corneal-retinal potential (CRP), which ranges from 0.4 to 1.0 mV and is
predominantly caused by the hyperpolarization and depolarizations of retinal nerve cells,
is the potential between the front and back of the eyeball. A method for capturing voltage
variations while the eyes move within their orbits is called electrooculography. The
electrooculogram (EOG), a record of the voltage variations obtained as the individual
moves their eyes from one fixation point to another within the visual field without
moving their head.
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