physiology lessons lesson 8 eog 1 …physiology lessons for use with the biopac science lab mp40 pc...

Physiology Lessons

for use with the Biopac Science Lab MP40

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Lesson 8 EOG 1 Electrooculogram

Lesson Revision 11.02.2006

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Biopac Science Lab

Lesson 8 ELECTROOCULOGRAM 1

MUSCLE Inferior Rectus Superior Rectus Lateral Rectus Medial Rectus Superior Oblique Inferior Oblique

EYE DIRECTION Downward Upward Laterally Medially Down and Laterally Up and Laterally

Fig. 8.1 Muscles of the (labeled for the left eye)

I.

The movement of each eyeball in its orbit is caused by the individual contractions of six small voluntary muscles attached to the surface of the eyeball. Four of the six muscles run straight from origin to insertion, and thus are termed recti muscles (rectus, straight): the superior rectus, the inferior rectus, the medial rectus, and the lateral rectus. The remaining two muscles are obliquely attached to the eyeball surface and are called the superior oblique and the inferior oblique (Fig. 8.1). Collectively, the four recti muscles and the two oblique muscles are called extrinsic eye muscles.

SCIENTIFIC PRINCIPLES S.R. S.O.

M.R. L.R.

I.O. I.R.

Contractions of the extrinsic muscles are controlled by way of motor pathways in the brain and three pairs (one right, one left) of cranial nerves. Cranial nerve III, the oculomotor nerve, supplies all extrinsic eye muscles except the superior oblique and the lateral rectus. Cranial nerve IV, the trochlear nerve, supplies the superior oblique. Cranial nerve VI, the abducens nerve, innervates the lateral rectus.

When a normal person gazes at an object, the fixation point of the gaze is projected onto corresponding sensory areas in the foveas of the retinas. The occipital lobe cortex integrates the sensory information from each retina, producing normal, single binocular vision. If there is a disruption in the alignment of the eyes, there is a loss of retinal correspondence and the result may be diplopia or double vision. Nine cardinal directions of gaze in concerted eye movement and the extraocular muscles moving the eyes to the gaze position are shown in (Fig. 8.2).

Position Right Gaze Right eye Left Eye

Straight Ahead Both eyes

Left Gaze Right eye Left Eye

Upward Superior rectus Inferior oblique Superior rectus, Inferior oblique Inferior oblique Superior rectus

Centered Lateral rectus Medial rectus Central Gaze Medial rectus Lateral rectus

Downward Inferior rectus Superior oblique Inferior rectus, Superior oblique Superior oblique Inferior rectus

Fig. 8.2 Nine cardinal directions of gaze

When a person maintains visually focused on a moving object without moving the head, such as in watching the swinging pendulum of a clock, each eye must move precisely and in concert with the other for the brain to receive the sensory information required to produce a clear, single image of the moving object. The eyeball movement involves the extraocular muscles, their cranial nerves, and motor control centers in the brain. For example, as the clock pendulum swings from left to right, the left eye moves medially (medial rectus/cranial nerve III), and the right eye moves laterally (lateral rectus/cranial nerve VI). When the pendulum swings back, the eye movements are reversed. Visual sensory information regarding the change of position of the moving pendulum is used by the brain to grade the contractions of extraocular muscles so as to maintain the visual fixation point as the pendulum slows and speeds up during its swing. The oscillating, or back and forth voluntary movements of the eyes, are a form of tracking movement in which the eyes maintain a visual fix on an object moving within the visual field.

Coordinated voluntary eye movements are initiated and controlled in the motor cortex of the frontal lobes. Cortical activity associated with motor control of the extraocular muscles can be detected and recorded using conventional electroencephalographic techniques. Electrooculography (EOG) is the measurement and interpretation of electrooculograms, which are the electroencephalographic tracings obtained while the subject, without moving the head, moves their eyes from one fixation point to another within the visual field.

An EOG recorded from temporal electrodes placed at the lateral margin of the orbits of a subject visually tracking the movement of a pendulum is shown in (Fig. 8.3). The sinusoidal nature of the tracing disappears when the pendulum, and hence the visual tracking, is stopped. If the subject closes the eyes and imagines a swinging pendulum, the EOG again becomes sinusoidal but jerky, suggesting a reduction in neuromuscular control of the eyes due to the loss of visual sensory input to the brain.

Lesson 8: EOG 1

Other changes in the EOG may be recorded when a subject is asked to silently read a brief paragraph, pause, then reread aloud the same paragraph. As the words in each sentence are read, the eyes move quickly and in a jerky manner from one fixation point (a word) to another. Quick, jerky, voluntary movements of the eyes are called saccades (saccade – jerky). When the reading is silent, the eyes move more quickly from left to right as the lines are read. When the lines are read aloud, the auditory input slows eye movement to allow time for each seen word to be spoken.

EOG is commonly used to assess visual defects involving neuromuscular control of the eyes, such as in diagnosis and treatment success of sixth nerve palsy (paralysis of the lateral rectus). Similar eye movement/cranial nerve tests using other cardinal gazes (Fig. 8.2) may be employed in diagnosis and assessment of eye disorders. In addition, recent applications include the use of EOG in the design of robotics, such as motorized wheelchairs and other devices that can be guided or otherwise controlled by movement of the subject’s eyes.

Fig. 8.3 EOG Tracking

In this lesson, you will record horizontal eye movement and study saccades and fixation.

II.

III.

EXPERIMENTAL OBJECTIVES

1) Record EOG on the horizontal plane and compare eye movements under the following conditions: pendulum tracking, pendulum simulation, reading silently, reading aloud, reading challenging material.

2) Measure duration of saccades and fixation during reading.

MATERIALS

Computer system (running Windows XP or Mac OS X) Biopac Science Lab system (MP40 and software) Electrode lead set (40EL lead set) Disposable vinyl electrodes (EL503), three electrodes per subject Pendulum (metronome may be used; signal pattern will be constant vs. diminishing) Passages for reading: Passage 1 – easily understandable (i.e., entertainment article) Passage 2 – challenging material (i.e., scientific article)


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IV. EXPERIMENTAL METHODS

A. Set Up

EQUIPMENT

Fig. 8.4

SUBJECT

Fig. 8.5 Lead connections

FAST TRACK Details

1. Turn the computer ON.

2. Set the MP40 dial to OFF.

3. Plug the equipment in as follows:

Electrode leads (40EL) MP40

4. Attach three electrodes to the subject as shown above.

IMPORTANT For accurate recordings, attach the electrodes so they are horizontally aligned.

5. Connect the electrode leads (40EL), matching lead color to electrode position as shown above.

IMPORTANT Clip each electrode lead color to its

specified electrode position.

Attach three electrodes to the subject as shown in Fig. 8.5: Attach one electrode to the right temple.

Attach one electrode to the left temple, such that it is horizontally aligned with the right electrode.

The other electrode is for ground, and it can be placed anywhere on the forehead or on the wrist, as optimum for the subject’s comfort and minimal cable strain.

6. Start the Biopac Science Lab software.

7. Choose lesson L08-EOG-1 and click OK.

8. Type in a unique file name. No two people can have the same file name, so use a unique identifier, such as the subject’s nickname or student ID#.

9. Click OK. This ends the Set Up procedure.

Lesson 8: EOG 1

B. Check

FAST TRACK Details

MP40 Check

1. Set the MP40 dial to EOG.

2. Press and hold the Check pad on the MP40.

3. Click when the light is flashing. 4. Wait for the MP40 Check to stop. Continue to hold the pad down until prompted to let go.

5. Let go of the Check pad.

6. Click Continue.

The MP40 check procedure will last five seconds.

The light should stop flashing when you let go of the Check pad.

When the light stops flashing, click Continue.

Signal Check

7. Position the Subject. Have the Subject adjust the seating position such that the eyes are in line with the center of the computer screen.

8. Note the distance from the eyes to the computer screen: _________cm

This distance is required later in the recording to position the subject the same distance from the computer.

9. Click Check Signal and click OK.

10. Track the onscreen dot from right to left until the Signal Check stops.

Subject should follow the dot with eyes only, trying not to move or blink.

11. Review the data.

If correct, go to the Record section.

If incorrect, click .

The 14-second Signal Check recording should resemble Fig. 8.6.

Fig. 8.6 Signal Check recording data

If the recording shows large spikes or baseline drift, the Subject likely blinked and should click Redo Signal Check.


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C. Record

FAST TRACK Details

1. Prepare for the recording. Watch the Help menu videos to prepare for the recording. You will record two segments: subject tracking a pendulum and subject imagining pendulum movement.

Select two different passages for reading:

Passage 1: easily understandable (i.e., entertainment article)

Passage 2: challenging material (i.e., scientific article)

In order to work efficiently, read this entire section so you will know what to do before recording.

2. Position the Subject such that the eyes are in line with the center of the computer screen, using the same distance from the Signal Check.

SEGMENT 1 — Pendulum

3. Set pendulum in motion.

4. Click Record.

When you click Record, the recording will begin and an append marker labeled Pendulum will automatically be inserted.

5. Subject tracks movement until pendulum stops.

6. Click Suspend.

The Subject should be seated and relaxed and should track movement with eyes only, trying not to move head or blink.

When you click Suspend, the recording will halt, giving you time to review the data.

7. Review the data.

If correct, go to Step 8.

Your data should resemble Fig. 8.7.

Fig. 8.7 Pendulum movement

If incorrect, click Redo. The data would be incorrect if it did not show decreasing amplitude. If data is incorrect, click Redo and repeat Steps 3-7; the last data segment you recorded will be erased.

Note If a metronome was used instead of a pendulum, the signal pattern will have a constant instead of diminishing amplitude.

SEGMENT 2 — Simulate

8. Click Resume.

Recording continues…

Subject should remain relaxed and seated and should try not to move or blink during the recording.

When you click Resume, the recording will continue and an append marker labeled Simulation will be automatically inserted.

Lesson 8: EOG 1

9. Subject simulates pendulum movement. After the display shows no swing cycles (no movement), Recorder clicks Suspend.

Subject simulates pendulum movement (decreasing swing cycles) with eyes only until the display shows no swing cycles.




Fig. 8.8 Simulated pendulum movement

If incorrect, click Redo.

The data would be incorrect if it did not show decreasing amplitude. If data is incorrect, click Redo and repeat Steps 8-10; the last data segment you recorded will be erased.

SEGMENT 3 — Read Silently 1

11. Click Resume. Subject should remain seated, in a relaxed state and should try not to move or blink during the recording.

When you click Resume, the recording will begin and an append marker labeled Read silently 1 will automatically be inserted.

12. Subject reads Passage 1 silently (to self) for 20 seconds and then Recorder clicks Suspend.

The Subject should read silently (to self) for 20 seconds.



If all went well, your data should resemble Fig. 8.9.

Fig. 8.9 Reading silently 1


The data would be incorrect if it did not show saccades. If data is incorrect, click Redo and repeat Steps 11-13; the last data segment you recorded will be erased.

SEGMENT 4 — Read Silently 2

14. Click Resume.

Subject should remain seated, in a relaxed state and should try not to move or blink during the recording.

When you click Resume, the recording will begin and an append marker labeled Read silently 2 will automatically be inserted.


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15. Subject read Passage 2 silently (to self) for 20 seconds and then Recorder clicks Suspend.

The Subject should read silently (to self) for 20 seconds.




Fig. 8.10 Reading silently 2 (challenging passage)


The data would be incorrect if it did not show saccades. If data is incorrect, click Redo and repeat Steps 14-16; the last data segment you recorded will be erased.

SEGMENT 5 — Read Aloud

17. Click Resume. Subject should remain relaxed and seated and should try not to move or blink during the recording.

When you click Resume, the recording will begin and an append marker labeled Read aloud will automatically be inserted.

18. Subject reads Passage 1 aloud for 20 seconds and then Recorder clicks Suspend.

The Subject should Passage 1 aloud until the recording stops.




Fig. 8.11 Reading Passage 1 aloud


The data would be incorrect if it did not show saccades; the saccades should be slower (wider jerks) than in the Read Silently segments. If data is incorrect, click Redo and repeat Steps 17-19; the last data segment you recorded will be erased.

20. Optional: Click Resume to record additional segments.

Optional: You can record additional segments by clicking Resume instead of Stop. A time marker will be inserted at the start of each added segment.

21. Click Stop.

22. Click Yes.


Lesson 8: EOG 1

23. Optional: Click Dot Plot. Click 'Dot Plot' to explore microsaccadic eye movement. Subject should focus on the center of the black cross. After five seconds, a dot will appear. Continue to focus on the center of the cross.

Subject should try to maintain fixed focus on center of display.

Colored dot position represents point of focus.

Fixed focus would hold the colored dot in center of cross.

Dot movement indicates microsaccadic eye movement (proportional to the number of degrees the Subject's eyes moved from center).

Note that data for this segment will NOT be saved. 24. Click Done.

25. Choose an option and click OK.

When you click Done, a dialog will be generated. Make your choice, and continue as directed.

26. Remove the electrodes. Unclip the electrode leads and peel off the electrodes.

END OF RECORDING


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V. ANALYZE

FAST TRACK Details

1. Enter the Review Saved Data mode. To review saved data, choose Analyze current data file from the Done dialog after recording data, or choose Review Saved Data from the Lessons menu and browse to the required file.

Note Channel Number (CH) designation:

Channel Displays

CH40 Horizontal

The data window should come up the same as Fig. 8.12.

Fig 8.12

2. Set up the measurement boxes as follows:

Channel Measurement

CH 40 Delta T

CH 40 P-P

CH 40 Slope

The measurement boxes are above the marker region in the data window. Each measurement has three sections: channel number, measurement type, and result. The first two sections are pull-down menus that are activated when you click on them. Brief definition of measurements:

Delta T: The Delta Time measurement is the difference in time between the end and beginning of the selected area, which is the duration of the selected area. P-P. The p-p (peak-to-peak) measurement shows the difference between the maximum amplitude value in the selected range and the minimum amplitude value in the selected range. Slope: uses the endpoints of the selected area to determine the difference in magnitude divided by the time interval; slope indicates the relative speed of eye movement.

The “selected area” is the area selected by the I-beam tool (including the endpoints).

3. Set up your display window for optimal viewing of the first data segment.

Segment 1 data begins at the append marker labeled “Pendulum” at Time 0 and continues to the next append marker.

The following tools help you adjust the data window: Autoscale horizontal Horizontal (Time) Scroll Bar Autoscale waveforms Vertical (Amplitude) Scroll Bar Zoom Tool Zoom Previous Grids — Turn grids ON and OFF by choosing Preferences from the File menu.

4. Measure the amplitude change for each pendulum tracking cycle (diminishing cycle).

A

TIP When interpreting the different bumps in the data, in general: • Large horizontal bumps are eyes moving left or right

(or when reading, eyes moving left to start the next line). • Small bumps are saccades (fixations).

5. Measure the amplitude change for each simulation cycle.

A

Analysis continues…

Lesson 8: EOG 1

6. Zoom in on a small section of Reading Silently 1 data.

7. Find a part of the data segment with a small spike or bump, indicating flicking movement (Fig. 8.13) and measure the duration and slope.

A

Use the horizontal scroll bar if needed to find a segment similar to Fig. 8.13.

Fig 8.13 Flicking

8. Count the number of flicking movements in one-second intervals from 1-4 seconds.

B Table 8.2

Use the horizontal scroll bar to move through the data.

The slow drifting movements and flicking movements are small movements, so you will need to Zoom and Autoscale waveforms. The flicking movements will occur as abrupt directional changes (steep slopes) and for shorter durations than the drifting movements.

The flicking movements are difficult to measure. If it is too difficult to note them in your data, state that in the Data Report.

9. Find the saccades in the data (Fig. 8.14).

B

You can paste measurements into the Journal to record the results of each saccade per line of reading.

Fig 8.14

10. Repeat Steps 6-8 using Reading Silently 2 data.

B

11. Repeat Steps 6-8 using Reading Aloud.

B

12. Save or print the data file.

13. Exit the program.

14. Set the dial to Off.

END OF DATA ANALYSIS

END OF LESSON 8

Complete the Lesson 8 Data Report that follows.


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The Data Report starts on the next page.

Biopac Science Lab

Lesson 8 ELECTROOCULUOGRAM I Eye Movement: Tracking & Saccades


DATA REPORT

Student’s Name:

Lab Section:

Date: I. Data and Calculations A. Subject Profile

Name Age Gender: Male / Female Height Weight

B. Complete Table 8.1 using Segment 1 and Segment 2 data. Be careful to be consistent with units (msec vs secs). Table 8.1 Segment 1 Tracking vs. Simulation

Pendulum Simulation Cycle

Slope Delta T P-P Slope Delta T P-P 1

2

3

4

5

6

7

C. Complete Table 8.2 with Segment 3, 4, and 5 data. (Note: You may not have seven saccades per line.)

Table 8.2 Saccade data Measurement Read Silently

1st line 2nd line Read Aloud-Easy

1st line 2nd line Read Aloud-Hard

1st line 2nd line Number of saccades Duration of saccade

#1

#2

#3

#4

#5

#6

#7

Total duration of saccades/line

Total reading time/line

Saccade % of reading time total

These are sample questions. You should amend, add, or delete questions to support your curriculum objectives.

Biopac Science Lab

II. Questions

A. Explain how an electrooculogram is recorded.

B. Define visual field.

C. Define saccade.

D. Note and explain Amplitude and Frequency variations: i. Did amplitude increase, decrease or remain constant during pendulum movement? ii. Did amplitude increase, decrease or remain constant during simulated movement? iii. Did the period frequency increase, decrease or remain constant during pendulum movement? iv. Did the period frequency increase, decrease or remain constant during simulated movement?

E. Looking at Table A (Delta T from peak to peak), does the period of each cycle diminish for each peak?

F. Looking at Table B (saccades data), why is eye movement slower when you read a challenging passage?

G. Looking at Table B (saccades data), why is eye movement slower when you read aloud?

H. Compare your saccade results with at least 3 students. What is the range of variation in % time of saccades per line? What factors might explain this?

I. Define double vision (diplopoa) and a cause.

J. What cranial nerves are tested if you hold a pencil in front of a subject and ask the subject to follow it with the eyes as you move the pencil in a circle?

K. Name two clinical advantages of electrooculography.

End of Biopac Science Lab Lesson 8 Data Report

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VI. ACTIVE LEARNING LAB

Design a new experiment to test or verify the scientific principle(s) you learned in the Biopac Science Lab recording and analysis segments.

For this lesson, you might try to influence the environment (music, chatter) or change to reading on a computer screen.

Design Your Experiment

Use a separate sheet to detail your experiment design, and be sure to address these main points:

A. Hypothesis

Describe the scientific principle to be tested or verified.

B. Materials

List the materials will you use to complete your investigation.

C. Method

Describe the experimental procedure—be sure to number each step to make it easy to follow during recording.

See the Set Up section or Help > About Electrodes for electrode placement guidelines.

Run Your Experiment

D. Setup

Set up the equipment and prepare the subject for your experiment.

E. Recording

Use the Record, Resume, and Suspend buttons in the Biopac Science Lab program to record as many segments as necessary for your experiment.

Click on Done when you have completed all of the segments required for your experiment.

Analyze Your Experiment

F. Set measurements relevant to your experiment and record the results in a Data Report.


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