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Grades 7 - 8


This lesson is used while studying the human eye and has been designed to illustrate the difference between seeing and perception: Can our eyes be trusted? This lesson can be used with units relating to light, color, optics, study of the senses, optical illusions, health units, scientific method, recording data, measuring, calculating averages, and graphing.

Students will observe how the movie makers are able to fool us by the use of studio techniques, and will be actively involved investigating two different visual phenomenon while performing an activity demonstrating retina fatigue and after image, and the purpose for humans having binocular (two-eyed) vision. Vocabulary terms may be introduced, but are actually learned through video investigation and hands-on activities in small group interactions. Activities and video interaction requires predicting, measuring, recording, calculating averages, graphing information, presenting small group information, and subsequent synthesizing of class information. The length of this lesson is from 2-4 class periods, depending upon the number of enrichment activities utilized.
ITV Series
READING RAINBOW #801: An Illusionary Tale
Learning Objectives
At the end of this lesson, the students should be able to:
Red Clover...Green Heart Previewing Activity
It's As Clear As Your Hand
Post-Viewing Activity 1
Are Two Eyes Better Than One? Post-Viewing Activity 2
Are Two Eyes Better Than One? Post-Viewing Activity 3
Seeing - to perceive with the eyes.
Perception - the mind's awareness of what the eyes are seeing. (A person could read an entire page in a book, and at the end realize they did not comprehend a word. As their mind wandered to other things, their eyes could see the words, but until the mind uses that information, the person would not perceive what was read.) Fatigue _ being very tired.
Retina - the lining of the inside of the eye where the image is inverted (turned upside-down) after traveling into the eye through the pupil opening.
Retina fatigue - tiring of the rod cells and cone cells that are located in the retina of the eye.
Rod cells - special cells in the retina that collect light, without light we can not see.
Cone cells - special cells in the retina that collect color, (which is the result of different parts of light being reflected from pigments in objects) and generate electrochemical impulses that are processed by the brain to perceive these colors.
After images - the image that appears after retina fatigue (tiring of rod and cone cells).
Complementary colors - colors that are opposite, i.e., black is complementary to white.
Optical illusion - an eye trick; fooling of the sense of sight by use of lines, colors, movement, shadow or depth that changes the minds to perception of what is really being seen. The eyes are tricked and the brain becomes confused.
Mirage - a type of optical illusion cause by a layer of heated air of varying density (thickness). In contrast to the man dying of thirst, crossing the desert, having an hallucination of an oasis lake, a mirage usually is an inverted reflection of an actual object some distance away.
Pre-Viewing Activities
Note to teacher: Depending upon your teaching style, the following vocabulary terms may be introduced prior to the lesson activities and video presentations, or the students can be allowed to discover the meanings as they progress through an investigative approach.


Arrange students into groups of 4. Hand out 1 set of markers per group and 1 work sheet per student. Within each group, have the students pair off and decide within those pairs who will be the clover and who will be the heart. Have 'clovers' color the clover on their sheet RED, and the 'hearts' color the heart on their sheet GREEN. (This only takes a few minutes.)

Give the following directions: "To perform this activity everyone will need to hold the red clover or green heart in both hands, elbows on the table, bent at a comfortable position and distance from your eyes. When I tell you to, I want you to stare at the object in front of you. I want you to focus on the black spot in the center, but keeping the colored object in full view. Try not to blink. Your eyes will have a tendency to want to cross, producing two images. Try to avoid that happening by redirecting your focus back to the center spot. It is natural for your eyes to tear. Some of you may actually appear to cry. This is normal."

Pause for a few moments to see that the students have the papers held properly and at a natural distance for viewing. Then say, "I will give you the command, 'Ready, stare.' When I do, begin your focused gaze. I will continue to talk to you to remind you to keep in focus. When I say, 'Ready, switch.' I want you, without blinking, to move your eye to the square with just the little black object in it, and to continue to stare for a few more moments. Please do not shout out what happens, as not all students will see this the first time." Pause and look around to see that the students are ready. Ask, "Is everyone ready?" Pause. When they appear ready, give the command, "Ready. Stare." Watch a clock with a second hand. Continue to talk to the students softly, reminding them to try not to blink, to focus on the spot, avoid going cross-eyed, etc., for about one minute. Then give the final response, "When you hear the command, try to avoid blinking, and continue to stare. Ready. Switch." You will hear "Ooohhs, Aaahhs and Wows!" as well as, "Can we do it again?"

Check to see if all students have experienced something unusual. You may have a couple who did not. Say, "We are going to try this again, so everyone can experience this with the other object. Partners, switch your hearts and clovers. Get into the ready position." When you determine they are ready, repeat the process with the students again.

If you still have someone who cannot see something, repeat process again inviting anyone who wishes to repeat it also. Almost all students want to repeat it again. Ask students what they saw. Their responses will be consistent- "green clovers and red hearts" had appeared in the blank spaces with the little black object.

Ask students if they can explain what they saw. (Accept responses.) You may have an individual copy of a color wheel (see attachments), or you may use an overhead transparency, or other resource to show the students. Try to get them to discover that it was the complimentary colors_those opposite the color they stared at_on the color wheel.

Give the following account to the students. "At about the time colored computer monitors first came out, a rash of unexplained medical complaints flooded doctors offices. They mostly came from women, and at first doctors actually considered that it was a "woman thing" and they were "seeing things." But the complaints persisted, and the number of complaints continued to grow so large that the medical community realized there was indeed a problem somewhere that was causing this complaint. The complaint...everything these afflicted people saw was pink! Sometimes for hours, and they usually suffered severe headaches, as well. The only thing they seemed to have in common was that they all spent most of their day working at a colored monitor of a computer."

Pause. Give the students time to absorb what you have said. Then ask, "Having just performed this lab, can you identify the cause?" Wait for responses. Then add this, "What color were the original colored monitors? Remember, they did not have the options of changing the color on the early models." Usually, there is a computer buff, or a student will remember their first colored monitor. If you do not get the answer, it is "bright, neon-like, green." Continue to direct students to discover, that these women, (and there were some men), had experienced the same phenomenon as the students had with the green hearts becoming pinkish-red.

Note to teacher: It is helpful to have a simple diagram of the human eye to point to as you explain. Also, if you like the investigative approach, ask the students for the definitions, or terms, before you give them.

Continue to explain, "Medical investigators finally tracked down the cause by gaining a fuller understanding of how the eye works. In the back of our eyes, there is a lining inside called the RETINA. It is here that the image comes in through the dark, central spot, called the PUPIL. When the image passes through the LENS, the image is INVERTED, or turned upside-down. When it strikes the retina, the image is absorbed by two special cells in the retina. These cells are the ROD CELLS, which detect and collect light, and the CONE CELLS, which detect and collect color. The rod cells and the cone cells had become fatigued (tired). Because of this, the cells could no longer respond to those colors, and substituted the opposite color, in this case, pinkish-red. This phenomenon is called RETINA FATIGUE, and what you saw was an AFTER IMAGE, or the image you saw after the fatigue of the rod and cone cells happened. As a result, color monitors now have many options of color choices. People who work repetitively at a computer monitor, even in black and white, are advised to take regular breaks. (Best of all, these women were not crazy, as was eluded to by doctors, but they were seeing things!)

Ask students, "Can anyone give me other examples of how your eyes can be tricked, or how you can be tricked by your eyes?" (The two most common responses will be "optical illusions and mirages.")

If you wish to take the time, or feel the need to explain these further, this is a good time to do so. OPTICAL ILLUSIONS are eye tricks caused by use of lines, color, depth, and movements presented in such a way that the brain becomes confused when it receives the STIMULI (information received). A MIRAGE is a type of optical illusion produced by a layer of heated air of varying density (thickness). The image can be one of water on a road, but a true mirage is an inverted (upside-down) image of a real object that may be miles away!

Our common understanding of a mirage gives image of a person crawling through a desert, dying of thirst, suddenly seeing an oasis, which of course does not exist. The heated air of the desert provides excellent circumstances for a mirage to occur.
Focus Viewing
To give students a specific responsibility while viewing, say, "We are now going to watch a very short segment of video. I want to test your skills of observation focusing on sight only, so I will have the sound of the video turned off."
Pass out the Focus For Viewing Sheet (attached). Continue with, "I want you to write down everything you see, as completely as you are able. Write what is happening, what objects are close, and which are far away. Really look closely. You should see at least 10 different things happening, or specific objects. I will allow a few extra minutes at the end of the segment for you to finish writing."

Viewing Activities
Note to teacher: It is important to turn the sound on the video off. You want them to focus their viewing on what they see, not what they hear. LeVar could call attention to things you would like them to discover for themselves.

START the video right after the introduction song of Reading Rainbow. LeVar is climbing a mountain. Play the video segment for 10 seconds.

PAUSE the video allowing the students to really focus on the details they are looking for. RESUME the video for an additional 12 seconds.

PAUSE the video before he pulls the rope down! It is helpful to play this segment a couple of times to ensure the correct pausing point.

Give the students the additional time to write.

Using your Focus for Viewing sheets, compare what you saw with the person sitting next to you. Put a star beside the things you both saw and agree on. Underline anything you have that they do not have. Write anything they have that you do not have under the horizontal line you have drawn. (This helps the students to really think about what they saw, and to realize differences in what another person sees when watching the same thing.)

Ask for several students accounting of what they saw. You may want them to compare similarities and contrast differences between what everyone saw or did not see. Say, "As you watch the next segment of the video, check off all items or actions you had observed in the first segment of the video. Add anything you do not yet have on your list." When you feel the point has been made that everyone sees the same thing, but perceives the event somewhat differently begin the next segment for viewing.

Turn the sound back on. RESUME the video from the point you ended earlier.

PAUSE the video when LeVar walks toward the blue background and says, "Where did we get those mountains in the distance?" Ask the students if they had even considered that what they were observing earlier was real or not. Then ask if they have any ideas how the mountains did appear in the background. Accept responses. Say, "Watch now, and see if you were correct." RESUME the video.

STOP the video when you see LeVar climbing the mountain as he did in the beginning segment and he says, "What a blizzard..."
Post-Viewing Activities
Say, "How many of you saw something during the second segment of video that you did not see in the first segment?" (Accept responses.) Continue, " Our brain will usually accept what we see with our eyes. We are probably fooled every time we watch something on television or in a movie, but our vision is specifically designed to help us survive our real environments. "On the paper that you wrote your earlier observations on, write at least four prey animals and four predator animals." Give them a minute. (If you need to define the terms, a predator is an animal that hunts, kills and eats its food, whereas, the prey is the hunted and eaten animal.)

Now ask them, "How do the eyes of the predators differ from the eyes of the prey animals?" (Most predators have eyes that face and focus forward, and prey animals have eyes located on the sides of their heads for a more panoramic view.) Lead the students to this discovery if they do not grasp it readily.

Then ask the students, "Of all the animals that have eyes, can you think of any that have less than two eyes?" Pause for responses. (no) "Can you think of any animals with more than two eyes?" Pause for responses (some may say a spider). Say, "Organisms that have two eyes have BINOCULAR VISION. This means that they use the images seen by two eyes and the brain interprets these images as one image. Then say, "On back of your notebook papers, answer the following; With the exception of spiders, why do you think animals have two eyes?"


Say, "Roll up your paper to make it the longest tube possible. Hold the paper in your right hand. Gently place the paper in front of your right eye. Place your left hand, palm facing you (the student) next to the end of the tube farthest away from your left eye. Keeping both eyes open, look through the tube and at your hand at the same time. Focus on seeing me (you, the teacher) in the center of the tube. Be sure to keep both eyes opened." Note to teacher: Try this yourself first. You will find a hole the size of the rolled tube of paper in your left hand with whatever you are looking at there in the hole in your hand!

Pause for "Ooh, Ahh, Wow's." Then ask, "Why did this happen?" (Wait for responses.) Explanation: Each of your eyes see a little different perspective. They send this image to your brain, which interprets this as one image. This mixture of stimuli sent to the brain results in a nonsense perception. This mini-lab demonstrates nicely that we have binocular vision; two eyes, one image.


Say, "We are now going to do two lab activities to see if you were right. Put this paper back in your note book (desk) and keep your writing utensil out." Have the students work with the same person they were paired with for the first lab. Hand out the Post-Viewing Activity Sheet "Are Two Eyes Better Than One?" For the second activity, one per group of two. (See attachments.)

Each pair will need one lump of clay, a washer, and a 12" long dowel that just fits the diameter of the washer.

Roll the clay into a handle and insert the washer into one end of the clay_making sure the center hole remains unobstructed.

Have students predict how many times out of 10 attempts, each will successfully get the dowel to pass through the washer as asked for under "P" on Table A. (Refer to example below.)

Then one person needs to hold the clay with washer, while keeping count and recording the results. The other needs to close one eye, and attempt 10 times to have the dowel pass through the center of the washer, without hitting the washers' side the then guiding it in. Repeating the process with the other eye closed. Then repeating it again with both eyes open. Then have the pairs reverse roles.

If time permits, you may repeat this activity having each student hold their own washer/clay while aiming the dowel. Discuss why they were more successful. (Their brain was causing their body to respond to help line up the washer hole and dowel.)

After the students have completed the lab and activity sheet, discuss your findings as a class. You will usually have the greatest majority experiencing success with both eyes open, and very limited success with just one eye open. The boys usually predict a greater success than the girls, and the girls usually experience a greater success than the boys on this first activity, as it involves fine motor control. Girls are usually more adept with small, close-at-hand tasks, and have more experience with them.

Prepare for the final lab activity by dividing the class into groups of 3 students. You will need a large area, outside if weather permits, or a gym or hallway.

Each trio will need one writing utensil, a small rubber ball, about 1" in diameter, but larger can be used, and the "Are Two Eye's Better Than One" Activity Sheet 2. A blindfold is helpful for some students who have difficulty keeping an eye shut.

The students within each group need to put their names on TABLE B (example on page 17) and record the predicted the number of catches each will make in the appropriate column.

It is necessary for the teacher to demonstrate how the ball will be tossed. It needs to be a CALM, UNDERHAND toss that can result in being caught easily. Express safety first and tell the students that any rough handling of the ball will result in a 0% on this lab grade (or what ever consequences are consistent with your classroom management plan).

Two students will stand back to back and pace off 5 average steps apart. They will then turn and face each other. One person will be the tosser, the other the catcher. The third person will count and record the number of GOOD tosses the catcher catches with one eye closed out of 10 (if the recorder considers the toss a bad toss, it is repeated.) Then he/she will be the tosser and the other will be the catcher. Students are to keep trading positions until each has tossed, caught, and recorded.

Have students calculate data and record their findings on Table B. Then have them record their group findings from Table B onto Table C. Students sometimes have difficulty with this. (You can also have the student round up or down to use only whole numbers.) See completed example provided on page 28. After the lab, ask the groups to present their findings. You may wish to have them present these formally, after preparing charts, or informally, keeping a tally on the board.

Your overall findings will be that the boys again predicted a higher rate of success, and the girls slightly lower. In this case, the athletes will usually fare better overall than the non-athletes as this task involved gross motor skills.

You may wish to have the students compare and contrast both post-viewing activities. This can be done on an individual basis, or compile class data, with the focus on fine motor skills versus gross motor skills.

Ask, "What do you think is the reason for having two eyes?" (Responses will have to do with accurately judging distances, or depth perception.) Ask , "How many of you wrote the correct answer on the viewing sheet?" You may wish to have them share some of their other responses.

Conclude this lesson with the following. "You have now discovered that there are many ways that your eyes can be fooled. What were some of the different ways your eyes have been fooled, or your brain has been fooled by the images sent to your brain?" The answers should include retina fatigue/after image, movie making techniques and because we are binocular beings, we need both eyes to accurately judge distances with depth perception.
Action Plan
Have students collect several different examples of optical illusions and compile, and perhaps publish, a class book.

Encourage students to watch the presentations of how some famous movies are made. These often appear on public television.

Have students design an "Optical Illusion" show for elementary students. There are several other segments in this READING RAINBOW: OPT: An Illusionary Tale, video they could use in much the same way you have used this one with them.

If you have access to a television network, take a field trip to see the "behind the scenes" productions.

Have an artist come in and show how the use of lines and colors can fool our senses.

Have students take their "Green Hearts and Red Clovers" home and let their parents experience retina fatigue and after image, then explain to them what they have experienced and the history of colored computer monitors.
Math: Expose students to E. C. Escher's tessellations.

Math: Graph the similarities or differences between both post-viewing activities.

Science: There are many other optical illusions that can be explored.

Science: Dissect a cow's eye to really give them the hands-on approach to the structures of the eye.

Art: Have students create their own images to use with retina fatigue/after image.

History and Technology: Have students research other problems the use of technology has had that have had to be overcome.

Health and Science: Have students investigate other eye/visual problems. Physical Education and Athletics: Discover how many sports/activities require depth perception.

Physical Education and Athletics: Research to discover how many athletes, and in what sports, are successful having only one eye.

Video available from

Can be taped off of television. Check with your local PBS station for schedule.

Lesson plan developed by Master Teacher Linda A. Brown, Parma Middle School, Parma, Idaho

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