Elisabet O. Orville
The first WRITING ASSIGNMENTS will be group activities which develop word lists about the senses.
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1. Ask your students how many of their senses they have used already this morning. Set up the five headings of
hearing
,
sight
,
touch
,
smell
and
taste
(in any order) on the board and write down how they used them. For instance,
smell
, frying eggs or
sight
looked at the newspaper. Have them copy the lists on paper and remind them to bring notebooks the next day.
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2. Have them write which sense has been the most important to them today, and why. Have as many students read their answers our loud as possible and quickly tabulate the class’s results. Vision will probably be chosen by almost all students as the most vital sense.
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3. This informal poll should make vision the logical starting point. Now build up a list of adjectives that are strictly visual in the following manner: put a vase of particularly colorful flowers on the desk or table and if possible have students arrange their desks in a semicircle around it. Elicit one visual adjective from each (all nonvisual adjectives are rejected) and have the students write them down as you put them on the board.
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4. List all the synonyms that students can think of for seeing. ( for instance, squint, peer, gaze). You could make it a contest between the two sides of the room.
What is light?
The ancient Greeks thought that the eye sprayed out beams of light that lit up whatever we were looking at but of course we know now that the light source is always external and is reflected from the perceived object
into
our eyes.
The sun, which is the source of most of our visible light, also gives off radio waves, infra red, ultraviolet and X-rays. All these forms of energy travel as waves at 186,000 miles/second. The only difference between them is their wavelengths radio waves are very long and X-rays are extremely short with visible light somewhere in between. (you will probably need to explain about waves and wave lengths).
ACTIVITY:
The Electromagnetic Spectrum and Vision
Reproduce Diagram 1 at the end of this unit for your students to tape into their notebooks. They will also need colored pencils.
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1. Discuss the various forms of electromagnetic energy and explain the meaning of the exponents (104 = 10x10x10x10) Emphasize that the only difference between visible light and X-rays, for instance, is the wave length.
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2. Have students locate the tiny band of light visible to human eyes, and then color in the spectrum as indicated. (from left to right, red, yellow, green, blue, violet). Explain that color is determined by the wavelength of light. Red, for instance , has a longer wave length than violet.
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3. Color the rest of the electromagnetic spectrum black, indicating that it is invisible to human eyes. Therefore our eyes are sensitive to only a tiny band, although we can feel infra red as heat and ultraviolet produces a sunburn.
Although human eyes are quite limited is that true of animals also? Actually bees can see ultraviolet as a visible color. A flower that reflects ultraviolet will look quite different to a bee than a human, but on the other hand bees can’t see red—it probably looks black to them. A bee’s visual world is very different from a human’s visual world.
Most mammals and all nocturnal animals see very little color at all. We humans (along with bees and birds) are exceptions in having color vision.
WRITING ASSIGNMENT: Describe what it would be like to go clothes shopping if you could see NO colors, only shades of black, gray and white.
The outside of the eye:
ACTIVITY: Have your students work as partners, taking turns looking carefully at each other’s eyes. Have them draw each other’s eye, label the parts they know and write down all observations (for instance, how many times do they blink in a minute? does the iris open and close?)
Follow up with an EYE CONFERENCE to compare results. Give them the correct scientific terms (sclera, cornea, iris, pupil) to label their drawings. (
The Life Science Library Book on Light and Vision
, page 83, has an excellent large photograph showing the exterior of the eye.).
The inside of the eye:
ACTIVITY 1: Xerox the picture of the cross section of the eye (Diagram 2 at the end of unit) and give each student a copy to tape into her notebook. Label and discuss the functions of the parts.
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A. cornea—The transparent front of your eye. It bends the light entering the eye.
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B. sclera—The white of your eye. It protects and holds the shape of the eyeball.
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C. iris—The colored ring that determines whether your eyes are brown, blue or other colors. It controls the amount of light entering the eye.
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D. pupil—This is merely the hole in the center of the iris.
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E. lens—A crystalline body that changes its shape (until you age) in order to focus on near or far objects.
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F. vitreous humour—This is the jelly like substance that fills most of the eyeball and helps it keep its shape. (It may contain floaters, those specks that drift).
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G. retina—The all-important back layer that converts the light energy into electric energy. It contains two kinds of cells—the
cones
that see color and the
rods
see only black and white.
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H. blind spot—There are no rods or cones in this part of retina.
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I. optic nerve—The individual nerve fibers from the retina exit as the optic nerve. It carries the electric impulses to the brain.
Again the
Life Book on Light and Vision
, pages 84-95 has excellent drawings and photos.
ACTIVITY 2: You can have your students make cardboard models of the eye by using manila folders. Cut a large eyeshaped hole in one side of the folder and glue in white paper for the sclera, cellophane for the cornea, colored paper for the iris. They can even glue on thread for the eyelashes. Suggest that they are fourth grade teachers who are going to use the models to explain the eye to their students.
ACTIVITY 3: Compare the eye to a camera. See if students can figure out the similarities and differences. This should help sharpen thinking as to the functions of the eye parts.
Similarities
: The iris and diaphragm open and close to control the amount of light. Both lenses focus light. The retina and the film record the light that strikes them to form an image.
Differences
: Our iris is automatic. The diaphragm may or may not be. Our lens changes its shape to focus but the lens in a camera moves forwards or backwards to focus. Film must be developed to show an image. The retina sends impulses to the brain to get an image.
WRITING ASSIGNMENT: Comparing the eye to a camera should reinforce students’ knowledge of the eye. First have them make a simple picture of each and then write down the similarities and differences.
If you bring your camera to class why not take students’ pictures with very fast black and white film, discussing f-stops and times?
Simple experiments to demonstrate how our eyes work
After the students have tried each of these experiments with their partner, they should be able to WRITE very clearly a) how they did it and b) what it showed them about their eyes. Then you can have a VISION CONFERENCE to compare results.
Materials needed: magnifying glasses and penlights (available from Teachers Institute) paper and pencil.
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a.
Automatic adjustment of the iris
. Put your hands tightly over your eyes for a few minutes. Then have your partner shine a penlight in your eyes the moment you remove your hands. What happens to the iris? (answer: it closes , otherwise we would be blinded by excess light)
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b.
Depth perception by the lens
. Hold your finger about 12 inches in front of your face. Focus on your finger and then focus on the background. Can you focus clearly on both at the same time? (answer: no because the lens must change its shape each time).
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c.
How the lens focuses light on the retina
. You will need a magnifying glass and a white sheet of paper. Face the wall on the far side of the room from a window. Put the paper against the wall and bring the magnifying glass close enough to it to form the image of the window on the paper. Is the image right side up OR upside down? (answer: upside down because the lens has turned it. The reason the whole world does not look upside down is because the brain rights the image for us.)
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d.
The rods and color perception
. One student sits and stares straight ahead with both eyes. Her partner, who stands behind her, slowly brings a brightly colored object around the side of the subject’s head until it can just be seen. What color is it? (answer: you can’t tell because the rods which see only black and white are the only cells on the periphery of the retina.)
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e.
The blind spot
. Draw two simple figures about three inches apart on a piece of paper. (for instance, a circle and a cross). Close one eye and focus on the circle as you bring the paper towards you. What happens? (answer: the cross will disappear as its image passes over the optic nerve exit where there are no rods or cones. This is called the blind spot.).
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f.
Putting two images together
. Roll up a tube of paper and look through it with one eye. Place your open hand against the middle of the tube and look at it with the other eye. What do you see? (answer: your hand with a hole in it. The brain is receiving two very different images and is putting them together as best it can. Seeing is a matter of the eyes and brain working together).
Optical Illusions
(or now that you know how the eye works, can you trust it?) There are a few optical illusions that students might already be familiar with. For instance, on hot summer days we can see pools of water shimmering on the highway ahead of us which always disappear as we approach. These are of course mirages, caused by light bouncing off the hot air above the road.
The moon always looks larger when it is on the horizon than when it has risen higher (Students in the city may not have notices this). The reasons for this are not clear.
Diagram 3 (at the end of the unit) contains several different kinds of optical illusions which you can make copies of for your students. In these illusions you eyes are sending the correct images to the brain, but the brain because of previous experiences becomes confused and gives us the wrong answers.
ACTIVITY. Diagram 3 is divided into three types of optical illusions, those of perspective, reversible images and impossibilities. Have your students study each type and then write about them.
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1.
Optical illusions of perspective.
In most pictures the brain knows what the clues are for judging distance. Near objects are larger than close ones, the sides of a road converge in the distance and far objects are less distinct than near ones.
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____
____
If possible bring in a landscape print or photograph and have the students discuss and write their reasons for thinking something is near or far. Because we have subconsciously learned these conventions of perspective we are usually fooled by optical illusions that change the clues around.
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____
____
Then have the students examine the optical illusions of perspective and WRITE in notebooks (they can make a rough sketch of each) a) which line they thought was longer and b) why they were fooled (if they were). (In illusion D., ask if the lines are parallel)
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2.
Optical illusions that are reversible images
. In these illusions we see one possibility at first but then suddenly another appears and so we alternate between both images, never seeing more than one at a time. The brain just doesn’t seem to be able to handle more than one solution. You can have your students WRITE a) what the two configurations are as they perceive them and b) what their explanation is of the phenomenon. (It may be as good as that of scientists).
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3.
Optical illusions that are impossibilities
. What is wrong with the illusions in group c. ? Have the students WRITE about each one in their notebooks.
What is it like to be blind?
WRITING ASSIGNMENT.
The New Haven Register
ran a series of articles in April, 1981 on various handicaps, including blindness. In the learning package (30 copies at the Teachers Institute) there is an article about Susan Chambers, a blind Centrex operator at Yale.
Students should read the article in class and then the following points can be discussed and written about:
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a. What machines are required for a blind person to work as a telephone operator?
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b. What are some of the difficulties that she must cope with in her life?
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c. How do sighted people tend to treat blind people?
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d. Can you think of other jobs that a blind person could do? Are there any that would be impossible for a blind person?
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e. Do you know any blind people? How do they cope with life?
ACTIVITY WITH BRAILLE. A blind person must develop her sense of touch in order to read. Braille is a system of raised dots representing the letters of the alphabet which was invented by Louis Braille in the nineteenth century. A really fast reader can scan up to 2000 dots per minute with her fingertips, an equivalent of almost 100 words per minute.
The Oak Hill School for the Blind (120 Holcomb Street, Hartford, 06112) is extremely generous about sending Braille alphabet cards as a public service. It should be possible to get up to 25 of them if you write or call.
Give each student a card. Read the explanation together and then have her close her eyes. Explore the number and position of the dots for each letter by touch. (Our fingers are so insensitive it is often difficult to tell). Next work as partners. Exchange short messages in Braille by cutting out letters and gluing them onto another sheet.
LESSON 1 at the end of this unit is a Lab on Phototaxis in Invertebrates. This would be a good time to run it, before the section on Healing is started.
