Module: Visual Perception
What You See Is Not Always What You Get
In this series of activities students will learn about how they receive information about the world, by their sense of sight, and how that information is processed through their senses. Students will also learn about how the principles of light are related to what they see. Since astronauts' performance is so heavily dependent on their ability to see, an understanding of this subject is crucial.
30 minutes per part with some additional time for part 3-preparing the shoeboxes
In Class Time
Three to five 45-minute class periods
For the teacher: a utility knife or large pair of scissors
For each group of 24 students
For each student:
For each student:
For the whole class:
For each student:
For each group of 34 students:
Review the section "Background for Teachers" at the end of this document.
For each student, make a photocopy of "How You See" worksheets, Parts 1, 2, and 3. (see hyperlinks in materials list)
Ask students to bring in shoe boxes from home to use for the pinhole cameras. The shoe boxes can be almost any size as long as they are rectangular in shape.
In one end of each shoe box, cut two slits that are about 2 mm (1/16") wide, 4 cm (1.5") in height, and 1 cm (1/2") apart. The opposite side of the shoe box (inside) should have a white surface. If necessary, place an unlined 3" x 5" or a plain piece of paper there to make it white.
Optional: make transparencies of the labeled eye diagrams at the end of this activity write-up.
Part One-The Eye as a Camera
1. Sources of light. Have students think about and list sources of light on their worksheets. In a classroom discussion, allow students to share their ideas and items on their lists. Provides guidance, elaborations, and corrections as needed. Ask, "How can we see other people?" Guide the discussion toward the fact that people reflect light. Give the students an example by turning off the light and then ask what they notice about other students. How well can they describe what someone else is wearing?
2. Cameras. Explain that the class is going to investigate how light behaves and that one way is to find out how a camera works. Have students think about and then write down on their student worksheet a description of the parts of a camera and how it works.
3. Make pinhole cameras. Have the students assemble their pinhole cameras out of shoe boxes. Each student should have their own shoe box or you can accommodate students in groups of 24 to share a shoe box. Students should follow these directions while making their pinhole cameras:
4. Use the pinhole cameras. Darken the room and have students point the pinhole ends of their cameras at a brightly lit object and look at the screen. The students should see an upside-down image of the object focused on it. Let the students explore with the camera on several objects. Have the students describe on their worksheets what they notice about the images they see.
5. The eye is like a camera. Have students recall their ideas about parts of a camera and how it works. They can refer to their worksheets. Point out that even though their pinhole cameras do not have lenses, they still are like real cameras that make an upside-down picture on the film. Brainstorm similarities between the eye and a camera:
What happens: 1. Light rays from the object pass into the camera through the pinhole and form a focused image on the screen. The final image is upside down because the light rays cross over each other as they pass through the pinhole. The same thing happens in the human eye.
6. Use the pinhole cameras outside. Have the students try taking their camera outside and looking at moving sunlit objects. CAUTION: STUDENTS SHOULD NOT LOOK DIRECTLY AT THE SUN WITH THIS CAMERA. They will need to block out all of the light by covering their head with a piece of dark cloth (like a jacket). Have them gather the cloth under their chin so that no light can get through the screen.
Part Two-Parts of the Eye
1. Draw the eye (front view). Have students work in pairs. Have each student draw a large picture of one their eyes on the student worksheet, putting in as many details as they can, by looking in a mirror or by looking at their partner's eye. Have them notice the color and the texture of their eyes, and use crayons to lightly color the drawing. Then they can label the picture that they have drawn and compare the colors and textures of each other's eyes. Have them use the terms listed on the sheet to label their diagram. Students may use any resource or reference that they want.
2. Draw the eye (side view). Have the students fill in the diagram of the side view of the eye with the terms marked on the student worksheet.
3. How the pupils change with light. Make the room as dark as possible (turn off lights, pull drapes, etc.) For your students to see their pupils automatically get larger and smaller, have them look at their eyes in a mirror as you turn the light in the room off for 10 seconds then back on again. You may elect to have student use restroom mirrors for this part. Alternatively, your students can team up and watch this happen in their friend's eyes. Have them record what happens on their worksheet.
4. Feel the cornea. Students can feel the slight bulge of the eye in the cornea Have all of the students close their eyes. Have them press their finger gently on their eyelid as they slowly move their eyes left and right. Have students record on their worksheet what they noticed and discuss it with their partner.
5. Read an eye chart. Place an eye chart on the wall. Have students predict how many lines they will be able to read in the dark and again in the light. Have a place to record near the chart what a student's predictions were versus the actual results. You could also have a place to have the students speculate why the results were different.
6. Optional: Take students to as dark an area as you can, such as the stage in your multi-purpose room. Put objects in this area of various colors: white items like paper, darker items, glow in the dark items, etc. Have students identify what the items in the room are. Or have students bring in items from home and have them plan what items to place in the room. Each small group can design items to go in the room for the other groups to identify.
7. Clean up work areas.
Part Three-Reflection and Refraction
1. Divide the class into groups of 34 students. Each group should have a shoe box with slits already cut, a flashlight, small piece of clay, a small square mirror (about 3" x 3"), and a small round clear jar filled with water.
2. Set up the mirror. Remove the lid of the box and keep it to the side. Have the students place the clay inside the box and stick the bottom of the mirror into it so the clay acts as a stand for the mirror. The reflective side of the mirror should be facing the end with the slits.
3. Observing what a mirror does. Make the room as dark as possible (turn the lights off, pull the drapes, etc.). Have the students predict and write on their worksheets what will happen when they shine the flashlight through the slits onto the mirror. Have the students shine the flashlight through the slits and look down into the box from above. (They should see two lines of light reflected in straight lines from the mirror's surface.)
4. Swivel the mirror. Have the students swivel or move the mirror to change the angle of reflection and record their observations on the worksheet.
What happens: A mirror reflects light rays at the same angle as they arrive. Students will be able to see this by looking at the light from above. If the students swivel the mirror, they will be able to direct the light rays in any direction, even back where they came from.
5. Instruments with mirrors. Explain to the students that many instruments in science, including ones used by astronauts and NASA scientists, use mirrors. Ask them if they can think of any. (Telescopes, cameras, periscopes, microscopes, and many with very complicated names that we don't want to go into here!) Explain that some "Heads-up Displays, which allow the Shuttle pilots to see instrument readings and look out the windshield at the same time, use the principle of reflection of light for the display, even though it is not a full reflecting mirror that is used.
6. Light rays through a jar. Ask the students to take the mirror and clay out of the box and carefully place the jar of water in the middle of the box. They should shine a flashlight through the two slits. They should look into the box from above and will see how the light rays are refracted (bent) by the jar of water, and how they eventually cross. Have students predict and write on their student worksheet what will happen and then what actually happens. If students cannot see the light rays right away, they should try moving the jar around until they can. They can also try adjusting the flashlight position to get the best rays. Explain to the class that the lenses in their eyes bend light just like the jars of water did.
What happens: The water in the circular-shaped the jar make an effective lens (like the eye) that refracts the light rays. Notice that the bending happens most at the edges of the jar and only where the light passes from the jar to the air, or from the air into the jar.
7. Straw in water. Students can now take the jar filled with water out of the shoe box and place it on the desk. Have them place straw in the jar record on their student worksheet what they see when they look at the straw in the jar from the side.
What happens: The light from the straw reaches your eye by a variety of different paths. Light from the bottom half of the straw travels through the water and is refracted as it passes from the water into air. This makes the straw look bent.
8. Clean up work areas.
Tie-In With NASA Research
Ask the students, "Why might it be important for NASA scientists to study how people see?" Keep this open ended and add your own views as you wish. The following ideas may be brought out by you or the students:
Apollo Program Anecdote:
During one of the Apollo lunar missions, the pair of astronauts that were on the surface of the moon saw an area of lunar highlands that they wanted to explore. The highlands appeared to be rather close. When the astronauts informed mission control that they wanted to do this exploration, the astronauts were surprised when mission control told them that they could not use the lunar rover to explore the highlands It turned out that the close appearing highlands were over 22 miles away! The astronauts were deceived by the appearance of the "alien" landscape of the moon.
Landing the Space Shuttle
When reentering the Earth's atmosphere, while attempting to land the Space Shuttle, astronauts become disoriented during the period of re-entry. While the Space Shuttle is decelerating, the astronaut who is piloting the Shuttle thinks they are going down and pulls up on the controls to compensate for this feeling. They are really steady and there is no need for overcompensation.
When the Shuttle lands have you ever wondered why the astronauts do not just walk right out of the shuttle? It takes several hours for the astronauts to become readjusted to the environment of the earth.
Navy Aircraft Carrier Pilots
On Navy carriers there was a problem with A-7 aircraft ending up in the water about three miles after they had taken off. What was happening was that when the aircraft was launched with the help of a catapult, the pilot thought that the nose of the aircraft was up and that the aircraft was going to stall. Stalling was a real fear on an A-7 because it does not have afterburners. To compensate for the feeling that the nose of the aircraft was up, the pilot would push on the controls to lower the nose and the plane would end up in the ocean.
NASA studied this problem and found out that the pilot had to perform certain tasks immediately after takeoff that prevented them from looking at all of their instruments. The instruments indicated that the plane was indeed heading in a safe direction and that the attitude of the aircraft was all right. The g-forces (gravity forces) that the pilot experienced at takeoff made it appear that they were going to stall. The procedures of the pilot were changed so that they could monitor their instruments and get a clear indication of what their situation was.
Working in Microgravity
The perception of where things (buttons, instruments, etc.) are in microgravity is different than what we are used to. The buttons appear to be in a different place.
In microgravity there are no gravity cues: there is no up or down, or left and right. Astronauts could actually be working upside down in the Spacelab or on some other project. Astronauts in the space station will be in space for long periods of time.
More Activity Ideas
1. Use a diffraction grating or prism. Cover up the two slits on the shoe box with a half an index card and shine the flashlight through a pinhole instead. Place a diffraction grating in the shoe box on a clay "stand." In a dark room, shine a flashlight through the pinhole. When light goes through the diffraction grating, what happens? Have students draw and color a picture of what they observe. The diffraction grating splits white light into the colors of the rainbow in the same way that a prism does. Notice the order in which the colored spots appear, it is the same order as the colors in the rainbow.
2. Use red and green filters. Have students look at a green leaf and a red tomato through the red filter. Have them draw and discuss what they observed. Then have them do the same thing with green filters and compare this to what they saw using the red filters. The red filter lets red light only pass through it. When you use it to look at the green leaf, which is giving off green light, most of the green light is blocked by the filter. This makes the leaf appear dark, if not black. In a similar way, looking at a red object through a green filter makes it appear dark.
3. Miller Lyer Illusion-Get 2 yardsticks and attach to both ends of one yardstick directional arrows (< and >) out of cardboard or wood These arrows should be large enough for the entire class to see from the front of the room and they should be oriented in opposite directions like this: <---------->
Cover up the numbers on the yardsticks with black construction paper or it will ruin the illusion. When you are done with the yardstick, it should not look like a yardstick. Using masking tape, attach the yardsticks to the front chalkboard, separated by a few feet. Ask the students which of the two sticks looks longer. Have the students predict which line is longer by writing it on their prediction sheet. Then move the arrows from one stick to the other. Again ask the students which line looks longer, the one with the arrows or the one without. Again have the students predict on their prediction sheets.
4. Perception Faire. Another good idea of an activity would be to design a series of stations based on visual and hearing illusions. Students could rotate through the stations, collect data, and draw some conclusions about what caused the illusions. This is possible since they have some knowledge of how vision works.
Background for Teachers
The Inner Eye:
Additional Science Background
The light that you see and use everyday is a form of energy. We make use of light more than almost anything else to tell us about the world we live in.
The Sun provides us with more light than any other source. But because no part of Earth is in sunlight all the time, we need artificial sources of light as well. Light is produced from both electrical and chemical energy.
Light travels in a straight line. But it can be affected by the solids, liquids, and gases that it passes through. Most of the interesting properties of light are seen only when it meets an object. A ray of light can be reflected, bent around corners (diffraction), scattered in many directions, and made to interfere with other light rays to make wonderful colors.
When objects reflect light, light rays bounce off of them. People reflect light from the Sun and from other sources of light. If an object does not reflect any light at all, it looks black. Smooth, shiny surfaces are good at reflecting light. If a smooth shiny surface is flat, you will see undistorted reflections. But on irregular or curved surfaces, such as the surface of a polished metal spoon the reflection of your face is distorted.
Reflections from flat mirrors are the right-side up, but reversed from left to right. The same happens to a reflection of your face in the bathroom mirror. You recognize this reversed face as your true appearance, which is why photographs, which do not reverse the image, can seem unfamiliar.
Many materials let light pass through them. When they are completely transparent, like the clear glass in a window, all the colors of light can pass through equally well. If the material is colored by a pigment, only light with same color of the pigment gets through. The other colors are absorbed by the pigment.
Light and Sight
People have been bending light to serve specific purposes for many hundreds of years. Much of this has been with lenses. These are useful because they bend light in a very specific way. The lens in magnifying glass, for example, bends light so that you can see a larger image of the object you are looking at.
Our eyes and brain together are extremely good at collecting and interpreting images of our surroundings. The lens of our eye focuses images onto a layer of light-sensitive cells called the retina. These images travel as nerve signals along the optic nerve to the brain, where separate parts of the brain decipher clues that will help it interpret the image.
An image that we look at is upside down on the retina because light rays cross each other in the eye. The brain interprets the image so that we see it the right side up.
There are two types of light-sensitive cells in the retina-rods and cones. The rod cells are sensitive to dim light, but can't distinguish colors. This is why we can only see black and white in the dark. Cone cells are sensitive to colored light, but only if it is bright.
Editing by: Alan Gould, Lawrence Hall of Science, University of California, Berkeley
Keywords: eye, vision, reflection, refraction