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Module: Visual PerceptionSeeing at the Right AngleGrades: 4-8
OverviewHere on Earth, human beings orient themselves to the spatial environment by means of both gravitational cues from our body and visual cues such as the walls of a room. NASA is especially interested in the role of visual cues in spatial orientation, because in aircraft flight or in weightlessness in space, gravity cues are either absent or confusing, so pilots and astronauts must rely on their vision for their orientation. Fighter pilots have sometimes misjudged where the horizon was and crashed their planes into the ground or the sea. Pushing a wrong button in a space vehicle can have dire consequences on a mission. In order to study this use of the eyes, NASA's visual perception scientists have developed studies done with "pitch boxes," which is a visual environment with slanted walls. There is a room-sized pitch box at NASA in which they study how people can gauge where the horizon is when the room is slanted at different angles. In this activity, students will use a pitch box to experience how, in relying completely on visual cues to do a task in an odd spatial environment, confusing optical illusions can occur.
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a. Cut black construction paper in a circle to mask the reflective part of the flashlight. Insert the mask into the reflective dish. b.Use a hole punch or nail to make a neat hole in a scrap of poster board. Tape this over the front of the flashlight to mask the light coming out. When turned on, the flashlight should show a small dot on the wall of a dark room instead of a wide disk as usual |
3. Set up the pitch box apparatus.
c. Have stack of books ready to place under front edge of pitch box.
d. Place light pointer beside pitch box on the desk.
4. Have pencils and data sheets ready to distribute.
5. Read the Background for Teachers section at the end of this write-up.
1. Gravity cues for spatial orientation. Ask each student to stand and face a wall a few feet away. Give the directions, "Look straight ahead and pick a point on the wall you think is exactly even with the height of your eyes." Ask, "How do know how high to look? How does your brain know that your eyes are looking at the correct level?" Accept responses. Ask the students to close their eyes and (a) move their heads as if they were to look at the ceiling, (b) tilt their heads down as if they were looking straight ahead again, then (c) open their eyes. Ask, "How did you know you were looking upward, or straight ahead even though your eyes were closed?" Accept answers. Explain: "Your brain gets information not only from your eyes but also from sensors (nerves) in your muscles and inside your ears. Your brain uses the information it receives from these sensors to understand the position of your body in relation to the force of gravity."
2. Estimating where the horizon is. Ask students to test their perception by walking to the wall, keeping their eyes aimed at the spot they believe to be at eye level (outdoors that would be the horizon). Ask, "Was the point you chose exactly at eye level as you predicted?" Accept responses. Explain, "When you are in normal conditions on the Earth, you are able to understand the space around you because your brain gathers information not only from you eyes, but also from your muscles and inner ear which tell it not only what you are seeing but also how your head and body is positioned in relation to the Earth and its gravity." Mention that pilots must be able to know where the horizon is (where the sky and Earth meet) for safe landing of a plane.
3. Imagine what it's like in space. Have the students imagine that they are on a space mission. With the body weightless, the brain no longer receives input from your muscles and inner ear to help orient your body in relation to the Earth. Ask, "Do you think you can rely solely on your eyes to give you a clear understanding of objects in the space around you? Why or why not?" Mention that fighter pilots have sometimes experienced such confusing clues from their muscle and inner ear "sensors" when flying at odd angles that they have misjudged where the horizon was and crashed their planes into the ground or the sea. In a space vehicle, pushing a wrong button can have dire consequences.
4. The pitch box. Explain about right angles, and how the way a wall meets with the floor is a right angle-both are straight and create a corner. That is the way the eyes usually meet with the horizon, at right angles to the floor (or level ground). Explain that to better understand how people react to odd seeing conditions, NASA scientists us something called a "pitch box." Pitch means upward or downward tilt. Point out that the sides of the pitch box are at right angles to each other. Also show how the pitch box may be pitched, or tilted by placing a stack of books under the front edge of the box.
5. Using the pitch box. Put one stack of books under the back of the pitch box and the other stack of books (equal height) under the front of the pitch box, so the pitch box is flat. Tell the students that they will use the laser pointer to indicate where they think the "horizon" is. Make a firm rule: no looking straight at the laser light under any circumstances. Ask for a student volunteer to be a test subject and sit in the chair in front of the pitch box. Adjust the height of the chair and/or the pitch box so their eyes are level with the center of the box ("0" mark of the number line). If using a PVC-type pitch box, place black cloth over the top so the cloth blocks any distracting visual cues from the open sides of the box. Have the rest of the class to sit or stand behind the pitch box so they can see the number line. Ask for another volunteer to be "number reader" and have them close enough to the viewing screen to read the number like. The numbers are to be called off using the color of the number, such as, "Blue 3" or "Red 1." Ask the test subject to quickly pick up the laser/flashlight pointer and direct the beam to a point on the paper screen they believe to be even with their eye level-the "horizon." Have the number reader call out point on the number line where the pointer was shining. Ask the class "If the "0" of number line was at eye level, did the subject aim the light pointer correctly? Was their aim above or below eye level, or exactly right on?"
6. Change the angle of the pitch box. Ask the test subject to close his or her eyes while the box is tilted. Add books to the stack of books under the edge of the box closest to the test subject, so screen with numbers facing the class is tilted downwards. Adjust the position of the box so the distance from the subject's eyes to the center of the screen is the same as before the box was tilted. The "0" point of the number line should remain at eye level. Allow the test subject to open his or her eyes.
7. Make predictions. Ask, "Do you expect the test subject to aim the pointer to the same spot as before? If not, do you expect them to aim high or low when they try to find the point on the screen that is exactly even with eye level?" Discuss students' predictions and their rationale for making the predictions.
8. Conduct the experiment. The test subject quickly picks up the light pointer and directs the beam to a point on the screen they believe to be at eye level-the horizon. A number reader calls out the number where the light hits the screen. Ask, "Did the student aim correctly when the box was tilted backwards? Was their aim higher, lower, or the same as when the box was sitting flat on the desk top?" Repeat the experiment but with several books removed from under the edge of the box nearest the test subject, so the pitch box is tilted towards the subject.
9. Collect data from the whole class. Distribute data sheets and pencils. Repeat steps 5, 6, and 8 with each student. For each change, the "number caller" becomes the "laser pointer" and each new "number caller" is chosen by the person who has just finished flashing the laser. As each test subject tries the experiment, each class member writes the subject's name in appropriate column on their data sheet. Each student may have up to three tries for each of the three "pitches"-no tilt, backward tilt and forward tilt. For each subject, adjust the distance from the subject's eye to the center of the screen and the chair height so the subject's eyes are level with the center point of the screen.)
1. Allow time for students to calculate the average of the class' scores. Then ask the students to graph both their personal data and the class average.
2. Discuss the results of the experiment. Is there any relationship between the direction the box is pitched and the test subject's perceived eye level (as determined by the position of the light point on the screen)? How do students' individual scores compare with class average scores? Discuss similarities and differences between various individual's scores. Is there any difference in the magnitude of the misperception that occurs when the box is tilted forward (negatively) rather than backwards (positively)?
4. Compare your results with the test results recorded by NASA researchers. Data from these tests is presented in the article, "Effects of Optical Pitch on Oculomotor Control and the Perception of Target Elevation" in Perception and Psychophysics 1995, 57 (4) pp. 433-440.
5. Write a lab report which describes the pitch box experiments you have completed. The lab report should include a title and introduction as well as sections describing rationale, materials, method, results and conclusions. Help students to streamline their descriptions so the minimum amount of information necessary for an outsider to understand the experiment is included. Avoid including unnecessary and excessive details about materials and method, for example, about how the pitch box was made or how the seat was adjusted, etc. Send copies of these reports to Dr. Robert Welch (rwelch@@mail.arc.nasa.gov) at NASA Ames Research Center, Moffet Field, California.
6. Discuss the effectiveness of the methods you used to conduct the experiment. Were there any variables that you were not able to control but may have affected your results? Can you think of any other problems or issues that may have affected the results? (Some examples of variables are: foreknowledge of the purpose of the experiment, visual cues received from outside the box, movement of the subject's head up or down to compensate for the tilting of the box, inconsistency between the direction your eyes are looking and where you are pointing the light beam, etc.) Discuss the scientific validity of your conclusions.
1. Do the pitch box experiment described above but with the following variations:
a. with test subjects lying on their side instead of sitting upright
b. by tilting the box sideways instead of front to back
c. with the box tilted to more extreme angles
d. when a deeper or more shallow pitch box is used
2. Go to places where you can stand on a hillside. How do you think your perception of where the horizon is changes when you stand looking uphill versus looking downhill, or sideways across the hill?
3. Do a math lesson about addition of negative and positive numbers. For example, have each student draw a vertical number line from -10 to +10. As the teacher calls out a pair with one negative and one positive number, students use markers (beans, paper clips, ...) to depict the value of these numbers on the number line. They may then remove an equal number of markers from each side of the origin, leaving the number of markers that correspond to the value of the math equation in which the two numbers (one positive and one negative) are added. For example, if the teacher says, "Six, and negative eight," students place six markers above the origin and eight below. Then they remove an equal number of markers from both sides of the origin (six) leaving two markers below the origin. Thus the answer to the equation six plus negative eight is negative two.
4. Study optical illusions and perspective drawings. What impression does the drawing create? For perspective drawings, how do the parts of the drawing create the impression of space and distance? For optical illusions, how does each part of the drawing help to create the illusion you observe?
5. Study anatomy and physiology of touch and pressure sensors in the muscles and skin, and structure and function of the inner ear and the eye.
6. Brainstorm situations where perspective could affect a pilot or astronaut's performance. Write a short story describing a scenario where an astronaut or pilot's perception of space is in error. Include a description of the consequences of the misperception that occurs.
7. Find NASA sites on the Worldwide Web or use your library to do a report of an aircraft, space craft, flight pilot, or astronaut.
8. Art-Do one point, two point or three point perspective drawings using a straight line as the horizon in each of the pictures.
Prerequisites
Vocabulary
Skills
Concepts
Human perception depends upon information received by the brain from a variety of nerve receptors. These include nerve cells in the retina of the eye, pressure and touch sensors in the muscles and skin, and special hair cells of the inner ear which indicate the position of the head with respect to gravity. Under normal circumstances, on Earth, this variety of receptors work in unison to give the brain an accurate sense of the space and objects outside the body. Under special circumstances, one or more of these receptors misinform the brain. This may lead the brain to misunderstand objects and space outside the body. For example, while in flight or in outer space gravity affects the inner ear differently than while in a normal earth environment. In this case, signals from the inner ear which are essential for your brain to understand the orientation of your body are inaccurate. In practice this misperception can lead to potentially disastrous mistakes made by pilots and astronauts while in space flight.
Additional Background information
Pitch box and pitch room experiments conducted by researchers at NASA use an ISCAN infrared video system to record the direction the test subjects are looking. The experiments are conducted with a tool called a bite board which keeps the subject's head perfectly still. The subject's eyes are closed while the pitch box is tilted. The subjects cannot see any part of the room beyond the pitch box. Results of NASA experiments show that subject's visually perceived eye level is higher or lower than normal depending on the tilt of the box's frame. In the STELLAR activity Seeing at the Right Angle, students are asked to locate a target within the pitch box. Research at NASA shows a correlation between the natural resting position of the eyes and where the target is perceived to lie. Researchers are now looking for ways to help the brain adapt in order to minimize misperceptions that occur when information received from the muscles about gravity does not agree with information received from the eyes. In this way disastrous mistakes that are common to astronauts and jet pilots may be avoided.
Editing by: Gregory Steerman, Alan Gould, Lawrence Hall of Science
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