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Grades 5 - 8


This project is an investigation of the scientific basis for optical illusions. Students will begin with optical illusions in nature, progress to common abstracted illusions, then look at theoretical underpinnings that attempt to explain what we see. We take for granted the value of "eye-witness testimony" believing that what we see carries the weight of truth. In the courtroom as well as in other aspects of life, this assumption deserves closer examination. Illusions arise when the eyes gather im-pressions that the brain can't make sense of. The brain's automatic corrections for this ambiguity can make up for built-in limits to the senses, conflicts between the senses, false expectations or phenomena from the physical world itself.
ITV Series
"Reading Rainbow: Opt: An Illusionary Tale (#76)"
Learning Objectives
Students will be able to:
Reading Rainbow: Opt: An Illusionary Tale (#76 ) videotape
one set of display cards (provided at the end of the lesson)
pictures of animals in camouflaged settings

Per 2 Students

Per Student
Pre-Viewing Activities
Tell students: Animals use their coloration to protect themselves. Watch these optical illusions of nature, hiding prey from their predators. Play a 4-minute segment taken from the end of the Opt: An Illusionary Tale video, which shows animals in their camouflaged states. (The segment begins "... animals who blend in...", which shows a snowshoe hare, owl, fish, flounder, rock fish, horned lizard, walking stick, leaf clipper, caterpillar, leaf insect, thorn bug, green insect, horn beam eater, caterpillar, and ends with "you might find yourself looking at everything twice." Stop tape.)

Distribute a zebra herd photo to each pair of students. Question students' previous knowledge of the habitat and predators of zebras. (Animals of the plains hunted at dusk by lions which have night vision, but not especially keen eyesight.) Question what protection the striped pattern offers to the herd. (Lions try to attack lone animals, stragglers or weaker animals. The stripes give the impression of a massive animal, not a single target.) Have teams try to differentiate one zebra from the herd by tracing its outline, then try to trace the remaining zebras. Student teams may compare their tracings to see if they came up with the same pattern of tracings, as lions would try to identify single zebras.

Zebra Herd Photograph Any type of zebra photograph that shows a closely grouped herd can be used here. The object of the lesson is to distinguish between striped animals. One photograph can be found in the January 1996 edition of Smithsonian Magazine, page 24, from the Imax/Omnimax film Africa: The Serengeti, produced by Graphic Films Corporation and the Houston Museum of Natural Science.
Focus Viewing
To give students a specific responsibility while viewing, each video segment corresponds to a brief worksheet activity ("Prediction and Verification" worksheet) on which students record and/or measure responses to questions posed by the video segments about their perception of several optical illusions. Say: You will be watching a series of seven optical illusions in order to make a prediction about what you see.

Explain: Scientists have discovered that animals such as fish and birds can be tricked by optical illusions. Let's see some of the ways that we can be influenced by these tricks of the eye.

Viewing Activities
REWIND tape to the beginning. Teachers: you will be watching a series of illusions. First, each is presented and a question posed. You will be directed to watch each segment, pause at the end of each question and allow students to record their predictions then resume the video for the next segment and question.

FAST FORWARD to LeVar Burton showing letter with diagonals.

Play tape, beginning with "Here I am... "

PAUSE after "which one is longer?" Direct students to record prediction, then measurement on "P and V" worksheet at letter A.

RESUME for video explanation.

PAUSE tape. Say: Because of our experience with geometry, we see the lines as diagonals of one large and one small area.

Optional: Sample A represents a geometric illusion. The diagonal of the larger shape is assumed to be longer than that of the smaller one.

RESUME for sign with arrows.

PAUSE after "...are they the same or different sizes?" Direct students to record predication, then measurement on "P and V" worksheet at letter B.

RESUME for explanation.

PAUSE tape. Say: This puzzle is an example of a Muller-Leyer illusion. Scientists think that our experience with perspective causes us to associate this illusion with near and far corners. Try turning your arrows until they point up and down to test this reasoning.

Optional: Sample B is assumed to represent a psychological illusion based on our experience of perspective (objects seen at a distance appear to be smaller than those up close). The inward and outward pointing corners cause your eye to measure those distances instead of the inside segments.

RESUME for LeVar Burton with trident.

PAUSE after "...how many prongs do you see?" Direct students to record predictions on "P & V" worksheet at letter C.

RESUME for explanation.

PAUSE tape. Say: What did you notice about the base and points of the trident? (The rules change in mid-drawing from flat to three dimensional representation.)

Optional: Sample C is an illusion based in geometry, drawn using rules for representing three dimensions at the base and two dimensions for the prongs.

RESUME for LeVar Burton with two flowers.

PAUSE after "... which flower has the larger center?" Direct students to record prediction on "P & V" worksheet at letter D.

RESUME for explanation.

PAUSE tape. Say: Just as you may be influenced by your surroundings, the centers of these flowers seem to change size. Use the dime in your kit to compare sizes of the centers on your worksheet, then record your findings.

Optional: Sample D is an illusion of psychology. The environment of an event can change our perception of what has been seen.

Distribute one "Longest Object" worksheet to each team and direct students to: 1) decide which is the longest object, and 2) measure and record lengths (in centimeters) of the remaining objects. While students are working...

FAST FORWARD to LeVar Burton standing before some art work in a gallery setting.

PAUSE tape. Have students return to the "P & V" worksheet.

RESUME for LeVar Burton with the portrait.

PAUSE after "Each picture is more than it seems... in this case there are two pictures in one." Ask: How many faces do you see? Direct students to record prediction on "P & V" worksheet at letter E.

PAUSE for explanation.

PAUSE tape. Say: The idea of ambiguity, or having two ideas exist at one time, is a difficult one for some Western cultures to accept, but it is a part of Eastern philosophy. (Can be illustrated with yin/yang figure.)

Optional: Sample E is a psychological illusion based on the mind's inability to hold two images of an ambiguous figure at the same time.

RESUME for LeVar Burton with the black and white grid.

PAUSE after "where the lines cross, gray spots appear." Ask: What color is the spot in the middle of your field of vision?, then What color are spots on the periphery (edges) of the field of vision. Direct students to record observations on "P & V" worksheet at letter F.

Say: One explanation for this illusion describes a light sensing chemical called visual purple, which is activated and tires as you stare at the grid. The after-image of black on white appears while the visual purple refreshes itself.

Optional: Sample F is a physiological illusion, explained above.

RESUME for LeVar Burton with boxes.

PAUSE after "See these boxes... let's count them." Say: Count the cubes you see on your worksheet. Number them using one color. Direct students to record prediction on "P & V" worksheet at letter G.

RESUME for video counting.

PAUSE tape. Tell students: Now turn your worksheet upside down to count and record, in a second color, the number of cubes you see.

RESUME for reversal and counting.

STOP after "...you never know which way it will go."

Optional: Sample G is a geometric illusion based on the representation of three dimensions on a two dimensional surface.
Post-Viewing Activities
Review results of "P & V" worksheet items A-G. Introduce display cards with samples of other well-known illusions. Help students decide which illusions are based on the same principles as those in the worksheet. If desired, lead a discussion developing whether each tricks through psychology, physiology or geometry. (Use optional portions above.)

Return to "Longest Object" worksheet and have teams report on their choice of apparent and actual longest objects. Say: You all have the same objects in view, yet you have made different choices of the longest object. Take a few minutes to see how this might explain some differences in the reports given by eyewitnesses to an event. (Different people focus on different aspects of an event; tricks of the eye may cause people to think that they have seen something that did not actually happen.)

Students may also create a "Face-Vase" optical illusion for their own "Gallery". This exercise in ambiguity was used in history to conceal portraits of unpopular political and religious leaders. You will need scissors, glue and two sheets of contrasting color construction paper. Fold one piece of paper in half lengthwise and sketch a profile. Cut through both sides to make two symmetrical "faces". Glue "faces" to background paper, keeping straight edges aligned. Display student work on a bulletin board and have students study the illusions they have created.
Action Plan
Investigate and paint a trompe l'oeille mural.

Contact a professional or regional theater to meet a set designer or painter.

Contact and visit the production facilities of a television station.

Ask an artist to demonstrate the skills needed to create a painting in perspective.

Write a letter to a trial attorney or judge and ask about the importance of eyewitnesses to a trial.

Stage an "incident" and interview witnesses, then write a summary for publication.
1 Science:
Investigate illusions that confuse other human senses.

2 Computer:
Use Logo language or drawing/painting programs to draw polygons that illustrate
3-D illusions.

3 Art:
Research the invention of perspective and/or compare pre- and post-Renaissance

4 Architecture:
Research the use of illusion in the design and construction of Greek temples.
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