Optical Illusions Grades 3-6

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					            Optical Illusions                                                        Grades 3-6


      Magician “props” (i.e., hat, wand, scarves)
      3-D Hologram chamber
      Subjective Contours example picture
      Captain Underpants book(s)
      10 pc. Construction paper (letter sized)
      10 Blind Spot test pages
      Anatomy of Eye poster
      Half sheets of blank paper (thin, easy to see through)
      10 washable markers
      Computer with rotating image program
      Pages of samples of optical illusions
      Books with optical illusions
      Magic Eye posters
      Handouts with sample illustrations/resources

SET-UP:        Prior to students arriving

      Place 3-D hologram chamber on table and verify visibility of hologram item.
      Cover hologram chamber with magician’s scarf.
      Wear the magician’s hat and wave the wand if you are feeling dramatic….

Please note:

This experiment relies heavily on explanation, so each step includes a script, interspersed
with activities/demonstrations that illustrate these explanations. Paraphrasing is expected
and welcome, as long as the concepts are covered.

Science Alive 2009                                                                         Page 1
               Optical Illusions                                                          Grades 3-6


   1. INTRODUCTION: (suggested script)

               “Magicians use illusions all the time. In fact, they are sometimes called illusionists.“
                (uncover 3-d Hologram chamber)
               “Illusions are misperceptions that are common to most people.
               Some experiments with animals indicate that several species of mammals and birds are
                “fooled” by illusions in much the same way we are
                (if you have ever tricked a dog while playing fetch by hiding the ball behind your back,
                you know what I’m talking about).
               However, not all humans are fooled by all illusions.
               Factors such as prior experience, visual context, and focus all play important roles.
               For that reason, our “experiment” at this station will instead be more like an experience,
                with a certain amount of failure to be expected, according to these factors.
               In this illusion exploration, we will be testing the boundaries of our perceptions, and
                everyone’s perceptions will be similar, but still slightly different.
               You will come to understand that seeing is believing, but may not be the same thing as
                universal truth, which is something entirely different.”

   2. FILLING IN THE GAPS: (suggested script)

               Get out picture labeled “Subjective Contours”

               “Sometimes there is a disconnect between what our brain knows and what we perceive
                with our eyes, as you noticed with the 3-d hologram.
               You knew that item couldn’t be floating in the air, but your eyes saw otherwise because
                of the mirrors.”

               Show subjective Contours example picture.

               “A real life example is a television or computer screen.
               The images we see there are not actually moving…what we see is actually a series of
                images flashed quickly in order, that our brain interprets as moving.
               Some of you might have seen the Captain Underpants books before. One fun activity
                that the author often includes is called Flip-o-Rama, which illustrates this effect.”

               Show Flip-O-Rama pages in a Captain Underpants book, let kids experience

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               Optical Illusions                                                                Grades 3-6

   3. DEPTH PERCEPTION:               (suggested script)

               Identify an item in the room that the group can look at to use as a visual “target”
                — a clock, a picture, a doorway, etc. Also set out construction paper.

               “Also the way our eyes are placed apart in our skulls affects how we see things. We
                actually see two separate pictures that our brain squashes together into one.

               Look at this target (identified from beginning of this section).
               Close one eye.
               Hold your finger so that it is pointing directly in line with the target as you look at it with
                one eye.
               Now open both eyes.
               You should now see two fingers.
               Now close the other eye.
               Even though your finger hasn’t moved, it is no longer in front of the target.
               This phenomenon allows us to see in three dimensions, also called depth perception.

               Pick up the construction paper and roll it into a tube.

               Hold up your left hand and find the “v” formed by your thumb and pointer fingers.
               Using your right hand, hold the tube at the point of the “v”.
               Look through the tube with both eyes open.
               You should see a hole in your left hand—because your brain is getting two very different

   4. ANATOMY OF THE EYE:                    (suggested script)

               Get out Eye poster, and have Blind Spot pages handy.

               “There is a common misperception that the optical system is like a camera.
               However, the visual/perceptual process is actually a much more complicated process.
                (pointing to eye poster).
               Light waves enter each eye and form a two-dimensional image in the retina in the back
                of each eye.
               The two retinas and two images with different points of view give a perception of three
                dimensions, or depth.
               Interestingly, when your eye takes in these light waves, they pass through your eye
                upside down, and your brain flips the image back to where it belongs, without your

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               Optical Illusions                                                           Grades 3-6

               Also, the images reverse as well, with the content on your left side passing to the right
                retina and vice versa.
               Everyone also has a spot on their retinas that does not have light receptors, called the
                “blind spot”.
               It is the spot where the optic nerve exits the eye on the way to the brain, and an image
                that falls in this region will not be seen. “

               Set out Blind Spot pages.

               “Pick up the picture in front of you and hold it about 20 inches away from the front of
                your face.
               Close your right eye.
               With your left eye, look at the +.
               Slowly bring the image closer while looking at the +.
               At a certain distance, the dot will disappear from sight…this is when the dot falls on the
                blind spot of your retina.
               Reverse the process.
               Close your left eye and look at the dot with your right eye.
               Move the image slowly closer and the + should disappear.

   5. BRAIN INFLUENCES PERCEPTION: (suggested script)

               Have blank papers and markers handy, and rotating image on computer set up.

               “Your brain continually interprets images according to subconscious “rules” or
                understandings that we all hold about size, shape, contrast, color, motion, etc.
               We all use these constraints to make sense of our world, without even realizing it, and
                we can’t stop our brain from using them.
               That is why we are misled by optical illusions.
               Illusions can be a fun way to reveal that this process happens not only in our eyes, but
                in our brain as well.
               Another interesting aspect of our perception is that our brain is divided into two halves,
                a right half and a left half, and the sides cross.
               For example, the right side of the brain interprets information from the left side of the
                body, and vice versa.
               Many scientists even believe that the left and right sides of the brain process
                information differently.
               A common belief is that the left side of the brain processes information more logically,
                and the right side more creatively.

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               Optical Illusions                                                             Grades 3-6

               The right and left sides of the brain are mirror images of each other, and this influences
                perception as well.

               Pick up a marker and a piece of paper.
               Hold the paper against your forehead, and hold the point of the marker on the left side
                of your forehead.
               In cursive, write your name across the paper from left to right. Write quickly, imagining
                that the paper is in front of you.
               Don’t stop to think about what you are doing.
               Look at the paper.
               Chances are, your writing will be as meaningful as hieroglyphics.
               However, hold the paper up to the light overhead or the window light, and you may see
                more sense in it.
               When you write in this position, your right and left brain get confused, and automatically
                reverse the writing motion that is in your muscle memory.

               Another example of left and right brain perception is this image on the computer.
               When you see the Ferris wheel spinning in one direction, your right brain is dominating
                the perception.
               When you can see it spin in the opposite direction, your left brain is dominating.
               Some people can only see it spin one direction, others can see both.
               There are many other complexities to the human brain and perception that we won’t
                cover today, but they can be fascinating to study.

   6. EXPERIENCEING THE OPTICAL ILLUSIONS:                              (suggested script)

               Have sample illusions and optical illusion books ready for setting out on the

               “The last part of our station is studying some optical illusions.
               There are several kinds of illusions, some based on contrast, some based on color,
                some on motion, and other kinds as well.
               Some were “discovered” by a certain scientist and are named after them.
               One of the illusions, the Magic Eye, has special instructions included so that you can
                experience it.

               So while some of you are at the table passing around samples of illusions from these
                pages and books, we will take a couple of you at a time over to the Magic Eye posters
                to take turns trying to find the hidden pattern.”

Science Alive 2009                                                                                   Page 5
            Optical Illusions                                                             Grades 3-6

Set out sample illusions & books, and choose 2 students at a time to visit Magic Eye posters.


   A. Put your nose right up against the poster. The image will become very blurry. Admire those
      glowing blotches of color. You have just easily defeated your tendency to focus right at the
      surface of the poster. In order to see the 3D image you must look through the poster, not at the

   B. Ask yourself what your eyes feel like because you need to maintain the same feeling and the
      same posture of your eyes as you move away from the image. Check yourself again. Your
      focus is completely relaxed. The image is blurry. You are staring through the poster, off into

   C. Now slowly take a step back from the poster while maintaining the same position of your eyes.
      Allow the image to remain blurry. Relax, breathe, blink.

   D. Continue to back up very slowly, away from the poster. The hidden 3D image will gradually
      come into view.

   E. Continue aiming your eyes beyond the poster. Do not look directly at the image. If you
      suddenly shift your focus and look right at the image, you will lose the 3D effect. Try again.

   F. Once you recognize the 3D shape, if you continue to look into the background rather than
      directly at the shape, the 3D effect will increase. Stereoscopic perception seems to have a
      saturation effect in the brain, so if you keep looking at the image for a while you will notice that
      your perception of the depth increases.

Continue helping students try find the hidden 3-d images in the Magic Eye posters until all
  students have had a chance.

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               Optical Illusions                                                          Grades 3-6

   7. CONCLUSION:            (suggested script)

               What did you think of the illusions?
               Which was your favorite?
               Which did you have trouble seeing?
               Did you learn anything about vision and perception?
               What would be other real life applications of what you learned about illusions
                (computers, animation, possibly law/crime/eyewitness testimony, etc.)?

Pass out handouts with samples and resources for them to try at home.

   8. CLEAN UP:

               Put everything away except 3-d hologram chamber, and cover chamber with scarf to
                start again.

Science Alive 2009                                                                               Page 7