Shape Shifters

Gianni A. SarCone Marie-jo Waeber optical illusions: SHAPE SHIFTERS

Be amazed by OPTICALOPTICALOPTICAL mind-boggling optical illusions, then create your own to astound your friends!

Hands-on experiments, easy-to-understand explanations, and top tips for making optic art all combine to create an awe-inspiring collection of optical illusions.

Make impossible shapes and structures, watch images change before your eyes, see why you can’t always trust your sense

of space - and learn the science Gianni A. SarCone / Marie-jo WaebER Includes activities and behind these awesome MAKE-your-own illusions SHAPE SHIFTERS. to trick your eyes and baffle your brain!

ISBN 978-0-71124-231-9 ILLUSIONSILLUSIONS 9 780711 242319 ILLUSIONSShape Shifters Optical Illusions SHAPE SHIFTERS

Gianni A. SarCone and Marie-jo Waeber Optical Illusions 3

Concepts, text, and research: Gianni A. Sarcone CONTENTS IS SEEING BELIEVING? Design and Editorial: Tall Tree Ltd Can you really believe what you see? This book will show you some amazing Project Editor: Harriet Stone illusions that will trick your eyes and brain. It also contains simple experiments to show you how you can make your own incredible illusions. © 2019 Quarto Publishing plc Is Seeing Believing?...... 3 This library edition published in 2019 Lines and Space...... 4 by Quarto Library, How You See Impossible Shapes...... 6 an imprint of The Quarto Group. At the front of your head are two forward-facing Polypodous Elephants...... 8 Cornea Retina 6 Orchard Road jelly balls, called your eyes. Rays of light are Suite 100 Roman Temple...... 9 bent as they pass through the cornea and enter Pupil Lake Forest, CA 92630 Hybrid Illusion...... 10 Lens your eye through a tiny peephole, called the T: +1 949 380 7510 Making Magic Dice...... 11 pupil. The lens bends the light rays a little more F: +1 949 380 7575 Bigger or Smaller?...... 12 to focus them, before they pass through the www.QuartoKnows.com Incredible Circles; Sarcone’s Ellipses...... 13 middle of the eye and hit the retina, the lining Optic nerve Bilateral Animals...... 14 Eyeball at the back of each eyeball. As light hits the All rights reserved. No part of this publication Amazing Jastrow Playing Cards...... 16 retina, it stimulates millions of light-sensitive cells, may be reproduced, stored in a retrieval system, Jastrow Magic Experiment...... 17 Visual cortex called photoreceptors. These send electrical or transmitted in any form or by any means, Impossible Structures...... 18 nerve signals along the optic nerve to the back electronic, mechanical, photocopying, recording, Make an Impossible Triangle...... 20 or otherwise, without the prior permission of the of the brain and a part called the visual cortex. Wider or Taller?...... 21 publisher, nor be otherwise circulated in any This produces the final images that you see. form of binding or cover other than that in which Answer and templates...... 22 it is published and without a similar condition Without any Surrounded by being imposed on the subsequent purchaser. Glossary...... 23 Index...... 24 context... different contexts... Brain A CIP record for this book is available from the Library of Congress. Context ISBN 978-0-71124-231-9 While that all sounds nice and Manufactured in Dongguan, China TL012019 scientific, your seeing equipment can 9 8 7 6 5 4 3 2 1 sometimes be fooled into seeing things that aren’t there, or incorrectly seeing Words in bold are explained things that are there. These effects are in the glossary on page 23. called optical illusions. Many illusions are created because we don’t see objects on their own. Instead, we see ...the two red dots ...the same two them in context and surrounded by look the same. dots look different. other objects which can influence how we see things. 4 SHAPE SHIFTERS Optical Illusions 5

C LINES B AND SPACE Look at lines C and D. Line C How long? How far seems to be longer, but are away? How much? A you sure? We measure distances and estimate the dimensions of objects all the time, usually without thinking about it.

We can usually tell the difference Which line between the actual size of an object is longer? and its apparent size. A or B?

• The actual size of an object cannot be determined D from observation alone, because our eyes need to see the object from a distance in order to focus on it. To tell its actual size, the object must be measured. • The apparent size of an object depends on its size and how far away it is. Objects that are closer will Are lines E appear larger than if they are farther away. and F the F same length? Perspective and size constancy also play a part in how we see things. They obey these simple rules:

• For two objects with the same ACTUAL size, the one E that looks bigger is thought to be closer. In all three illusions, the pairs of lines • When we see two objects with the same APPARENT are the same length as each other. size, the one that appears to be farther away is thought to be larger. what’s going on? All the illusions on these pages use your ideas about perspective Different Lines to play tricks on you. Your mind The illusions on these two pages play around thinks that the lines that appear with your ideas of perspective and space to to be farther away are bigger fool your brain! ?when both lines are, in fact, the same size. 6 SHAPE SHIFTERS Optical Illusions 7 Impossible Shapes

How many Can you prongs does this trace and color fork have? Three It looks like one end of the fork has four prongs, while in these If you look closely enough at these monkeys you’ll see that or four? the other end only has three! Try scanning or copying monkeys? this picture and then see if you can color it in. You coloring them in would be impossible as their outlines don’t will soon find that coloring between the lines is a real join up! Turn to page 8 to find out how you can create your challenge because it is an impossible shape! own impossible animals. 8 SHAPE SHIFTERS Optical Illusions 9 Polypodous Elephants Roman Temple You saw impossible monkeys on page 7. Now find out how you can create your own impossible elephants. WHAT YOU NEED • Soft pencil 1 • Tracing paper Using the soft • Sheet of paper pencil, trace this • Eraser elephant, making • Black pen sure that you space • Colored pencils the legs evenly.

2 Erase the elephant’s feet and draw them again, but this time add them to the space between each leg, as shown.

Do the The columns of the temple are, in fact, perfectly straight 3 columns of this Roman temple and parallel to each other. Check them with a ruler! Trace this new elephant and reproduce converge or it to form a circle, with the tail of one diverge? what’s going on? elephant in the trunk of another. Use the This interesting illusion shows how vertical bars pen to define the outlines and then color containing patterns that are tilted to one side can the elephants as best you can. look like they are leaning slightly over. The Latin words on the temple mean “the world wants to be deceived, so let it be deceived.” ? 10 SHAPE SHIFTERS Optical Illusions 11

Hybrid Illusion Making Magic Dice As with the hybrid illusion on page 10, this visual trick depends on the point of view of the spectators. Just make sure they are standing close to you for this WHAT YOU NEED illusion to work. • Two dice • Small mirror • White correction fluid

1 Before you start your performance, you will need to “prepare” a die by painting correction fluid on some of the pips.

Top view 2 Only paint the pips on four faces of the die, as Side view shown, and make sure you only paint the bottom half of each pip. Bottom view

When you look at the image close-up, the clown seems sad, but as you step back he will begin to smile. 3 Is this clown Ask a spectator to examine the normal die, and sad or is he Normal die what’s going on? place it on the mirror—everyone can see the smiling? black pips reflected in the mirror. At this point, This type of illusion is known as a cryptic or hybrid optical ask another spectator to take a closer look at the illusion. It is made by merging two photos with different mirror and while he is doing this, secretly swap resolutions. The result is that one of the photos is hidden Prepared die the normal die with the prepared one. Now, What happens when depending on your distance. When you see the picture when you lay the prepared die on the mirror, you step back about close-up, the fine details dominate (the sad clown). When make sure that the number two is facing up. six feet and look at him? ?you look at it from a distance, the larger, more blurred The die will seem normal viewed from above, tones become visible and the grinning clown appears. but its pips have turned WHITE in the mirror! 12 SHAPE SHIFTERS Optical Illusions 13 Bigger or Smaller? Incredible Circles

A B

Which of these blue circles is the biggest? A A or B?

Both circles are actually the same size. what’s going on? This is known as the “Delboeuf Illusion.” The bottom blue circle seems larger because it is close to the D C edge of the outer circle, making it appear “tighter,” B and? therefore bigger. Sarcone’s Ellipses

Which pink Most people think that cross A is bigger. However, you may be cross is the biggest? A or B? surprised to learn that crosses A and B are the same size. Similarly, Which pink square most people believe that square C is bigger than square D, but is the biggest? again, both squares are the same size. C or D? what’s going on? Which what’s going on? The cross illusion is known as “Sarcone’s Cross Illusion,” while the line is longer? Ninety percent of people will say the red line, but the blue line is square illusion is called “Obonai’s Square Illusion.” They show that the The red one or actually longer. Your brain gets it wrong because it assumes that the apparent size of an object can be affected by other objects that are the blue one? larger ellipse must contain the longer line, so it believes the red line ?placed close to it, although the effects can vary. ?is longer than the blue one, even though the opposite is true. 14 SHAPE SHIFTERS Optical Illusions 15 Bilateral Animals

The “Duck or Rabbit” illusion is probably one of the oldest intentionally ambiguous figures created for psychological tests. Thousand of variations of the “Duck or Rabbit” illusion exist. The original illusion (see the image below) is usually credited to the American psychologist Joseph Jastrow who was the first to use it in an article. However, there’s every chance it’s much older than that!

What can you see here? Ducks, rabbits, or dolphins?

what’s going on? This illusion is a good example of what scientists call “rival- schemata ambiguity.” In other words, even though the image is ambiguous, there is no “dominant” shape, as both images (such as ?the duck or the rabbit) can be seen at the same time. 16 SHAPE SHIFTERS Optical Illusions 17

Amazing Jastrow Jastrow Magic Experiment This optical illusion is named after the American Playing Cards psychologist Joseph Jastrow who first discovered it. WHAT YOU NEED • Sheet of cardstock A • Pair of scissors • Colored pencils

B 1 A Photocopy or trace the two curved templates showing dolphins on page 22 onto a sheet of card, and cut them out. Use colored pencils to color them in, in contrasting colors.

2 Place the two dolphins on a table, with dolphin A on top as shown, and ask a friend to pick which one of them is longer. Most people will say that they B look the same size. However, the dolphin in shape A is actually bigger!

Both sets are, in fact, the same size and width. 3 Which of these Turn to page 22 for proof. To prove it, take dolphin B and move it above fanned-out sets of cards is the what’s going on? dolphin A. It’s now obvious that one of the shapes widest? is indeed longer than the other. When two curved shapes are arranged one above the other A or B? as shown here, the lower one always appears wider because your brain believes it is nearer! This illusion is named after the American psychologist Joseph Jastrow. The instructions on what’s going on? page 17 and templates on page 22 will show you how to This illusion is created by your prior assumptions ?make your own Jastrow illusion. ?about perspective as described on page 4. 18 SHAPE SHIFTERS Optical Illusions 19 Impossible Structures

what’s going on? Could you Impossible structures are objects that cannot exist in real life. But that doesn’t mean you can’t construct these No, these are structures that no one could ever build, no draw them or even create your own illusion of one—the experiment on page 20 shows you models with matter how many blocks they have. They are known as how to make your own impossible structure. Generally, when part of an object looks like it’s building blocks? “impossible structures.” in the wrong place, such as behind, in front, above, or below another, then the chances are ?it is part of an impossible structure. 24 SHAPE SHIFTERS

Fick illusion 21 Obonai’s Square illusion INDEX 12 hybrid illusion 10, 11 ambiguous figures 14, 23 perspective 4, 5, 17, 20, impossible shapes and 23 bilateral animals 14–15 structures 6–7, 8, 18–19, polypodous elephants 8 brain 3, 4, 13, 16, 23 20, 23 impossible triangle 20 rival-schemata ambiguity context 3 14 contrasting colors 17 Jastrow illusions 14, 16, Roman temple 9 cryptic illusion 10 17 Sarcone’s Cross illusion Delboeuf illusion 13 leaning illusion 9 12 dice 11, 20 light rays 3, 23 Sarcone’s ellipses 13 Duck or Rabbit illusion size constancy 4 14–15 magic dice 11 mirror 11 templates 22 experiments 8, 11, 17, 20

PICTURE CREDITS (t=top, b=bottom, l=left, r=right, c=center)

All other images courtesy of Gianni A. Sarcone.