Optical Illusions

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Slide 1: 

The Museum of Science and Boston College’s IASL Emotion Lab Presents: Vision 3-D Images and Optical Illusions: How pictures can trick your mind! Put your 3-D Glasses On!

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YOU MAY NOW REMOVE YOUR 3D GLASSES.

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Vision is one of our five senses! Can you name the others? Check out the eye models outside this room! Taste! Touch! Hearing! Smell! 3-D Images are so COOL! Our eyes can do sooo many things!

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The brain can be tricked when looking at certain pictures. The brain can see things that are not really there. These pictures are called optical illusions. Our brain is so smart that it has its own tricks to help us see things very quickly. You might think that you see with your eyes but you see with your brain!

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Check out these optical illusions and try not to get tricked!

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The Kanizsa Triangle Can you see the white triangle?

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You can see a white triangle but there are no connecting lines. The white triangle also seems to be brighter than the white background. Why do we see this triangle even though it’s not drawn? Because the brain automatically fills in information that is not there. This is known as Perceptual Completion.

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In the next picture, stare at the black dot and walk towards the screen and then step back. The PinnaBrelstaff Illusion

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The two circles should be moving in opposite directions from each other. Even though the image is not moving itself, the way the picture is shaded and shaped tricks our brains into thinking it’s moving!

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The Rotating Snake Illusion Are the circles moving?

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The circles appear to be slowly rotating… Focus on the red X. The “snakes” stop spinning. When our eyes try to focus on all the “snakes”, we are tricked into perceiving movement. Choosing a single point to focus on eliminates this illusion.

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The Ponzo Illusion Which of the two lines is longer?

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The yellow line on top appears to be longer but… The lines are actually the same length! This illusion uses our brain’s ability to see which object is closer compared to another. It tricks us using our own perspective depth cue!

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The Hering Illusion Are the purple lines straight?

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The purple lines appear to be bent but … The purple lines are actually straight! Using depth cues, the background is able to trick us into seeing bent lines in the foreground.

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The Café Wall Illusion Does this wall have straight lines or crooked lines? Look at each tile, are they all squares?

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The lines appear to be bent and the tiles seem to be wedge shaped but… There are no bent lines! The gray lines that separate the black and white squares and the way the blocks are arranged make the image seem like it is moving. When the same tiles are arranged in a checkerboard sequence and the grey lines are taken out, it is clear that the lines are straight and the tiles are square.

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Stare at the black dot for 20 seconds. The Grey Circle Illusion

The grey circle should disappear after several seconds of staring at the black dot. : 

When the eyes are focusing on the black dot they become tired and no longer process the surrounding grey circle. The grey circle should disappear after several seconds of staring at the black dot.

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The Gradient Illusion Is the bar the same shade of grey throughout?

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The bar is actually the same shade of gray! This illusion fools us by making us compare the shade of the bar to the shade of the background. The bar appears to be different shades of gray but…

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The Muller LylerIllusion Are the lines the same size?

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The middle line should appear to be the longest. The top line should appear to be the shortest. The lines are actually all the same size! The arrows confuse your brain’s size constancy mechanism and cause you to misperceive the actual lengths of the lines.

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Is this a courtyard or a terrace? Courtyard or Terrace Illusion

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You decide! This is an impossible picture. It can either appear to be a courtyard or a terrace, depending on which reference point you choose to focus on. From this view, it is a courtyard… But from this view, it is a terrace!

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Which flower’s inner circle is larger? The Circle Illusion

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The inner circle on the left appears to be significantly larger than the circle on the right. Believe it or not, they are the same size! The size contrasts trick our brain into thinking the left inner circle is larger, when in reality it is identical to the right inner circle.

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Scintillating Grid Can you count the red dots?

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AHHH! There are so many! Your eye is constantly moving to adjust itself. That, along with the brightness of the picture, causes you to see constantly moving red dots.

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Bunch of Beans Can you find the face in the pile o’ beans?

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Look hard! The similar color and shape of the face causes it to become camouflaged in the pile of beans, and difficult for our eyes to quickly locate.

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Stare at the blue apple for 30 seconds. The Afterimage Effect

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The afterimage effect occurs when your eye’s photoreceptors tire after staring at a color for an extended period of time. When you redirect your gaze to a blank space, the opposite color becomes visible. Did you see the apple turn red?

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The Lilac Chaser Stare at the black “+” for 20 seconds. Does the color of the pink dots change?

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This is caused by “negative afterimage”. When the purple dot flashes to the next spot, you are left seeing its complementary color, green.

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Motion Induced Blindness Stare at the “x” in the center of the image.

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After several seconds of staring at the center “x”, the three yellow dots should slowly disappear. The fixation of your gaze on the “x” along with the movement of the blue dots in the background results in this disappearance. Blink or shift your gaze to make the yellow dots reappear.

The Frankfurter Illusion : 

The Frankfurter Illusion 1. Hold your hands in front of you at eye level. 2. Point your index fingers against each other, leave about 2 cm distance between them. 3. Now look “through” your fingers, into the distance behind them. Do not focus on your fingers. 4. An image similar to the one above should appear. 5. You can change the length of the floating finger by varying the distance between your finger tips.

This phenomenon is caused by Binocular Rivalry : 

This phenomenon is caused by Binocular Rivalry There is a rivalry between seeing your hands and seeing the background. That is what causes you to see a “floating sausage finger”.

Slide 45: 

We are done with our optical illusions show but there are plenty of museum exhibits that have to do with the human eye. 2) There is an optical illusions desk in the middle of the Human Body Connection. Right next to you is a project about vision conducted by Boston College! Ask one of the researchers if you would like to participate and be a part of a real scientific study! 3) In the blue wing, there is a whole hallway displaying optical illusions. 4) There is even a free Mind Games and Illusions Show CHECK IT OUT!!!

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