Seeing isn't believing: Mind-bending optical illusions

Is reality an illusion? Whatever the case may be, our brain has a nasty habit of playing tricks on us, bending objective reality into the subjective. Scientists have just solved the mystery behind one optical illusion, but the wide world of illusions continues to confound.

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    Galilleo_illusion

    In this illusion, the white square on a black background appears larger than the same-size black square on a white background.
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    optical_illusion_08

    A static image appears to be moving due to the cognitive effects of interacting color contrasts and shape position.
    Fiestoforo
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    optical_illusion_02

    Shape, position, colour, and 3D contrast converge to produce the illusion of black dots at the intersections.
    António Miguel de Campos
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    optical_illusion_25

    The edges between the diamond-shaped areas are straight lines.
    Wikimedia
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    optical_illusion_03

    The two circles seem to move when the viewer's head is moving forwards and backwards while looking at the black dot.
    Fibonacci
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    optical_illusion_07

    Stare at the crosshair long enough and the pink dots seem to disappear.
    Wikimedia
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    optical_illusion_05

    The two orange circles are the same size.
    Wikimedia
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    optical_illusion_09

    Spiral illusion.
    Nevit Dilmen
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    optical_illusion_12

    The Poggendorff illusion: Does the black line connect to the blue or the red line?
    Fibonacci
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    optical_illusion_15

    Mysid/Wikimedia
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    optical_illusion_13

    Cornsweet illusion: The left part of the picture seems to be darker than the right one. In fact they have the same brightness.
    Fibonacci
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    optical_illusion_17

    The Fraser spiral illusion: The overlapping black arc segments appear to form a spiral; however, the arcs are a series of concentric circles.
    Mysid
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    optical_illusion_18

    The Zöllner illusion: Despite their appearance, the black lines are parallel.
    Fibonacci
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    optical_illusion_20

    All lines and edges are strictly horizontal/vertical, and fully parallel/perpendicular to each other but may appear otherwise.
    Wikimedia
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    optical_illusion_21

    Delboeuf illusion: the two dark circles are the same size.
    Wikimedia
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    optical_illusion_22

    Moving the image dissociates circle and background.
    Nevit Dilmen
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    optical_illusion_23

    The red-orange lines are strictly horizontal/vertical, and fully parallel/perpendicular to each other, but may appear otherwise.
    Wikimedia
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    optical_illusion_28

    The impossible cube.
    Wikimedia/Wapcaplet
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    optical_illusion_30

    An optical illusion similar to Rotating Snakes by Kitaoka Akiyoshi.
    Cmglee
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    optical_illusion_01

    The square A is exactly the same shade of gray as square B. Don't believe us? Here's proof.
    Edward H. Adelson/MIT
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    optical_illusion_06

    Café wall illusion: the horizontal lines are parallel, even if they seem otherwise.
    Fibonacci
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    optical_illusion_11

    Look at the red squares. Are they crooked?
    Nevit Dilmen
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    optical_illusion_16

    The Wundt illusion: The two red vertical lines are both straight, but they may look as if they are bowed inwards to some observers.
    Fibonacci
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    optical_illusion_14

    The Hering illusion: Two straight and parallel lines look as if they were bowed outwards.
    Fibonacci
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    optical_illusion_10

    This is not a GIF.
    Nevit Dilmen
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    optical_illusion_19

    Each one of the four lines is of the same length, even if the horizontal red one seems shorter.
    Wikimedia
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    optical_illusion_24

    Rectangles A, on the left, look much darker than the rectangles B, on the right. However, rectangles A and B reflect the same amount of light.
    Wikimedia/Zhengyi4411
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    optical_illusion_27

    The two squares are the same size.
    Nevit Dilmen
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    optical_illusion_26

    The "Blivet" or "Poiuyt" impossible object shown against a warped checkerboard optical illusion background. There are no curved lines in the picture, except the ovals at the ends of the tines of the fork.
    Wikimedia
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    optical_illusion_29

    Kanizsa's Triangle: These spatially separate fragments give the impression a bright white triangle, defined by a sharp illusory contour, occluding three black circles and a black-outlined triangle.
    Fibonacci
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