Below that is a different illusion. The bottom horizontal line segment appears to be to the right of the other horizontal segment.
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© Copyright 2003, Jim Loy
Here are some geometric optical illusions:
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1. Blind spot: Your eye has a blind spot, where the optic nerve is attached to the eye. Close your right eye and stare at the black dot. Move forward or backward (depending on the size of your computer screen), and at a certain distance, the star will appear to disappear, and the vertical line will appear continuous. Your brain fills in the missing data for this blind spot. | |
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2. Delboenf's illusion: Here we have four circles. The outer circle on the left, and the inner circle on the right are of the same size, but the right one appears larger. | |
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3. Helmholtz' irradiation illusion: The two figures are of identical size, but the small white square (inside the larger black square) looks larger than the small black square. | |
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4. Hermann's grid illusion: Looking at this grid produces the illusion that there are gray spots or squares at the intersections of the streets or canals. | |
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5. Kanizsa's triangle: This produces the illusion of a nonexistant white triangle. Sometimes the black angles are not shown, just the black dots with slices taken out. And it is possible to bend the sides of the nonexistant triangle. | |
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6. Müller-Lyer illusion: The horizontal line segment on
the far left looks longer than the other one, even though both segments are of
the same length (within the limits of my paint program). Below that is a different illusion. The bottom horizontal line segment appears to be to the right of the other horizontal segment. |
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7. Orbison's illusion: The outer rectangle (really) and the square appear distorted. A circle would also appear distorted. | |
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8. The parallelogram illusion: Diagonals a and b are of equal length. | |
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9. Poggendorff's illusion: In the top diagram, the diagonal lines do not appear to line up, but they are the same line. Below that we have the same illusion as it is often shown, with a second segment which seems to line up with the other line on the other side. | |
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10. Ponzo's illusion: The upper horizontal line segment appears to be longer. | |
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11. The vertical-horizontal illusion: The vertical line appears longer than the horizontal line, but they are of equal length. Sometimes this illusion is done as a top hat. | |
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12. Zollner's illusion: The horizontal lines are parallel. | |
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13. Another illusion: The horizontal lines are straight and parallel. | |
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14. A famous illusion: The left-most object appears longer. | |
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15. Shades of gray: The left-most gray square appears darker (and smaller as in #3, above). They are the same shade of gray. See Checker Shadow for a more dramatic version of this. | |
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16. Two squares: Sometimes the right-most square looks larger. |