Optical Illusions Quiz: What Do You See First?

Quiz: Can You Name These 11 Famous Optical Illusions?

How you see an illusion does not reveal a personality type, but the illusions themselves are fascinating. How many of these classics do you know?

1. Two lines of equal length look different because one has arrow-heads pointing in and the other out. What is this illusion called?

   • Ponzo illusion
   • Zöllner illusion
   • Hering illusion
   • Müller-Lyer illusion

   Franz Carl Müller-Lyer published it in 1889.

2. A picture that can be seen either as a vase or as two faces in profile is known as…

   • The Penrose stairs
   • The café wall
   • The Ames room
   • Rubin’s vase

   Danish psychologist Edgar Rubin used it around 1915 to study figure and ground.

3. A simple line drawing of a cube that seems to flip between two orientations is the…

   • Kanizsa cube
   • Rubik cube
   • Necker cube
   • Escher cube

   Louis Albert Necker described it in 1832.

4. The Moon looks larger near the horizon than high in the sky. What is true?

   • It is much closer to Earth at moonrise
   • Its light spreads out near the horizon
   • The atmosphere magnifies it like a lens
   • Its size in the sky is essentially the same; the difference is in perception

   Measured with a camera, the Moon’s width in the sky barely changes; the "Moon illusion" happens in the brain.

5. Stare at a bright red square for 30 seconds, then look at a white wall. What colour is the afterimage likely to be?

   • Black
   • Green-blue (cyan)
   • Red
   • Yellow

   Tired red-sensitive responses leave a complementary greenish-blue afterimage.

6. A 2015 viral photo of a dress split the internet. What colours was the dress really?

   • White and blue
   • White and gold
   • Blue and black
   • Green and gold

   The manufacturer confirmed the dress was blue and black; lighting assumptions caused the disagreement.

7. In the famous ambiguous drawing, a rabbit can also be seen as which animal?

   • A duck
   • A swan
   • A goose
   • A cat

   The duck-rabbit figure was made famous by psychologist Joseph Jastrow and later by Ludwig Wittgenstein.

8. Three "Pac-Man" shapes arranged so that a bright triangle seems to appear between them form the…

   • Penrose triangle
   • Kanizsa triangle
   • Sierpinski triangle
   • Bermuda triangle

   Gaetano Kanizsa described this illusory contour in 1955.

9. In Edward Adelson’s checker-shadow illusion, squares A and B look very different. In fact they are…

   • Different colours
   • Different sizes
   • Exactly the same shade of grey
   • Different shades of grey

   The brain adjusts for the shadow, so identical greys appear light and dark.

10. A distorted room in which people seem to grow or shrink as they walk across it is called…

    • The infinity room
    • The Hermann room
    • The mirror maze
    • The Ames room

    Adelbert Ames Jr. designed it; the room’s trapezoid shape fools our sense of distance.

11. Grey smudges seem to appear at the crossings of white lines on a black grid. This is the…

    • Ebbinghaus illusion
    • Hermann grid illusion
    • Ponzo illusion
    • Poggendorff illusion

    Ludimar Hermann reported it in 1870.