Perception involves interpreting sensory information to identify objects. Visual perception involves light entering the eye and being transmitted to the brain as electrical signals. The brain must work to make sense of the two-dimensional, upside-down image. Visual illusions occur when the brain misinterprets images due to past experiences. Illusions can be ambiguous, distortions, fictional perceptions, or paradoxes. Depth is perceived through binocular cues like disparity and convergence as well as monocular cues like size, texture, and motion. Visual constancies allow objects to appear the same size, shape, and color despite changes in the retinal image.

1. Perception

7. In this picture the word a is written twice, but most people don’t notice because in our previous experience sentences usually make sense.

10. The Necker Cube : There is uncertainty as to whether the marked face is at the front or the back. If we stare at it for a while it will flip from one perspective to the other. This is because our brains first try one possibility find it works and then the other and fin it works as well and so cannot decide which alternative is best. The Old/young woman and the duck/rabbit : Again there are two equally sensible options to see so the brain cannot decide.

12. They are both exactly the same length but the information around the lines makes the brain think otherwise. Again they are both the same size, but we see them as different because of the lines around the monsters giving us information about distance. Which monster is bigger? Which line is longer?

13. The Ames Room

14. The Ames Room

15. Fictions The Kanizsa triangle : Looking at this picture we have the impression that there are two triangles, one that is drawn with a black line and one that is white. The white one appears on top of the line one. There appear to be three circles covered partially by the corners of the white triangle. But there actually no triangle or circles! We create the triangles in our minds. They are not really there. They are fictional. This is because our brain decides that it is more likely there are triangles than these strangely arranged shapes, so that is what we see. These illusions cause us to see things that are not true.

16. Paradox A paradox is something that may appear ridiculous but is actually true. These illusions are also called impossible figures because they are impossible. If you tried to make these into real (3D) objects you would not be able to. For example this drawing by Escher shows an impossible building look carefully at the water!

17. The impossible Trident : How many prongs does the trident (fork) have? This trident does not work, it would be impossible to create in 3D. The Penrose Triangle : The same is the case for this triangle, it can be seen on paper but cannot be made into a real object. L’Egistential Elephant : This elephant would have problems walking!!!

18. Some other illusions just for fun!!!! All these squares are straight edged!!!

19. Rotating Snakes

20. The Hermann Grid Illusion

21. Rotating rollers

25. How do we know that the person in the red circle is further away than the person in the blue circle?