1. Survey of Modern Psychology
Optical Illusions

2. Illusions generally happen when:
The stimulus is unclear
Information is missing

3. When we do not have sufficient information about a stimulus, we fill it in ourselves
Gestalt theory
Learning based inference

4. The brain perceives patterns in stimulation
Gestalt Theory
The brain perceives patterns in stimulation
For example, we see a triangle as a single figure rather than as three lines

6. Closure We fill in the blank space to form a closed figure
Other examples:
Filling in blanks in words/sentences
If you see an image with part of a face obscured, you mentally fill in the missing pieces

8. Figure and Ground The figure is the part that grabs our attention
The ground is anything surrounding the figure
The figure can be seen as either a vase or as two faces

9. Huang, L. , Pashler, H. (2009). Reversing
Huang, L., Pashler, H. (2009). Reversing the Attention in Figure-Ground Perception. Psychological Science, 20,

10. A

11. When a person focuses their attention on the red lines, the red lines appear to be in front of a green background

12. B
When a person focuses their attention on the red lines, the red picture appears to be behind green columns

13. Again here, when a person focuses their attention on the red lines, the red lines appear to be in front of a green background

14. Explanation
We look for the simplest possible explanation of stimuli, and interpret them as 3-D
In image B, when paying attention to the red lines we saw a picture of a face
Normally, this would mean that we’re looking at a whole face with columns in front of it
In image C, the strips were shuffled so the red or green did not form a continuous image anymore. It was therefore interpreted in the same was as figure A

15. X O

16. Perceptual Grouping
We group together stimuli that appear to belong together
The X’s are similar to other X’s, and we therefore group them together as columns X O

18. Meaningfulness – “Prägnanz”
We look for the simplest interpretation possible, with the least amount of effort
We know what we expect to see, and that makes proofreading difficult

19. Meaningfulness – “Prägnanz”
Note: humans are good at this, computers are not.
This is why spammers use symbols rather than letters to get through filters

20. Learning Based Inference
We use what we know/have learned to interpret new stimuli
Our knowledge gives us a context for recognizing and interpreting new stimuli
For example, it might be more difficult to recognize someone in a place you did not expect to see them

21. Context and Expectation
FOX; OWL; SNAKE; TURKEY; SWAN; D?CK BOB; RAY; DAVE; BILL; TOM; D?CK

22. Context and Expectation
FOX; OWL; SNAKE; TURKEY; SWAN; D?CK
BOB; RAY; DAVE; BILL; TOM; D?CK
In the first list, “U” made sense
In the second list, “I” made sense

23. Context and Expectation
.rat eht saw tac ehT
Turn this around in your mind and read it

24. .rat eht saw tac ehT
People usually interpret the sentence logically as saying “The cat saw the rat.” In reality, when reversed the letters said, “The cat was the tar”

25. What difference(s) do you see in these two pictures?
From Psychology Core Concepts Fifth Edition Zimbardo, Johnson and Weber
What difference(s) do you see in these two pictures?

26. We have difficulty seeing details of faces that violate our expectations of a face

27. More Context and Expectations:
Based on our knowledge of words, H and A (respectively) made the most sense and the ambiguous figures are seen as those letters
This sort of optical illusion is useful when trying to decipher bad handwriting!

29. What do you see?

30. Priming
(Priming is subconsciously cuing a particular response)
The images or labels shown surrounding an ambiguous image will tend to lead to a particular interpretation. In this case, you may have been more likely to initially see the image as a young woman

32. The Ponzo Illusion
We look at see the tracks as cues for distance. Because A appears to be further away, we perceive it as being larger than B
We are used to this type of visual cue for distance.
In places where roads are typically winding rather than straight, people are less likely to perceive A as being longer because they do not use the same visual cue

33. Hybrid Images Sharp features (ex. wrinkles) are removed from one photo
General features are removed from the other (shape of the nose or mouth) are removed from another
The images are then superimposed
When the stimulus is shown quickly (30 milliseconds), only the low resolution image is visible
When shown for a slightly longer amount of time (150 milliseconds), only the high resolution image is visible
Detailed features (high spatial frequencies) are only visible up close
Low spatial frequency features are only visible from a distance
At either extreme distance, only one image is visible

34. Hybrid Images

35. THIS IS NOT ACTUALLY LINKED TO BEING “LEFT BRAINED” OR RIGHT BRAINED”
Dimensions
“Spinning Dancer” illusion
We tend to view objects as three dimensional even if they are really not
The image is not actually “spinning” but we interpret it as 3-D spinning
It is processed as both counter clockwise and clockwise, but one interpretation wins at any given time
THIS IS NOT ACTUALLY LINKED TO BEING “LEFT BRAINED” OR RIGHT BRAINED”

36. Necker Cube

37. Cues for Depth Perception
If two objects that one would assume are the same size show different sized images on the retina, the observer judges them as being different distances away.
The relative size of the objects is used to judge depth and distance.

38. Cues for Depth Perception
Lighter colored objects seem closer to us, and darker objects seem further away

39. Cues for Depth Perception
Closer objects obstruct our vision of more distant objects behind them.
Partially hidden objects are therefore further away than the object that hides it.

40. Ames

41. Violates our expectations of how a room should be shaped

42. Stare at this image

44. Negative Afterimage
Caused by a change in the rate of firing in retinal ganglion cells
After the cells are inhibited or excited for an extended time, they show a rebound effect (fire faster or slower than normal)

45. http://www. moillusions

46. M C Escher

47. M C Escher

48. Julian Beever

49. Julian Beever

50. Julian Beever

51. Julian Beever