Visual sensation, perception, optical illusions

1. Vision, sensation,
perception
Dr. Irene Karayianni

2. What basic processes underlie the sense of vision?
How do we see colors?

3. It all starts with light

5. focusing the light more sharply

6. Opening depends on the amount of light into the environment

7. Bends the rays of light so that they are properly focused on the rear of the eye

9. electromagnetic energy of light is converted to electrical impulses

10. Let’s zoom in
to check out the retina

11. Shape
Function
Distribution
Dark adaptation
https://www.youtube.com/watch?v=Lcv8g-0VdMI https://www.youtube.com/watch?v=gvozcv8pS3c

13. Processing the visual image
Feature detection
Separate neural systems exist for processing information about specific aspects of the visual world
Integration

15. https://www.youtube.com/watch?v=evQsOFQju08
Is Your Red The Same as My Red?

16. red-green color blindness blue-yellow color blindness
7%0.4%

18. trichromatic theory of color vision
blue-violet green yellow-red

19. BUT…

21. opponent-process theory of color vision

24. Perceptual Organization
Constructing Our View of the World

26. The Gestalt Laws of Organization
Closure
Proximity
Similarity
Simplicity

27. Closure

28. Proximity

29. Similarity

30. Simplicity

31. The whole is more than the sum of its parts
Prosopagnosia
https://www.youtube.com/watch?v=XLGXAiSpN00

35. Top-Down and Bottom-up Processing
Ca- yo- re-d t-is -en-en-e, w-ic- ha- ev-ry -hi-d l-tt-r m-ss-ng?

36. Depth perception
Translating 2-D to 3-D
binocular disparity

37. 1 2 3 4 5 6 7 8 9 10

38. Monocular cue - motion parallax
Depth perception
Translating 2-D to 3-D

39. Monocular cue – relative size
Depth perception
Translating 2-D to 3-D
smaller image on the retina is farther away

40. Depth perception
Translating 2-D to 3-D
Monocular cue – texture gradient
he details of things that are far away are less distinct

41. Monocular cue – linear perspective
Depth perception
Translating 2-D to 3-D
distant objects appear to be closer together

42. For next time:
Take photos to demonstrate any of the perception principles we discussed

43. Perceptual Constancy
objects are perceived as unvarying and consistent
despite changes in their appearance (size)

44. Motion Perception
Apparent moving: perception that a stationary object is moving -
different areas of the retina are quickly stimulated, leading us to
interpret motion
movement of an object across the retina (vs. stable background)
image on the retina expands in size

45. all these rotating white dots are actually moving in straight lines

46. “Our senses can be trusted but they can be easily fooled”
Aristotle

47. https://www.youtube.com/watch?v=OAVXHzAWS60
motion aftereffect
Certain neurons fire and are worn out, they adapt to the motion.
When you then shift your gaze to a stationary scene, other competing
neurons over-compensate, causing the illusion of movement in the other
direction.

48. Which of the two red lines is shorter?
Müller-Lyer illusion

49. Müller-Lyer illusion
One explanation:
eye movements are greater when the arrow tips point inward, making us perceive the
line as longer than it is when the arrow tips face outward

50. Müller-Lyer illusion
Another explanation:
we unconsciously attribute particular significance to each of the lines
relatively more distant inside
corner
relatively more close outside
corner
These lines provide cues
for depth

51. Chubb illusion
apparent contrast of an object varies, depending on context

52. Ebbinghaus illusion
apparent size of an object varies, depending on context

53. apparent color of an object varies, depending on context

54. Ponzo illusion
context is also fundamental for depth perception
We see the line as longer when we see cues that suggest it is further away

55. Ames room
many cues of depth perception have been
changed to give the illusion of equal depth
https://www.youtube.com/watch?v=Ttd0YjXF0no

56. concentric circles

57. Hermann grid illusion
“ghostlike” grey blobs perceived at the intersections of a
white grid on a black background

58. Hering illusion
the lined pattern on the background, that simulates a
perspective design, and creates a false impression of depth

59. Jastrow illusion

60. Necker cube
the brain can “flip” between 2 different views, as it
attempts to translate a 2D drawing into a 3D cube

61. inside/outside illusion

82. When looking directly at a ring, our brains notice the motion of the spots  anticlockwise.
When looking at a ring in the peripheral vision, our brains notice motion of stripes  clockwise

89. an impossible object

115. https://www.youtube.com/watch?v=XglX4LCzE8I

116. Subliminal perception
(priming)
• Perception of messages about which we have no
awareness
• Stimulus is not intense enough for you to report having
experienced it
• Can influence behavior in subtle ways
• Little evidence that it can lead to major changes in
attitudes or behavior

123. https://www.youtube.com/watch?v=OW9ou1kB1cU

124. Extrasensory perception