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Perception & Sensation

Perception & Sensation. Complementary Afterimage #1. Complementary AfterImage #2. Complementary AfterImage #3. Illusion Haze. Top-down vs. Bottom-up Processing.

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Perception & Sensation

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  1. Perception & Sensation

  2. Complementary Afterimage #1

  3. Complementary AfterImage #2

  4. Complementary AfterImage #3

  5. Illusion Haze

  6. Top-down vs. Bottom-up Processing • So far, we have studied the flow of information from the world into the perceptual system (bottom-up processing). But there is an equally important influence of pre-existing knowledge on our eventual perception of things in the world (top-down processing). • That is, our prior experiences and expectations have a very strong influence on the things we see. As a result, our perceptions of the world result from a combination of sensory information (data-driven) and pre-existing knowledge (concept-driven).

  7. Prior knowledge guides vision

  8. Prior knowledge guides vision

  9. Face Perception: Which one is Vanna?

  10. Face Perception: Which one is Vanna?

  11. Gestalt Grouping Principles • group nearby figures together

  12. Gestalt Grouping Principles: Proximity Objects near each other tend to be seen as a unit

  13. Gestalt Grouping Principles • group figures that are similar

  14. Gestalt Grouping Principles: Similarity Objects similar to each other tend to be seen as a unit

  15. Gestalt Grouping Principles: Similarity Objects similar to each other tend to be seen as a unit

  16. Gestalt Grouping Principles • Fill in gaps to create a complete, whole object

  17. Gestalt Grouping Principles: Closure • Fill in gaps to create a complete, whole object • But, doesn’t the white triangle look whiter than the background?

  18. Gestalt Grouping Principles: Continuity • Objects that are connected by a smooth curve tend to be seen as a unit

  19. Gestalt Grouping Principles: Common Movement • Objects moving in the same speed and at the same direction tend to be grouped • The Hidden Bird Illusion • THIS IS THE APPLET

  20. Gestalt Grouping Principles: Common Movement • Which direction are the triangles pointing?

  21. Who do you see?

  22. What do you see?

  23. How do we create a 3 dimensional world from 2 dimensions? Depth Perception

  24. Stereogram • Cross eyes so that the left eye is looking at the right square and the right looking at the left • Try ‘fixating’ on an imaginary point in front of the viewing screen at which point you will see three squares- left center and right. The center one will be the stereo image • t

  25. Relative Size

  26. Retina Pupil B A Image A Image Perceived Size and Perceived Depth • To perceive the size of objects accurately we must also perceive their distance accurately. • Thus, many visual illusions occur simply because a particular image lacks sufficient depth cues. This figure shows that image size depends upon both object size and distance

  27. The Size-Distance Problem • The Ames room is designed so that the monocular depth cues give the illusion that the two people are equally far away

  28. In each of these examples, the top and bottom lines are actually the same length. In each case the top line looks longer. Why? (a) Müller-Lyer illusion (b) Ponzo illusion Other Size-Distance Illusions

  29. Perceptual psychologists have hypothesized that the top horizontal line looks longer because it also looks farther away. Specifically, the inward pointing arrows signify that the horizontal line is closest to you, and the outward pointing arrows signify the opposite case. Muller-Lyer Illusion

  30. Ponzo Illusion • Converging lines indicate that top line is farther away than bottom line

  31. Another Size-Distance Illusion

  32. Another Size-Distance Illusion

  33. Linear Perspective

  34. Texture Gradients The elements of a texture become smaller and smaller as they recede into the distance...another reliable depth cue.

  35. Cues to Depth Perception Texture Gradient

  36. Cues to Depth Perception Texture Gradient

  37. Which Triangle is closer?

  38. Relative Height horizon line Objects closer to the horizon appear to be farther away...

  39. Cues to Depth Perception Relative Height

  40. Point B Point A Size Constancy • Cylinders at positions A and B are the same size even though their image sizes differ • The depth cues such as linear perspective and texture help the visual system judge the size accurately

  41. It is hard to tell if the figure on the upper right is a trapezoid or a square slanted backward. If we add texture, the texture gradient helps us see that it is actually a square. Shape Constancy

  42. Attention Demos

  43. The Stroop Effect, part 1 As fast as you can, read the names of the colors

  44. The Stroop Effect, part 2 As fast as you can, (don’t read the word) but read the name of the color of the word.

  45. The Stroop Effect, part 2 As fast as you can, (don’t read the word) but read the name of the color of the word.

  46. The Stroop Effect, part 2 As fast as you can, (don’t read the word) but read the name of the color of the word.

  47. Attention as a Selector: Find the Green Scarf

  48. Attention as a Selector: Find the Bald Man

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