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Outline Chap. 3 Visual Perception Unconscious inferences Preattentive organization
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  1. 10/31/2014 • Outline • Chap. 3 • Visual Perception • Unconscious inferences • Preattentive organization • Retinal vs. cortical effects • Gathering Visual information • Visual Sensory Memory Study Questions. Describe the unconscious inference theory of Helmholtz. How does the theory explain some visual illusions? Describe the gestaltist principles of grouping Define visual sensory memory. How did Sperling empirically distinguish between a capacity and a duration hypothesis.

  2. Perception and Pattern Recognition • Visual Perception

  3. Perception and Pattern Recognition • Visual Perception

  4. Perception • Perception is in the brain • Melzak : “Pain is in the brain” • Phantom limb pain • Filling in the blind spot • Complimentary colour mixing • Visual illusions • E.g., The moon illusion • Other illusions

  5. Perception • The unconscious inference theory (helmholtz) • Analyze cues in sensory input • Construct a perception with depth, size and motion. • Send perception on to conscious mind. • The Müller-Lyer illusion

  6. Perception • Problems with the unconscious inference explanation.

  7. Perception • The frame illusion

  8. Perception • Assimilation theory: We incorporate nearby elements into an object’s boundary when assessing size. Online Demo

  9. Perception • Size illusions based on linear perspective Example 1 Chasing illusion A great size constancy illusion: The power of persective Shadow and ball illusion

  10. Coding of Contrast and Contour • Three examples of exaggerated contrast

  11. Coding of Contrast and Contour • Receptive fields and on-off areas • Contrast heightening

  12. Hermann - Hering grid

  13. • Receptive fields and the Hermann-Hering illusion

  14. Gestalt Perception • Sensation and bottom-up processing • “The whole is greater than the sum of its parts” -> Perception involves an interplay between bottom-up and top-down processes.

  15. • Context and top-down processing.

  16. • Pitting the gestalt against sensation

  17. • Illusions deriving from top-down processing

  18. Gestal principles of grouping • Proximity.

  19. Gestal principles of grouping • Similarity.

  20. Gestal principles of grouping • Closure.

  21. Gestal principles of grouping • Good continuation. Online Demo

  22. Figure/ground • We divide a visual scene into figure (the object to which we attend) and ground (background). Example 1:

  23. Example 2: Figure and Ground in MC Escher’s art.

  24. Example 3:

  25. Rubin Vase byShigeo Fukuda

  26. Perception and Pattern Recognition • Visual auras and migraine headaches • Cortical or retinal? • A retinal effect:

  27. Perception and Pattern Recognition • Visual auras and migraine headaches • Cortical or retinal? • A retinal effect: • A cortical effect:

  28. Perception and Pattern Recognition • Extracting visual information • Saccades - eye movements, which occur in a jerking, start-stop fashion.

  29. Perception and Pattern Recognition • Visual sensory memory • Visible persistence • Selection from brief displays

  30. B M H L X S Q Y W R E T

  31. N Q F Z C D W U E T R Y

  32. M W G X V F E I R Y T U

  33. Perception and Pattern Recognition George Sperling • Visual sensory memory • Visible persistence • Selection from brief displays • Original findings • Observers remember 4 or 5 items (span of apprehension) • Sperling’s question: Where is the limitation? • Capacity hypothesis: The visual system only registers 4 or 5 items • Duration hypotheis: All the letters get registered but fade rapidly • The partial report procedure • E.g., Standing’s experiment

  34. Perception and Pattern Recognition 10 8 6 Estimated # letters available 4 2 0 0 .15 .30 1.0 Full Report Cue Delay (Seconds) • Visual sensory memory • Sperling’s results

  35. Perception and Pattern Recognition • Visual sensory memory • Visual Masking • Averbach and Coriell (1961) • Two types of cues: Bar markers and circles • Partial report of 1 item.

  36. N H W R T P J V M K X I Y S Q O

  37. N H W R T P J V M K X I Y S Q O

  38. Perception and Pattern Recognition 100 80 60 Bar probe Percentage Correct 40 Circle probe 20 0 400 500 0 200 300 -100 100 Cue Delay (ms) • Visual sensory memory • Averbach and Coriell (1961)

  39. Perception and Pattern Recognition • Visual sensory memory • Is selection from VSM precategorical? • Merikle (1980) • Demo

  40. B M H 6 X S 8 Y W 9 E 7