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Visual Perception III

Visual Perception III. More on Depth and Starting on Objects. Ocular Dominance Columns. Ocular Dominance Columns. Vision is lost permanently in sutured eye!. Development of ODC. Kittens have eye sutured shut at birth, and opened after 2 weeks. Development of ODC.

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Visual Perception III

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  1. Visual Perception III More on Depth and Starting on Objects

  2. Ocular Dominance Columns

  3. Ocular Dominance Columns

  4. Vision is lost permanently in sutured eye! Development of ODC • Kittens have eye sutured shut at birth, and opened after 2 weeks.

  5. Development of ODC • Kittens who have both eyes sutured (for a comparable period) develop almost normally.

  6. Visual Cliff • Infants between 6.5 and 12 months avoid deep side • So do newborn chicks • But not 4 week old kittens raised in the dark

  7. Is Depth Perception Innate or Learned? • Presence of development doesn’t imply non-innateness: Notion of Critical Period (16 weeks for cats, 2.5 years for humans)

  8. Critical Period

  9. Monocular Cues to Depth • In addition to stereopsis, other aspects of visual scene, which don’t require reference to multiple views, can provide cues to depth.

  10. Occlusion • Objects that are occluded are perceived as more distant.

  11. Occlusion

  12. Relative height • Objects that are higher are perceived to be further away.

  13. Relative height • Objects that are higher are perceived to be further away.

  14. Linear perspective Parallel lines converge as they become more distant

  15. Linear Perspective

  16. Texture gradients • Rate of increasing density and homogeneity of regularly spaced objects provides cues about angle of incline.

  17. Texture gradients

  18. Texture gradients

  19. Relative size • Visually smaller objects are interpreted as more distant (and not physically smaller)

  20. Sometimes clues give surprising results… Size constancy

  21. More size constancy Intervention of top-down information?

  22. Shading • Pattern of reflection indicates shape and orientation of surfaces

  23. Shading

  24. Shading • “Direction” of depth depends on direction of luminance gradient. • We assume that there is only one light source, coming from above. • If brighter on top, we assume convex, if brigher on bottom we assume concave.

  25. Shading • Rotating image 180 degrees, turns holes into bumps.

  26. Shading • Rotating image 90 degrees, yields no sensible interpretation on assumption that light comes from above. As a result, no stable percept.

  27. Relative motion Random dots, but assumed to be located on a rigid object moved in 3-dimensional space

  28. Relative motion:biological motion Moving Light Displays (after Johansson 1973) Does not work if lights are applied midway between joints!

  29. Relative motion:biological motion

  30. Review:Monocular cues to depth • Occlusion • Relative Height • Linear Perspective • Texture Gradients • Relative size • Shading • Relative Motion • …

  31. Where are we?

  32. Marr’s 2 1/2-D Sketch Viewer centered representation

  33. Where are we? • We have no explicit representation of 3-D shape of objects or spatial relations What does the back of Churchill’s head look like?

  34. Modularity questions • Is information about depth and position necessarily combined?

  35. What vs. Where:Mishkin, Ungerleider and Macko

  36. Two visual pathways Ventral pathway: What Dorsal pathway: Where

  37. Modularity of what and where • AH: Hopkins undergraduate, highly intelligent, “underperformer”

  38. Representation of “where” information

  39. AH’s results

  40. What vs. Where in the “normal” brain • Visual Search (Treisman) • Is there a white square in the picture? Reponse time is proportional to number of distractors

  41. What vs. Where in the “normal” brain • Visual Search (Treisman) • Is there a white triangle in the picture? Reponse time is independent of the number of distractors

  42. What vs. Wherein the “normal” brain • Treisman: feature maps can detect the presence of some specific visual feature (e.g., color, shape), but not location. • Such identification proceeds in parallel for all points in the visual field. • Difficulties arise when two feature maps must be aligned: forces serial computation.

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