1. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20021 Recovery of World Structure: Art and Image

2. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20022 Task of visual perception Stay alive, reproduce, make art Estimate properties of world using light falling on retina Information: –originates from light reflected from objects –internal knowledge (evolutionary/experience) Combined to recover “true” object properties

3. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20023 Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

4. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20024 1.Illumination intensity, hue, motion varies from spot to spot, moment to moment recover “true” surface properties From http://www.discount-line.com/bath.htm What material is this?

5. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20025 Projection (3D world to 2D images) recover depth and spatial organization depth enables two abilities: a.shape constancy true 3D shape of object b.size constancy true 3D size of object

6. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20026 Fragmentation (occlusion) objects not always connected in image From http://www.heavenforcars.com/products/gifts/index7.htm

7. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20027 Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

8. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20028 Projection a. shape constancy Perceived shape of object does not change as orientation changes Shape of image on retina changes From http://zeus.rutgers.edu/~ikovacs/SandP/prepIII_1.html

9. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 20029 Projection a. shape constancy Same image could be due to: - different shapes - different orientations - different depths

10. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200210 Projection a. shape constancy if shape known –depth and orientation can be “guessed”

11. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200211 Projection a. shape constancy if depth known –shape and orientation can be “guessed”

12. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200212 Projection b. size constancy known object size retinal size determines depth depth cues determine size From http://psychlab1.hanover.edu/classes/Sensation/SizeConstancy/index.html

13. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200213 Projection b. size constancy known object size retinal size determines depth depth cues determine size

14. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200214 Projection b. size constancy known object size retinal size determines depth depth cues determine size

15. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200215 Projection b. size constancy

16. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200216 Projection b. size constancy

17. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200217 Projection b. size constancy

18. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200218 -angle  depends only on ratio s/d Projection b. size constancy

19. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200219 Projection b. size constancy

20. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200220 Projection b. size constancy Angle  the same as long as s/d the same larger or smaller objects can have same  -  1 = s2 d1 d2

21. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200221 Projection b. size constancy  is known (from retinal size) -> tan       if size is known, distance follows if distance is known, size follows

22. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200222 Size and Shape Constancy depend on experience depend on expectations “top down” processes how else can we recover depth from images? what depth cues are available?

23. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200223 Depth cues 1.Pictorial cues (single image) –art techniques (perspective, shading, occlusion) 2.Multi-point cues (multiple images) –motion cues (kinetic depth, motion parallax) –binocular cues 3.Physiological cues (real stimuli) –accommodation of lens –vergence movements

24. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200224 Pictorial cues occlusion/interposition shading shadows perspective texture gradient height in plan aerial perspective familiar size

25. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200225 Occlusion/Interposition nearer object occludes further one

26. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200226 Occlusion/Interposition nearer object occludes further one critical feature “T-junction”

27. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200227 Shading lightness constancy: shading determines shape uniform reflectance: 3D shape from shading lighting from above –bumps are light on top –dents are light on bottom

28. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200228 Countershading confuse interpretation of shape

29. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200229 Countershading on the BB-55 USS North Carolina (1937-1961) more difficult to see or determine barrel diameter From http://www.navsource.org/archives/01/55.htm

30. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200230 with shadows perceived as standing (3D) Shadows dark patches interpreted as shadows lighting from above Ball and shadow demo

31. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200231 without shadows perceived as flat (2D) (applications to computer interfaces) Shadows dark patches interpreted as shadows lighting from above Ball and shadow demo

32. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200232 Perspective parallel lines in world converge to a vanishing point in image lines that converge are parallel in world

33. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200233 Texture gradient perspective: location of texture items and changes in size/shape of texture items

34. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200234 Change in texture gradient: change in shape and depth From http://psych.hanover.edu/Krantz/art/texture.html

35. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200235 Height in plane (distance from horizon) objects closer to horizon appear further away Same object, one closer to horizon: smaller or further away?

36. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200236 Aerial perspective (da Vinci) smog, haze, etc. scatter light –objects father away: more scattering –if object surrounded by haze, appears farther away

37. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200237 Without haze, objects appear equally distant Aerial perspective (da Vinci) smog, haze, etc. scatter light –objects father away: more scattering –if object surrounded by haze, appears farther away

38. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200238 Aerial perspective Why do mountains look closer on a clear day? “Whoa, look at the mountains!” Visual system assumes average amount of haze –more haze, more distance object must be –less haze, less distant object must be –on a clear day, less haze than usual mountains appear closer than normal

39. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200239 Familiar size if size of object is known –perceived size = true size –depth is inferred

40. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200240 1. Pictorial cues occlusion/interposition shading shadows perspective texture gradient height in plan aerial perspective familiar size

41. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200241 2. Multi-point cues kinetic depth (motion of object) motion parallax (motion of observer) binocular stereopsis (see lecture from January 29 for kinetic depth and motion parallax)

42. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200242 Binocular Stereopsis recovery of 3D depth via 3D displacement of eyes each eye sees slightly different image

43. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200243 Left eyeRight eye Binocular Stereopsis recovery of 3D depth via 3D displacement of eyes each eye sees slightly different image

44. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200244 Binocular Stereopsis amount of difference between image depends on depth –depth can be calculated exactly from differences –as if angles between eyes were used limitation: depth less than 3 meters limitation: requires matching images (escalator)

45. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200245 Binocular Stereopsis: stereoscope use two static images one for each eye –coloured glasses, polarized lenses, lenses –divergence of eyes: practice, practice, practice

46. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200246 Binocular Stereopsis there are always two slightly different images entering visual system double vision rarely occurs to avoid double vision (binocular rivalry) –suppress input from one eye –dominant eye is “attended” –non-dominant eye is “unattended” –if two completely different images are presented attention (and cortex activity) switches back and forth

47. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200247 Binocular rivalry Tong et al 1998 two different images –face and house presented either –simultaneously –sequentially same fMRI responses rivalry resolved below high-level areas From http://www.princeton.edu/~ftong/

48. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200248 2. Multi-point cues kinetic depth (motion of object) motion parallax (motion of observer) binocular stereopsis (see lecture from January 29 for kinetic depth and motion parallax)

49. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200249 3. Physiological cues - real stimuli accommodation –focusing of an eye vergence –angle between two eyes

50. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200250 Accommodation (one eye) lens changes shape to focus on objects –rounder for near object –flatter for far objects limitation: depth between 20cm and 2m

51. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200251 Eyes fixate on object - rotate inwards if near by Eyes fixate on object - less rotation if far away Vergence (two eyes)

52. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200252 Vergence difference from binocular stereopsis –angle of eyes rather than different images limitation: depth less than 3m

53. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200253 Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

54. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200254 Fragmentation objects connected in world –not always connected in image on retinas determine which patches in image belong together Visual completion A B

55. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200255 Visual completion (fragmentation) Two abilities –modal completion: completion of pieces fragmented by occluders in world –blindspot completion: completion of visual image fragmented by existence of blindspot

56. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200256 Modal completion handle fragmentation due to external occluder

57. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200257 Modal completion handle fragmentation due to external occluder

58. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200258 Modal completion handle fragmentation due to external occluder

59. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200259 Modal completion handle fragmentation due to external occluder

60. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200260 Result: - pieces are linked when - edges intersect at >= 90° - there is a visible occluder but no “filling in” behind occluder Modal completion handles fragmentation due to external occluder

61. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200261 Blindspot completion handles fragmentation due to blindspot in eye

62. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200262 Information actually picked up What kind of completion occurs? Pattern of light on retina Blindspot completion

63. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200263 Blindspot completion Result - area is filled in (limited) filling in includes –texture, complex patterns (but not text) –smooth transitions between colours, alignment, intensity, etc. 123456 891012 345678 AB CD

64. 2002/02/12PSYC202, Term 2, Copyright Jason Harrison 200264 Recovery of World Structure: Art and Image 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)