Lecture #23

1. Lecture #23 Object recognition 4/23/13

2. MBEX final survey • If you took survey at the beginning of the semester and then complete it now, you will receive 5 pts towards homework • Please take it by April 30th • Thanks for helping biology education research

3. The end is in sight 4/25 One of main wiki pages done 5/2 Question for exam 5/9 Wiki due last class: Intro page and 3 main pages done 5/16 Final Thursday 1:30-3:30

4. Wiki references • With text, refer to your references with either (author, year) or [1] • Make sure to write out the reference to include author, year, title, journal • This helps the reader see what they are • Links are great but they are in addition

5. Writing • Don’t obfuscate your writing with jargon that is recondite and abstruse • Write in your own voice and not that of a medical encyclopedia • Make it so your parents could understand it, while still relying on the primary literature!!

6. Writing • Most important thing that you do as a scientist / business person / medical professional • Do it often • Strive to improve it

7. Once you’ve written something • Getting your first version done is just the first step • Read it again • Edit, edit, edit • Simplify, simplify, simplify

8. How do people write?

9. What do you do when you get stuck?

10. What to do when you get stuck • Deal with subunits • Does each paragraph hang together • Topic sentence • Outline paper based on topic sentences • Tests organization • Have many people read it • Different learning styles and perspectives

11. I. Object perception • What enables us to recognize two objects as being the same thing?

12. Low level vision • Retina detects dots • Center - surround wiring • Visual cortex detects lines, edges and blobs of color

13. Gestalt • Visual perception is more than just detection of dots of color and lines • Whole is greater than sum of parts • Gestalt = “whole” • There are rules by which visual scenes are interpreted as combinations of “perceptual groups”

14. Walls + windows + door + columns + roof = White House Middle vision • To build an object you need to: • Find edges • Group similar areas • “White” • Decide what goes together to make a whole • Organize elements into groups by grouping rules

15. Higher level vision • Determine what an object is • Match middle level views with memory of what object is • Independent of Viewing angle • Whether seen before or not

16. Grouping rules • How do you think you organize what you see into individual elements or groups?

17. Finding edges • Edge detection can be difficult and produce partial lines

18. Rule #1 : Good continuation • This figure is most likely the result of these lines and not these

19. Rule #2 : Occlusion • If an edge stops, it is likely being occluded • So assume it must actually extend

20. Kanizsa figure • You see the object even though it is only hinted at from objects present

21. Rule # 3 - Texture segmentation • Group parts of image that have similarly sized texture • This is based on two principles: • Similarity • Proximity

22. Similarity and proximity • Image bits,that are similar and close to each other, are grouped together • Can be based on • Color • Shape • Size • Orientation

23. Similarity and proximity • Can fool visual system if overlapped characteristics • Same forms and colors occur in both groups

24. Rule #4: Parallelism and symmetry • Lines that are parallel are seen as a group • Lines that are mirror images are seen as group

25. Additional rules • Group by proximity

26. Additional rules • Group by proximity • Group by common regions • Group by connectedness

27. Sinauer web site

28. Camouflage • An attempt to thwart the visual system’s ability to discriminate an object from its background – disrupt similarity/ proximity grouping

29. Camouflage • Color and texture matching - flounder

30. Camouflage to the extreme • Flounder can even match a checkerboard!

31. Zebra uses stripes to break up outline

32. May work even better for lion under dim light

33. Stripes make it hard to tell where one zebra stops and the next starts

34. Insects use shape, texture and color Katydids Walking stick

35. Video by Roger Hanlon

36. BBC: Vision and photography

37. Perceiving the alphabet • Each letter is composed of shapes - lines and curves

38. Perceptual committees • Low level vision provides shape and orientation info • Feature demons are specialists which detect certain aspects • Cognitive demons combine information to recognizeeach letter • Decision demon makes decision out of pandemonium Oliver Selfridge 1959

39. Similarities with brain • Areas of visual cortex that detect features • Feed info to other areas where cognition happens • Detection happens in parallel http://www.sinauer.com/wolfe/chap4/pandemoniumF.htm

40. Similarities with brain • Probably are neurons which interconnect and make these comparisons • Have to train neurons on the alphabet characters for your language

41. It is possible to wear out the demons • After images result if you have two demons which oppose each other • If wear one out, the other wins

44. It is possible to wear out the demons • After images result if you have two demons which oppose each other • If one gets tired, the other wins

45. Tilt after effect

46. Tilt after effect

47. Tilt after effect

48. Additional grouping rules:Figure and ground • Like grouping, there are rules which help the brain decide which object is in front of which • Ideas?

49. Rules • Surroundedness - if one object surrounds other, the surrounded object is figure • Size - smaller object is figure • Symmetry - symmetric object is figure • Parallelism - regions which are parallel are part of a figure

50. Which are figures?