1. High level vision

2. High level vision Models of object recognition Top down influences
Navigation/Movement

3. Last Time. . ..
We spent a lot of time focusing on lines; how you get them, why you would want them, and so on.
We need to move from lines to objects.
How do you recognize an object from an organization of lines?
How does perception connect to memory?

4. Models of object recognition
Template
Feature
“New wave” of feature models (3D features)

5. Template model

6. Template--problems
Problems: Size
Orientation
Need too many templates

7. Feature model--pandemonium

8. Feature models
Good: visual input does seem to be decomposed into features
Good: Physiological evidence about simple features from Hubel & Wiesel
Problems: orientation
missing features
natural objects

9. Natural objects: What are the features of a dog?
Nose
Ear
Front Leg
Tail
Back Leg

10. Principle from Gestalt Psych
Good continuation B D

11. Good continuation can be used to find the parts of objects

12. “new wave” of feature models
These models use three-dimensional features.

13. Biederman’s geon model
Geons
Simple objects
You usually only need to see the edges of a geon
Geons have properties that are invariant to rotations

14. Experiment
Which can be better identified at a very brief exposure?

16. Problems with Geons Do geons really represent all shapes?
How are relationships among geons coded?

17. An alternative: Local viewpoints
Note that you can identify objects from many different orientations. Templates & Feature models couldn’t account for this—geons can.
BUT how good are you at doing this really?

27. Alternative
Some researchers have suggested that object representations are NOT viewpoint independent. Rather, we store views of objects the way we see them.
HUH? Isn’t that the template theory?
The difference is that you do some “fixing” (size, rotation) of the image to fit the template

28. Tarr’s local view experiments

29. Tarr Results

30. Problems with local view
Chicken & egg: how do you know how to rotate the image before you can identify it?
What is stored is clearly not literal pictures…but what is it?
How is what you see and what is in memory matched?

31. Chicken & egg problem. . .
Bottom up processing refers to beginning with relatively raw, unprocessed sensory information, and building towards more conceptual representations.
Top-down processing refers to conceptual knowledge influencing the processing or interpretation of lower-level perceptual processes

32. NOTE--we’ve been acting as though all processing were bottom up.

33. Example: ambiguous figures

34. Example

35. Example:

36. It appears that in top down processing you use conceptual information to generate hypotheses about what the stimulus might be, then test these hypotheses

37. More formal work
Watch for the object appearing

43. The Parsing Paradox
If perceptual organization is a matter of mapping sensations onto structural schema, which happens first: interpreting the whole or interpreting the parts? How can someone recognize a face until he has first recognized the eyes, nose, mouth and ears? Then again, how can you recognize the parts until you know that they are part of a face?
--Stephen Palmer

45. Question: do you process the top-down information at the same time as the bottom-up info?
You’ll see a circle--try to identify the object that appears in the circle.

53. The result: people are better at identifying the object when the scene makes sense, compared to when it’s jumbled

54. How is this possible? Word superiority effect
It is easier to recognize a letter in a word than in isolation.

55. Identify the letter that will appear in the circle

56. TAKE

57. WOLP

58. Word superiority effect
Faster and more reliable in identifying a letter when it’s part of a word than a non-word.
Isn’t there the same chicken-egg problem? Don’t you need to know the letters to identify the word? So then how is the word helping to identify the letters (which you already know?)

59. Model of word identification

60. Navigation vs. Object identification
There is increasing evidence that spatial information that helps us get around is independent of the information that helps us identify objects.

61. Mishkin & Ungerlieder

62. Mishkin & Ungerlieger

63. Mishkin & Ungerliedger
Spatial
Object