Understanding Visual Perception: From Neural Mechanisms to Gestalt Principles

1. PSYC 330: Perception Form Perception

2. The world as we see it…. ….. so far.

3. The Neural Picture • Rods and cones • Ganglion cells (M cells, P cells) • LGN (magnocellular tract, parvocellular tract) • PVC (striate cortex) • Simple, complex, hypercomplex)

5. The world as we see it…. ….. so far. The Visual Picture • Simple features • Low level vision

6. Affordances…. • What information is important to glean from the environment? • How do I learn about the objects and events in the environment that I inhabit? • ASSIGNMENT FOR NEXT CLASS MEETING

7. Machine Vision • Limits of machine vision • Limits of simple features • Limits of low-level vision

8. Mid level vision • What intermediate processes intervene between the collection of basic features and the understanding of objects? • How do we “parse” a scene? • AI definition – interpreter, compiler of data in a context of ambiguity • Top down, bottom up types

9. Why is the visual scene not like a bar code? • Stimulus variation • Differences in illumination • Multiple edges, lines • Incomplete boundaries • Multiple interpretations • Observer variation • Viewpoint – accidental or otherwise

10. How do we begin to extract meaning from the messy visual array? • How do we use and choose from the features at hand? • On what basis do we “decide” what interpretation to “go with”

11. A final comparison of machine and man (and, of course, woman too) • Effort • Acquisition of skill • Flexibility of the rules

12. Pragnanz

13. What is available in the stimulus? • Edges • Textures • Figure-ground • Parts and wholes

14. Edge detection • Sum up the simple features? • ___ + ___ + ___ = _________ • Problems • Variation in illumination • Incomplete forms • Illusory contours

16. Gestalt rules of organization • A bit of history….. • Rules of organization • Good continuation

17. Edge detection • Gestalt rule of good continuation

19. Edge detection • Gestalt rule of good continuation • Gestalt rule of occlusion

21. Edge detection • Gestalt rule of good continuation • Gestalt rule of occlusion • Closure

23. Perceptual Committees Good continuation VS Occlusion ….. and the winner is?

24. What is available in the stimulus? Edges • Textures • Figure-ground • Parts and wholes

25. Texture Segregation (texture segmentation) • Similarity

27. Texture Segregation (texture segmentation) • Similarity • Proximity

29. Texture Segregation (texture segmentation) • Similarity • Proximity • Parallelism and Symmetry

31. Texture Segregation (texture segmentation) • Similarity • Proximity • Parallelism and Symmetry • Common region

33. Texture Segregation (texture segmentation) • Similarity • Proximity • Parallelism and Symmetry • Common region • Connectedness

35. What is available in the stimulus? Edges Textures • Figure-ground • Parts and wholes

36. Figure Ground • What is the stimulus? • What is the background?

37. Surroundedness • Size • Symmetry • Parallelism • Extremaleges – shading • Relative motion

38. Extremal edges