1. ILLUSIONS What are they? What can we learn from them? D.J. Aks 11/10/09 Proseminar Lecture for Z. Pylyshyn, RUCCs Photo credit: Andy Goldsworthy

2. ILLUSIONS Correspondence Problem Appearance vs. Reality

3. ILLUSIONS Discrepancy between… physical & perceptual stimulus Mueller-Lyer Illusion

4. ILLUSIONS Discrepancy between physical & perceptual stimulus Poggendorff Illusion

5. ILLUSIONS Discrepancy between 2D & 3D info Andy Goldsworthy

7. Experiments & Illusions http://aks.rutgers.edu/… illusions/Pogg/HalfCircDrag.html

9. ILLUSIONS Discrepancy between….? 2D & 3D info

10. ILLUSIONS Discrepancy between….? 2D depiction of 3D info i.e., conflicting perspective of parts of object

11. SIZE CONSTANCY - the stability of perceived size despite changes in objective distance and retinal image size. CONSTANCY SCALING - Our mind adjusts retinal size to correct for registered viewing distance = Size Distance Scaling

13. SIZE CONSTANCY - the stability of perceived size despite changes in objective distance and retinal image size. CONSTANCY SCALING - MOON ILLUSION - moon appears larger near the horizon than when high in the sky Depth cues (on land) give impression that moon is at a "far" distance.-- Thus, we ‘expect’ a far object (moon) to appear small on the retina - but when it does not, the mind compensates and we see the object (moon) as large

16. Size-contrast

17. Violation of assumptions We tend to assume: 1) overhead lighting SHADING 2) regularity of.. SHAPE

18. Shading & Structure Rodin

21. ILLUSIONS THAT VIOLATE ASSUMPTIONS Overhead lighting SHADING - we perceive convex shape when top is lit & concave when lit at bottom

22. ILLUSIONS THAT VIOLATE ASSUMPTIONS Overhead lighting SHADING - we perceive convex shape when top is lit & concave when lit at bottom

23. ILLUSIONS THAT VIOLATE ASSUMPTIONS Overhead lighting & Shading

26. ILLUSIONS THAT VIOLATE ASSUMPTIONS SHAPE & SIZE CONSTANCY - apparent shape of an object remains constant despite changes in the shape of the retinal image - –REGULAR SHAPES –AMES ROOM

27. ILLUSIONS THAT VIOLATE ASSUMPTIONS SHAPE & SIZE CONSTANCY –REGULAR SHAPES –AMES ROOM ILLUSION

28. Occlusion & Shape Perception Does shape of occluder drive shape percept of ‘occludee’? How about orientation of edges w/in occluder shapes?

30. Camouflage & Occlusion

31. Occlusion & Shape Perception

32. Motion & Shape Perception Kinetic Depth Effect

33. Motion & Shape Perception Johansson

34. Neuronal Interactions, Attention & Eye-movements

35. Visual-Auditory Integration Sound localization & ventriloquism Kevin Johnson on David Letterman http://www.youtube.com/watch?v=DnNBgIKOvr4

36. Experiments & Illusions http://aks.rutgers.edu/… illusions/Pogg/HalfCircDrag.html