Reading

1. Reading • Gregory 24th • Pinker 26th

2. Seeing Depth • What’s the big problem with seeing depth ?

3. Seeing Depth • The world is 3D, the retina is 2D !

4. Depth Cues • Pictorial Depth Cues: aspects of 2D images that imply depth • Physiological Depth Cues: Proprioception in ocular muscles indicates accommodation and convergence • Motion Depth Cues: foreground and background move in opposite directions • Stereoscopic Depth Cues: disparity between two retinal images indicates distance

5. Pictorial Depth Cues • Occlusion

6. Pictorial Depth Cues • Shadows and Shading

7. Pictorial Depth Cues • Retinal image size • far objects smaller than near objects

8. Pictorial Depth Cues • Linear perspective

9. Pictorial Depth Cues • Texture gradient

10. Pictorial Depth Cues • Height in the plane

11. More Depth Cues • Pictorial Depth Cues • Physiological Depth Cues • Motion Parallax • Stereoscopic Depth Cues

12. Physiological Depth Cues • Two Physiological Depth Cues • accommodation • convergence

13. Physiological Depth Cues • Accommodation

14. Physiological Depth Cues • Convergence

15. Physiological Depth Cues • Convergence • small angle of convergence = far away • large angle of convergence = near • What two sensory systems is the brain integrating? • What happens to images closer or farther away from fixation point?

16. Physiological Depth Cues • Convergence and accommodation are reflexively linked Under what circumstances might this be a problem?

17. Motion Depth Cues • Motion • Parallax

18. Motion Depth Cues • Parallax

19. Motion Depth Cues • Parallax • points at different locations in the visual field move at different speeds depending on their distance from fixation

20. Motion Depth Cues • Parallax

21. Seeing in Stereo Seeing in Stereo

22. Seeing in Stereo It’s very hard to read words if there are multiple images on your retina It’s very hard to read words if there are multiple images on your retina

23. Seeing in Stereo It’s very hard to read words if there are multiple images on your retina It’s very hard to read words if there are multiple images on your retina But how many images are there on your retinae?

24. Binocular Disparity • Your eyes have a different image on each retina • hold pen at arms length and fixate the spot • how many pens do you see? • which pen matches which eye?

25. Binocular Disparity • Your eyes have a different image on each retina • now fixate the pen • how many spots do you see? • which spot matches which eye?

26. Binocular Disparity • Binocular disparity is the difference between the two images

27. Binocular Disparity • Binocular disparity is the difference between the two images • Disparity depends on where the object is relative to the fixation point: • objects closer than fixation project images that “cross” • objects farther than fixation project images that do not “cross”

28. Binocular Disparity • Corresponding retinal points

29. Binocular Disparity • Corresponding retinal points

30. Binocular Disparity • Corresponding retinal points

31. Binocular Disparity • Corresponding retinal points

32. Binocular Disparity • Points in space that have corresponding retinal points define a plane called the horopter The Horopter

33. Binocular Disparity • Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points)

34. Binocular Disparity • Points not on the horopter will be disparate on the retina (they project images onto non-corresponding points) • The nature of the disparity depends on where they are relative to the horopter

35. Binocular Disparity • points nearer than horopter have crossed disparity • points farther than horopter have uncrossed disparity The Horopter

36. Binocular Disparity • Why don’t we see double vision?

37. Binocular Disparity • Why don’t we see double vision? • Images with a small enough disparity are fused into a single image