1. Physiological Depth Cues – Convergence

2. 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?

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

4. Motion Depth Cues – Motion 1. Parallax

5. Motion Depth Cues – Parallax

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

7. Motion Depth Cues – Parallax

8. More Depth Cues Pictorial Depth Cues Physiological Depth Cues Motion Parallax Stereoscopic Depth Cues

9. 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?

10. 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?

11. Binocular Disparity Binocular disparity is the difference between the two images

12. 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”

13. Science Science is like a set of procedures: Identify a question

14. Science Science is like a set of procedures: Identify a question Make a Hypothesis

15. Science Science is like a set of procedures: Identify a question Make a Hypothesis Make a Prediction

16. Science Science is like a set of procedures: Identify a question Make a Hypothesis Make a Prediction Test It

17. Science Science is like a set of procedures: Identify a question Make a Hypothesis Make a Prediction Test It Prediction holds Prediction Fails

18. Example: The horizontal- vertical illusion

19. Question:

20. Example: The horizontal- vertical illusion Question: Why does the vertical line seem longer? Hypothesis:

21. Example: The horizontal- vertical illusion Question: Why does the vertical line seem longer? Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently Prediction:

22. Example: The horizontal- vertical illusion Question: Why does the vertical line seem longer? Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently Prediction: Stabilized image should eliminate the illusion Test:

23. Example: The horizontal- vertical illusion Question: Why does the vertical line seem longer? Hypothesis: Wundt -> vertical and horizontal eye movements scan the image differently Prediction: Stabilized image should eliminate the illusion Test: Illusion is still present in afterimage!

24. Muller - Lyer Illusion

25. What theory does Gregory take up?

26. Muller-Lyer Illusion What theory does Gregory take up? –Thiery / Woodworth : Muller-Lyer figure “suggests perspective”

27. Muller-Lyer Illusion What theory does Gregory take up? –Thiery / Woodworth : Muller-Lyer figure “suggests perspective” –Is there something about the presence of pictorial depth cues in an image that distorts size?

28. Depth Cues and Size Distortion The Ponzo Illusion:

29. Depth Cues and Size Distortion The Ponzo Illusion:

30. Depth Cues and Size Distortion The illusion of depth in an image seems to distort the perception of size in the image

31. Pictures are Weird What does Gregory find ambiguous about pictures?

32. Pictures are Weird What does Gregory find paradoxical about pictures?

33. The Apparatus What does he do to remove the paradox so that the Muller-Lyer figure no longer looks flat?

34. The Apparatus

35. Removing the Background With background removed, Muller-Lyer figure actually looks 3D What prediction can you make about how the perceived size and the perceived distance of the center line are related? How did Gregory test that?

36. Removing the Background Perceived size and perceived distance are tightly related

37. Next Time Stereo vision Read Pinker for next Thursday