1. Reading Assignment Read chapter by Pinker for Wed. of next week.

2. Shape from Shading

3. Investigating Perception Perception is mysterious So how do we go about understanding how it works?

4. Investigating Perception What is Science?

5. Investigating Perception What is Science? Science is a method for understanding how nature works

6. Science What isn’t Science? Headlines on www.reuters.com Science Page: –Juan Strengthens Into Hurricane, Misses Bermuda

7. Science What isn’t Science? Headlines on www.reuters.com Science Page: –Juan Strengthens Into Hurricane, Misses Bermuda –Japan's Mt Fuji Shows Subsidence, No Eruption Danger

8. Science What isn’t Science? Headlines on www.reuters.com Science Page: –Juan Strengthens Into Hurricane, Misses Bermuda –Japan's Mt Fuji Shows Subsidence, No Eruption Danger –Official Report: French Heat-Wave Death Toll 15,000

9. Science What isn’t Science? Headlines on www.reuters.com Science Page: –Juan Strengthens Into Hurricane, Misses Bermuda –Japan's Mt Fuji Shows Subsidence, No Eruption Danger –Official Report: French Heat-Wave Death Toll 15,000 –Man Questioned in Australia Over Mutilated Whale Carcass

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

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

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

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

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

15. Example: The horizontal-vertical illusion

16. Question: Hypothesis: Prediction: Test:

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

18. 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: Test:

19. 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:

20. 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!

21. Muller - Lyer Illusion

22. What theory does Gregory take up?

23. Muller-Lyer Illusion What theory does Gregory take up? –Thiery / Woodworth : Muller-Lyer figure “suggests perspective” –implicit is that the brain shrinks things that are perceived as near and expands things that are perceived as far away

24. Size Constancy Brain shrinks things that are near and expands things that are far The Ponzo Illusion:

25. Size Constancy The lines of perspective in the Ponzo Illusion make the top line appear farther away Why isn’t it this simple for the Muller-Lyer Illusion ?

26. Size Constancy The lines of perspective in the Ponzo Illusion make the top line appear farther away Why isn’t it this simple for the Muller-Lyer Illusion ? –Because the Muller-Lyer figure looks flat !

27. Paradox of Pictures What does Gregory find so paradoxical about pictures?

28. Paradox of Pictures What does Gregory find so paradoxical about pictures? What does he do to remove the paradox so that the Muller-Lyer figure no longer looks flat?

29. Paradox of Pictures

30. 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?

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

32. Size Constancy in Motion What does Gregory wonder about size constancy and motion? How does he test that?

33. Size Constancy in Motion Gregory finds that motion does invoke size constancy in certain cases:

34. Size Constancy in Motion Gregory finds that motion does invoke size constancy in certain cases: –only when observer is accelerating

35. Science Works at Different Scales What’s the “Big Picture” theory, amid the more specific hypothesis? (hint: look in the first paragraph)

36. Science Works at Different Scales What’s the “Big Picture” theory, amid the more specific hypothesis? (hint: look in the first paragraph) That illusions occur because of perceptual mechanisms evolved to handle vision under normal circumstances

37. Science Works at Different Scales What is Gregory’s theory about how the brain accomplishes this?

38. Science Works at Different Scales What is Gregory’s theory about how the brain accomplishes this? “it is as though the brain entertains alternative hypotheses of what object the eye’s image may be representing”

39. Next Time More on seeing in 3D Read chapter by Pinker for Wed. next week