Autostereograms

1. Autostereograms What would happen if you remove the divider of a stereoscope? • Convergence is on a point at the same distance as the images • Boxes and faces are on the horopter • How many boxes would you see? boxes and faces are on the horopter

2. Autostereograms Now cross your eyes: • right-eye line of sight crosses left-eye line of sight in front of image (crossed convergence) • each retina is now pointed at the opposite box • How many boxes would you see? • What would happen to the face? crossed convergence

3. Autostereograms • There would be three boxes • middle box: right eye sees face shifted to right; left eye sees face shifted to left therefore: • uncrossed disparity • Face in the middle box appears behind square crossed convergence

4. Autostereograms Crossed convergence shifts right image to the right of the left image and vice versa: Left Eye’s Image Right Eye’s Image

5. Autostereograms What would happen if the convergence was uncrossed?

6. Autostereograms Uncrossed convergence shifts right-eye’s image to the left of the left-eye image and vice versa: Left Eye Right Eye

7. Autostereograms What would happen if the faces were switched relative to the boxes?

8. Autostereograms • one doesn’t even need two different images!

9. Autostereograms RIGHT EYE LEFT EYE Faces fuse Convergence tells your brain that the plane of the image is farther away than it really is

10. Autostereograms • Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate

11. Autostereograms • Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate • TRICK: Seeing depth in autostereograms requires you to suppress the reflexive coordination between convergence and accommodation

13. Autostereograms Any repeating objects that have a spacing different from the background will have either crossed or uncrossed disparity RIGHT EYE LEFT EYE If you uncross convergence, your right eye gets these faces shifted slightly to left, left eye gets them shifted to right = CROSSED DISPARITY What would you see?

15. Autostereograms Any repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity RIGHT EYE LEFT EYE If you uncross convergence, right eye gets these faces shifted slightly to right, left eye gets them shifted to left = UNCROSSED DISPARITY What would you see?

17. Autostereograms • by adjusting the disparity at different parts of the image (with a computer usually) one can make shapes that emerge or recede in depth

18. “Magic Eye” Stereograms • Usually viewed with uncrossed convergence • Imagine gazing farther than the surface (let your eyes “relax”) • Now try to notice objects or forms in the blurriness • As you become aware of shapes, try to focus (accommodate) the plane of the image without converging your eyes

19. Autostereograms

20. Autostereograms

21. Autostereograms

22. COLOR VISION

23. Wavelength and Color • Recall that light is electromagnetic radiation

24. Wavelength and Color • Recall that light is electromagnetic radiation • Light waves have a frequency/wavelength

25. Wavelength and Color • Recall that light is electromagnetic radiation • Light waves have a frequency/wavelength • Frequency/wavelength is the physical property that corresponds (loosely) to the perception called color

26. Color Vision Wavelength and Color • Different wavelengths correspond roughly to the “colors” of the spectrum

27. Color Vision Wavelength and Color • White light is a mixture of wavelengths • prisms decompose white light into assorted wavelengths

28. Color Vision Wavelength and Color • White light is a mixture of wavelengths • prisms decompose white light into assorted wavelengths • likewise, adding all wavelengths together makes white light What happens if you mix several different paints together?

29. Color Vision Wavelength and Color • Objects have different colors because they reflect some but not all wavelengths of light • the surfaces of objects are like filters that selectively absorb certain wavelengths

30. Color Vision Perceiving Color • Primary colors What are the primary colors?

31. Color Vision Perceiving Color • Primary colors RedGreenBlue

32. Color Vision Perceiving Color • Primary colors What makes them primary?

33. Color Vision Perceiving Color • Primary colors • Every color (hue) can be created by blending light of the three primary colors in differing proportions

34. Color Vision Perceiving Color • Primary colors • Every color (hue) can be created by blending light of the three primary colors in differing proportions • Led to prediction that there must be three (and only three) distinct color receptor types

35. Color Vision Perceiving Color • Four absorption peaks in retina: 3 cone types plus rods Absorption/Cone response

36. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” Blue “Green” “Red”

37. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” “Green” Green “Red”

38. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” “Green” “Red” Red

39. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

40. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

41. Color Vision Theories of Color Vision Signal to Brain Wavelength Input Cone “Blue” Equal Parts Red and Green = “Green” Yellow “Red”

42. Next Time: • Color Vision • Read Land Article for Thursday Feb 28th • Go skiing