1. Binocular Disparity points nearer than horopter have crossed disparity points farther than horopter have uncrossed disparity

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

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

4. Binocular Disparity Why don’t we see double vision? Images with a small enough disparity are fused into a single image The region of space that contains images with close enough disparity to be fused is called Panum’s Area

5. Binocular Disparity Panum’s Area extends just in front of and just behind the horopter

6. Stereopsis Our brains interpret crossed and uncrossed disparity as depth That process is called stereoscopic depth perception or simply stereopsis

7. Stereopsis Stereopsis requires that the brain can encode the two retinal images independently

8. Stereopsis Primary visual cortex (V1) has bands of neurons that keep input from the two eyes separate

9. Stereopsis If the brain only gets normal signals from one eye early in life, that eye’s neurons crowd out the other eye’s neurons

10. Amblyopia Amblyopia is a visual deficit in which one eye has poor vision because the brain never developed the ability to use signals from that retina

11. Amblyopia Amblyopia is a visual deficit in which one eye has poor vision because the brain never developed the ability to use signals from that retina Usually caused by –strabismus - when eyes don’t lock onto the same point –anisometropia - when one eye has very bad optics and the other is normal

12. Stereograms seeing depth requires “only” two different images on the retina

13. Stereograms seeing depth requires “only” two different images on the retina this could be accomplished by an optical device that projects separate images into the two eyes

14. Stereograms Left Eye Right Eye Divider Right eye sees same image as left eye Face appears in same plane as square

15. Stereograms Left Eye Right Eye Divider What would you see?

16. Stereograms Left Eye Right Eye Divider Right eye sees face to the right; left eye sees face to the left therefore: uncrossed disparity Face appears behind the square

17. Stereograms Left Eye Right Eye Divider What would you see?

18. Stereograms Left Eye Right Eye Divider Right eye sees face to the left; left eye sees face to the right therefore: crossed disparity Face appears in front of square

19. Presenting Binocular Images Various ways to add depth: –1. Stereoscope

20. Presenting Binocular Images Various ways to add depth: –2. glasses with different lenses

21. Presenting Binocular Images Various ways to add depth: –2. glasses with different lenses

22. Presenting Binocular Images Various ways to add depth: –2. glasses with different lenses

23. Presenting Binocular Images Various ways to add depth: –3. LCD Shutter Glasses

24. Autostereograms Optically separate images aren’t needed

25. Autostereograms Optically separate images aren’t needed WARNING! Confusing stuff coming in the next slides

26. Autostereograms Optically separate images aren’t needed WARNING! Confusing stuff coming in the next slides Keep the definitions of convergence and disparity separate.

27. Autostereograms right-eye line of sight crosses left-eye line of sight in front of image What would you see? crossed convergence

28. Autostereograms Right eye sees face shifted to right; left eye sees face shifted to left therefore: uncrossed disparity Face appears behind square crossed convergence

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

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

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

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

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

34. RIGHT EYELEFT EYE Convergence tells your brain that the plane of the image is behind the plane of the surface Autostereograms

35. Next Time: Read Pinker !!