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

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

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

5. 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

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

7. Binocular Disparity • Panum’s Area extends just in front of and just behind the horopter • Images outside of Panum’s area are often blurry because accommodation is reflexively set according to vergence

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

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

10. Stereopsis • Primary Visual cortex normally keeps input from the eyes separate • If normal input is restricted during development, the cortical representation of the “bad” eye is reduced • Amblyopia can result

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

12. 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

13. Amblyopia • People with Amblyopia can’t see stereograms

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

15. 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

16. Presenting Binocular Images • Various ways to add depth: • 1. Stereoscope

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

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

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

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

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

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

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

24. Gregory

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

26. Example: The horizontal-vertical illusion

27. Example: The horizontal-vertical illusion • Question:

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

29. 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:

30. 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:

31. 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!