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 Make a Hypothesis Identify a question Make a Prediction
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!