1. Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina

2. Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina The brain selects one that matches with common experience

3. Infinity of Interpretations There are an infinite number of interpretations of the 2D pattern of light on the retina The brain selects one that matches with common experience Ames Room is example of how this can lead to an illusion

4. Infinity of Interpretations Ames Room

5. Adding stereoscopic depth cues to 2D pictures

6. Stereoscopic Depth Disparity between the two retinal images indicates object distance from the plane of fixation

7. Stereoscopic Depth Disparity between the two retinal images indicates an objects distance from the plane of fixation Two different images (containing disparity) can be presented independently to each eye or…

8. Stereoscopic Depth Disparity between the two retinal images indicates an objects distance from the plane of fixation Two different images (containing disparity) can be presented independently to each eye or… Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate

9. Autostereograms Seeing depth in autostereograms requires you to suppress the reflexive coordination between convergence and accommodation

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

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

15. 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

17. Auto (aka Magic Eye) Stereograms Usually viewed with uncrossed convergence (leads to crossed disparity) 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

18. Autostereograms

21. The Correspondence Problem What is the Correspondence Problem?

22. The Correspondence Problem What is the Correspondence Problem? –How does the brain know what contours to match up…what images correspond?

23. The Correspondence Problem Maybe shape analysis is done first to make it easier to match up corresponding parts

24. The Correspondence Problem Bela Julesz tested this with random-dot stereograms No contours or form available in monocular image! Surface in depth still visible Left Eye Right Eye

25. The Correspondence Problem A different model must be adopted:

26. The Correspondence Problem A different model must be adopted: Visual system can extract form by matching up individual elements (dots) in an image, computing disparity between them, and finding the most likely surfaces. Might this involve top-down mechanisms? How could you test that hypothesis?

27. Next Time: Color Vision Read Land Article for Friday