Visual Illusions: Ponzo & Poggendorf

1. Visual Illusions: Ponzo & Poggendorf Leo Do Beckie Aguirre Cluster 7

2. Outline • What are visual illusions • What are the Ponzo and Poggendorf Illusions? • How are our illusions tested? • Results - how did everyone do? - how did the variables affect what we saw? • How did our illusions work? • Conclusions

3. Background • What are illusions? • Visual Illusions occur when you “see” something differently than that which is actually there. • Who invented the Ponzo illusion? • Mario Ponzo in 1913. • Who invented the Poggendorf illusion? • Johann Poggendorf in 1860. • Visual Illusions also help us learn about our visual systems.

4. MethodsPonzo Illusion • 3 variables: • Color of ties • angle of tracks • reference bar position • 3 settings per variable • 3 attempts per setting • 11 subjects tested • Harder than it looks Reference bar Ties Tracks Measured bar

5. Ponzo Illusion Measure bar length Reference bar length Ratio (R) = R < 1 R = 1 R > 1

6. Ponzo Illusion:Color of Ties Black ties Blue ties

7. Color of Ties The color of the ties does not appear to affect how well people can make the bars the same length.

8. Ponzo Illusion:Angle of Tracks Angle: 5 degrees Angle: 22 degrees More Depth Less Depth

9. Angle of Tracks • As expected, the misperception increased as the angle of the tracks increased from 5 to 15°. • However, the misperception decreased between 15 and 22° when it appeared that the reference bar was further away. More Depth Less Depth (degrees)

10. Ponzo Illusion:Reference Bar Position Reference bar position: 50 units Reference bar position:120 units Less Distant More distant Positions tested: 50, 72, 120 units

11. Reference Bar Position People misperceive a larger difference in bar lengths when the reference bar is more distant from the measurement bar Less Distant More distant

12. Why do we see the Ponzo Illusion? • Size Constancy & Perspective • We expect an object that is further away to appear smaller than the same object when it’s closer • We expect the reference bar to look smaller than the measurement bar because you think it’s further away.

13. Conclusions • Color of ties: No impact on subjects ability to make bars the same length • Angle of tracks: Misperception initially increased with angle, but then unexpectedly decreased • Reference bar position: Harder to make bars same length when reference bar appears more distant • Most subjects averaged Ratio > 1 • Size constancy and our past experience influence how we see this illusion • Our brains function with our eyes to make us see what we see

14. How the Poggendorf illusion works • There is a box in the middle of two lines which are connected even though it doesn’t look that way. • But the question is why is this misperceived? • Subjects were told to move the top line to where they think it is connected to the bottom line.

15. Methods The Poggendorf test • Variables tested: • Angle of the line • Height of the box • Line color • Border and box color • 11 subjects were tested • Each test was conducted three times

16. Ratio Ratio = 1.0

17. Ratio Ratio less than 1.0 Ratio = 1.0

18. Ratio Ratio less than 1.0 Ratio greater than 1.0 Ratio = 1.0

19. Poggendorf IllusionAngle of the line • Reference angle: 20° • Angles tested: 40°, 65° Angle = 20° Angle = 65°

20. ResultsAngle of the line When the angle between the line and the box increases, the misperception of lining up the two lines decreases.

21. Height of the box Height = 25 Height = 75 • Reference height: 50 • Height tested: 25, 75

22. Results of the box height Changing the box height has little effect on subjects ability to line up the two lines.

23. Line color Cyan lines Black lines Reference: black line, cyan box Tested: Cyan line, cyan box

24. Results for line color When the color of the line matched the color of the box, the subjects were able to line up the two lines more accurately.

25. Border and box color Red Border and Box Cyan Border and Box Reference: Line black, cyan border and box Tested: Line black, red border and box

26. Results for box color The misperception is somewhat smaller when the color changes from cyan to red.

27. How does the Poggendorf work? Hering Illusion • Acute angle dilation • Our brains make small angles appear larger than they actually are. • Subjects line up the two lines better when the angle is larger. • Here is another illusion that works the same way - Hering illusion

28. How does the Poggendorf work? Hering Illusion • Acute angle dilation • Our brains make small angles appear larger than they actually are. • Subjects line up the two lines better when the angle is larger. • Here is another illusion that works the same way - Hering illusion

29. Conclusion • I have learned that with the different variables, - angle of lines increased: subject misperception decreased - box height: No effect - line color: misperception lower for cyan line than black line - box color: misperception lower for red box than for cyan box • Illusions trick your brain into seeing something that is not actually present. • Your eye sees something that’s physically there, but your brain interprets it as something different.

30. Acknowledgements • Thank-you: • Mr. Jason Porter (J “GheTto” Dawg) • Ms. Maribell, Mrs. Hilary, Mr. Gabe, Mr. Gary, and • Dr. Gene Switkes • Ms. Pascha • Everyone from CFAO, and everyone from Cluster 7. • This work has been supported in part or full by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST-9876783.