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

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

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 Who invented the Poggendorf illusion? – Johann Poggendorf in Visual Illusions also help us learn about our visual systems.

Methods Ponzo 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

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

Ponzo Illusion: Color of Ties Black ties Blue ties

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

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

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. (degrees) Angle of Tracks Less Depth More Depth

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

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

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.

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

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.

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

Ratio = 1.0 Ratio

Ratio less than 1.0 Ratio = 1.0 Ratio

Ratio less than 1.0 Ratio = 1.0 Ratio greater than 1.0 Ratio

Poggendorf Illusion Angle of the line Reference angle: 20° Angles tested: 40°, 65° Angle = 20° Angle = 65°

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

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

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

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

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.

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

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

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

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

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.

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