Visual Illusions: Ponzo

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Visual Illusions Ponzo Poggendorf
Leo Do Beckie Aguirre
Cluster 7
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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

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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.

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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
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Ponzo Illusion
Measure bar length

• Ratio (R)

Reference bar length
R lt 1
R 1
R gt 1
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Ponzo IllusionColor of Ties
Black ties
Blue ties
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Color of Ties
The color of the ties does not appear to affect
how well people can make the bars the same length.
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Ponzo IllusionAngle of Tracks
Angle 5 degrees
Angle 22 degrees
Less Depth
More Depth
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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.

Less Depth
More Depth
(degrees)
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Ponzo IllusionReference Bar Position
Reference bar position 50 units
Reference bar position120 units
More distant
Less Distant
Positions tested 50, 72, 120 units
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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
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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 its
  closer
• We expect the reference bar to look smaller than
  the measurement bar because you think its
  further away.

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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 gt 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

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How the Poggendorf illusion works

• There is a box in the middle of two lines which
  are connected even though it doesnt 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.

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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

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Ratio
Ratio 1.0
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Ratio
Ratio less than 1.0
Ratio 1.0
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Ratio
Ratio less than 1.0
Ratio greater than 1.0
Ratio 1.0
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Poggendorf IllusionAngle of the line
Angle 20
Angle 65

• Reference angle 20
• Angles tested 40, 65

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ResultsAngle of the line
When the angle between the line and the box
increases, the misperception of lining up the two
lines decreases.
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Height of the box
Height 25
Height 75

• Reference height 50
• Height tested 25, 75

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Results of the box height
Changing the box height has little effect on
subjects ability to line up the two lines.
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Line color
Cyan lines
Black lines
Reference black line, cyan box Tested Cyan
line, cyan box
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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.
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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
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Results for box color
The misperception is somewhat smaller when the
color changes from cyan to red.
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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

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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

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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 thats physically there,
  but your brain interprets it as something
  different.

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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.