By Don Kang and Oliver Housman

1
Visual Illusions
How the eye and brain really interact

• By Don Kang and Oliver Housman
• COSMOS 2005
• Eye image from www.hkvisioncare.com/
  leftmenu.htm
• Brain Image from www.turobread.com/ poor
  concentration.htm

2
Eye-Brain Connection

• Both eyes are needed to have depth perception

• A problem with a childs eye must be corrected
  before the age of six
• If not, the weak eye will stop sending messages
  to the brain

http//www.nei.nih.gov/nehep/summer03/
3
Brain-Eye Injuries
Another reason to study illusions is...
Strokes
Eyewitness Accounts
http//www.31alumni.com/photos/31-eyewitness-ratin
gs-ad.gif
http//www.medem.com/MedLB/article_detaillb.cfm?ar
ticle_IDZZZRWUDSIACsub_cat189
4
Poggendorf Illusion
Line A
Line B
http//www.chemistry.ucsc.edu/teaching/switkes/COS
MOS/VISION/WWW_05/illusions/OLIVER/Poggendorf_Oliv
er.html
5
Percieved correct line
Actual correct line
http//www.chemistry.ucsc.edu/teaching/switkes/COS
MOS/VISION/WWW_05/illusions/OLIVER/Poggendorf_Oliv
er.html
6
Color no effect
Black Orange Cyan
Orientation no effect
Vertical Horizontal
7
Angles do have an effect
10
lateral
-
-
-



-
-
-
Inhibition
8
Conclusions from Poggendorf Experiment
Results can be skewed by the way an experiment
is set up
Orientation of the box does not affect a person's
perception of the line
Angle of the line affects a person's perception
of the correct line
Color has no effect on angle perception
9
Muller-Lyer Illusion
10
Possible Explanations

• The corner theory
• the lines with fins can be compared to building
  corners
• there is a finite distance between the two
  corners, making the exterior corner always appear
  larger
• subconscious

http//www.pc.rhbnc.ac.uk/illusions/Image46.gif

• The area theory
• People try to match areas instead of the length
  of lines
• subconscious

11
Results of the Change in Fin Angle

• Hypothesis the smaller the fin angle, the
  stronger the illusion

• Possible explanations
• Corner theory the closer to a corner, the
  sharper the angle the farther away the corner,
  the more similar the lengths of lines
• Area theory the smaller the angle, the more
  dissimilar the areas

45
60
75
12
Results of the Change in Fin Length

• Hypothesis 20 units will give the weakest
  illusion, 100 units stronger, and 65 units the
  strongest

• Possible explanations
• Corner theory the longer the fin length, the
  more the lines look like a building corner
• Area theory the shorter the fin length, the more
  similar the areas

65
20
100
13
Results of the Change in Shape

• Hypothesis circles will give the weakest
  illusion, ellipses stronger, and the fins the
  strongest

• Possible explanation
• Area theory the difference of the areas of the
  two lines for each set is the same, so the
  strength of the illusion should be the same for
  each shape

14
Conclusion for Muller-Lyer Illusion

• The theories used to explain the illusion are
  incomplete because they did not support all the
  result
• The area theory, however, is a more thorough
  explanation because is can be used for all the
  variables
• Not enough people were tested to give sufficient
  data

15
Conclusion Poggendorf vs. Muller-Lyer

• The Poggendorf illusion is physical, in that it
  involves the interaction of angle sensitive cells
  in the eye and the brain
• The Muller-Lyer illusion is psychological,
  because it incorporates ones past, cognitive
  knowledge

16
Acknowledgements
Sally Robinson Kathy Cooksey
Gene Switkes
Hillary OBryan Jason Porter Test
Subjects John Martin CfAO