Visual Illusions: Visual Illusions: Ponzo & PoggendorfPonzo & Poggendorf

Leo Do Beckie Aguirre Cluster 7

OutlineOutline

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

BackgroundBackgroundWhat 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.

MethodsMethodsPonzo IllusionPonzo Illusion

3 variables:– Color of ties– angle of tracks– reference bar position

3 settings per variable3 attempts per setting11 subjects tested Harder than it looks

Reference barTies

Tracks

Measured bar

Ponzo IllusionPonzo Illusion

Ratio (R) =Measure bar length

Reference bar length

R < 1 R = 1 R > 1

Ponzo Illusion:Ponzo Illusion:Color of TiesColor of Ties

Black ties Blue ties

Color of TiesColor of Ties

0.85

0.9

0.95

1

1.05

1.1

1.15

Black Blue Gray

Color of Ties

Rati

o

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

Ponzo Illusion:Ponzo Illusion:Angle of TracksAngle of Tracks

Angle: 5 degrees Angle: 22 degrees

Less Depth More Depth

0.85

0.9

0.95

1

1.05

1.1

1.15

5 15 22

Angle of Tracks

Rat

io• 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:Ponzo Illusion:Reference Bar PositionReference Bar Position

Reference bar position: 50 units Reference bar position:120 units

Positions tested: 50, 72, 120 units

More distant Less Distant

Reference Bar PositionReference Bar Position

0.85

0.9

0.95

1

1.05

1.1

1.15

50 72 120

Reference Bar Position

Rat

ioPeople 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 Why do we see the Ponzo Illusion?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.

ConclusionsConclusions 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 How the Poggendorf illusion worksworks

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.

MethodsMethodsThe 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 IllusionPoggendorf IllusionAngle of the lineAngle of the line

Reference angle: 20°Angles tested: 40°, 65°

Angle = 20°

Angle = 65°

ResultsResultsAngle of the lineAngle 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 boxHeight of the box

Reference height: 50Height tested: 25, 75

Height = 25 Height = 75

Results of the box height

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

Line colorLine 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 colorBorder 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?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?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

ConclusionConclusion

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 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.