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NetLogo Models Library:
Sample Models/Art

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Optical Illusions

[screen shot]

If you download the NetLogo application, this model is included. (You can also run this model in your browser, but we don't recommend it; details here.)

## WHAT IS IT?

This model presents seven optical illusions.

## HOW IT WORKS

The optical illusions are constructed using a combination of NetLogo turtles and patches.

### Illusion #1

White circles on a gray background produce an illusion of the circles changing colors between black and white, depending on where you focus your eyes.

### Illusion #2

Diagonals moving away from the center create an illusion of depth, which makes the parallel horizontal lines seem to bend in the center.

### Illusion #3

The perpendicular lines that do not match row to row create an illusion of the lines between them being not parallel.

### Illusion #4

Relative sizes of other circles skew the perception of the middle circles, creating an illusion of difference in size.

### Illusion #5

Circles of diamonds seem to rotate as you focus your eyes on their center.

### Illusion #6

Intensely saturated colors create an illusion of rippling waves of motion.

### Illusion #7

Four simple concentric circles look like interlocking spirals.

## HOW TO USE IT

Press a button to choose an illusion, and it will be presented in the NetLogo view.

Some explanatory text will appear in the monitor below the view.

## EXTENDING THE MODEL

Add more illusions.

## NETLOGO FEATURES

Many of the illusions in the model, such as illusions 2, 4, 5 and 7, involve turtles positioned in a circle around a middle point. This shows how to use `create-ordered-turtles`, `forward` and `heading` to position objects in a pattern.

## RELATED MODELS

Other models that were created "for fun" include Frogger, Lunar Lander and other games included in the Games section of the Models Library.

## CREDITS AND REFERENCES

Illusion #6 is based on the cover of the album "Merriweather Post Pavilion" by Animal Collective, which in turn is based on an illusion by Akiyoshi Kitaoka.

## HOW TO CITE

If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the model itself:

* Wilensky, U. (2005). NetLogo Optical Illusions model. http://ccl.northwestern.edu/netlogo/models/OpticalIllusions. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

Please cite the NetLogo software as:

* Wilensky, U. (1999). NetLogo. http://ccl.northwestern.edu/netlogo/. Center for Connected Learning and Computer-Based Modeling, Northwestern University, Evanston, IL.

## COPYRIGHT AND LICENSE

Copyright 2005 Uri Wilensky.

![CC BY-NC-SA 3.0](http://ccl.northwestern.edu/images/creativecommons/byncsa.png)

This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-sa/3.0/ or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at uri@northwestern.edu.

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