Teachers, Parents, Students and All Others

This site is here to explore and present optical illusions. If you have any suggestions to improve this site or a particular illusion you would like researched and presented here, please contact me.

If you have self-created illusions that you or your class brought to life, contact me and I will let them live here for all to enjoy.

If you are 13 years old or younger and wish to have your work displayed here please talk with your parents and have them send it to me with their permission.


Muller-Lyer Optical Illusion

The Muller-Lyer illusion is a size constancy illusion. In this illusion, the red and the blue lines below are the same length, but due to the effects of the arrows the red line appears longer.

muller-lyer optical illusion
The red and blues lines are both 170 pixels long

The illusion has been well studied since it was described by German psychiatrist Franz Carl Muller-Lyer in 1889. However, there is no certain explanation for the apparent difference in the perception of the lengths.

muller-lyer optical illusion

Muller-Lyer attempted to explain the illusion he had discovered as follows: "the judgment not only takes the lines themselves, but also, unintentionally, some part of the space on either side."

One of the better explanations I've read comes in the form of a PDF file from Catherine Q. Howe and Dale Purves of the Center for Cognitive Neuroscience, Duke University.

Below is an amazingly strong illusion that combines both the Ponzo and Muller-Lyer optical illusions.

The two red vertical lines are the same length.
Placing your pointer over the image will aid you in exposing this illusion

In the tickets image above the perspective of distance lends itself to the Ponzo optical illusion, the angles at the end of each line add to this the Muller-Lyer illusion, combined they create a very effective optical illusion.

Project: Create your own illusion. See how the following variations might effect the relative strength of this illusion.

Does changing the color of the background change the effect?
Does changing the color of the arrows change the effect?
Try changing the color of the equal lines,
is there any combination of colors that is stronger then the others?
Try fat lines. Try skinny lines. Does the thickness of the lines affect this illusion?
Does the distance from which you view the illusion change the illusion?

What can you conclude, if anything, about how we perceive things from this project?


Anonymous said...

A Classic! You could show any youngster and they'll think ur magic!

Anonymous said...

please could you set it out more neatly and put more illusions in x

Anonymous said...

I like this site!!

Anonymous said...

I know the logical explanation. The first line is overlapping the arrow. So it appears to be small. When we compare the two line with the overlapping space. It is the same line!

Anonymous said...


Anonymous said...


Copyright Notice
The documents distributed here have been presented on this blog in the spirit of providing an entertaining venue to educate those interested in optical illusions.

All Flckr.com photos are presented here via Flckr's "blog this" feature. This feature is enabled by each artist on Flckr. If you find material here that belongs to you and you would like to have it removed or credited please contact me and I will gladly follow your wishes.

Copyright and all rights therein are maintained by the authors or by other copyright holders. It is understood that all persons copying this information will adhere to the terms and constraints invoked by each author's copyright. These works may not be reposted without the explicit permission of the copyright holder.