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.

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
1889

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.


Source
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?

Continue reading the full article...

Ponzo Optical Illusion

The Ponzo illusion is an optical illusion that was first demonstrated by the Italian psychologist Mario Ponzo (1882-1960) in 1913. He suggested that the human mind judges an object's size based on its background.

The typical example of this is the figure below. This is the typical railroad track scheme usually used to represent this illusion. The vertical lines appear to go off into the distance like train tracks. This gives us the impression that the line in the distance is larger then the line that appears to be nearer to the viewer.

Mario Ponzo
1913

Seeing this illusion against a great real photo backdrop can be amazing. Most of the time people pick train tracks. Below is an outstanding photo that presents this optical illusion slightly different...

The two red lines (or three if you move your mouse over the image) below are duplicates, they are the exact same size. Which image is more convincing the one with two lines or the one with three lines?

Ponzo Illusion
(c) 2006 Walt Anthony

Project: Create your own illusion. Here is a suitable image of train tracks (right click and select "save target as" or "save link as" depending on your browser). You can use Windows Picture and Fax viewer to print it out.

Now that you have it printed try and create your own illusion.

Use 2 Popsicle sticks painted red or just draw red lines with a marker.
Does changing the color change the effect?
Does using two different colors alter the illusion?
Try fat and skinny lines. Does the thickness of the lines affect this illusion?
Vary the distance between the lines, does this change the effect?
Is a three dimensional Popsicle stick as effective as 2 dimensional red line?
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?

Continue reading the full article...

Hering Optical Illusion

This optical illusion was discovered by the German physiologist Ewald Hering in 1861. The two blue lines are both straight and parallel to each other. If you are like most folks you may see things differently. The lines in fact may look as if they are bowed outward.

Ewald Hering
1861

The distortion is produced by the lined pattern on the background, that simulates a perspective design, and creates a false impression of depth. If you pass your mouse over the image the background lines will be removed and you can see for yourself that the blues lines are definitely straight.

Project: Create your own illusion. Select a sheet of paper and place a dot in the center of the sheet. Now draw 10 lines through the center, mimicking as close as you can the background of the above illusion. Now on a sheet of clear document protector draw your two vertical lines.

Increase the amount of background lines to 18. Does that affect the illusion?
Does changing the color of the background change the effect?
Does changing the color of the background lines change the effect?
Does using two different colors for the vertical lines alter the illusion?
Try fat lines. Try skinny lines. Does the thickness of the lines affect this illusion?
Vary the distance between the vertical lines, does this change the effect?
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?

Continue reading the full article...