Sunday, April 30, 2017

Z is for Zollner Effect - An Optical Illusion that Shows It's All About the Context

Take a look at the image below.  

Do you see the horizontal lines angled toward each other?  If so, you’re not alone. The reality is that the vertical lines are completely parallel.   Don’t believe me?  Then try this link where you can hide the shorter lines and see for yourself.  Then play around with the shorter lines to adjust the angel and watch as the horizontal line seem to become more or less tilted toward each other.

What Do You See?

The Zöllner illusion is a commonly demonstrated optical illusion. Created in 1860 by an astrophysicist, Johann Karl Friedrich Zöllner, this illusion presents a series of seemingly tilted long lines crossed with overlapping shorter lines. The seemingly tilted long lines appear as if they would intersect one another if they were extended.  However, the lines are actually parallel to each other.\

How Does It Work?

This optical illusion shows how an image’s background can distort the perceived appearance of straight lines. Several explanations for the Zöllner illusion have been offered. First, the angle of the short lines compared to the long lines creates the perception of depth. One of the lines appears to be closer to us and the other farther away. Another possible explanation is that our brain tries to increase the angles between the long and short lines. The result is a distortion resulting from our brain attempting to bend the lines away and towards each other.

Most optical illusions result from the way that the images are captured with the eyes and are reconstructed by the visual cortex.  While we may believe that the information we receive from our senses is accurate, this information doesn’t actually correspond exactly to reality.  With vision, for example, the image that hits the retina contains considerably more information than what the optic nerve conveys to the brain.  The brain compensates for this enormous loss of information to provide us with visual perceptions that possess contrast, color, and movement.  In order to do this, the brain uses abstract boundaries that clarify, fill in or elaborate the small segments of reality that are actually provided. The brain's tendency to interpret visual information in this way sometimes results in impression of coherence being created where none exist.  

This is the case with an optical illusion.  The brain uses well-rehearsed strategies to fill in the blanks that are supplied by the image and the incomplete segments of the image that are supplied.  For example, if the brain interprets an image as representing distance it will use perspective related strategies to interpret the different segments.  Parallel lines going away from us into the distance (think railroad tracks) appear to converge as if they will eventually intersect somewhere out of our line of sight.   Of course, while we may perceive railroad tracks as seemingly converging, we logically know they are not doing so and therefore, ignore what our eyes are communicating to our brain and dismiss the image as an optical illusion.  

Yet when we happen upon novel images that use specific features, in this case an image of straight lines crossed by smaller, angled lines our brain automatically corrects for the parts that aren't communicated based on it’s interpretation of distance.  However, in this case we do not have any context as we would with railroad tracks.  We don’t look at it (unless you are already familiar with the illusion) and say, “Oh, yeah, that’s the Zollner Illusion that makes a bunch of parallel lines look like they’re converging.  Of course, I know better.”  So we become convinced our visual perception is accurate and have a lot of trouble when someone tells us that our perception is faulty, trying to change the way we see it, to no avail.  As with everything in life, the context is all important.

An interesting effect occurs if the color of the lines and background are changed.  If you make the color of the lines green and make the color of the background red, the effect entirely disappears and the lines will appear to be parallel as they actually are, as long as the two colors are equally bright.



I'd like to thank all of you out there who came along with me on this journey. At times it seemed like the longest month ever while at other times I had no idea where the days had gone and how I'd keep up the pace.  But I'm glad I did it and it managed to call up some new ideas and even generate a few new full length articles.  You never know what the next year will bring but as of now I'll say I look forward to repeating this challenge the next time April rolls around!  I'll keep you posted.  You do the same.  Don't stop stoppin in though, now that the excitement is over.  Hopefully, I'll keep posting things you find interesting, though not at the same pace as this month. 
 Ciou - SYOTB

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