Perhaps you have heard of the highly common phrase “seeing is believing.” This aphorism generally means that the eye is window to all things true, for when one sees something, they can be certain that it is as it appears.

It’s a fact, isn’t it?

Not so much.

The greatest counterexample is illusion. The eye and brain work in tandem; however, the mind has a few tricks of its own up its sleeve. In fact, what we see is a twice-inverted version of what is truly around us. As light waves reflect off of our environment and enter our eye, they land on our retina, with one main modification: the image is upside-down. It is our brain which converts this image right-side-up; therefore, what we see is actually slightly altered and therefore not exactly original.

a
Whenever we look at something, the light rays cross over in our eye and result in an inverted/upside-down image on our retina. The image is turned to electrical impulses, which the optic nerve carries to the brain which, in turn, reforms into the image that you see. Image from outlanderanatomy.com.

So why do we see things that aren’t necessarily there? The answer lies far into the depths of our head, in our mind. Truth be told, the brain likes taking shortcuts, and the result is the semblance of an illusion. In short, optical illusions entail the art of deception.

What exactly are optical illusions? The internet defines it as “something that deceives the eye by appearing to be other than it is”. Indeed, what we see is not necessarily what actually is. And here’s why.

In a waking state, we are constantly looking around us; therefore, the human eyes receive a continuous stream of light, resulting in a lot of information entering the human mind. Because of the magnitude of information entering the brain from the eyes alone, the mind isn’t able to focus on every little detail. As a survival instinct, the human mind takes shortcuts to simplify the deluge of information by narrowing down what is important and allowing us to hone in and concentrate on what’s important (1).  

Optical illusions take advantage of the brain’s shortcuts, thus fooling the mind and bringing forth an image or even a perception of motion that is pretty much imagined.

Take Hermann’s Grid, for instance.

HERMANN’S GRID

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Hermann’s Grid. Image from illusionsindex.org.

When you look at this image, there appears to be a fuzzy gray blob at every intersection; however, when you look directly at one of the blobs, it disappears, because it was never there. Hermann’s Grid consists solely of black squares spaced evenly apart against a white background; yet, in the process, our mind creates the image of gray dots that were never there to begin with. In other words, between the brain and the eyes, the individual is tricked into believing and very much seeing an illusion (2).

Another prominent example is the Zollner Illusion.

THE ZOLLNER ILLUSION

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Zollner’s Illusion. Image from illusionoptiquetpe.e-monsite.com.

Sometimes, adjacent or overlaying objects can tamper with our perception of the things around us, thus creating an illusion. In Zollner’s illusion above, the lines seem to be crooked or oblique in nature. In reality, however, the lines are parallel to one another and will neither converge nor diverge. Take a ruler or any straight edge and test it out!

Then why does it look so slanted, you ask? Well, it is the short lines which give the appearance of crookedness. In other words, the background distorts the image and brings forth the appearance of oblique lines (3).

Some optical illusions can give the appearance of motion as well.

THE MOIRE EFFECT

optical-illusion-brainteaser-704015

Image from cdn.images.dailystar.co.ukcdn.images.dailystar.co.uk.

The picture of a bunch of pinwheels (or arguably, a bunch of rolled-up snakes) here exhibits the Moire effect. The image is, in fact, stationary; however, upon looking at it, the “snakes” seem to move in a rotation motion. Upon research, scientists found that people have fast eye movements which they term “saccades”. A study of volunteering participants was conducted in the following manner: test subjects pressed down a button whenever the snakes were still, and let go of it whenever they seemed to be in motion. An analysis by expert neuroscientists showed the right before detecting movement in the optical illusion, the participants blinked rapidly (experienced one or more saccades), and the movement stopped as the participant’s eyes were stable for a while. This leads to the generalization that saccades or eye movements are what cause the ostensible movement of the snakes/pinwheels (4).

Conclusion

We humans perceive and understand the world around us with the help of our brain and our five sense organs, one of which is sight. Since we are constantly looking around, our brain gets a lot of information at any given moment in time; at the same time, other processes are going on, and information from our other senses are constantly streaming in as well. To manage this great magnitude of information, our brain takes shortcuts, and optical illusions form by taking advantage of them.

Optical illusions can be caused by contrasting color, effects of the background, and geometric placement/design, all of which can lead to a perception of a color that is not there, a slant in a line that is actually straight, or even movement! Nevertheless, optical illusions can be fun to experience, and it is always a pleasure to be able to understand why we perceive things differently, as we sometimes do.

For more fun optical illusions, click here.


References

  1. “How Do Optical Illusions Work?” Inside Science, 30 Nov. 2016, www.insidescience.org/video/how-do-optical-illusions-work.
  2. Salaita, Meisa. “How Optical Illusions Work.” HowStuffWorks Science, HowStuffWorks, 8 Mar. 2018, https://science.howstuffworks.com/optical-illusions.htm.
  3. Cherry, Kendra. “6 Fascinating Optical Illusions.” Verywell Mind, Verywellmind, www.verywellmind.com/optical-illusions-4020333.
  4. “How Illusions Trick the Brain: ‘Rotating Snakes’ Appear to Dance.” ScienceDaily, ScienceDaily, 1 May 2012, www.sciencedaily.com/releases/2012/05/120501100037.htm.

 

 

 

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