Illusions: How and Why?

Illusions. They fascinate us. We are constantly baffled by their distortion of reality. Illusions defy normal perception and thus allow us to give insight into our perceptions. Some common illusions are: the moon illusion, the Ponzo illusion, the Ames room illusion, the horizontal-vertical illusion, and the Muller-Lyre illusion. I recently stumbled across a TEDEd video called "Why Do We See Illusions?" I was faced with a question on the page of the video: why can't our extremely complex eyes clarify simple illusions?! Well, here is what I found.

The educator on this video, Mark Changizi, began by explaining this simple illusion:

The brain has evolved to handle the natural stimuli it receives. How does the brain counter this simple image, two straight lines, and interpret it as "bulging out?" Well, when we move, we leave an optic blur on the retina, and everything shoots to the side. Cartoonists use these "blurred lines" created by the optic blur to produce the illusion of movement, which the brain interprets as movement. However, it's the stimulus that has these blurred lines, which in return informs the brain that we are moving. When we move forward, our eyes fixate, much like a camera, and every time we move, everything whooshes to the side, and we are able to distinguish the direction we are moving in. In the illusion shown above, the brain is fooled into thinking we are moving towards the center.

The brain takes 1/10 of a second to create a perception. Perception is behind. In order to keep up with the world, the brain has to think, "What will the world look like in a tenth of a second?" However, by the time the brain has completed thinking of the future, the future will have already arrived, and walla, we perceive the present! The brain is filled with mechanisms to compensate for its "slowness."

The illusion is explained by the following example. When approaching a doorway, the sides look parallel. However, after nearing it, the parallel lines seem to be blown out. When first coming towards the doorway, the brain receives no cue, and perceives it as two vertical lines. But, when adding cues, such as the optic blur cue, the brain perceives the door as bulging, creating an illusion.

And that's why we see illusions!

On a side note, illusions are failed perceptions because they are static images on a page. They don't change.

Anyways, I found this cool.

Here's the link to the video. It's super delightful.




http://ed.ted.com/lessons/why-do-we-see-illusions-mark-changizi#watch