When you look at an optical illusion, something is obviously out of whack. Why won't your eyes cooperate? What's happening? Are your eyes playing tricks on you?
Many readers will remember the emergence of Magic Eye books in the early 1990's. Countless hours were spent staring at pages that seemed at first like senseless patterns. But the trippy materialization of 3-dimensional figures had people exclaiming aloud, and of course, drawing the attention of friends nearby, who could sometimes achieve the same experience. The optical illusions were a conversation piece for people who never would have had anything else in common, and paved the way for some cool products.
All Eyes on the Eyes
A visual illusion can be blamed on (or credited to, depending on your perspective) three causes. According to the American Academy of Ophthamology, you're tricked either because your two eyes aren't cooperating with one another (binocular vision), your brain is identifying one thing while your eyes are observing another (called the eye-brain connection), or because you think you're seeing something after it is gone (persistence of vision).
Binocular Vision
The first potential cause of an illusion is because your eyes usually work together as a seamless team, but they still have their own components, each seeing a different image. So when the brain combines the information from each eye, we get a complete picture. This includes depth perception, which is responsible for the Magic Eye illusions we mentioned earlier. It also explains how one eye can fill in missing information for the other if needed. When a designer creates an image that circumvents our eyes' teamwork, an illusion is the result.
Eye-Brain Connection
We all know that train tracks are parallel, and thus never converge. Why then, when we stand in the middle of a track and view the horizon, do we see the tracks coming closer to one another? This is an example of the eye-brain connection, where the eye simply reports a set of data to the brain, and the brain does the work of interpretation. Usually, the brain and eye are "on the same page", so to speak, and the brain concludes accurately. But occasionally, logic needs to trump our brain's visual explanation. Otherwise, we would never board a train again.
Persistence of Vision
For 1/30th of a second after you see something, the image lingers in your mind. A fraction of a second doesn't seem like a long time, but when a series of images flash before you, the impression from one blends to the other, creating the illusion of motion. Actually, this is where we get cartoons and motion pictures. The reality is that half of the time, the screen is truly dark. The other half of the time, images appear quickly, one after the other. As your brain fills in the gaps, using this lingering impression, or "persistence of vision", motion is detected, or rather, created. And if our brains are doing half of the work, then perhaps movie tickets should be half the price!
Of course, if in daily life you see spots on your vision or any blurring, make an appointment right away. This can be a sign of trouble, and your doctor can help.
Today, optical illusions are still used for the novelty experience, but they're also used for treatment of some eye disorders. Not to mention, these tricks bring the miraculous functions of the human eye to the attention of people who may not have considered how their eyes work.
For questions or comments, contact Woodhams Eye Clinic.
