Remember that time you attended a magic show when you were a kid and gasped in wonder as the “magician” stuck his arm through a fan like it was no big deal? Also, remember when, years later, someone explained a bunch of magic tricks to you and you felt that childlike wonder melting away, only to be replaced by disappointment that magic isn’t real? Fun stuff, yes.
These magicians sometimes call themselves “illusionists”, because that’s what magic tricks are: illusions, or misinterpretations of stimuli. They create these illusions by using our brain’s several shortcomings against itself. Human brains, like their owners, can be very stubborn – if they believe something is true, they can alter our perception to fit that reality. Often, the brain moulds the way we see the world around the limited information it has, making assumptions along the way, instead of the other way around. For example, in a theatre, the speakers are at a good distance from the screen. But when the on-screen characters speak, the sound seems to come directly from their mouths, because the brain makes the connection between moving mouths and speech, thus creating the impression of the characters talking – an illusion, if you will.
Illusions work on pretty much everyone, which is probably for the best, for a single person seeing things differently would create feelings of insanity. Of course, illusions are quite different from hallucinations, which are not as benign.
Another interesting aspect of the brain is how lazy it can be. One of the things it learns when we’re young is that most of what comes into our field of view is essentially useless. So it fills in the areas around our focus with information it already has, or at least, thinks it has. For example, the first time you visit a new place, your brain is on high alert, taking in loads of new information – this creates the impression of time slowing down too. After repeated visits, however, your brain is a little more relaxed – you’ve been here before, you should be able to handle yourself. In other words, you begin to function on autopilot.
The brain sometimes bears an uncanny resemblance to video compression software. When a video is compressed, the pixels that remain the same for several frames are grouped together in one block of memory. When a video is repeatedly compressed, it ends up as an indistinguishable sludge of colour. In the same way, when a stimulus remains in our senses without changing for a long enough time, the brain simply discards the information. This is called Troxler’s fading and here’s a great example (Source: Reddit). Stare at any point in the image without blinking and see what happens! Troxler’s fading also works for hearing (hence the concept of ambient sound) and for touch – so, the next time you hold your significant other’s hand, make sure to keep swinging it or you might just forget it’s there.
On a darker note, a few sensory illusions can be brought on by diseases or mishaps. One of the more common ones is the phantom limb illusion, in which an amputee gets the sensation that their amputated limb is still attached to their body. This is again caused by the memories that the brain has stored of the limb and of using it. After years of using the limb, the brain comes to take it for granted, which is, in normal scenarios, a solid assumption to make. However, after an amputation, the brain continues to send signals to the limb and this information overload can cause pain. In several cases, amputees have reported being able to feel their amputated hand clenching, right down to their nails biting into their palm. Losing a hand or a leg turns your life upside-down, and the brain can take years to adjust.
Apart from being a source of entertainment, illusions help make our lives a little easier – if we constantly tried to perceive every little stimulus around us, we would quickly be overwhelmed. Will evolution result in hyper-aware human beings some day? The current situation points to the negative, at least for the near future – sensory overload is real, and we need our wits about us. For now, let’s enjoy our magic tricks in peace.