Illusions: Fooling the Brain

Clad in a tuxedo, the tall and bearded conjurer tosses the ball up. Once, twice, thrice — voila! The ball disappears midflight. You’re absolutely sure that your gaze didn’t waver from it, so where did the ball go? Of course, it didn’t actually disappear forever — you know that — but your senses were fooled, and you aren’t sure how. This is the famous “Vanishing Ball” illusion, and it’s pretty impressive.


Magicians long ago mastered the art of deception. The question is, how did they get so good at it? That is what many neuroscientists and cognitive psychologists are trying to find out by studying the science of magic or, as some call it, neuromagic.

“Fifty years ago, no one had formal training in the neurosciences,” says Stephen L. Macknik, director of the Laboratory of Behavioral Neurophysiology at Barrow Neurological Institute in Phoenix, Arizona. “On the other hand, magic has been performed for over 2,000 years by smart people. While magicians haven’t used the scientific method, they have studied the human brain a lot longer than scientists have. And they have discovered important things.”

Macknik’s colleague Susana Martinez-Conde, director of the Laboratory of Visual Neuroscience at the institute, expands on the idea. She explains that “The visual sciences have always borrowed from the visual arts. Some illusions, perceptional phenomena we know now and take as a given in visual sciences — rules of perspective, for example — didn’t come from science. They were discovered by artists during the Renaissance.”

THE TRICK BEHIND THE TRICKS

Magicians use a combination of tools, such as illusions, special effects, and secret devices, to produce results that seem to defy the laws of physics. There are typically three main types of illusion: optical, visual, and cognitive. Think of it like this: Visual illusions occur when our fallible brain constructs a false perception of our physical reality. The “Colored Dress” trick by Las Vegas magician Johnny Thompson — aka the Great Tomsoni — perfectly demonstrates how magicians make use of visual illusions.

Here’s how the trick is played out onstage. Tomsoni’s gorgeous assistant, probably clad in a short white dress, is bathed in the spotlight. Tomsoni claps his hands. The spotlight dims for a jiffy, only to transform into a glistening red light. Presto! The woman — as well as the dress — is now red. You think — wow, is that it? However, Tomsoni’s trick is not over yet. He claps again. This time, the lights dim for a few moments, and the white spotlight is back. Guess what? Her dress is still red.

Tomsoni deceives our senses very subtly. Since the assistant is an attractive woman, the audience becomes fixated on her, so much so that they burn a deep afterimage of her into their retinas. An afterimage is something we experience on a daily basis. If you stare at a waterfall for a few minutes and then transfer your gaze to nearby rocks, they seem to flow, if only for a few moments.

When you continue to gaze at the red-lit dress, neurons in the brain, whose job is to perceive the color red, get adapted to the red-lit dress by being less active. Such neurons are better adapted to the red stage and will have a bigger afterdischarge once the light is turned off. The afterimage of the red woman in a red dress lingers for about a tenth of a second. During this little interval, Tomsoni brings out the trump card. The white dress, held on to the assistant with the help of Velcro and invisible cables leading under the stage, is pulled off her body and whisked into a trap door. Voila — the lights come on, and the bright red dress the woman had been wearing underneath becomes exposed.


Macknik says, “The retinal afterimage of the dress makes it appear red so that you can see the woman during the 100 milliseconds or so when the white dress is removed. The physical reality (lights are off) differs from the perception (you can see the lady), and therefore that component of the trick is a visual illusion.”

Now, cognitive illusions fiddle with the brain’s higher functions, such as memory and attention. For most magicians, diverting our attention — called misdirection — from the method to the effect is a way of achieving the desired result. During overt misdirection, a magician drives the audience’s attention away from where the action is really taking place by shifting its gaze. During covert misdirection, the audience is looking at the method, but its attention is elsewhere.


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