Magic of neuroscience

Misdirection

 

 

This article was adapted from Scientific Amercian Dec 2008 "Magic and the Brain" By Susana Martinez-Conde and Stephen L. Macknik

Magicians use the general term misdirection" to refer to the practice of diverting the spectator's attention away from a secret action. In the lingo of magic, misdirection draws the audience's attention toward the "effect" and away from the "method," the secret behind the effect. Borrowing some terms from cognitive psychology, we have classified misdirection as "overt" and "covert." The misdirection is overt if the magician redirects the spectator's gaze away from the method—perhaps simply by asking the audience to look at a particular object. When the Great Tomsoni introduces his lovely assistant, for instance, he ensures that all eyes are on her.

"Covert" misdirection, in contrast, is a subtler technique; there, too, the magician draws the spectator's attentional spotlight—or focus of suspicion—away from the method, but without necessarily redirecting the spectator's gaze. An example of this is the vanishing ball trick where the magician throws a ball that vanishes in mid air. This trick provides further evidence that the magician is manipulating the spectators' attention at a high cognitive level; the direction of their gaze is not critical to the effect.Under the influence of covert misdirection, spectators
may be looking directly at the method behind the trick yet be entirely unaware of it.

Cognitive neuroscience already recognizes at least two kinds of covert misdirection. In what is called change blindness, people fail to notice that something about a scene is different from the way it was before. The change may be expected or unexpected, but the key feature is that observers do not notice it by looking at the scene at any one instant in time. Instead the observer must compare the postchange state with the prechange state.

Many studies have shown that changes need not be subtle to cause change blindness. Even dramatic alterations in a visual scene go unnoticed
if they take place during a transient interruption such as a blink, a saccadic eye movement (in which the eye quickly darts from one point to
another) or a flicker of the scene. The "colorchanging card trick" video by psychologist and magician Richard Wiseman of the University of Hertfordshire in England is a dramatic example of the phenomenon Click to go to the page. In Wiseman's demonstration—which you must see to appreciate—viewers fail to notice shifts in color that take place off camera. It is worth noting that despite its name, the color-changing card trick video does not use magic to make its point.

 

Inattentional blindness differs from change blindness in that there is no need to compare the current scene with a scene from memory. Instead people fail to notice an unexpected object that is fully visible directly in front of them.

Have a look at the video on the right and count how many times the white team pass the ball.

Solution

Did you notice the gorilla in the view?

Now play the video again and watch the gorilla walk past the field of view.

Click to hide solution

 

 

View the video on the right and see if you can see how the trick is done.

Can' figure it out? Click

here for the solution

Is this an overt or covert misdirection? Explain

What are the implications of change blindness for eyewitness accounts? Explain how the eyewitness account can be wrong without the eyewitness realising it.

 

 

The image on the right shows a phenomenon called motion induced blindness. Focus on the green dot. After a few seconds one or more of the yellow dots disappear.

Click to read neural adaptation.

What do you think is happening here?

Will this work if the background was not rotating?

A simple explanation may include neural adapataion. If you stare at the image long enough, all structures are imaged on a particular part of the retina. This leads to local neural adaptation on the retina. By adding additional background noise, here the rotation, effectively we bring on more rapidly neural adapation.

Why do you think that moving the background the dots disappear faster than if you stared at a fixed scene?
What implications does this have to real life?

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