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2014 The Bad Science Show - Melbourne School Shows & School Incursions

The Miracle Of The Card In The Pocket

Peripheral Vision and the Human Eye.

Deceptology - The Neuroscience Of Deception

“After all, the true seeing is within.” 

*This resource is intended for use after viewing Deceptology. If you've haven't seen the show, this won't make much sense.
 

What's The Point?

To explain the limitations of the human eye and how the brain makes up for these short comings. 

 

The Trick

In Deceptology, I was able to make a signed playing card vanish from the deck and appear in my pocket three times before finally making the entire deck appear in my opposite pocket. I'm very clever.

 

The Explanation

The secret is an easy one. I hide the card in my hand...and the put it in my pocket.

The explanation as to why no one noticed is much more complicated.

We assume that our view of the world like a giant movie screen, a crystal clear image playing out in front of us in sharp focus.

In reality, only the very centre of our eye, the fovea, is in focus at any given moment. The further an image moves from the fovea the less focused it becomes. Not only that, but the image that lands on our fovea is flipped as it passes through the lens of our eye.

What we think we see                                  What our eye actually sees

 

So how do we see through this tiny blurring mess? 

Our eyes perform what are call saccades, quick jumps from point to point allowing us to pick up information. Our visual cortex takes that data and creates a patchwork image, filtering out the unimportant factors like the blindspot or the fact the image is upside down.

This means that while the audience believes they are looking at both of my hands at once, they can only really focus on one hand at a time. So while they are fixated at my right hand, my left hand is secretly putting the card into my pocket.

Our brains attentional systems also work against us, preventing us from giving our attention to two objects in two seperate locations at the same time. So even if our eye does see the card going into the pocket, our brain doesn't notice it.

 

Activities

1) Hold your arm out straight in front of you and stick up one thumb. Focus on your thumb.

2) Shift your focus from your thumb to a point on the wall directly beyond your thumb. What happens to your thumb?

3) Keeping your focus on the point on the wall, slowly move your arm so that it is sticks out straight to the side. What happens to your thumb as it moves? 

4) The moment your thumb is no longer visible stop. Now wiggle your thumb. Can you see your thumb wiggle? Why do you think you can see your thumb wiggle even though you can't see your thumb?

My career as a hitchhiker was hampered by the fact that I never left my lounge room.

Also, I look like a serial killer.

 

Further Reading

Backyard Brains - How Your Eye Detects Colour and Motion

Scientific American - Put Your Vision To The Test

The Card To Pocket Instructions

Nicholas J. Johnson

2017

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