Introduction: Hole in Your Hand Illusion

About: Where there's a will, there's a way! Never give up, never give in...BE the good you want to see in the world. :)

This simple illusion is really mind-blowing, but quite easy to understand!

All you need to create this illusion is a cardboard tube (such as a paper towel or toilet paper tube), or you can use a sheet of computer paper as an alternative.

Let the fun begin!

Step 1: How to Do the Illusion

Hold the cardboard tube in your RIGHT hand and up to your right eye.

Leaving BOTH your eyes open, hold your LEFT hand halfway up against the cardboard tube, with your fingers facing upward.

When you see both images at the same time, it will look like the hole is in your hand!

Step 2: Try Different Approaches

Practice using different width tubes.

Try rolling a sheet of paper up to about 1/2" diameter. Does it change the effect?

Try using a toilet paper roll instead of a paper towel roll, or use a shorter length of paper. How does that change the effect?

Move your hand up the tube closer to your eyes, then further away. What happens now?

Add the full length paper tube to the shorter toilet paper tube. What effect does that create?

Change up the shapes of the tubes (maybe make one oval or heart shaped). Does this alter the effect?

Add and subtract lighting from the environment. Does this alter the effect?

Add a picture to the end of the tube (keeping it about 1/4" away from the tube, as to let in light so you can see it). What happens now?

SWITCH EYES AND HANDS. Is the effect stronger on one side or the other? Why do you think that is?

What do you think is controlling the image you're seeing? Is it your eyes or your brain?

Step 3: How It Works

Your eyes work in pairs. Your brain takes the right eye's image and the left eye's image and blends them together to present you with a full image. How does it do this? Simply put, there are some nerve cells in the occipital cortex (the part of the brain that processes most of our visual input) that receive signals from both eyes. It is those cells that allow us to process the visual input from both eyes simultaneously and thus have depth perception and 3D vision. Therefore, when one of your eyes sees a hole and the other sees a hand, your brain merges the two images together to create a hand with a hole in it!

INTERESTING POINT: If you found the effect stronger on one side than the other, it indicates that one eye is likely dominant. What's that mean? It means your brain has a slight preference for visual information from that eye over the other. It's a similar idea to having a dominant hand or foot. However, your dominant eye may not be the same as your dominant hand or foot.

Step 4: Experiment & Have Fun!

Bring this into your classroom (which is most likely in your home right now during this pandemic), and explore the science and biology behind it. Test out different options and different illusions! The eyes are an awesome scientific wonder!

Use it as a fun and interesting way to bring your kids--who am I kidding, adults like it too!--some entertainment....for a little while anyways!

And most importantly, HAVE FUN! Because what's life without a little fun?

Cardboard Speed Challenge

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