This week, we will look at the science of proprioception. What in the world is that? It is your ability to tell where your body is. That may sound confusing, but it will make more sense as we go along.

Start by closing your eyes. Are they closed? No, because if they were, you could not be reading this. OK, read this first, and then try it. Close your eyes. Then touch your nose. Scratch your elbow. Touch one big toe with the other big toe. That was easy, right?

But why was it easy? How do you know where your parts are? It comes so naturally that we don't really think about it, but there is a very complex system of special nerve receptors called proprioreceptors that provide feedback on position, just as heat, pressure, and pain receptors provide information about other sensations. This feedback tells our brains where our body parts are, how they are moving, and how much force they are exerting. Proprioception is vital in learning a new skill, such as walking, riding a bike, catching a ball, or drawing a picture. For each new skill, your brain has to learn the right proprioceptive signals, to let your perform the skill properly.

Some things can interfere with your sense of proprioception. This is why police officers often have someone suspected of intoxication try touching their nose while their eyes are closed. Intoxication often distorts proprioception, causing a subject to misjudge the position of his nose.

One way to confuse your sense of proprioception is by having nerve impulses cross your body's midline, as we did with Kneesy-Earsy-Nosey ( http://thehappyscientist.com/science-video/kneesy-earsy-nosey ). This time, we will try a proprioception illusion that I learned as a childhood trick.

Start by sitting comfortably. Extend your arms out if front of you, with your palms facing outwards. Cross your right arm over your left, so that your palms are now touching. Interlace your fingers and curl them around your hands.

Now, bend your elbows, bringing your hands towards your body and upwards, so that your elbows wind up at your side, and your clasped hands are pointing upwards, just in front of your chin.

Now for the fun. Have someone point at various fingers, without touching them. It is your job to move the finger that they are pointing to. Because we have twisted your arms a bit, and crossed your midline, you will find that you often move the wrong finger. Your eyes are telling you that the finger is on your left, so your brain wants to move your left finger. You will probably find that some fingers are more difficult than others. Thumbs are easy (at least for me), but ring fingers tend to be confusing. Sometimes you will find it easy to move a finger one time, and get it wrong the next time.

Next, close your eyes, and have the person ask you to move your fingers by name (right index finger, left ring finger, etc.) You will find this very easy, showing that it is the conflict between your visual signal and the proprioceptive signal that is causing the problem.

Play with that for a minute or two, and your body will learn which finger is which, making it easier. Your sense of proprioception is adapting. Then straighten your arms and try it again, this time crossing your left arm over your right. Again, you will probably find that you frequently move the wrong finger, until your body learns the new positions again.

It can be amazing how quickly your body learns and adapts to new conditions. Try doing ordinary things in a different way, such as crossing your hands to tie your shoes. Even something as challenging as eating a bowl of ice cream with your eyes closed can be learned, if you are willing to spend a lot of time practicing. And of course, science experiments should be repeated several times to be sure of your results.

Have a wonder-filled week.