Even with our eyes closed, we have a sense of body position – where our arms and legs are, for example, and that we are moving them. Muscles, tendons, joints and the inner ear contain proprioceptors, also known as stretch receptors, which relay positional information to our brains. Our brains then analyze this information and provide us with a sense of body orientation and movement.

No assembly needed.

Activity one: Finding Fingertips

Close your eyes and raise both hands above your head. Keep the fingers of your left hand totally still (no wiggling!). With your right hand, quickly touch your index fingertip to your nose, then quickly touch the tip of your thumb of your left hand with the tip of your right index finger. Quickly repeat the entire process while attempting to touch each fingertip (always return to your nose in between fingertip attempts).

Switch hands and try again.

How successfully do you find each fingertip? Do you improve with time? Is there a difference when the different hands are used?

Activity Two: “X” marks the spot

Mark an “X” on a piece of paper. Pencil in hand, raise your hand above your head, close your eyes and make a dot as near as possible to the X. Open your eyes and check your success. Raise your hand above your head, close your eyes, and attempt to make a dot closer to the X. Do this several times. Repeat with your eyes open.

Handwriting analysis

On a lined sheet of paper, write the word “proprioception” or some other vocabulary word of the day. Place your pencil on the same line next to the written word, close your eyes, and write “proprioception” again. Is there a difference in the appearance of the two written words?

A pinhole in an index card can act like a magnifying glass, helping your eyefocus on a an object that is very close to you. However, by limiting the amount of light that reaches your eye from the object, the pinhole also makes the object appear dimmer.

(5 minutes or less)

Cut a hole about 1 inch (2.5 cm) square in a file card. Tape a piece of aluminum foil over the hole in the card and use the pin to punch a hole in the center of the foil. You can make a good pinhole by placing the foil on a thick piece of cardboard and rotating a needle.

(15 minutes or more)

Hold the card near your eye and look at the lightbulb several feet away. Move closer to the bulb until you almost touch it, and notice the magnified writing on the bulb. Use the pinhole magnifier to examine other small brightly lit objects. You can, for example, examine a computer screen or a television screen up close using a pinhole magnifier.

Try using pins or needles with different diameters to make different-sized holes. Notice that the smaller the pinhole is, the dimmer your view. As the pinhole is made smaller, the image at first becomes sharper, but then is blurred by diffraction.

You can even form a pinhole by curling your index finger. Or try this as a magnifier:

The pinhole magnifier works on a very simple principle: The closer you get to an object, the bigger it looks to you. This is because the closer you are to the object, the larger the image the object forms on your retina (see Figure 1). Unfortunately, however, there is a limit to this. If you get too close to the object, your eye is not able to bend some of the light rays enough to obtain a focused image. As a result, the image becomes blurry or fuzzy (see Figure 2). The pinhole magnifier gets around this problem by limiting the rays that come to you from each part of the object (see Figure 3).

Sadly, there is a trade-off between the resolution, or sharpness, of the image and its brightness. A tiny pinhole produces a very sharp image, but because it cuts down on the number of rays that enter your eye, the pinhole makes the object look much dimmer.