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Unit 19: Biology Part 2 Page 106 of 137

make a decision to move a part of your body, and the brain relays the
message. This works well… sometimes a little too well. See for yourself.

1. Stand in a doorway.
2. Clench your hands into fists and press your hands against either side
of the doorway as hard as you can. Try to hold this position for about
one minute.
3. Step forward, out of the doorway, and relax your hands.

What’s Happening: Most people will find that their hands rise, at least a
little bit. The “trick” is that your arm muscles have been getting the
message to tense up for a minute. Even though the brain is no longer giving
this message once you relax your arms, your muscles still make the motion,
simply based on the “memory” of the message.

Experiment: Jumping Finger

One of the reasons human vision is so good is that we can see in three
dimensions (no 3D glasses required.) This possible because we have eyes
on the same side of our face, a certain distance apart. (Look at how the
eyes of a cow and zebra are on different sides of the face.) A simple activity
can show you how our eye location makes 3-D vision possible.

1. Hold your finger out a full arms length in front of you.
2. Close your eyes, one at a time, and look at your finger. You will notice
that it seems to change location a little.

3. Now bring your finger very close to your eyes, and again close your
eyes, one at a time.
4. Observe the difference of having your finger close up versus far away.

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