Which is more sensitive, your arm or your finger tip?





This experiment requires three people to work together.

1 piece of paper
1 push pin
1 ruler
1 pair of safety goggles
2 straws
6 toothpicks


1. First you have to make your test probes. Starting near one end of the straw, make a pair of holes with the push pin that are 3" apart. The holes must both go through the straw in the same direction.

2. Cut off the piece of straw with the holes in it.

3. Repeat this making pairs of holes that are 2", 1", 1/2" and 1/4" apart.

4. Break the toothpicks in half.

5. Stick one half through each hole so that:
- the pointed ends go in the same direction
- the pointed ends stick out of the side of the straw an equal amount
- the pointed ends stick out about 1/4"

6. Now make your control probe. Poke a single hole in a small piece of the remaining straw. Put a single piece of toothpick in the hole.

7. You are going to use the safety goggles as a blindfold so tape the paper over them.

8. You are going to test the nerves in each others' arm. There will be three people involved: the subject whose arm is being tested, the tester, and the recorded who will write down the observations. The test can be repeated three times so that everyone gets a chance to do each job. To be able to measure the response of the nerves and not that of the conscious brain, this will be a blind test. This means that the subject will be blindfolded.

9. The subject should put on the blindfold and place their arm on the desk.

10. The tester will select a probe and gently poke the subject's arm. Poke hard enough so that you can see the skin pushed down. Be sure that both points touch with the test probes.

11. The subject must call out one or two depending on if they felt one poke or two. The recorder will record which probe was used and the subject's response.

12. During the test, you should use each test probe at least three times. The control probe will be used more often. The order in which you use the probes should be random so the subject does not try to "guess" the correct response.

Subject: Probe Used
Location: Arm Control 3 inches 2 inches 1 inch 1/2 inch 1/4 inch
Felt 1 poke

Felt 2 pokes

13. After each person has had a turn at each job, repeat the same test on the subject's finger tip instead of their arm. Since the larger probes obviously won't fit on the finger tip, draw an "X" through the boxes of the probes you don't use.

Subject: Probe Used
Location: Finger Tip Control 3 inches 2 inches 1 inch 1/2 inch 1/4 inch
Felt 1 poke

Felt 2 pokes