We have the ability to tell whether objects are cold, hot, smooth or rough. To demonstrate the different types of receptors in the skin, gather a num ber of objects that are:

1.smooth (an apple)
2.rough (sand paper; rock)
3.cold (ice)
4.warm (a sun-warmed piece of metal)

Tell someone to close their eyes (or use a blindfold) and touch the items to t he person's hands or fingers. Ask them what they feel.

Sand Paper Rankings

For grades K-12

To demonstrate the exquisite sensitivity of our sense of touch, try this one. Get 5 to 10 different grades (roughness) of sandpap er from the hardware store. The degree of roughness should be printed on the back. Cut the sandpaper into pieces about 3 in by 3 in. (If you want to get fancy, you could glue the sandpaper on to block of wood, but this is not really necessary) Make su re you write down the grade of roughness on the back of each cut piece of sandpaper! Mixup the pieces of sandpaper and place them with the rough side up. Using your (or have someone else do it) finger, line up the pieces of sandpaper in order...from t he smoothest to the roughest.

Questions and Comparisons

Check to see if you (or your test subject) did it right.
Where were mistakes made? At what grade of sandpaper?

M aterials:

Wood Blocks (optional)
2-Point Discrimination

Grades 3-12

Ok, so we can judge different textures. What areas of our bodies are most sensitive to touch? Hands? Fe et? Fingers? To find out, perform a 2-point discrimination exam of a friend. Bend a paper clip into the shape of a U with the tips about 2 cm apart. Make sure the tips of the U are even with each other. Lightly touch the two ends of the paper clip to the back of the hand of your subject. Your subject should not look at the area of skin that is being tested. Do not press too hard! Make sure both tips touch the skin at the same time. Ask your subject if he or she felt 1 or 2 pressure points. If your subject reported 1 point, spread the tips of the clip a bit further apart, then touch the back of the subject's hand again. If your subject reported 2 points, push the tips a bit closer together, and test again. Measure the distance at which the subj ect reports "I feel 2 points".

Questions and Comparisons

Try different parts of the body...the arm, leg, fingers, back, neck, etc.
Compare the distances required for a "I feel 2 points" response on different body regions.
What part of the body is most sensitive? In other words, where on the body can 2 points be detected with the smallest tip separation?

The receptors in our skin are NOT distributed in a uniform way around our bodies. Some places, like our fingers and lips, have more touch receptors than other parts of our body, like our backs. That's one reason why we are more sensitive to touch on our fingers and face than on our backs.

Here are som e data (rounded) from a 2-pt discrimination threshold experiment (published in The Skin Senses, edited by D. R. Kenshalo, Springfield, IL, 1968):

Site
Threshold Distance
Fingers
2-3 mm
Upper Lip 5 mm
Cheek
6 mm
Nose
7 mm
Palm
10 mm
Forehead
15 mm
Foot
20 mm
Belly
30 mm
Forearm
35 mm
Upper arm
39 mm
Back
39 mm
Shoulder
41 mm
Thigh
42 mm
Calf
45 mm

How did your measurements compare?

Materials:

Paper clip (or a hair pin)
Pencil and paper to track responses.

SOURCE: Neuroscience for Kids-Touch Experiments

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