Touch Sensitivity: Testing Two-Point Threshold
As we have discussed, neurons in your skin send a variety of sensory information to your
brain (touch, pressure, temperature, pain). Some areas of your skin contain more of
these neurons than others and are thus more sensitive.
One way to measure the skin’s sensitivity to pressure is through the use of the two-point
threshold method. The two-point threshold is the minimum distance by which two rods
touching the skin must be separated before the person will report that there are two rods,
not one, on 50% of occasions. Today, you and a partner will be using this method to
assess the sensitivity to pressure of different parts of the body.
For this experiment you and your partner will need 5 paperclips and a ruler. Unfold the
paperclips so that the two ends are nearly touching (it should resemble a capital “D”).
You will need to set the distance (in millimeters) between the two ends of each paperclip
by gently squeezing or pulling apart the two sides and then checking the distance with the
ruler. You should have one paperclip set to each of the distances in the chart below.
One partner will serve as the experimenter and the other as the subject for the first trial.
The experimenter’s role will be to set the distance between the two ends of the paperclip,
lightly touch the paperclip to the various parts of the subject’s skin, and record test
results. The test subject must simply report whether or not they feel “one” or “two”
objects touching their skin. It is very important to the experiment that the test subject be
honest in their reporting! Once each body part and distance has been tested, switch
roles.
Experimenters should fill out the chart below with the subject’s response, either a “1” or
“2”. Be sure to skip around in the distances (for instance: 6mm, 12mm, 3mm, etc.) and
to test each distance twice (thresholds often require only 50% accuracy). To save time,
test check part of the skin at one distance, then change distances and test again.
2.5mm
bottom of foot
finger tip
elbow
bicep
tip of nose
cheek
back of calf
knee
forehead
1
1
5mm
1
10mm
1
1
2
15mm
2
2
20mm
2
2
25mm
2
2