Two-Point Discrimination Test

A week before Thanksgiving a couple years ago, I had the misfortune of stepping barefoot on a big piece of broken glass on kitchen floor. The glass was a leftover piece of an olive oil bottle that fell and broke in the kitchen and was unfortunately overlooked in the cleanup process. It was at that moment that I appreciated my mom’s advice to always wear slippers in the house (which now I do).

Being a science teacher, I immediately recalled the sensitivity of the foot in relation to the sensory neurons. I also knew I was in for a long and painful recovery. This brought me to wanting to suggest to you a lab that you can do with your classes that will test which parts of the human body are more sensitive than others.

Have you ever heard of the two-point discrimination test? This test assesses the ability to discern that two close-by points placed on a small area of skin are indeed two points and not one point; it looks for the minimum distance at which you feel the two points. It evaluates the sensory neurons and sensory receptors. The person being tested should not be looking at the object during any of the tests, which is why they are told to either close their eyes or wear a blindfold while it is being performed.

In the medical field, the two-point discrimination test is sometimes performed by neurologists during a neurological sensory exam to test for peripheral nerve damage. Some reasons a neurologist may perform this test on a patient is if they suspect a problem with the sensory information coming into the skin, problems with interpretation of sensory information, or problems with pathways to the brain. Say a patient suffered a severe cut, a doctor can use this test to check for nerve damage after the injury and may perform it a second time weeks later after healing has taken place to see if the damaged nerves have regenerated.

Students can perform this simple test on another student in class to find out which body parts are more sensitive than others—a great lab for those students who are aspiring to be doctors, or for those who are curious to learn a little more about their bodies. Students will perform this on another student with a simple measuring tool that can be made in class with just tape, an index card, and toothpicks.

This lesson idea fits in perfectly when teaching about sensory neurons and sensory receptors in the nervous system and integumentary system. Sensory neurons are neurons that help you detect changes in your environment. When you touch a surface that is sticky, slimy, rough, smooth, soft, wet, dry, cold, hot, or cuts you and causes pain, it is the sensory receptors in skin that sense these different types of stimuli and relay the information to sensory neurons. Sensory neurons then pass on the information to the brain. Different types of sensory neurons detect different types of stimuli from the environment.

In this lab, students will choose several body parts to test using a homemade toothpick measuring index card they can make in class. You may want to tell students which body parts to test by giving them a list on the class whiteboard. The back, arm, palms, fingers, calf, shin, top of foot, bottom of foot, face, shoulder are possible testing spots.

Some parts of the human body, like the palms of the hands or fingers, are more densely packed with neurons. These places in the body are more sensitive, allowing the brain to process fine details and different textures better than other parts of the body. For example, your back might be able to feel two pricks as only one prick at 1.5 inches, whereas on the palms of hands it could probably detect two points at 1.5 inches. This is because the back has less sensory receptors and are widely spaced. Want to find out yourself? Perform this test with your students and find out. You can even do this test at home with your family.

How to Make the Index Card Two-Point Discrimination Tester:

1.Begin by taking out one index card.

2.Label one side: .25 inch (1/4), another side: .50 inch (1/2), another side: 1 inch, and the

last side: 1.5 inch (1 1/2 inch).

3.Using these measurements, with a ruler, mark two small lines or dots to mark the

distances for each side.

4.Next, tape the toothpicks over each mark that was made. Be sure to tape them

securely so that they do not move around. *Helpful tip: One student can hold down the

card and toothpick to keep it in place, while the other student tapes the toothpicks to

the card. A student can do it alone, but it's not as easy because the card and toothpick

tend to move as you try and tape it.

5.Make sure the toothpicks for each measurement are evenly spaced and securely taped

on the index card. Also be sure that the toothpicks are the same length when you tape

it. To test this, take the index card with the taped toothpicks and place the point ends

to touch a surface, like a table. If one of the toothpick's end is touching the table and

the other is not, adjust one of them so that they touch a surface at the same time. This

way when they are used to perform the two-point discrimination test on a student, the

two ends of the toothpicks touch the person's body at the same time.

Index Card Two-Point Discrimination Tester

Helpful Tip:

Tell students not to press too hard when they perform the test on their partner. You do not want anyone getting injured during the two-point discrimination test, and also, it could provide false results. The toothpick poke should be a gentle one with equal pressure applied.

Materials:

1.Blindfold (or they can just close their eyes)

2.Metric Ruler

3.Toothpicks (8 for one index card)

4.Science Journal to record their data

5.Index cards (one for each pair of students)

6.Tape

Procedure:

1.Students can take turns performing the two-point discrimination test on each other.

Begin by blindfolding the student that will have the test done on them. You do not want

them to see the test being done. If you don't have blindfolds, or a student does not feel

comfortable wearing one, they can just close their eyes, but make sure they don't open

them during the test.

2.The student who is performing the test will start the test with any side of the index

card. They will place the ends of the toothpick for that measurement on the first spot

being tested. Then they will ask the other person if they feel one or two points and

then record their answer in their science journals.

3.The student doing the test will repeat step 2 for the other three distances on their

index card.

4.The student performing the test can move to the next body part being tested and

repeat steps 2 and 3.

5.When all the required body parts for the two-point discrimination test have been done,

students can switch roles.

Extension for the Real World

Have you heard of the Bionix-Shotblocker? The Shotblocker is a unique, U-shaped device that has tiny bumps on one side of it. If used correctly, the side with the tiny bumps is supposed to block or minimize the discomfort felt during an injection. The Shotblocker works by saturating sensory signals around the injection site (with the tiny bumps), so that a person receiving a shot should not feel the sting of the needle that is usually felt during a shot.

Notice the tiny bumps on the Shotblocker. This is the side that will be applied to the skin.

I bought this for my daughter a few weeks before one of her wellness checkups because she was going to have a few shots at her next appointment and she has always been terrified of shots...so much that in the past we have had to have the clinic's on-site psychologist come in during her visits to help calm her.

I mean seriously, when she was 11, I took her to the doctor, she went to hide under the doctor's table and would not come out from under the table when she knew she was going to have a shot. Even when the nurse came in to give her the shots, she remained under the table. A whole crew came in the room to try and convince her to come out and she refused still, so they had to bring in the psychologist to talk to her. It took a while, but they finally got her to come out from there and then still had to hold her down for the shot. That's when I said enough was enough, and I decided to look for numbing shot creams, and instead I found the Shotblocker online.

I bought the Shotblocker so my daughter could try it at her next flu shot appointment. It was a huge success! My daughter tolerated it! I tried it myself and I did not feel the needle going in my skin much. It definitely makes the poke of a shot less noticeable. Now I keep one in my purse, so I never leave it at home by accident when we have a doctor's appointment.

Show students one of these during class and ask them how they think this device might lessen the pain of a shot? Be sure to show them both sides of it. Have them explain their reasoning to you. Then, have them try it for themselves by having another student apply and press the Shotblocker on their arm (bare skin) while they themselves apply pressure to their skin using the end of a toothpick or paperclip. They should perform this "test" in the middle of the U shape of the Shotblocker, as shown in the picture below. Tell them not to press too hard, press just enough to cause a poke, not an injury.

Next, have them press the end of the toothpick, or something pointy, on their skin without using the Shotblocker and let them see if they feel it more in that spot than without it. Afterwards, they will switch places with their partner so that both students can see if they can feel a difference between using the device and not using it. Make sure they use it correctly. They should press firmly for about 10 seconds before the poke or shot and remove the device once the poke or shot is complete.

Other Extensions:

1.Ask students if they have ever heard of numbing sprays or creams to lessen the pain of

a shot? You can talk to students about how these products work to reduce pain.

2.Place an ice cube on the body part for 15 seconds, right before doing the two-point

discrimination test. Ask students if there was any difference between using the ice and

not using the ice.