Two-Point Touch Discrimination

Author: Krista Botton
Discrepant Event - Teacher's Guide
SED 695B
 
Detailed Explanation of Discrepant Event

Students will use a 2-point discriminator (calipers or cork with straight pins) to test touch reception in various areas of the body. Students should be encouraged to remain objective and not allow previous test and/or answers to influence their responses.

1. One student in the pair or team will sit with eyes closed, palm of one hand facing up and motionless on desk.

2. Experimenter will gently touch the fingertip, palm, forearm, back of the neck and lower leg (calf region) with the 2 point discriminator and the student, keeping their eyes closed, will report if they feel one point or two.

3. Experimenter will vary the 2 points on the discriminator in the following increments: 0 mm, 2 mm, 5 mm, 10 mm, 15 mm, 20 mm. The student (with eyes closed) will describe whether 1 or 2 points are felt.

4. For the best results, the experimenter should repeat the procedure in each of the locations two or three times.

Results:

Students will discover that they cannot discriminate the difference between 2 points the same in all of the body regions tested. Some regions have a greater concentration of touch receptors than others. In order to feel two different points, two or more touch receptors must be stimulated. In regions where the concentrations of touch receptors are less dense, the discrimination of 2 points will not occur as easily and the calipers (or pins) will be moved farther apart.

Principles illustrated

  • Understanding of basic concepts of touch sensitivity
  • Understanding of sensory nerve transmission and differential distribution of sensory receptors in various regions of the body
  • Homeostasis as it relates to the importance of touch receptors in various regions of the body

Standards

7th Grade Life Science
  • Standard 5b: Students know organ systems function because of the contributions of individual organs, tissues, and cells. The failure of any part can affect the entire system.

Biology / Life Science

  • Standard 9b: Students know how the nervous system mediates communication between different parts of the body and the body's interactions with the environment.
  • Standard 9d: Students know the functions of the nervous system and the role of neurons in transmitting electrochemical impulses.
  • Standard 9e: Students know the roles of sensory neurons, interneurons, and motor neurons in sensation, thought, and response.
 

Questioning Script

Prior knowledge & experience:

  • What is the largest organ in the body?
  • What are the functions of skin?
  • What kinds of receptors are present in the skin?
  • How is information passed through the body?

Root question:

  • Is sensory reception (related to touch) the same over all body surfaces?

Target response:

  • Is the touch discrimination of two points the same in all regions of the body?
  • Where is touch discrimination the greatest? the least?
  • What causes the variation in the discrimination in touch from region to region of the body?
  • What can be deducted about the concentrations of sensory receptors in the body regions that were tested?

Common Misconceptions:

  • Distribution of sensory receptors is the same throughout regions of the body.

 

References & Links:

Wikipedia - Sensory Receptors

Carolina Biological - 2 point Discriminators

Cheap (or FREE) Alternative: Use corks from wine bottles (free if you're a wine drinker or have friends/family/colleagues who are) straight pins donated by a family, and a metric ruler! :)

Carolina Biological - Cutaneous Sensations Lab (3 activities, including two-point discrimination, touch receptor distribution, and temperature receptor distribution)