Two Point Discrimination

Materials: ★☆☆ Easy to get from supermarket or hardware store
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required

Categories: Senses and Perception, The Brain and Nerves

Alternative titles: Touch Receptor Sensitivity Test, Skin Sensory Receptor Mapping

Summary

Students test how well different areas of the body can distinguish between one and two points of touch using a simple two-point discrimination device. The activity demonstrates the uneven distribution of touch receptors across the skin and why some areas are more sensitive than others.

Procedure

Discuss with the class the structure of the skin and the function of touch receptors.
In pairs, construct a two-point discrimination tool by taping toothpicks to each end of a compass so that they protrude 2–3 cm.
Person A sets the distance between the two toothpick points, starting at 2 mm and later increasing to 5, 10, 15, and 20 mm.
Person B closes their eyes. Person A carefully touches both toothpicks to Person B’s skin at the same time, on designated areas such as lips, fingertips, palms, arms, knees, and feet. Do not reveal whether one or two points are being used.
Person B responds whether they felt one or two points. Repeat each distance three times per body area.
Record the results in a table.
Swap roles so that both partners are tested.
Plot results on a body outline diagram to visualize areas of high and low sensitivity.

Links

Normal Sensory Exam ; Two-Point Discrimination - onlinemedicalvideo:

📄 Two-point discrimination - Science Learning Hub: https://www.sciencelearn.org.nz/resources/1896-two-point-discrimination

Variations

Extend distances beyond 20 mm to see at what point discrimination becomes easy on less sensitive areas.
Use smaller intervals (e.g., 1 mm steps) for highly sensitive areas such as fingertips or lips.
Research and compare findings with neurological two-point discrimination tests used in clinical settings.

Safety Precautions

Do not press too hard with toothpicks; apply gentle pressure only.
Ensure toothpicks have smooth ends to avoid scratches.
Be cautious with participants who may have skin allergies or sensitivity issues.
Supervise students to prevent misuse of the compass points.

Questions to Consider

Why did we conduct each test three times? (To ensure accuracy and reliability of results.)
Which areas of the body showed the greatest sensitivity? (Typically the lips and fingertips.)
Why might certain areas like the hands and lips need to be more sensitive? (They are used for detailed exploration and communication.)
What advantages are there to having areas with low sensitivity? (It reduces unnecessary stimulation and distraction in regions less critical for fine touch.)
How might the results differ if a person had nerve damage in a tested area? (They would likely show reduced sensitivity and higher discrimination thresholds.)