Back to: Human Cognition: Investigation 3t-Lab

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Investigation 2: Lab

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MINDSET

This investigation is designed to:

  • Deepen student understanding of reflexes as examples of simple information processing in the nervous system.

  • Develop proficiency in identifying components of the reflex arc and observing reflex actions through hands-on testing.

  • Strengthen skills in analyzing sensory differences across body regions using two-point discrimination.

  • Encourage students to connect reflexes with their protective role and their relationship to more complex brain functions explored in later Investigations.

INVESTIGATE

Teacher Preparation:

  • Place all reflex testing materials (reflex hammers, penlights, calipers) at the distribution center.
  • Divide students into cooperative lab groups of 3–4.
  • Review safe handling of reflex hammers and use of penlights. Emphasize gentle tapping and respectful interaction when testing classmates.

Student Preparation:

Each lab group will need the following materials:

  • Chromebook/Laptop with Student Guide
  • Reflex hammer
  • Penlight (1 per group)
  • Caliper (i per group)

EXPERIMENT

This experiment is made up of three parts:

  • Two-point discrimination test
  • Knee-jerk (patellar) reflex
  • Pupillary light reflex

Below is the full step-by-step procedure teachers and students should follow:

PART 1: Two-Point Discrimination

  1. Subject closes their eyes.
  2. Using a divider or compass, examiner gently touches two points on the skin at the same time.
  3. Begin with points close together and gradually increase the distance.
  4. Ask the subject whether they feel one point or two.
  5. Test different body regions (e.g., fingertip, forearm, back of hand, upper arm, calf).
  6. Record the minimum distance at which two points are felt as separate in each location.
  7. Compare results with classmates to see which body areas are most sensitive.

PART 2: Knee-Jerk Reflex

  1. Subject sits on a stool or chair with legs dangling freely.
  2. Locate the patellar tendon just below the kneecap.
  3. Tester gently taps the tendon with a reflex hammer and observes the lower leg kicking forward.
  4. Record the strength of the response using a 0–3 scale.
  5. Repeat the test on both legs.
  6. Perform the test again while the subject does the Jendrassik maneuver (clasp fingers and pull outward firmly while clenching teeth).
  7. Record and compare results with baseline trials.

PART 3: Pupillary Light Reflex

  1. Subject sits in a dimly lit room.
  2. Examiner holds a penlight in one hand and uses the other hand vertically between the subject’s eyes as a shield, so only one eye is illuminated.
  3. Shine the light briefly into the right eye and observe both pupils.
  4. Direct response: right pupil constricts.
  5. Consensual response: left pupil constricts at the same time.
  6. Record the observations.
  7. Repeat with the left eye while shielding the right.
  8. Switch roles so both partners act as subject and examiner.

WRAP-UP

Use your results to discuss why reflexes are fast and protective, why some responses are stronger with reinforcement, and why certain body regions are more sensitive than others. These observations will help you connect simple reflex pathways to the more complex information processing you will study in the next Investigations.