Taking Turns!

Experiment #1

Air date: 1/8/98

WHAT YOU'LL NEED:	a chair or stool that rotates (see alternative) stopwatch or clock with a second hand paper and pencil metric tape measure focal point
WHO YOU'LL NEED:	7 people: subject spinner timer observer recorder

WHAT YOU NEED TO KNOW:

A nystagmus [nis-TAG-mis] is the movement of the eye in the opposite direction of the movement of the head. It's your eye's attempt to stabilize an image and make sense of what you're seeing so that it isn't just a blur.

Head motion is detected by vestibular organs--three semi-circular canals--located in the ear canal. The three canals are positioned at right angles to one another. Any kind of head motion causes fluids in the canals to send signals to your brain. These signals tell the brain whether your head is nodding up and down, tilting toward your shoulder or rolling side to side, as if you were shaking your head "no."

On Earth, the information sent to the brain by the vestibular organs helps you to keep your balance. In space, without gravity to pull the canal fluids "down," the brain gets confusing messages about body position which frequently results in motion sickness.

On Earth, where do you get your sense of head movement---from your visual sense, your vestibular system or both?

WHAT TO DO:

1. Develop a one-sentence hypothesis.

   

2. Subject chooses a focal point at eye level at a distance of 2 meters from the subject's face.

3. Subject sits with eyes open on a chair or stool that rotates. (Alternative: If you don't have a rotating chair, subject can turn while standing in one spot, trying to keep the head level.)

   NOTE: It's important that the subject's head does not wobble.

4. The spinner (who has previously practiced turning the chair smoothly at a constant rate of one rotation per second) begins to turn the chair clockwise.

   

5. Without stopping the stopwatch, timer announces when one minute is up. Subject remains seated and focuses on the focal point.

6. The observer notes the direction of the nystagmus (right to left or left to right) and counts each eye motion or "twitch" until the nystagmus, has stopped.

7. Subject reports when he/she no longer feels motion. Timer stops the stopwatch and tells the recorder the full amount of time that has elapsed including the one minute spin time.

8. Allow subject to recover before proceeding to next phase.

   NOTE: The same subject should be used for each of the four phases of the experiment.

9. Repeat steps 2 through 8, spinning counter-clockwise.

10. Repeat entire experiment, both clockwise and counter-clockwise, this time with eyes closed for the one-minute spin.

11. Record results on reply card and return to WHAT'S IN THE NEWS, Wagner Annex, University Park, PA 16802.

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Reply card

Printable copy

Hypothesis:

Visual Conditions	Spin time	Eye direction for clockwise spin	# of eye movements	Elapsed time until subject feels no rotation	Eye direction for counter- clockwise spin	# of eye movements	Elapsed time until subject feels no motion
Eyes Open	One rotation every 3 seconds	Right to left ____ Left to right ____	.	.	Right to left ____ Left to right ____	.	.
Eyes Closed	One rotation every 3 seconds	Right to left ____ Left to right ____	.	.	Right to left ____ Left to right ____	.	.

The results of this investigation:

______ support the hypothesis
______ refute the hypothesis
______ are inconclusive

Graphic created by Medical Illustrator Howard Bartner, contained in HUMAN PHYSIOLOGY IN SPACE, by Barbara F. Lujan and Ronald J. White.