Now You See It, Now You Don't

MATERIALS  ping-pong balls (1 per group)  razor blade, X-acto® knife, or utility knife (for adults' use only)  bag of cotton balls  glue  clock or watch with a second hand  red lights that give off a uniform intensity of light; e.g., no bright spot at the center (use holiday lights, party lights, or flashlights covered with red cellophane); minimum of 1 per group

CONTEXT This activity explores an unexpectedly extreme condition: nothingness. What's the emptiest landscape students can remember seeing? A desert? A prairie? As empty as that landscape was, it didn't approach the total emptiness confronted by some polar travelers in "whiteout" conditions—when there is literally nothing to see but empty white space.

Explain that polar travelers can experience something called visual deprivation when confronted by whiteout conditions or a completely white, unchanging landscape. (Visual deprivation is different from snow blindness, a condition caused by the actual burning of retinal tissue because of extreme light conditions. This activity will not cause any lasting eye strain, but it mimics a condition of temporary blindness and will allow students to experience something akin to the visual deprivation they might undergo in certain circumstances at the poles.)

PREPARATION  Slice the balls in half along the seam. Discard the half with the logo.  Stretch out several cotton balls and glue one around each rim of the remaining half-balls.

PROCEDURE 1. Assign an equal number of students to each available red light. Distribute the ping-pong ball halves, one per group. Remind students to be careful with the light bulbs as they may get hot.

2. While sitting comfortably in a chair, each student in turn can place the outside of the ball on the light (for small lights) or near the light (for larger lights). He or she then should completely cap one eye with the open end of the ball while shutting the other eye and covering it with a hand. The light should be visible through the ball and uniform in its intensity (e.g., not bright at its center and diffuse around the edges). The student should stay as steady as possible and not blink for up to 30 seconds and report any changes or observations to a recorder.

3. Within seconds, many observers will perceive that the light has gone out or faded, even though it has not changed! Ask for ideas on why this happened. Was the eye or brain or both "tricked"? (The brain is responding to the "retinal fatigue" caused by the observer's focus on the single red light. The eye's responders to the red light have essentially been overstimulated and have temporarily shut down.) Would this experiment work without the ping-pong ball device? What is the function of the ball? (To shut out all other visual stimuli.) 4. Why didn't some people experience the same effect? What variables might have affected their results? Here are a few to explore:  Motion is a strong visual stimulus, and so any movement will "reset" the observer's vision. After an experimenter sees the light "disappear," actually turn off the light and then turn it back on again. What effect does the change in the observer's field of vision have?  A non-uniform field of vision (such as a bright spot at the center of the light) can influence results. What would happen if you waved a pencil between the experimenter and the light?  People vary in their sensory perception. Those who didn't experience the phenomenon should try again. Does age or gender make a difference?

ASSESSMENT Ask students to propose other experiments to test temporary disability (or the seeming disability) of other senses. For example: Can students identify or produce a form of "white noise"—like the quiet whirring of an air conditioning system or the distant hum of a highway—that essentially goes unheard because of its monotonous quality? What happens when one student places a finger on the forearm of another? After awhile, does the second student "feel" the light pressure from the first?

EXTENSION Ancient people in warm climates didn't invent sunglasses. Inuits, a people native to the Arctic region, accomplished that feat. About 2,000 years ago, they created wood goggles to cut glare from snow. Challenge students to make cardboard goggles that shade the eyes from glare but allow the wearer to see well.

Adapted with permission from "And Then the Lights Went Out: Constructing a Simple Ganzfeld," by Stephen F. Davis and Cathy A. Grover, from the Activities Handbook for the Teaching of Psychology, Volume 2, published by the American Psychological Association, ©1987 by the APA.

Resources Julie of the Wolves, by Jean Craighead George (Harper & Row; 1972). A girl survives alone in the Arctic without her family.

Toughboy and Sister, by Kirkpatrick Hill (Margaret McElderry; 1990). An 11-year-old boy and his sister try to survive in the Alaskan wilderness after their father disappears.

Courtesy NSF/National Science Foundation