Materials Included In Kit

Additional Materials Required

Safety Precautions

Although the materials in this demonstration are considered nonhazardous, please observe all normal laboratory safety guidelines. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory.

Disposal

The Seeing Is Believing cards are reusable and should be stored for future use.

Lab Hints

• Enough materials are provided in this kit for 32 students working in pairs or for 16 groups of students. This laboratory activity can reasonably be completed in one 50-minute class period.
• Bright white paper will provide the best results.
• Good illumination, preferably natural light, is ideal.
• Students should maintain focus on the appropriate point-of-focus for their card. If their eyes wander they will not be able to see the image.
• Students who are colorblind may find this activity difficult to complete.

Teacher Tips

• This activity is an appropriate introduction for a unit on light, color or vision.
• This activity could also accompany a discussion on inheritance and sex-linked traits.

Answers to Questions

Before: (Students should color the image in the original colors as they appear on the Seeing Is Believing cards.)

After: (Students should color the image in the colors they see them after one minute of focus. Yellow should be blue, black should be white, cyan should be red and magenta should be green in these images as compared to the original.)

1. Which cones were overworked with each image?

   With the U.S. Flag card, the cones that sense red and green are overworked when looking at the star field and the green and blue cones are overworked when looking at the red stripes.

   With the Flower card, the cones that sense red and blue are overworked when looking at the stem. The red and green cones are overworked when looking at one flower and the green and blue cones are overworked when looking at the other.

   With the African Continent card, the cones that sense red and blue are overworked when looking at the land and the red and green cones are overworked when looking at the water.

   With the Apple card, the cones that sense green and blue are overworked when looking at the body of the apple and the red and blue cones are overworked when looking at the worm and stem.

2. If one were completely colorblind, although a rare condition, what colors would they see while focusing on each image?

   Black, white and gray.

Discussion

The primary colors of light are red, blue, and green. Light enters the eye through the pupil, travels through the lens and is projected onto the retina. The retina contains light-sensitive nerves that transmit this inverted signal to the brain. Some of the nerves, the rods, detect light and dark, and the cones each detect one of the three primary colors of light. The brain interprets the image as right-side up and as a combination of these three colors and their intensity.

Each image is printed on the cards using the primary pigments yellow, cyan and magenta. These primary pigments are complements of the primary colors of light. Magenta is a combination of red and blue, yellow is a combination of red and green, and cyan is a combination of green and blue. When the student focuses on one of the images, the cones that are sensitive to each color are overworked. Since white is the combination of all three primary colors, the color from the cone that was able to rest during the one minute is the most prevalent when the “overworked” eyes look at the sheet of white paper.

Teacher Handouts

12718_Teacher1.pdf

References

Bacher, Angela Bornn, et al, “Physical Science,” Prentice Hall, 1988.

Berson, Frank G., “Basic Ophthalmology,” American Academy of Ophthalmology, 1993.

Introduction

“The function of art is to disturb. Science reassures.”
—George Braque

Concepts

• Color
• Vision
• Observation
• Colorblindness
• Discrepant event

Background

The retina, a thin tissue that lines the back of the eye, contains two types of nerve cells that are sensitive to light. Rods are nerve cells that are sensitive to the amount of light present, or its intensity (light and dark). Cones are nerve cells that are sensitive to colors—each cone cell is sensitive to a primary color of light (red, green or blue).

Defective cone cells, generally found in males through an X-linked inheritance pattern, may result in several forms of colorblindness. Complete and blue colorblindness are very rare conditions. The most common forms of colorblindness affect the red or green light-absorbing cones. Ishihara plates, or pseudoisochromatic plates, are used to test for color vision. The plates contain a figure or number on a background of colored dots. Persons with certain color vision impairments will not be able to discern some of the numbers or figures from the background.

Materials

Safety Precautions

Although the materials in this demonstration are considered nonhazardous, please observe all normal laboratory safety guidelines. Wash hands thoroughly with soap and water before leaving the laboratory.

Procedure

1. With a partner, obtain one Seeing Is Believing card and a sheet of white paper from your instructor.
2. Locate the point-of-focus for the assigned card. The point-of-focus for each of the following is:
   • African Continent card—Lake Victoria (the largest lake in Africa)
   • Flowers card—the head of the bee
   • Apple card—the spectacles on the worm
   • U.S. Flag card—the star in the lower right corner.
3. Place a Seeing Is Believing card and a blank sheet of white paper side-by-side.
4. Stare at the point-of-focus for one minute. Do not allow your eyes to wander. Stare intently only at the point-of-focus. Your partner will monitor the time.
5. After one minute, quickly look at the sheet of white paper. What colors do you see?
6. Record your results on the Seeing Is Believing Worksheet.
7. Trade with another group, as time allows, and try each type of Seeing Is Believing card.
8. Return the cards to your instructor after the activity.

1. Which cones were overworked with each image?
2. If one were completely colorblind, although a rare condition, what colors would that person see while focusing on each image?

Student Worksheet PDF

12718_Student1.pdf