Materials Included In Kit

Additional Materials Required

Prelab Preparation

1. Cut each sheet of sight cards into 10 sets of eight cards each. A set is one row across.
2. Place each set of eight individual cards into a small separate envelope and label each envelope as “Reading” or “Color.”
3. Cut out each peripheral vision disk.

Safety Precautions

The materials in this activity are considered nonhazardous. Make sure students observe all laboratory safety guidelines.

Disposal

All materials included in this kit can be stored for future use.

Lab Hints

• Enough materials are provided in this kit for 30 students working in groups of three, or for 10 groups of students. All materials are reusable. Both parts of this laboratory activity can reasonably be completed in one 50-minute class period. The prelaboratory assignment should be completed before coming to lab, and the data compilation and questions may be completed the day after the lab or assigned as homework.
• As the sight card approaches the center of vision, it becomes very difficult for the subject to keep his eyes focused on the zero point. Audible reminders from the tester will help keep the subject from averting his gaze.
• Each student may want a “trial run” before actually recording results. Do not allow more than one trial run, since improvements in peripheral vision are possible with practice. If time is a factor, the teacher can demonstrate the procedure with one student.
• Student results for color and shape will vary greatly. Color is usually detected before shape. However, this depends on the color and shape being tested. Results of testing show red is easier to detect than blue, and green is hardest to detect. Therefore, the shape of a green-colored object may be discerned before the color.
• A normal eye has a near point (closest distance at which the eye can focus) of approximately 20–25 cm. The peripheral vision disk is within this range. If focusing on the zero mark is difficult for a student, he may focus on a point beyond the peripheral vision disk, as long as the point is aligned with the zero.

Teacher Tips

• This activity is appropriate for a unit on light and color, the nervous system or the senses.
• The testing done in this activity should not be considered for diagnostic purposes, but students may be interested to know that normal range for peripheral vision is 180º when using both eyes. When using one eye, the total visual field from left to right is normally 150º. A good extension to this activity would be to repeat Part 1 with one eye covered, and again with the other eye covered.
• Loss of peripheral vision is called tunnel vision. Students can research causes of tunnel vision such as glaucoma, retinitis pigmentosa, retinopathy or stroke.
• Research has shown that cell phone usage in an automobile severely limits use of peripheral vision, even for a period of time after the driver has stopped using the phone. Have students discuss the need for peripheral vision while driving and debate the pros and cons of restricting cell phone usage in cars.
• Some animals have wide peripheral vision to better detect predators. Have students research peripheral vision in animals and compare to humans.
• The Student Laboratory Kit, AP6843—Seeing Is Believing, can be used to further explore cone cells, and FB0439—Human Senses Experiment Kit, can be used to further explore sight and well as the other senses.

Answers to Prelab Questions

1. Which type of photoreceptors in the retina is used mainly for peripheral vision?

   Although cones can be found in the periphery of the retina, the rods are used mainly for peripheral vision.

2. Why is it hard to distinguish colors at night?

   The rods are more sensitive to light than cones and help us see in dim light, but they are not sensitive to color. The cones, which help us see color, do not work well in dim light.

3. Predict the sequence in which the following will be observed by using peripheral vision, from first to last—identifying color, detecting motion, identifying letters or numbers and identifying shape.

   Since rods are used in peripheral vision, motion should be detected first, followed by color, shape and letters or numbers last (near the zero degrees mark).

Sample Data

Observations

Data Table 1 Data Table 2

Answers to Questions

1. List your specific fields of vision (Total Visual Field) from greatest range to smallest range for all the categories tested.

   Motion—215
   Color—110
   Shape—110
   Reading—35

2. Compare your motion and reading fields of vision from Part 1 to Part 2. Did your peripheral vision improve in either area, stay the same, or get worse?

   In both motion and reading, the subject’s peripheral vision improved slightly from Part 1 to Part 2—5 degrees for motion and 10 degrees for reading.

3. On what area of the retina was the image of the sight card focused when it was first detected? On what area of the retina was the image of the letters focused? Which type of photoreceptors are more numerous in each area of the retina?

   The sight card was first focused on the periphery of the retina, which has more rods than cones. The letters were focused on the macula (or fovea), where a greater density of cones is found.

4. Think of activities or occupations where good peripheral vision would be advantageous. List several and explain why peripheral vision is important in each.

   Athletes need good peripheral vision. Basketball players can pass without looking directly at the intended receiver. A baseball pitcher uses peripheral vision to help him pick off a base runner. Driving is an activity where peripheral vision is essential in order to see road signs, pedestrians, and other vehicles to the right or left. Firefighters and law enforcement officers use peripheral vision to alert themselves to danger.

References

“Out of Sight!” Neuroscience for Kids, http://faculty.Washington.edu/chudler/heurok.html (Accessed April 2007).

Peripheral Vision, http://www.exploratorium.edu/snacks/perpheral_vision.html (Accessed April 2007).

Introduction

Stare at an object straight ahead. Can you see anything else out of the “corner of your eye”? Seeing beyond the center of our visual field (everything seen while looking straight ahead) is known as peripheral vision. Explore the range of your own peripheral vision.

Concepts

• Peripheral vision
• Retina
• Rods versus cones

Background

The retina, a thin tissue that lines the back of the eye, contains specialized nerve cells, called photoreceptors, that are sensitive to light. The two different photoreceptors are known as rods and cones, so named because of their shapes. Rods are more numerous (over 120 million) and are more concentrated around the periphery (outside edges) of the retina (see Figure 1). They are more sensitive to light than cones and help us see in dim light. After walking into a darkened room, at first it is difficult to see anything because the cones have been active in the brighter light. After several minutes in dimmer light, the eyes “adjust” and objects can be distinguished again. The adjustment occurs because the cones become less active and the rods are stimulated by the lower-level light. Rods are not sensitive to color, however, which is why it is difficult to distinguish colors in a dark room. Rods are very good at detecting motion. A moving object can usually be detected in the peripheral vision before the object can be clearly identified.

Although cone receptors are found throughout the retina, the center of the retina, the macula, has a much higher density of cones than the periphery. In the center of the macula is the fovea—a densely packed area of cones with no rods (see Figure 1). Cones are responsible for color vision. Even though the eye has fewer cone receptors (6–7 million) than rod receptors, cones are vital to our central vision and the ability to see fine details. Cones are used primarily when we read. Try focusing on a letter in the middle of a word in a sentence and see how many other words you can read to the right or left without moving your eyes.

When one looks at something directly, the image is focused on the macula. When something is seen out of the corner of the eye, the image is focused on the periphery of the retina, where more rods and fewer cones are found.

Experiment Overview

The purpose of this activity is to measure the peripheral field of vision. The angle at which motion and details such as color and shape can be detected will be measured using a peripheral vision disk.

Materials

Prelab Questions

1. Which type of photoreceptors in the retina is used mainly for peripheral vision?
2. Why is it hard to distinguish colors at night?
3. Predict the sequence in which the following will be observed by using peripheral vision, from first to last—identifying color, detecting motion, identifying letters or numbers and identifying shape.

Safety Precautions

Although the materials in this activity are considered nonhazardous, please observe all laboratory safety guidelines.

Procedure

Part 1. Visual Field: Motion and Reading

1. Choose one member of the group to be the subject, one to be the tester, and one to be the recorder. These roles will rotate so everyone will have his or her peripheral vision tested. Read the Procedure section completely before beginning the activity.
2. The subject obtains the peripheral vision disk and sits at a desk or table.
3. The subject holds the vision disk horizontally to his face, placing his nose in the center curve. The disk should be about halfway between the top and the tip of the nose. Use the thumb and forefinger of either hand to hold the disk at the zero point, with the forefinger on the zero (see Figure 2).
   {10834_Procedure_Figure_2}
4. The tester obtains the reading (black and white) sight cards and stands in front of the subject.
5. The tester chooses one of the eight reading sight cards without letting the subject see which one.
6. The recorder uses the Peripheral Vision Worksheet and a pencil to mark the angle at which the subject can distinguish the object and details (marking on the subject’s worksheet, not the recorder’s). The recorder should sit or stand where she can read the sight card as it moves, as well as the angle markings on the peripheral vision disk.
7. The tester holds the lower half of the sight card with letters facing inward against the disk before the largest angle (110°) on the subject’s left side, out of the subject’s sight. The vision disk should intersect the card, with the letters above the disk and the tester’s hand below the disk (see Figure 3).
   {10834_Procedure_Figure_3}
8. The subject focuses on his finger at the zero point, not moving his eyes to the right or left at any time during the test. The tester must watch the subject’s eyes to make sure they stay focused straight ahead. This task may be somewhat difficult for the subject initially, as the eyes may tend to wander, especially as the card becomes easier to distinguish. The subject may try to peek to see if his guesses are correct. (It may help if the tester audibly reminds the subject periodically by saying, “Look straight ahead,” or “Stay focused on your finger.”)
9. The tester slowly and steadily moves the card toward the zero point. As soon as the subject detects the card moving into his field of vision, he should say, “Motion.” The tester pauses the motion of the card at this point, allowing the recorder time to mark the angle on the left side of the diagram of the disk on Part 1 of the subject’s Peripheral Vision Worksheet, using the letter “M” for motion.
10. The tester continues to move the sight card slowly toward the zero point, reminding the subject to continue gazing straight ahead, until the subject can recognize the two letters and/or numbers on the card. The subject should say the letters/numbers out loud—for example, if the card reads 3T, the subject should say “Three tee.” If correct, the recorder marks this point on the diagram with the letter “R” for reading. If the subject does not correctly read the card, the recorder does not mark on the diagram and the tester continues to move the card toward the zero point, until the card is read correctly by the subject.
11. If at any time during the test, the subject averts his eyes from the center gaze and glances toward the card, the tester chooses a different card and places the new card at the same place the original card had reached. The procedure continues with the new card.
12. Repeat the entire procedure on the subject’s right side, choosing a different card and marking the angles on the right side of the disk diagram.
13. Repeat steps 1–12, assigning a different role to each group member. Continue until each group member has been tested.
14. Place the reading sight cards back in the envelope.

Part 2. Visual Field: Motion, Color, Reading and Shape

15. Follow steps 1–9 of Part 1, substituting the eight color sight cards for the black and white reading cards.
16. The tester continues to move the sight card slowly toward the zero point until the subject can recognize the color, the letter or number, or the shape on the card. The subject should announce the detail out loud—for example, “Square,” “Three,” or “Blue.” If correct, the tester pauses and the recorder marks this point on the diagram with the letter “C” for color, the letter “R” for reading, and the letter “S” for shape. If the subject does not correctly identify a particular detail, the tester continues to move the card toward the zero point, until the detail is announced correctly by the subject.
17. The tester continues to move the sight card toward the zero point until all details of the card—color, reading and shape (not necessarily in that order)—have been correctly identified.
18. If at any time during the test, the subject averts his eyes from the center gaze, and glances toward the card, the tester should choose a different card and place the new card at the same place the original card had reached. The procedure continues with the new card.
19. Repeat steps 15–18 on the subject’s right side, marking the angles on the right side of the disk diagram for Part 2. Remember to use a different card.
20. Repeat steps 15–19, assigning a different role to each group member. Continue until each group member has been tested.
21. Place the color sight cards back in the envelope.
22. Fill in the data tables for your own results to the nearest 5 degrees. Add the left and right angles for the Total Field of Vision.

Student Worksheet PDF

10834_Student1.pdf