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Two Eyes See More Than One Human Beings Have Two Eyes Located About 6 Cm (About 2.4 In.) Apart

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Two Eyes See More Than One Human Beings Have Two Eyes Located About 6 Cm (About 2.4 In.) Apart ivi act ty 2 TTwowo EyesEyes SeeSee MoreMore ThanThan OneOne OBJECTIVES 1 straw 1 card, index (cut in half widthwise) Students discover how having two eyes helps us see in three dimensions and 3 pennies* increases our field of vision. 1 ruler, metric* The students For the class discover that each eye sees objects from a 1 roll string slightly different viewpoint to give us depth 1 roll tape, masking perception 1 pair scissors* observe that depth perception decreases *provided by the teacher with the use of just one eye measure their field of vision observe that their field of vision decreases PREPARATION with the use of just one eye Session I 1 Make a copy of Activity Sheet 2, Part A, for each student. SCHEDULE 2 Each team of two will need a metric ruler, Session I About 30 minutes three paper cups, and three pennies. Session II About 40 minutes Students will either close or cover their eyes, or you may use blindfolds. (Students should use their own blindfold—a bandanna or long strip VOCABULARY of cloth brought from home and stored in their science journals for use—in this depth perception and other activities.) field of vision peripheral vision Session II 1 Make a copy of Activity Sheet 2, Part B, for each student. MATERIALS 2 For each team, cut a length of string 50 cm (about 20 in.) long. Cut enough index For each student cards in half (widthwise) to give each team 1 Activity Sheet 2, Parts A and B half a card. Snip the corners of the cards to eliminate sharp edges. 1 blindfold (optional)* 3 Each team of two will need a field of vision For each team of two collar, a length of string, a straw, half an index card, and a 2-in. piece of masking 1 box crayons* tape. 3 cups, paper 1 field of vision collar delta science modules Using Your Senses 23 © Delta Education LLC. All rights reserved. BACKGROUND INFORMATION Activity Sheet 2, Part A Two Eyes See More Than One Human beings have two eyes located about 6 cm (about 2.4 in.) apart. Each eye sees 1. How far apart are your eyes? about 6 cm the world from a slightly different viewpoint, 2. Draw a straight line from each eye to the ✗. or angle, and sends its own set of signals to 3. What do the two lines the brain. The brain combines these signals show? into one composite image that has depth to how each eye sees the it. Two images combined into one gives us world from a different depth perception, the ability to judge how angle far away an object is. Depth perception enables us to see the world in three dimensions instead of two. Our field of vision includes everything we can see at any given moment without 4. Work with a partner to drop pennies into the cups. a. Using two eyes. How many pennies dropped into the moving our eyes. When we look straight cups when you used two eyes? ahead, our field of vision encompasses a Answers will vary. b. Predict. Predict how many pennies will drop into the cups roughly circular region from shoulder to when one eye is covered. shoulder, forehead to waist. Moving our Answers will vary. eyes or turning our head changes what we c. Using one eye. How many pennies dropped into the cups when you used one eye? see but does not enlarge our field of vision. Answers will vary. 5. Was your depth perception better when you used one eye or Peripheral vision is the outer edges of two eyes? better with two eyes our field of vision. It enables us to see something without looking directly at it. Peripheral vision is what we use when Activity Sheet 2, Part B we see something “out of the corner of Two Eyes See More Than One our eye.” 6. Measure your field of 7. Now color in the diagrams vision. Your partner will to show your field of vision Due to the arrangement of light-sensitive record your test results in each test, like this: 0 below. 0 4 1 9 3 cells in the retina, our sense of sight is less 2 8 3 3 7 3 4 6 3 5 5 3 6 4 3 7 3 3 8 2 3 9 1 1 3 0 30 acute along the periphery of our visual field. 1 1 29 1 2 8 2 13 15 27 1 25 4 20 26 1 6 17 18 19 21 22 23 24 0 There we can detect motion, size, and With both eyes open I a. 0 a. 4 1 9 3 2 8 3 3 can see the index card 37 4 6 3 5 shape, but not color or fine detail. But 5 3 Varies 6 between 34 7 3 3 8 2 3 9 Varies 10 1 peripheral vision is important nonetheless. and . 3 30 11 29 1 2 8 1 2 3 1 7 1 5 5 2 4 20 2 26 It helps us cross the street safely! 16 17 18 19 21 22 23 24 0 0 4 1 b. With my left eye closed b. 9 3 2 8 3 3 37 4 I can see the index card 6 3 5 5 3 6 Depth perception is seriously compromised Varies 34 between 7 3 3 8 2 3 9 10 1 Varies 3 and . 30 11 29 with the use of just one eye. That is why 1 2 8 1 2 3 1 7 1 5 5 2 4 20 2 26 people who can see out of only one eye are 16 17 18 19 21 22 23 24 0 0 4 1 9 3 With my right eye closed 2 c. c. 8 3 3 often prohibited from driving or operating 37 4 6 3 5 I can see the index card 5 3 6 34 7 3 Varies 3 between 8 certain kinds of machinery. Likewise, our 2 3 9 10 1 3 30 Varies 11 and . 29 12 8 2 13 1 5 27 14 20 25 field of vision is much larger with two eyes 16 26 17 18 19 21 22 23 24 than it is with one. In short, one eye is not 8. Is your field of vision larger with one eye or with two eyes? simply a replacement, like a spare tire, for larger with two eyes the other. Our eyes work together to help us 9. How does your peripheral vision help you stay safe? negotiate our way in the world around us. Peripheral vision lets us see things, like a moving car, out of the corner of our eye. 24 activity 2 Two Eyes See More Than One © Delta Education LLC. All rights reserved. Guiding the Activity Additional Information Session I Safety Note: Encourage students to 1 Divide the class into teams of two. Distribute exercise caution when using the ruler a copy of Activity Sheet 2, Part A, to each around the eyes. student and a ruler to each team. Have students work together to measure the Tell students to hold the ruler flat against the distance between their eyes. tip of their nose (not in front of their eyes) while their partner looks at the ruler to see the distance from pupil to pupil. Ask, How far apart are your eyes? Students should find that their eyes are about 6 cm (2.4 in.) apart, or a little less. Tell students to record this measurement on question 1 of their activity sheet. 2 Draw an ✗ on the board. Tell students to hold out their thumb at arm’s length, close one eye, and line up their thumb with the ✗. Then tell students to switch eyes. Ask, What Students should notice that their thumb happens when you switch eyes? appears to “jump,” or change positions. It no longer aligns with the ✗. Ask, Has your thumb moved? no Explain that because our eyes are about 6 cm apart, each eye looks at the thumb from a slightly different viewpoint, or angle (see Figure 2-1). Switching eyes changes the angle from which the thumb is viewed, revealing the ✗ behind the thumb. Tell students to complete questions 2 and 3 on their activity sheet. Figure 2-1. At about 6 cm apart, each eye views the world from a slightly different angle. Ask, If each eye sees things from a different Students may suspect that the brain has angle, why don’t we see double? something to do with combining the images. Accept all reasonable answers. delta science modules Using Your Senses 25 © Delta Education LLC. All rights reserved. Guiding the Activity Additional Information Explain that when we look at an object with two eyes, each eye sends a set of signals to the brain. The brain combines the signals to form one image. Ask, Why do we need two eyes? Students may suggest that two are needed in case one gets injured. Tell students that one eye is not simply a replacement for the other. Our eyes work together to help us see better. They will learn how in the next exercise. 3 Distribute three paper cups and three pennies to each team. Ask students, Do you think you Students will probably say yes. could direct your partner’s hand to drop a penny into each cup with his or her eyes closed? With the help of a student volunteer, demonstrate how to do this activity, as follows: a) Place the cups on a desk or work table and sit about 4 feet away on one side of your student partner.
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