The human eye
Do you only think of your peripheral (side) vision—peripherally? This side vision is actually useful for many daily activities, including riding a bike, reading or playing basketball. You might not even realize when you are using it. But our survival once depended on the quick response of our peripheral vision. A detailed picture, created by our central vision, is only useful in situations where time allows us to focus on the details. But our side vision can help us avoid dangers quickly. In this activity you will find out how specialized our peripheral view is.
When you look at something, you use central vision to focus on the details—and peripheral vision to gather information about the surroundings.
The differences between central and peripheral vision start at the backs of our eyes where we have two types of light-sensitive cells, called cones and rods. Our central vision uses an area densely packed with cones. Cones are sensitive to color and need ample light to function well. Our peripheral vision uses mostly rods and almost no cones. Rods are sensitive to movement and quickly pick up changes in brightness. They function well in a broad range of light conditions.
The differences continue as signals travel to the brain. Some signaling cells are sensitive to color but not so much to contrast whereas other cells signal faster and respond to low-contrast stimuli. In the brain’s vision center (known as the visual cortex) more neurons will analyze a stimulus picked up by our central vision compared with the same stimulus picked up by our peripheral vision. All of this leads to our color-sensitive, high-resolution central vision and our fast-working, movement-sensitive peripheral vision.
With all this information on our visual system, will you be able to predict what your side vision will perceive? Try this activity to find out!
- Cardboard or foam board:
- One 30- by 60-centimeter board or two 30- by 30-centimeter square boards held together with tape
- Metric ruler (A 30-centimeter-long ruler works well.)
- A string, about 50 centimeters long
- A pushpin
- Stack of scratch paper or a newspaper
- Scissors or craft knife
- Disposable cup
- Glue or clear tape
- Construction paper or paper and markers. (We suggest red, yellow and green but other colors work, too.)
- Flat surface to hold your board
- If you have two 30- by 30-centimeter boards, tape them together so they form a 30- by 60-centimeter board.
- Place your board on a flat surface in front of you with the long side closest to you. Find the middle of the long side; this should be 30 centimeters from each corner. Mark this place with a pencil.
- Place a newspaper or stack of scratch paper under the board to protect your surface underneath and carefully stick a pushpin into the board on the indicated place.
- Tie one end of the string around the pencil. Tie the other end to the pushpin so the string is exactly 30 centimeters long.
- Use the attached pencil to draw a half circle on your board with a radius of 30 centimeters.
- Shorten the string until the distance from the pencil to the pushpin is two centimeters. Now draw a small half circle—within the larger circle—with a two-centimeter radius.
- Remove the pencil, the string and the pushpin and carefully use the scissors to cut along the big and small lines. (You may want to get help; thick cardboard or foam board can be difficult to cut.) You should be left with what looks like a rainbow. The big half circle is the outer edge of your vision protractor, the small half circle cutout makes a place for your nose.
- Pin the pushpin near the outer edge of the protractor, directly across from your nose hole. (Be sure the pin is not poking anything but the protective paper underneath.) If the protractor were a rainbow, this point would indicate the highest point of your bow. This pushpin will serve as a focus point, or a point to look at while you perform each test. (Tape some scratch paper around the point of the pushpin so it does not accidently poke any items or people.)
- Attach a disposable cup on the bottom of the protractor, near the center. This will serve as a handle. If you started with two 30- by 30-centimeter boards, you might need to attach reinforcement on the bottom side so the two pieces of the protractor stay flat. You can use the scrap pieces of board for this.
- Your vision protractor is now ready to use.
- You now need to create some shapes to look for before you can start the test. To do so, take three different colored sheets of construction paper. We suggest trying red, green and yellow but other colors will work, too. Cut out two 10- by two-centimeter rectangular strips from each sheet, for a total of six strips. If you do not have construction paper, you can use white paper strips and color them with markers. Note that each strip needs to be one uniform color.
- Take one strip of each color and cut off the corners so the top of the strip forms a triangle. You should now have three strips like this. Leave the other three strips as rectangles.
- If your strips bend over when held up, you can reinforce them with additional paper, craft sticks or straws.
- Hold the vision protractor up to your face with your nose in the center nose hole. The protractor should be held horizontally during the test so the half-circle stretches out in front and to the side of you. Keep your gaze on the pushpin during the test.
- Your helper will hold one of the paper strips against the outer edge of the vision protractor so two centimeters stick straight up above the vision board. He or she will hold it on your left, near the long straight edge of the protractor. While you continue looking at the pushpin, the helper will move the strip slowly and evenly along the curved protractor edge toward the middle. How far do you think the helper will need to move the strip before you observe something is there? Do you think the helper will need to move it farther before you can detect the color and/or shape of the strip? Much farther or just a little bit?
- Perform the test. As soon as you can first detect the strip, have the helper stop moving. Can you detect the shape or the color of the object or can you just tell there is something there? Remember to keep your eyes on the pushpin at all times during the test.
- Have your helper keep moving the object along the edge toward the center of the protractor. Ask the helper to stop again as soon as you can detect more detail, such as the color or the shape. What can you detect first—color or shape? Or are you able to detect both at the same time?
- Repeat the previous step until you can detect the shape as well as the color of the object. Can you detect other details of the object at this location or does it need to be moved even closer to the pushpin?
- Now let the helper choose a different strip. Do you expect the outcome to be different? Can your peripheral vision detect one color earlier than another?
- Extra: Repeat the test in a darker room after allowing your eyes to adjust to the new situation. Do you expect the results to be different and, if so, how do you expect your outcome to change?
- Extra: Repeat the test, but now, ask the helper to wiggle the strips while he or she is moving them along the side of the protractor. Do you expect the outcome to be different and, if so, how do you expect it to change?
- Extra: Write a letter or number with pencil or pen on the top two centimeters of the strips. When do you think you will be able to read the letter or number? Perform the test to find out.
Observations and results
You probably quickly observed something appearing in your side view but perhaps you could only later tell the color, and after that identify the shape.
Our peripheral vision is quick at detecting that something enters our field of sight but it is weak at distinguishing color, shape or detail. This is because fewer and different cells in our eyes and brains are activated when seeing an object with our peripheral vision than when “seeing” the object with our central vision.
Our peripheral vision has evolved to serve us well. It is very good at picking up objects and movement in dim as well as bright light, which allows us to escape from an approaching danger quickly. This explains the results of some of the extra instructions: in dim light you still can quickly detect an object with your peripheral vision, and you notice it even faster when the object wiggles. Our ancestors did not need details to identify the type of danger instantly. To see color, shape and details, they could wait until ample light was available and use their central vision to study a relatively still object.
More to explore
The Retina, from Neuroscience for Kids
When a Flashing Light Shows More, from Scientific American
Now You See It, Now You Don't! Test Your Peripheral Vision, from Science Buddies
This activity brought to you in partnership with Science Buddies