While some students will portray individually assigned parts of the eye, others will assume the role of photons of light with different frequencies of color. The entire group will represent how a beam of light enters the eye, how each part functions and how they interact.
The students will use props to act out their roles. This total physical response activity involves the students as main concepts so they can internalize the sight process: The structure and function of the eye and the way retina cells capture and send nerve impulses to the brain. After the activity, the students will be able to answer the questions: How do we see? How come when I go from a bright to dark place (i.e.: a theater) I can't see for a few seconds? What happens when I see contrasts in light?
Time Duration: 30 - 40 minutes
Grade Level: 4-5
scientific processes, energy, communication, comparison, inference, classification, sequencing, organization, evaluation and synthesis
cornea, iris, lens, retina, visual purple, rods, cones, refraction, reflection, spectrum, image.
NASA Perception Videos - The Way Things Look, etc.; Nystrom Human Body charts
The sight process is best understood, when we look at light as a stimulating agent. The particles of energy traveling into the eye are called photons. Photons from a light source (a lamp, the sun, etc.) bounce from the surfaces of objects when lit. They travel through the air or other medium and reach the eye. There they pass through two membranes: Conjunctiva and Cornea, then they pass through the Aqueous Humor (a liquid) and through the Pupil, the opening of the Iris and then through the lens. The Lens is strategically placed to bend the photons, making the beam of light crisscross directions, so the image being received at the Retina at the back of the eyeball is reversed.
The Retina is a tissue lined with two types of cells: The Rods and the Cones. The Rods are cells equipped with chemicals sensitive to dark and bright stimulus while the Cones are sensitive to the frequencies of red, blue and green light. Visible light is made up of the colors in the rainbow: violet, indigo, blue, green, yellow, orange and red. Each color of light is made up of photons that carry a given amount of energy and have different frequencies. For instance, a red-light photon has less energy than blue or violet, and is considered a low frequency color, while a blue/violet photon has a higher frequency and more energy.
Your eye absorbs all the photons, yet it is only able to send one-, two-, or three-color messages to the brain, red, blue and green. From these, all the other colors we "see" are interpretations of nerve impluses made in the brain!!
When the cells in the retina are hit by photons, the energy is absorbed, changing the cell's chemistry. The chemical that reacts to the photons is known as Visual Purple. Whenever there is a chemical reaction, energy is either released or absorbed. In this case, energy is released when the Visual Purple brakes up sending stimulus to the brain in the form of vibrations, like a messenger relay system.
This is why we have difficulty seeing for a moment or two when we enter a dark room after being in a bright environment. If a person walks into a dark room while the cells are "busy" sending messages to the brain, and few photons enter the eye and fall in any of those "busy - blank" spots, there are no messengers to relay the nerve impulse to the brain, thus creating the illusion of momentary blindness. A person bumps into things, has a hard time finding a seat if in a theater, etc. After a few minutes, the cells rebuild their visual purple, because fewer photons are hitting them. Gradually the "busy - blank" spots are filled, and the retina is nearly covered by Visual Purple again. The whole cycle begins again, but this time in the darkness of the theater, there are fewer photons entering the eye, thus not breaking apart the Visual Purple as fast, nor causing many chemical changes.
Therefore, the eye has adjusted to the new lighting and it is ready to receive the incoming photons in the theater and then transmit that information to the brain.
Student Roles: Number of Students Each, Function-
An extra position or two can be added, by increasing number of children on a given color. The teacher may guide the entrance flow of photons' kids by calling the colors one at a time. A more creative way of representing the act of sight is by telling a story of a child going to the theater, and this is what one of his/her eyes sees: The red carpeting at the theater's lobby. The orange doors at the entrance, the yellow popcorn for sale, the green uniform of the ticket taker, the blue wall paper down the hall. Then, all four white bright lights on the billboard, then total darkness- all black. Send into the eye the black group of photons while the white receiving RODS are still at the Brain. Instruct the black photon role players to hang around the eye, waiting for a Rod to be available to take him/her to the Brain.
(Consult an encyclopedia for the anatomy and further information about the eye.)
These activities will reinforce concepts of perception, light, sight process and the functions of the retina cells:
-Color a flag /design with the opposite colors of the color wheel, stare at it and then look at a white wall.
-Check the blind spot via a 3 x5 card with a + on the left to stare at while winking and a 0 on the right. Focus it.
-Make a spinning wheel-button using 1/3 segments of red, green and blue - spin and observe white form.
-Make a kaleidoscope with plastic slides, black tape and plastic decorated with permanent pens by the students.