|Night Hike/Evening Program Activity: Legend of the Pirates’ Eye Patch
Lesson Summary – Sight, one of our five senses can be seen as vision system. This is a lesson in Structured Inquiry. As an SOP instructor you will engage your students in an experiment after assessing their knowledge about vision, or how eye sight “works.”
Age group: Any
Venue(s): level dark place for sitting, preferably at night
Dry erase board
Dry erase markers
Optional Eye patches/blindfolds
Time: 35 minutes
10 minute introduction
10 minute hike
10 minute experiment
5 minute debrief
U1 Learning can be joyful and empowering and inspire a sense of wonder.
U2 Environments and communities require many interconnected systems
K2 Students will know that in a given place some thrive and some don’t
K3 Students will know that organisms interact in various ways
K4 Students will know that changes in an organism’s habitat are sometimes beneficial and sometimes harmful
K5 Students will know that systems are made up of subsystems and have inputs and outputs
S1 Observing: five senses and emotional
S3 Predicting, Analyzing, interpreting and representing information using creative, scientific and verbal approaches
S5 Applying what has been learned to new situations
Today we all have been outside walking, talking, eating, sitting, and learning in the daylight while the sun is up. We can see where we are going. We can see colors. We are able to explore the trails and paths easily. But what happens when the sun goes down and we are in the dark? How does this affect our vision?
Prior Knowledge Assessment questions for discussion:
Has anyone ever been on a walk in the dark without a flashlight? What was it like?
Can anyone tell me what they think is night vision?
Can anyone tell me what he or she thinks the word “nocturnal” means?
How does our sense of sight really work?
Additional questions for making the idea of vision relevant:
Does anyone know someone who wears glasses?
Has anyone ever had a difficult time seeing things?
Who can tell me how humans see?
Can anyone name any parts of the eye?
Lesson description and goal:
We are about to go on a hike in the dark to a place where we can all sit and perform a nighttime science activity. The reason why we will do this is to learn about our eyes and how they are part of a “vision system.” For our experiment we need to cover one eye and let it adapt to the dark. To pass the time I will tell you a story called “The Legend of the Pirate’s eye Patch.” While listening to the story remember to keep the one eye covered the whole time for the experiment to work properly. (If possible have the students put on an eye patch/blindfold AND cover the eye, the experiment is more effective). At the end of the story you will cover both eyes with your hands, then quickly cover and uncover each eye alternatively. Take note of any differences you experience in the vision between the two eyes. What difference in vision do you notice? Are there any differences in color, or focus? Why do you think this is happening? How do you think darkness adaptation helps or hinders human survival? Why might it be important for humans to be able to see at night?
Background Information on vision as a system of cells
Before taking the group on a hike in the dark, give a brief introduction to the lesson, starting with some questions posed in the lesson introduction. Introduce the idea of vision as one of the five senses in which we, as humans, explore, experience, and interpret our world. Students will begin to learn about how the human eye functions and how it changes based on light quantity. Students will learn about different parts of the eye and how the eye is a system of vision including cells.
Give the students some background information on the human eye and sight. Draw on a dry erase board showing a simple picture of the eye diagram (see background information and resources below) Identify the different parts of the eye in the diagram. Focus on how our eyes have many cells that work together, two of which are “rods” and “cones.” Explain the production of “rhodopsin.”
Next, explain that each and everyone will conduct an experiment on vision, or sense of sight, using our own two eyes. Part one is the night hike. During the night hike we will allow our eyes to adjust to the darkness. We will walk together in the dark, slowly, as a team, linked like a human caterpillar. (Blindfolds are optional). As we walk together try to imagine what the world is like for night animals, called “nocturnal animals.” If we are quiet we might hear some animals who are “out at night.”
Story and Candle lighting
After the short night hike (an alterative due to foul weather is an inside activity, such as Sound Shakers, which can be performed in the dark to pass the time while everyone’s eyes adjust). At the end of the hike, sit everyone down. “Now we are going to start the second part of the science experiment.” This requires covering one eye for a period of time to allow the rhodopsin to be produced in the covered eye. Hand out eye patches/blindfolds and instruct the students to use them to cover one eye. Simply using one hand cupped over the eye is fine, but using an eye patch or blindfold that covers only one eye is more effective.
Now, light a candle and ask that the students look at the candle for the duration of the story, as if that single eye was exposed to sunlight. Read the Pirate Story below, which will last 10 minutes.
***A fun way to keep the students quiet and listening is to involve the students in the story. Before the first line is read let them know that is story requires participation from the listener. Every time the storyteller says “Arrgh,” the listeners have to repeat “Arrgh” back, as if we were a band of pirates. Because, since we are all wearing eye patches…. WE ARE NOW PIRATES!
After reading the story, tell the students the experiment is over. We will make some observations. Ask them to remove their eye patch, or their hand from over their eye. Using one hand, tell them to cover each eye alternatively, back and forth, while making observations. The students will now discover the differences in vision between their eyes.
The Pirate Story1
(Narrated, if possible for a more dramatic and amusing effect, in a pirate’s voice)
“Along long, long long time ago on the open seas far far far far away there once were two pirates, twins in fact, name “Lucky” and “Lucille.” These pirates were greedy, shiftless, impatient, bad mannered, dirty and, of course, smelly. They also insisted on dressing exactly the same, they felt it gave them some sort of advantage in tricking people. They were also very, very cunning. What is cunning you ask? Cunning means wise. It means you’ve got the smarts. ”ARRGH” (and the students repeat with “ ARRGH!”)
Lucky and Lucille, you see were twins and had managed to live well on the high seas for many a year due to their cunning. They were retired, quite wealthy, surrounded by treasure. They may not have many friends, but they lived like kings because they had learned a thing or two about wearing an eye patch. You can acquire special powers by wearing an eye patch, you know. “ARRGH!”
But, it wasn’t always this way for Lucky and Lucille. When they were but a wee lad and lass, they learned the hard way that being on board a vessel can be the very death of a person. You see a long long time ago there wasn’t electricity. A long long time ago there was only oil lamps. People, and pirates, could get around at night using the light from oil lamps. What is an oil lamp you might wonder? An oil lamp is something you hold in your hand like a candle. It is a glass container full of whale’s blubber, with a wick attached. It was at one time, a fact that oil for lamps was made by melting down the blubber from a whale. The wick soaks up the gooey, stinky, liquid blubber and then it can burn for a long time. The oil lamp casts about as much light as a small flashlight. However, holding an oil lamp means you are holding fire. And fire is a dangerous thing. Arrgh (Arrgh.)
Now, how do you suppose pirates sunk other ships and captured prisoners and stole treasure? They had gunpowder. And they had cannons and guns and swords, or course. Pirates would store the gunpowder and treasure below decks. Now pirates love their treasure. Arrgh. (Arrgh). They like to check on the glimmering gold often, kike they can’t leave it alone. Now below decks it is dark. Many a time a poor wretch would go below decks with an oil lamp to check on the treasure, walk into a ladder or post and stumble or trip on something and KABOOM! The oil lamp would drop, crash and the fire would light the gunpowder. Oooooooh many a sailor and a pirate have gone down with the ship because of the darkness below decks and not being able to see.
And this happened once to Lucky. He and Lucille were on a ship and Lucky, greedy as he was, went to check on the treasure. He held and oil lamp, but he was unable to see the rope on the floor and fell. KABOOM!!!! The oil lamp broke, lite the gunpowder close by and knocked Lucky overboard, along with Lucille. It’s a good thing they were good swimmers! Arrgh. (Arrgh). They swam ashore and island and waiting until a ship dropped anchor off shore and then secretly climbed aboard. Because Lucky had been so near the gunpowder when it exploded, he was blinded in an eye. He made an eye patch to cover the grotesque scar over the hole in his head where the eyeball had existed. Lucille, his twin sister, had always dressed exactly like her brother, as I mentioned in the beginning of the story. So, she crafted her own eye patch. This way, other also had a hard time keeping them apart and often they could trick other pirates as to whom, was who.
Now this is where the story gets interesting. (Pause). Lucille, one night went to check on the treasure on this new boat, because she heard there were diamonds and jewels unlike those she had ever seen, even rubies. As she descended the ladder to go below decks she got a speck of dust in her eye, the one with the eye patch. Well, what do we all do when we have something in our eye? We rub the eye! Arrrgh. (Arrgh). So, she flipped up the eye patch and was going rub her eye when, “Holy Sunken Treasure,” she realized she could see out of the eye that had been covered!!!! Lucille had discovered the power of rhodopsin! Arrgh. (Arrgh).
From that day forth she and Lucky were able to use Lucille’s discovery to see below deck on many a ship and steal many a treasure. By wearing the eye patch for a period of time, the eye is able to adjust, produce rhodopsin and see fairly well in the dark. Over the years the twin pirates were able to climb aboard ships, pillage and plunder being able to see when others couldn’t. They were able to accumulate vast sums of gold and jewels and retire at the early age of 37. The reason you have never heard of this story before is because Lucky and Lucille only shared their secret with other pirates, who in turn only shared the secret with other pirates. And so, being as you are now all pirates, with proper eye patches, I’m sharing the secret with you! Arrgh. (Arrgh)”
After the students have participated in the experiment. This can be done as a discussion or questions for them to answer in their journals.
Ask the following questions:
While you were listening to the story, what was happening to the eye that was covered?
What was happening in the eye that was uncovered and looking at the candle?
Describe the word night vision, what does it mean to you?
What are some animals that might have night vision?
What does the word “nocturnal” mean?
Give me an example of how our eyes work as systems.
How does our vision shape or affect how we live, survive in our world?
Some students may not be comfortable in the dark. At the beginning of the activity mention that the group is a team and that we will be working together to help each other and cooperate. Ask if everyone is comfortable walking in the dark as a group and offer the blindfolds as optional, not required. Mention that at any time the instructor may say “Safety Freeze.” That means everyone must stop moving and stay still in case something is determined as unsafe. Also if a student feels unsafe at any time he or she can say “Safety Freeze,” and we should all stop and handle the situation, make it safe, correct our course, etc. before moving on.
*Bring a first aid kit and flash light
Explanation of visual as a system2
Our vision can be seen as a Visual system including the eyes, the connecting pathways through to the visual cortex and other parts of the brain. The illustration below shows the mammalian system.
Our visual systems perform all kinds of amazing jobs, from finding constellations in the night sky, to picking out just the right strawberry in the supermarket, to tracking a fly ball into a waiting glove. How do our eyes and brains recognize shape, movement, depth, and color? How do we so easily pick a friend's face out of a crowd, yet get fooled by optical illusions?13 The psychological process of visual information is known as visual perception, a lack of which is called blindness.
Introduce the idea of vision as one of the five senses in which we, as humans, explore, experience, and interpret our world. Students will begin to learn about how the human eye functions and how it changes based on light quantity. Students will learn about different parts of the eye and how the eye is a system of vision including cells.
The mammalian eyeball (Figure 2) is an organ that focuses a visual scene onto a sheet of specialized neural tissue, the retina, which lines the back of the eye. Light from a scene passes through the cornea, pupil, and lens on its way to the retina. The cornea and lens focus light from objects onto photoreceptors, which absorb and then convert it into electrical signals that carry information to the brain.
The cornea and lens bend or refract light rays as they enter the eye, in order to focus images on the retina. The eye can change the extent to which rays are bent and thus can focus images of objects that are various distances from the observer, by varying the curvature of the lens. Below is a diagram of the retina showing the different cells that make up the retina including the rods and cones4
Rods and Cones
The photoreceptors in the retina are of two types: rods and cones, so named because of their shapes. These cells are actually specialized neurons that detect light. Embedded in stacks of cell membranes in the distal portions of rods and cones are molecules that absorb certain wavelengths of light. These molecules are called photo pigments and are composed of two parts: a large trans-membrane protein, an opsin, and a smaller chromophore, which is a metabolite of Vitamin A called 11-cis-retinal. The chromophore, which is embedded in the opsin, absorbs light; in so doing it undergoes a shape change. This shape change in turn activates the opsin, setting off a cascade of events that leads to a change in the electrical state of a rod or cone cell membrane. This change in the rod or cone cell membrane is then conducted via the rod or cone axon to other neurons in the retina, and from there to the brain.
In dim light, we use our rods, which cannot work in bright light. Rods outnumber cones (120 million rods and about 6 million cones in each retina) and they amplify a light signal much more than cones. Scientists have demonstrated that absorption of even a single quantum (or photon) of light can trigger a chromophore shape change in one molecule of rhodopsin in a rod, leading to signal transmission. For transmission to occur, this initial tiny event must be amplified: the activated molecule of rhodopsin converts several thousand molecules of the next enzyme in the cascade to the active form, and this amplification continues until the electrical potential of the cell membrane changes and neurotransmitter release is affected. Cones, on the other hand, must each absorb hundreds of photons in order to send signals. Another retinal mechanism that helps us to see in dim light or to see a tiny amount of light in the dark is the convergence of rod cell signals onto other retinal neurons. Many rods (up to 150) synapse onto the same target neurons, where the signals are pooled and reinforce one another, increasing the ability of the brain to detect a small amount of light. (A synapse is a contact between a neuron and another cell where an electrochemical signal [most commonly] is transmitted to the second cell.) This convergence amplifies weak signals, but spatial resolution is lost because rod responses are averaged. That is, we cannot see fine detail using rods.
In order for our eyes to make the transition to dim light, rods must adapt after being saturated with light in brighter conditions. Dark adaptation of rods takes seven to ten minutes: during this time rhodopsin molecules, in which the chromophore components have changed to the activated state, return to the non-activated state so that they are able once again to register changes in illumination. Other changes also occur in adaptation to dark or dim conditions, including enlarging or dilating of the pupil, which is controlled by the autonomic nervous system.
Our vision in bright or moderate light is completely mediated by cones, which provide color vision, black and white vision, and high acuity, the ability to discern fine detail. Like rods, cones contain an opsin and the chromophore 11-cis-retinal, but the opsins differ from rhodopsin so that each cone is responsive to one of three colors: red, green or blue. Cones are spread throughout the retina but are especially concentrated in a central area called the macula. At the center of the macula is the fovea, where only cones (no rods) are found, and these are densely packed. When we want to read or inspect fine detail, we move our heads and eyes until the image of interest falls onto the fovea. Because the fovea lacks rods, it is easier to see in dim light by looking to the side of an object instead of directly at it. You can test this by looking to the side of a faint star so that its image falls on rods, rather than on the fovea where it probably will not register. When you look directly at the faint star, it disappears.
In contrast to the wiring of rods, only a few cones converge onto other retinal neurons to average their signals, so cones provide better spatial resolution. In fact, each cone in the fovea synapses onto only one neuron in the next relay in the retina. This gives this area the ability to transmit fine detail, such as we use in reading.
Thus, cones mediate day vision and rods take over in dim light and at night. Both rods and cones can operate at the same time under some conditions: in dim or dark conditions, rods are most sensitive, but cones respond to stimuli that are sufficiently bright. This is why we can see the colors of neon lights on dark nights.
Night vision is the ability to see in low light conditions. Biological night vision is a type of night vision, without the use of technology for enhanced images. In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in shape as they absorb light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark. Rhodopsin in the human rods is less sensitive to the longer red wavelengths of light, so traditionally many people use red light to help preserve night vision as it only slowly depletes the eye's rhodopsin stores in the rods and instead is viewed by the cones.
Sight Advantages of Nocturnal Animals
Humans have poor night vision compared to many animals due to a number o reasons. One is that the human eye lacks a tapetum lucidum. The tapetum lucidum (Latin: "bright tapestry") is a layer of tissue in the eye of many vertebrate animals. It is located in the back of the eye directly behind the retina. It reflects light back through the retina, increasing the amount of light available to the photoreceptors. This is found in many nocturnal animals and some deep-sea animals, and is the cause of eyeshine, or “glowing” eyes of cats or deer in the car headlights. The tapetum lucidum contributes to the superior night vision of some animals especially carnivores that hunt their prey at night.
A second reason nocturnal animals have superior vision to humans is that the former have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to contemporary rods, inverted rods have heterochromatin in the center of their nuclei and euchromatin and other transcription factors along the border. In addition, the outer nuclear layer (ONL) in nocturnal mammals is thick due to the millions of rods present to process the lower light intensities of a few photons. Rather than being scattered, the light is passed to each nucleus individually. In fact, an animal's ability to see in low light levels may be similar to what humans see when using first- or perhaps second-generation image intensifiers
Marjorie A. Murray, University of Washington
Peter Kaiser, York University
Geoffrey Mongomery, Howard Hughes Medical Institute
MythBusters is a science entertainment TV program created and produced by Australia's Beyond Television Productions for the Discovery Channel.
“Pirate Special,” Episode 71, 2007 Pirates wore eye patches to preserve night vision in one eye. Deemed Plausible on the show based on the following: This myth works under the assumption that the eye covered with the eye patch is already accustomed to low light conditions, while the other eye must take time to accustom. The MythBusters were sent into a pirate-themed obstacle course (which was dark, and Adam and Jamie had not seen the course in light, let alone the layout) with light-accustomed eyes and were told to complete certain objectives. Their movements were hampered by the darkness and it took them five minutes to finish. When they went back in with an eye that had been covered for thirty minutes, the MythBusters were able to complete the test in a fraction of the time. As a control test, the MythBusters then went back into the same exact room with light-accustomed eyes and ran into the same difficulty as the first test. The myth was deemed plausible rather than confirmed because there is no recorded historical precedent for this myth
1 Pirates are often portrayed as having eye patches and local IslandWood lore seems to stem from a common myth that pirates used eye patches for superior night vision. Seems IslandWood instructor are not the only ones spreading the story.
2 Wikepedia search “visions system”
4 Kaiser, Peter, from the Joy of Visual Perception