A2.4.2.VisualPerception - Belle Vernon Area School District



Name KEY Visual Perception – 60 Informal PointsIntroductionExcept for your brain, the eyes are the most complex organ you possess. Your eyes are composed of over two million working parts and their coordinated action can instantaneously set in motion hundreds of muscles and organs in the body. Your eyes allow you to track a fly ball into a baseball glove. They can help you pick out the perfect color to paint your room. Your eyes can help you find your best friend at a crowded concert. These amazing organs process light in a way that allows us to perceive color, to judge depth, to sense movement, and to enjoy optical illusions. All these components of a visual scene merge so we have one combined sensory experience. In the last activity, you explored the anatomy of the eye and began to think about the function of each structure you dissected. The cornea and lens of the eye bend or refract light rays as they enter the eye so that focused images fall on the retina. If the eyeball is an abnormal shape, the light will not focus on the correct point in the eyeball and vision may become blurry. Corrective lens can be used to compensate for this change in shape and bring the world back into focus. In this activity, you will explore the physiology of human vision by performing a series of tests to explore and assess many characteristics of human visual perception, including visual acuity, color vision, peripheral vision and illusions. You will also use a replica of the human eye to explore how the eye focuses light and how corrective lenses can help fix problems with this focus. As you complete this activity, think about how the property you are working with is related to the specific structure of the eye. ProcedureActivity #1: Visual AcuityBackground Information: The amount of detail the eye can distinguish is known as visual acuity. Light waves pass through the cornea, aqueous humor, lens, and vitreous body and then onto the retina. As the light travels through the eye, it is bent of refracted, allowing a large amount of light to be focused on a small area of the retina. The image of the object being viewed is projected upside down and backward onto the retina. Within the retina are photoreceptors known as rods and cones, which connect to neurons. These nerve cells send visual impulses to the brain via the optic nerve, where the visual cortex of the occipital lobe of the brain processes and interprets the stimuli. The Snellen eye examination chart uses lines of progressively smaller letters to measure how well the subject’s eye distinguish details, at a distance of 20 feet, compared to the human norm. Visual acuity measurements are stated as a series of two numbers. The first number is the distance from the subject to the chart in feet. The second number is the distance in feet that a normal eye can see as clearly as the subject can at that distance. For example, normal human vision is 20/20. A score of 20/100 means that the test subject can see at a distance of 20 feet what a normal human eye can see from 100 feet away. On the other hand, a score of 20/15 means that the subject can see rom 20 feet away what a normal observer must move 5 feet closer to see equally well. Normal vision is called emmetropia. Hyperopia, or farsightedness, makes it difficult to focus, especially on nearby objects, because the image strikes the retina before it is properly focused. Hyperopia occurs if the eyeball is not deep enough or if the lens does not have enough curvature. Myopia, or nearsightedness, causes distant objects to be out of focus because the image is projected in front of the retina. Myopia occurs if the eyeball is too deep or if the lens has too great a curvature. The Snellen eye examination chart is often used to detect myopia.There is a visual Acuity Chart hanging on the bulletin board in the front right of the classroom. Take turns standing behind the taped line (20 feet from the chart) and determining what your vision is for each eye.Cover the left eye and read the line with the smallest letters you can see. The numbers on the left tell your vision for your right eye. Repeat, covering your right eye to determine your left eye vision. Record your results below:Right Eye Visual Acuity: 20/______Left Eye Visual Acuity: 20/______Answer the following question in the space below: Your friend swears that no one can possibly have better than 20/20 vision. Use what you have learned about the Snellen eye examination chart and what numbers such as 20/20 really mean to set him/her straight.Activity #2: AstigmatismBackground Information: Astigmatism is a condition in which the cornea of the lends is irregularly shaped. This asymmetry causes incoming light rays to refract and converge improperly. Therefore, the light rays do not focus at a specific point on the retina. This results in blurred or distorted images. Many people possess some degree of astigmatism, whether they realize it or not.The test for astigmatism uses a picture that resembles a spoked wheel. A person with astigmatism will see thick, dark lines in certain areas when the chart is viewed from a distance.If glasses are usually worn, REMOVE them for this test. Contact lenses DO NOT have to be removed.There is an Astigmatism Test Chart hanging on the bulletin board in the front right of the classroom. Take turns standing behind the taped line (10 feet from the chart) and determining if you have astigmatism.Cover your left eye; view the astigmatism test chart and state whether or not any thick, dark lines are observed. If thick, dark lines are observed then the eye does have astigmatism. Repeat, testing for astigmatism in your left eye. Answer the following questions to record your results:Is astigmatism present in your right eye? __________Is astigmatism present in your left eye? ___________If yes, were you aware of the astigmatism before today? __________If yes, do you wear glasses to correct the astigmatism? __________Answer the following question in the space below: Explain what is happening in the eye to cause astigmatism. How does this impact how you see?Activity #3: Blind SpotBackground Information: The blind spot is the area on the retina that contains no photoreceptors. It is located where the optic nerve exits the eye on its way to the brain. An image that falls on the area cannot be seen. The blind spot is located using a blind spot diagram like the one below.Obtain a blind spot diagram. Hold the diagram at arms length, with the dot to the outside and the X directly in front of the right eye.Slowly move the diagram closer to your eye until the dot seems to disappear.Have a friend measure the distance from your face to the card (in cm.)Repeat the process for your left eye.Record your results:At what distance did the dot disappear for the right eye? _______cmAt what distance did the dot disappear for the left eye? ________ cmAnswer the following question in the space below: List at least two circumstances in which it would be important to be aware of your blind spots?Driving, playing sportsActivity #4: Color VisionBackground Information: The retina of the eye possesses tow types of specialized nerve cells known as photoreceptors. They are called rods and cones because of their distinctive shapes. Rods function in dim light and perceive shades of gray, like what you see when your eyes adjust to darkness. There are about 120 million rods in each eye, located at the front of the retina. Cones function in bright light and provide sharp, colorful daylight images. Human eyes contain about 6 million cones concentrated around the center of each retina. There are three different types of cones – red cones, green cones, and blue cones- and each type is sensitive to a different range of wavelengths of light. Different types of cones function together to interpret colors other than red, green, and blue. For instance, in order for the eye to see yellow light, red cones and green cones must work together.If any of the three types of cones do not function properly color perception deficiency occurs. Total color perception deficiency is very rare, but partial color perception deficiency is common, especially among men. The most common type is red-green color perception deficiency, which occurs when red cones are missing or do not function. A person with this color perception deficiency, which occurs when red cones are missing or do not function. A person with this color perception deficiency cannot distinguish between red light and green light. Open the booklet containing the mounted strands of yarn and place it on a flat surface.Mix the loose strands up in the bag.Have a partner time you (in seconds) as you match the strands from the bag with the strands in the booklet, laying them side-by-side in the booklet. Record your time below:Time it took me to match all strands correctly: _________ secondsReflect on this color vision activity by answering the following questions.Were any of the strands of yarn difficult to match? _______ If yes, list the colors that were difficult to match: __________________________________________To your knowledge, are you color perception deficient? _________Is anyone in your family color perception deficient? __________ If yes, who? ______________________________________________________________Given that the previous question asks about family members and color perception deficiency, what can you infer about the development of this condition?Some cities hang their traffic lights from left to right, rather than from top to bottom. Explain why this might cause a problem for a driver with red-green perception deficiency.Explain the specific roles of rods and cones in the eye.If we have three different types of cones – red cones, blue cones, and green cones – how do we see such a wide range of colors?Activity #5: Illusions (Optional)Background Information: Optical illusions are deceptive, self-contradictory, or misleading images. These visual tricks actually take place in the brain rather than in the eye. It is the job of the visual cortex of the brain to decipher the images sent form the eye and to make sense of them. However, surrounding objects, intense colors, distortions of expected patters, preconceptions, and many other factors can cause the mind toe “see” and interpret an image differently.Look through the optical illusion cards and see if you can figure out how your mind is tricking you!Conclusion QuestionsRead the article Refractive Errors and Refraction: How the Eye Sees at . Watch the animations on the right hand side that show how light interacts with the eye. Think about the way in which structures in the eye help translate light into images and describe in the space below. Explain how rods and cones in the eye help the police officer in pursuit of a suspect. What other properties of sight help this officer complete his task?The rods give the officer the vision and the cones help identify certain colors. The rods are responsible for vision at night because they are much more sensitive than cones. Rods are responsible for black and white colors which are much more easily seen in our peripheral vision than vibrant colors. At night, it is nearly impossible to see any color besides black and night which is why the rods allow the officer to adjust his eyes in darkness when needed. Depth perception also helps the officer during a chase because he is able to judge different distances quickly and react. Without depth perception, he would be unable to follow and chase the suspect in his car. The rods in his peripheral vision also contribute to when he is chasing the suspect. When the suspect moves his car fast or changes lanes or swerves down a street, the rods and cones in the peripheral vision will allow the officer to detect this change and follow and chase the suspect more accurately.What is refraction? What does it mean when we say that light is refracted as it enters the eye?The fact or phenomenon of light, radio waves, etc., being deflected in passing obliquely through the interface between one medium and another or through a medium of varying density. A refraction means that the light is not bending properly when it passes through the lens of your eye.Which parts of the eye are most important when it comes to focusing light so we can see a perfect image?The lens is the most important when it comes to focusing light so that we can see a perfect image. It focuses the light and images on the retina. As well as the pupil- the pupil is responsible for controlling the amount of light to enter into the eye.Lenses are described as convergent or divergent depending on how they refract light. What is the difference between these two types of lenses? Based on what you have learned, do you think the cornea and the eye lens act together as a convergent or divergent lens? Explain.Divergent lens are prescribed to people who have myopia or near nearsightedness. They need a divergent lens because their eye ball is too long there for the light needs to come together later in the eye to provide a clear image. In contrast, a convergent lens is for those who have too short of an eyeball or hyperopia. The light must come together quickly so it is able to be refracted off of the retina at the proper time. The cornea and the eye lens act together as a convergent lens, causing the light to bend and hit the retina.Think about the optical illusions you observed. Explain the relationship between “seeing” with the eye and “perceiving” with the brain.When the eye sees an image in front of it, the brain quickly assumes it is that of a past image seen. Therefore, it assumes it to be something it is not because it has a memory of a similar image.Do you think it is possible for a person to be blind, but have no problems with the structure and function of his/her eyes? Explain your answer.Yes, because the occipital lobe controls vision, not the eyes. So, the eyes can have no problems and a person can be blind if they have serious damage to their occipital lobe.How do our other senses -- taste, smell, touch and hearing -- influence communication within the body? Provide an example for each sense. Taste- If you taste poison, your body stimulates a reflex to stop eating the potentially harmful substance. Smell- If you smell a foul odor you your reflex is to hold your breath in an effort to prevent inhalation of a potentially harmful chemical or substanceTouch- If you put your hand on a hot stove, the pain receptors in your hand tell your brain to take your hand away from the hot surface.Hearing- If you hear a loud noise, such as a gunshot, your instinct is to run away from the potential danger. ................
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