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Speaker 1: Welcome to Brainstuff, a production of iHeartRadio. Hey Brainstuff, Lauren Fogelbaum. Here.

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Speaker 1: You may not spend a lot of time staring off

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Speaker 1: toward the horizon trying to make out distant objects, But

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Speaker 1: if you do, how far would be possible for you

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Speaker 1: to see? Pretty far, as it turns out, if you're

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Speaker 1: a person with normal visual acuity a rating of twenty twenty,

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Speaker 1: and you gaze out in a horizontal line from around

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Speaker 1: five feet or one and a half meters above the ground,

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Speaker 1: you can see for about three miles or five kilometers

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Speaker 1: into the distance, which is the point at which Earth's

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Speaker 1: curvature bends away so that the surface is no longer

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Speaker 1: in view. And while your ability to discern objects depends

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Speaker 1: upon their size and how much light the distant object

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Speaker 1: emits or reflects on a dark night, it's possible to

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Speaker 1: see a single candle flame from about one and a

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Speaker 1: half miles or two and a half kilometers away. To

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Speaker 1: understand how our eyes can see a distant object like

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Speaker 1: a candle flame flickering, it helps to know something about

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Speaker 1: how normal vision and the human eye work. A While

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Speaker 1: visual acuity varies among individuals, the naked eye is definitely

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Speaker 1: an impressive piece of equipment. It's capable of twelve times

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Speaker 1: the resolution of a high end smartphone's camera. We can

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Speaker 1: perceive a nearly infinite range of colors and shapes, as

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Speaker 1: will as detect very small changes in brightness and minute

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Speaker 1: amounts of motion. Human vision is a complex, intricate process.

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Speaker 1: A light emits from or reflects off of objects, and

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Speaker 1: then passes through the cornea and the lens of the eye,

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Speaker 1: a which bend and focus light onto the retina at

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Speaker 1: the back of the eye. There a layer of tiny

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Speaker 1: nerve cells called rods and cones are activated by the

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Speaker 1: light and send electrical impulses through the optic nerve to

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Speaker 1: your brain, which creates an image or visual perception. For

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Speaker 1: the article, this episode is based on How Stuff Works.

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Speaker 1: Spoke with doctor Eric Lowell Singhman, a practicing optomologist with

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Speaker 1: the University of Maryland Medical System and the Professor of

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Speaker 1: Optomology with the University of Maryland School of Medicine. He said,

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Speaker 1: the eye turns light into biometric energy transmitted to the brain.

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Speaker 1: Some nerve cells see colors, some see black and white,

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Speaker 1: Some see motion only in one direction, others see motion

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Speaker 1: in another. Direction, some see shapes, some just look at

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Speaker 1: the overall ambient lighting. Together, those cells work as a

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Speaker 1: team to tell your brain what to visualize, a transmitting

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Speaker 1: information about what's moving and what colors things are. The

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Speaker 1: singman said, these are actually different, separate channels, and then

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Speaker 1: your brain takes the images and converts them into something

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Speaker 1: that your conscious mind can appreciate. In addition, the human

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Speaker 1: visual system also transmits and creates visual information that you

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Speaker 1: you aren't even necessarily aware of, for example, the amount

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Speaker 1: of ambient light, which helps control your natural rhythms of

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Speaker 1: day and night. Without obstructions in the way, you can

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Speaker 1: see about three miles where five kilometers into the distance

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Speaker 1: from ground level before you reach the point where earth

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Speaker 1: curves enough to block your view of what's on the ground.

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Speaker 1: But that's based on a hypothetical person who's five feet

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Speaker 1: or one and a half meters tall. If you're taller,

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Speaker 1: you could see farther based just on your angle of sight. Similarly,

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Speaker 1: the higher you go in elevation, the farther into the

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Speaker 1: distance you can see. A person looking out from the

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Speaker 1: observation deck of the world's tallest building eight hundred and

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Speaker 1: twenty eight meters skyscraper in Dubai that's about twenty seven

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Speaker 1: hundred and seventeen feet. Reportedly can see for sixty miles

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Speaker 1: or about one hundred kilometers, and our visual acuity extends

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Speaker 1: beyond the horizon. Even if the curvature of the Earth

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Speaker 1: didn't exist, and instead Earth was a flat surface, would

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Speaker 1: have an uninterrupted visual angle from our eyes to the

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Speaker 1: farthest object visible. This is evidenced by the fact that

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Speaker 1: we can see extremely distant objects in space. As long

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Speaker 1: as the sky is clear and the object is bright

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Speaker 1: enough on a dark night without light pollution, you should

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Speaker 1: be able to see the Andromeda galaxy, which is two

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Speaker 1: point five million light years away. That's the equivalent of

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Speaker 1: fifteen quintillion miles or twenty four quintillion kilometers on Earth.

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Speaker 1: Our atmosphere is also a major factor in how well

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Speaker 1: you can see distant objects. Theoretically, in a vacuum, there's

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Speaker 1: no limit to how far away your eyes could see,

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Speaker 1: since light rays can travel an infinite distance. But even

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Speaker 1: though our air seems insubstantial, it actually contains a lot

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Speaker 1: of stuff. Houstuffworks. Also spoke with doctor Timothy McCully, a

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Speaker 1: professor and chair in the Department of Optomology and Visual

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Speaker 1: Science with McGovern Medical School at UT Health Houston explained,

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Speaker 1: you're seeing through the atmosphere and yellow particular matter in

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Speaker 1: the air is scattering the light. So depending on the

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Speaker 1: medium that the light is traveling through, those electromagnetic waves

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Speaker 1: will or will not reach your eyes. A similar problem

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Speaker 1: occurs on a foggy day or night, or during rain

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Speaker 1: or snow. That's why we're able to see that candle

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Speaker 1: flame flickering a long way off when there's a dark,

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Speaker 1: clear night sky, but not when the light is impeded

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Speaker 1: by precipitation, even though we can see a glowing object

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Speaker 1: far in the distance. The human eye does have its limitations,

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Speaker 1: especially when it comes to visual acuity, which is the

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Speaker 1: scientific term for sharpness of vision. Our cone cells, the

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Speaker 1: photoreceptors that are sensitive to red, green, and blue wavelengths

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Speaker 1: of light, are concentrated in the macula, an area in

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Speaker 1: the middle of the retina. Our sharpest vision is at

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Speaker 1: the center of the macula, in a spot called the

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Speaker 1: phobia that can zero in on a small part of

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Speaker 1: the world in front of you. A singmund said, you

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Speaker 1: might think that you have a very wide visual field,

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Speaker 1: but the reality is that your area of clearest vision

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Speaker 1: is actually just a few degrees. You don't see the

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Speaker 1: whole world clearly. If you take a big letter, eat

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Speaker 1: a big as your hand and move it about fifteen

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Speaker 1: to twenty degrees away to the side, you wouldn't be

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Speaker 1: able to tell what that letter was. The clarity of

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Speaker 1: your vision drops pretty quickly once you get off center.

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Speaker 1: That's why macular degeneration and eye condition in which the

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Speaker 1: macula becomes damaged so that you lose that central vision,

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Speaker 1: can be such a serious problem for people who get it.

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Speaker 1: The risk increases as you get older. But your eyes

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Speaker 1: are only part of the equation. That's evident in people

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Speaker 1: who have some sort of brain injury that interferes with

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Speaker 1: their vision, even if there's nothing wrong with their eyes.

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Speaker 1: Singmund said, you've got to remember that the brain is

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Speaker 1: a really big part of this process. There are types

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Speaker 1: of brain damage where you can't see something move, or

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Speaker 1: where you can't recognize faces. You'll look and pick out

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Speaker 1: an eye or a nose or mouth instead of the

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Speaker 1: whole face. The brain can also perform tricks to make

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Speaker 1: up for the eye's shortcomings. Singmann recalls the case of

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Speaker 1: a patient who, after eye surgery, suddenly discovered that when

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Speaker 1: he covered that eye, he couldn't see out of the

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Speaker 1: other but supposedly good eye. When a doctor examined the patient,

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Speaker 1: it was discovered that he had a cataract, a natural

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Speaker 1: clouding of the lens on that eye, but apparently had

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Speaker 1: never noticed it because of his brain's ability to filter

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Speaker 1: out the blur. Missingman said, that's a classic trick. The

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Speaker 1: brain can shut things off. Today's episode is based on

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Speaker 1: an article how far can the human Eye see? On

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Speaker 1: how stuffworks dot com written by Patrick J. Kiger. Brain

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Speaker 1: Stuff is production by Heart Radio in partnership with how

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Speaker 1: stuffworks dot Com and is produced by Tyler Klang. Four

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Speaker 1: more podcasts from my heart Radio, visit the iHeartRadio app podcasts,

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Speaker 1: or wherever you listen to your favorite shows. M