Too often, we take our bodies for granted. But under pressure, our bodies can show us how extraordinary they truly are. This complex machine grew out of millions of years of evolution. So?intricate, we are still mystified by many of the things going on inside us. A hidden world, but one we can now explore in 3-D as never before.

mystify: to confuse someone by being or doing something very strange or impossible to explain

? Our sight relies on the most complex system in our bodies.?Using three quarters of our brain power?when we're challenged,?our eyes?focus on the smallest detail at lightning speed.

? They allow us to see in the dark, even to see the magic of the impossible. Our brain allows us to see even while we sleep.?And someday we may be able to see without our eyes... That's how extraordinary our sight?truly is when we are pushed to the limits.

HUMAN BODY PUSHING THE LIMITS

SIGHT

? A murder suspect races?through downtown Los Angeles.

? Pursuing him is LAPD officer Stan Berry.

? What he's got to do in this?super-fast world is to figure out what matters and what doesn't at 100 miles an hour.

? And to keep up with the suspect without crashing.

? "I need to know if a truck?is?coming to the left of me... I?also need to focus on what's?ahead of you. Is there pedestrians walking down the street. And then also try?to keep up with the?fleeing suspect as well."

? Nature designed the eyes to let him do just that.

? Sight guides the human body.

? "2 1 900, I am..."

? Many animals have special kinds of vision, but in humans we can do it all. Like no other creature on earth, our vision can distinguish around 10 million colors. Switch focus from infinity to mere inches in a fifth of a second. Pinpoint detail in the brightest sunshine or?darkest shadow. Take in a wide-angle view?of all most 180?degrees. All of this takes the massive power of the human brain.

pinpoint: very exact

? "70% of the neurons in the brain in some way subserve the visual system. It's been given an extraordinarily high degree of emphasis by?all the mechanisms that have gone into its creation."

neuron: 神經(jīng)元

subserve: to promote the welfare or purposes of

? Human eyes?function as?survival sensors, giving us essential information at the crucial time. Berry constantly relies on them. The eyes'?mechanics are the most complex in the body. Their intricacy is unmatched.

? As a ball, the eye?pivots in all directions, locking onto moving targets. it does so with the help of unlikely allies, 2 cups of fat, shock absorbers for the eyeballs.?

pivot: to turn or twist

? Light enters through an aperture in the iris, an?elastic mesh of interlocking fibres. in bright light, it snaps down to the size of a pinhole in a fifth of a second.

aperture: a small and often narrowing opening, esp. one that allows light into a camera

iris: 虹膜

? Light hits the lens, not a hard disk, but a bag of fluid.?The lens projects an image, the size of a large postage stamp, onto the retina at the back of the eye.

len: 晶狀體

retina: 視網(wǎng)膜

project: to cause a film, image, or light to appear on a screen or other surfaces.

? Then the retina, a mass of nerves, send impulses to the brain. Surprisingly, the right eye signals?the left side of the brain, and the left eye transmits to the right side.?

? Our eyes have evolved a crucial feature that still keeps us from going extinct.

? 20 minutes into his chase, officer Berry?is about to test that feature to its limits. Speeding into a dangerous intersection, he faces questions literally involving life or death.

? Is anything moving?

? Where is it?

? What is it?

? A vehicle is stopped ahead blocking the way. To the right a car speeds toward the intersection. On the left, a?third driver about to move. But suddenly something else comes into view, and here's where the human eye's?design pays off.

? At the back of the eye, most of the retina consists of millions of rods. These cells see no color or detail, but let anything,?anywhere in our field of view move and the rods spot it.

rod:?視桿細胞

? The eyes swivel to look directly at the vehicle. Now, other cells at mid-retina?kick in.

swivel: to (cause to) turn around a central point in order to face in another direction

kick in:?something begins or starts to have an impact or effect. For example, if you take medication and someone asks when it will start working, you might say, "It usually takes about 30 minutes for the medicine to kick in."

? Pinhead-size dots?hold?6 million cells called cones. They're all about color and detail.

cone: 視錐細胞

? "That's why when we look at something, we look directly at it because we have our highest visual acuity right in the center."

acuity: the ability to hear, see, or think accurately and clearly

? Locking his eyes on the moving object, officer Berry can judge speed, direction and danger. The brain response sending signals an amazing 180 miles per hour to his hands and feet in time to clear the intersection.

? This is one of hundreds of life or death decisions that?officer Berry makes to bring the 40-minute chase to a safe end.

? He does this, thanks to the eye's incredible skill at adjusting when information threatens to overload what we're seeing. This ability matters as much today as it did for our ancestors. Evolution left us with another skill, one that's still priceless.

? In?the dark, we can make out the world with only the smallest of clues. When a fire fighter enters a smoky building, for instance,

??"Eyesight when it comes to being a firefighter is everything. The problem is that when you do go to the fire or you?do go into some type?of structure, your eyesight is taken away from you."

? Shadows and heavy smoke pose?the harshest test of our ability to see in the dark.

? The will to live through a fire depends on our skill at navigating the murderous darkness of smoke-filled rooms. Firefighters reached a house in Bradenton, Florida. But they don't know if anyone is trapped inside.

? Now, firefighter Dan Fleming enters a dangerous world of shadows and shapes. So murky and cloudy, you'd think it impossible to see anything.

murky: dark and dirty or difficult to see through

? Dan struggles to build a picture of the whole house from fragments he makes out in the haze.

haze: something such as heat or smoke in the air that makes it less clear, so that it is difficult to see well

? How is the house laid out? Where is the fire??Are there any?survivors?

? "You're trying to determine what the house looks like, what the occupants are about, who?would be inside this home."

? Despite the darkness, Dan's eyes immediately start to adjust.

? They have amazing sensitivity.?In complete darkness, from 14 miles away, we can detect the light from a single candle.

? "You try to find bits and pieces of light to help you find your way through."

? In low light, you?rely on the rod cells that cover most of the retina. Highly sensitive, they only register black and white.

register: to detect or perceive

? But Dan?needs to see in color.?He is searching for a fire.

? "It was very faint at first. Thought to myself, that must be the seed?of the fire. Very orange glow.?Really orange."

? "To see color, you use cone cells at the retina's?center. We get all our colour vision from being able to distinguish only three colors. The cone is?sensitive to different colors. There is those that is?particularly sensitive to blue light,?those to green light and those to red light, and they need a lot more like to fire. So if they get enough of the photons of the right color they fire and say to you, there's a spot of green or red or blue at this point."

photon: 光子

? Using these red,?blue and green signals, the brain creates an impression spanning the entire visual spectrum, a?range of over 10 million colors.

? Color vision leads Dan straight to the fire.

? "To my surprise, it?went out very quickly. And I started scanning around to see what else was in that room. Whenever you can get glimpses, that's so important, and I'm taking the whole room in as i'm scanning."

? In a flash, Dan's brain calculates what has to be there, even though he sees only tiny fragments. This is what our brains do constantly. Fill gaps with data from our visual memory bank.

? ? In fact, our brain interprets most of our vision out of a lifetime of stored images. Then Dan recognizes?something. A?white shape.?A?cup of coffee.

? Black and white squares. A half-completed crossword. Are these crucial signs that someone could still be in the house.

? There, through the smoke, Dan sees a?blurred and unusual shape.

blurred: difficult to see

? "My initial instinct was, there's?something on the couch. I'm not sure what it was. There's a saying, when in doubt check it out.?And that's what I did."

? Dan Fleming has used his brain's visual memory to transform a blur into the outline of a body, saving a man's life.

blur: something you cannot see clearly

? No computer can match human vision for its incredible power and range. But what if we could harness computers to stream images directly to the brain? What if someday we could see without eyes?

? The power of human sight comes from millions of years of evolution. We can't even understand it. And technology today can't begin to match the sophistication of our incredible eyes.

? But for the first time, science is pushing human vision to new limits by connecting directly with the brain's vision center. This means that one day we might even see the invisible world of infrared, have x-ray vision, or plug video games straight into the brain.

? Sherry Robertson from Missouri is about to step into this virtual world.

? "I was in a car accident when I was 19 years old. I was passenger in the car and the driver fell asleep at the wheel when we hit head-on with a small truck and then?both of my eyes were just destroyed."

? Hoping to regain her sight, Sherry volunteers for a pioneering procedure. It involves marrying technology to the huge processing power of the brain's visual cortex.

cortex: 大腦皮層

? “It was a chance for me to be able to see again when the doctors had always told me I would never see anything.”

? Sherry?is about to have an extraordinary experience. Doctors drilled through both sides of her skull, exposing her brain. Then they implant two triangular plates, each holding 200 tiny electrodes, directly onto Sherry's?visual cortex. Finally, the surgeons string cables from the plates to terminal sticking out of her skull. Next, the electrodes run through a computer to a camera on Sherry's?eyeglasses. All of this technology is designed to help Sherry regained some sight.

electrode: 電極

? “It was, I guess,?quite a shock for me, when I felt my head and I felt these terminals sticking out behind my head because I guess I really wasn't expecting that."

? But for her to see what the camera sees, many things have to happen and that requires a step into the unknown.

? Each electrode touches a different part of Cheri's brain. When the system triggers an electrode, she sees a flash somewhere in her visual field, where the doctors don't know. So, they trigger each electrode one-by-one to learn where in her visual field Sherry?sees flashes now. When she sees a flash, Sherry?points to top,?bottom, left or right. With every electrode?mapped, the doctors connect the camera, making certain that what it's like matches the flashes in Sherry's brain.

? Finally, with the camera mounted,?Sherry's?mother helps connect the gear to try the new settings.?

? Has technology helped bring Sherry's sight back?

? "When I finally saw my first light, it took my breath away, I could not believe it. Oh, we knew it worked. And that was very, very thrilling for me."

? We can't know what Sherry sees, but we do know what she describes.

? This early in the project, doctors have activated only some of Sherry's electrodes.?Eventually they hope to connect many more, vastly improving the scope of her vision.

? "Because I can only use ten of my electrodes. Whenever an object goes in front of my camera, I will see two flashes of light. And they're about?the size of a big? P,?M, and?M,?just one on top of the other. And that?way?I know, that there is an object there. Now, I'm not sure what it is. When I am able to use all of my electrodes, however, I will be able to see the outlines of things I'm looking at. So I'll know if i'm looking at a tree or person or car. So I'll?actually know what I'm looking at."

? No one pretends that Sherry's vision is back, but the fact she can sense any of the visual world makes her an extraordinary pioneer. Imagine if one day we could feed?complete vision signal directly to the brain. What could we see? We might see a world that we've been blind to, it as if we were seeing through night-vision lenses（夜視儀）, infrared cameras, even x-ray vision.

? The human body has extraordinary visual capabilities.A lifeguard?uses them every day to decide when swimmers are playing around or when someone is in trouble.

? Imagine a summer weekend on a California beach,?dense with bodies. But for one onlooker, this seemingly calm?scene?maybe a series of accidents waiting to happen.

onlooker: someone who watches something that is happenning in a public place but is not involved in it.

? How does a lifeguard know when a?raised arm means,?"I need help" not?"Hey?this is fun?"

? The guard's skill at spotting that one desperate person among thousands is phenomenal,

truly testing his sight and understanding.

phenomenal: extremely successful or special, especially in a surprising way

? We see the way we do so we can spot danger to ourselves, but nothing is threatening the lifeguard. In fact, the eye observing a harmless pattern across its view, normally relaxes. Motion-sensing rod cells switch off when they detect action that's consistent and constant.

? So the lifeguard has to trick his eyes.

? He does this by scanning, forcing his eyes to lock onto small details.

??”O(jiān)ur front-line defense are the tower guards and their job is to scan the water, so their eyes are moving across the water and letting their brain filter out?information that they see,?looking for something wrong,?looking for that odd one out that truly is in danger."

? Taking in?all this information is hard work. Human sight has only two degrees of detail vision at the centre. To?check the whole beach, the lifeguard sweeps, jumping from point-to-point for detail. Each jump is called a saccadic.

sweep:?move or traverse across an area in a systematic manner, often with the intention of searching or inspecting it thoroughly. In the context of the lifeguard checking the whole beach, "sweep" suggests that the lifeguard is methodically covering the entire beach area by moving from one point to another, possibly scanning for any potential hazards or signs of distress

? "A saccadic?is the movement that the eyes make together when they're looking directly at one thing, and all of a sudden, they look at something else. We have mechanisms that?wire the muscles that move our eyes to the image, and we can quickly lock-on to a new image all at once."

? The saccadic function?let's him jump visually from each potential risk to the next. He repeatedly scans his field of vision, updating?his visual memory?every few seconds, but even more is going on as he uses another complex skill, interpretation of detail.

? "Being a season lifeguard, I can recognize distressed victims?in?the water, whether they look really laboured, whether they're comfortable or not by their body language. Those are sorts of indicators allow you to recognize a rescue before it happens."

distressed: upset or worried

laboured: needing a lot of effort, often because someone is tired

? The muscles rotating our eyes give us an outstanding breadth of view. Even while perfectly still, we can rotate our eyes from far left to far right in a quarter?of a second. So when a riptide suddenly overcomes?a swimmer,?Drew knows within moments.

riptide: a dangerous area of strongly moving water in the sea, where two or more currents (= water moving in a particular direction) meet

? Now he has to judge whether the swimmer can get back to shore, whether he' s too far out for a rescue attempt, or whether despite the riptide,?Drew has a chance of reaching him.?That split second?call demands an accurate sense of?distance.

split-second:?It is used to describe something that happens or occurs in an extremely brief moment or instant. It is often hyphenated when used as an adjective, such as in "a split-second decision" or "a split-second reaction." The hyphenation helps convey that it is a compound adjective formed by combining "split" (meaning divided or separated) and "second" (referring to a unit of time).

call:?a decision or judgment made in a particular situation

? "We have two eyes and they're separated by this distance, and that permits each image to be slightly different than the other image; and that slight dissimilarity gives me a sense of how far away something is."

? We constantly judge shifting distances,?hardly giving the process a thought. But this special process only occurs in humans and other predators for spotting and catching prey.

? That's the hunting skill, the lifeguard uses to home-in on the struggling swimmer.

home-in:?a phrasal verb that means to direct one's attention, focus, or movement toward a specific target or destination. It implies the act of honing in on something with precision or accuracy.

? We can all find the detail we need in a busy scene when it's for our own safety. But when guarding the lives of others, that same skill requires training and intense focus.

? In day-to-day life, we fill in parts of the passing picture,?as our visual memory makes shortcuts and assumptions, putting together a picture of the world that seems complete. What happens when those assumptions prove wrong?

? That's where we get the phrase "smoke and mirrors," the tools of visual confusion illusionists use to exploit the science of sight to fool our vision.

illusionist: an entertainer who performs tricks where objects seem to appear and then disappear

? Movies presents spectacular sights and grand illusions.

? This is a movie set, but how big? What looks like a space station on an alien planet?is a trick.

? A?tiny model near the camera and a full-size stage further away. Filmmakers are essentially the masters of illusion. Here we see the two actors and we assume they're?in a massive set, because we don't have the ability to think?"hold on a second, this?is just a small set, and the actors are considerable distance away from it".

? They show?illusions trip up the perceptual system. A system that is normally right. Here, we're exploiting the loop holes when suddenly they're very, very wrong.

trip up:?means to cause someone to make a mistake or stumble in their perception or understanding

loop hole: a weakness or gap in a system, rule, or process that can be exploited or taken advantage of

? Illusions exploit how we see the world. They rely on the difference between what the eye sees and what the brain understands.?Magicians have always relied on this delicate confusion.

? "I'm Marco Tempest. I'm a magician. Now, here's a little optical illusion. Now, let me show you just how easy it is to fool the eyes. I have a three-dimensional objects right here, and I also have?a two-dimensional object. This paper disc. Now if I place?the?three-dimensional object next to the two-dimensional object, something very strange is happening.?Check this out.

? It looks like the two-dimensional object has become three-dimensional, but if we get rid of the three dimensional object, something else is happening. Check this out.??

? If you see the cube now looks like it's completely two-dimensional."

? From another angle, the secrets reveal themselves.

? Underlying the trick is a genuine scientific principle explaining how our brains build a three-dimensional visual world.

? "This is all about how we read perspective.?The three-dimensional cube once established as being three-dimensional stays three-dimensional in our minds, even when we look at the tape lines, it still looks three-dimensional to us. It's almost like our eye fills in the missing information and wants the?object to be three dimensional. And that's where I get you."

? Our world is filled with visual information. The brain copes by creating shortcuts, relying on experience to fill gaps with informed guesswork.

informed: having a lot of knowledge or information about something

? Light and?shadow.

? The size, shape and distance of objects.

? We assume the world operates according to fixed rules, but sometimes we're just plain wrong.

? Take this ordinary looking room.

? "I look to be much, much larger than Sarah, and this isn't camera trickery, instead it's an incredible illusion. Because when I'm in this corner, Sarah suddenly looks much, much larger than me. And?in reality, the two of us are roughly the same size. It's all to do with the amazing way in which this room has been constructed."

trickery: the activity of using tricks to deceive or cheat people

? Not regular in shape at all. The room has a bizarre geometry that's disguised as normal.

? We see square rooms so often. We fool ourselves into thinking this is one too,

? "It's amazing how easily our eyes get fooled. We?see an?umbrella, and?we immediately

think of rain. But on a beautiful day like today, we don't really need an umbrella."

? Magicians exploit more than our assumptions about the objects and spaces around us. You're about to see what looks like a simple trick, but it has a deeper, more illusive level.

? "Welcome to the color-changing card trick, using this blue-back deck of cards. Now the idea is very simple. I am just going to spread the cards in front of Sarah and ask her?to push any card towards the front of the table."

? "Okay, I'm going to go for this card here."

? "Excellent. Sarah could have chosen any of the cards in the deck, but she selected the one which is now laying face down on the table. I'm going to ask her to look at the card and tell us what it is."

? "The card I chose was in fact?the three of clubs."

? "The three of clubs, excellent, that comes back into the deck.?and now I'm going to spread the cards face up on the table. A?click of the fingers. And Sarah's card still has a blue back. What's more surprising is that all of the other cards now have red backs.?And that is the amazing color-changing card trick."

? But this trick really doesn't involve cards at all. It clearly shows how the brain picks up only a tiny bit of the available visual information.

? In fact, as the trick was occurring, four?other color?changes went on.

? As the trick unfolds, the camera stays on the cards. Most of us don't notice changes in clothing and background made off camera.

? "The color changing card trick exploits this idea that we have a very good idea of what's happening right in front of our eyes. In fact, 90% of the information we just not seeing. it doesn't feel like that.?It feels like as we look around we're perceiving the whole of the world.?That's not the case. We really?only?just focused on a tiny tiny area."

? Illusions are about more than entertainment in umbrella. They reveal how what we see depends on assumptions our brains?make

? Our eyes and brain collaborate to make sense of the world.

? But our brains need years of training before they can turn what our eyes see into a meaningful image in an instant.

? Follow a blind man as he uses his eyes for the first time and hear him describe what his brain can see.

? Michael May has undergone radical surgery to repair eyes ruined in a boyhood accident.?He hopes that when the bandages come off, he'll be able to see for the first time in 40 years.

boyhood: the period when a person is a baby, and not yet a man, or the state of being a baby

? "I didn't expect anything to happen for at least a couple of weeks, so to go into that room and have the bandages peeled back, and then to actually see light coming in,?was more than words can really describe. All of a sudden there's the overwhelming woosh of visual input. Things resolving in the colors and shapes.?Images wooshing?everywhere."

? Rebuilt?eyes allow light to reach Michael's retinas.

? "First thing you should see is your wife."

??But Michael has a problem.?After 40 years in the dark, his brain doesn't recognize what his eyes can see.

? "Vision wasn't as simple as just turning on the site and all of a sudden being able to read a book. It's much more complicated than that.?Vision isn't?something where you flip a switch."

flip: if you flip something, you turn it over quickly one or more times, and if something filp, it turns over quickly.

? So what visual sense will Michael have of a world he hasn't seen in 40 years?

? Once?blind,?Michael May's?repair eyes now worth almost perfectly, but surprisingly, he can hardly see.

? The reason is the age at which Michael lost his sight. A freak chemical explosion at age three blinded him. 40 years later, he underwent an experimental procedure to restore his sight. Doctors replaced a key part of the eye destroyed in the accident,?his?cornea.

cornea: 角膜

? This clear,?paper-thin coating protects the eye and helps it focus. The damage to Michael's eyes kept him from making out anything. He hoped that new corneas would mean another chance to see the world, but 40 years of blindness left him with a larger problem.

? "I was trying to latch on to images and make sense of the world. It wasn't as though?I saw a face and said "oh, that's a smile" automatically. I had to intellectualize this whole process, dissect it?and then figure it out.

latch on to:?"latch on to" is a phrasal verb that means to grasp, understand, or connect with something

intellectualize: to think about or discuss a subject in a detailed and intellectual way, without involving your emotions or feelings

dissect: to examine something or consider something in detail

? Michael May has no visual memory of the world. It's not something we're born.?At birth,?everything we see is new, but we archive the images, learning their content and meaning. We build our visual memory through experience.

? At the back of the brain, over half of a?billion brain cells make up our visual cortex, the processor and storehouse for vision. Early in our lives, we build our visual memory,?and as long as we live, that library helps us make sense of the world,

? "The interpretation and therefore, the recognition of certain things takes a tremendous amount of experience.?In this sense, the brain is learning to see.?And this is taking place over the first 6 years or to a smaller extent, even the first 9 years."

? But when Michael was blinded at three, he'd only just started to understand the things that make up his ability to see.

? Size, shape, and distance,?light and shade.

? Is that a curb, a step down, a step up or a shadow?

? "Just in terms of the brain's ability to?analyze the depth, to see the edge and to realize that there's a six-inch drop to the curb, I'm just not able to perceive that information."

? If he had spent a childhood seeing and playing with his bicycle and riding off curves of different sizes, he would have learned subtle different cues that let's them distinguish between a 3-inch curve at one distance, a 6-inch curve a little further, and?a 9-inch curve further than that. Deprived of that experience, it gets to be very hard to do so on an optical basis alone.

cue: in the given sentence, "cue" refers to the subtle signals or indicators that provide information or hints to help someone distinguish between different sizes of curves when riding a bicycle.

? Now Michael's adult brain has to struggle to catch up on the learning he'd missed as a child, but Michael does recognize and enjoy some things.?

? "I'll use a cane to deal with what's in front of me, and then I can look around and appreciate the things that I can perceive. Bright-colored flowers, landmarks, people walking by, things like that that I can use my vision for, and I don't even think about what's in front of me."

cane: a long stick used especially by old, ill, or blind people to help them walk

? Michael May inhabits a weird world between blindness and sight, frustrated by his lack of visual memory.

? For most of us, the same visual memory unlock another universe, the world of dreams.

? "When you're in a dream, that is your reality.?You visually are?seeing things, you are hearing things, you can literally feel things, you can see your body moving, etcetera; and you can experience anything that you would experience in waking life in a dream."

? Dreams consist of images we've collected with our eyes.?Like a film editor, the brain reassembles them.

? "I'm usually on my stomach with my arms out, kind of like superman, and I'm gliding over different sceneries. I find a bit of a high to go in-between,?dodge the buildings and go fast and go up and down and over. I feel like a bird soaring in the air. I've always wish I could fly.

in-between:?In the given sentence, "in-between" is used as an adverb to describe the act of going or moving between two or more objects, locations, or states.

? Interestingly, many people share the dream of flying and endure the nightmare of being pursued. The brain can create utterly realistic scenes, even though we've never experienced them.

? "Someone's following me and I have this urge to just run away."

? Reports of such bad dreams recur throughout history. And the meaning of these night visions has always fascinated us.

recur: to happen many times or to happen again

? 3,000 years ago, the Egyptians compiled a book of dreams. It listed familiar dream images and offered interpretations of them.?

? "Dreams were a sort of moment when the boundaries between this world and the next world seemed very thin. But for many of the dreams in the dream book, it's clearly the search for what will happen in the future."

? Now we explain bad dreams as useful in helping us conquer deep, often universal fears; just as we see good dreams as fulfilling our fantasies. Sites seen in dreams may well connect us to our ancestors' instincts and fears, yet another example of how our sense of vision has always dominated our lives.

? Our visual system shows better than any other how intricately our bodies work. Throughout history, it has supercharged human development, and it could allow us to take charge of our future. Sight dates back to our deep past, unsung, unnoticed, a faculty we take for granted. But when revealed,?sight shows how everyday life depends on it. Pushed to the limits, we can see the super hero inside us all, the human body.

unsung: not noticed or praised for hard work, courage, or great achievements

faculty: a natural ability to hear, see, think, move, etc.