雅思课外读物--摩肯族孩子水下视力的奥秘

北京雅思培训,雅思备考资料,雅思网课,雅思培训机构,雅思保分班,雅思真题,雅思课程

在泰国西海岸，安达曼海群岛上的摩肯族孩子，具有超常的水下视觉能力。科学家对他们进行了跟踪研究，发现了其中的奥秘。

“When the tide came in, these kids started swimming. But not like I had seen

before. They were more underwater than above water, they had their eyes wide

open – they were like little dolphins(海豚).”

Deep in the island archipelagos (群岛)on the Andaman Sea, and along the west

coast of Thailand live small tribes(部落) called the Moken people, also known as

sea-nomads(流浪者). Their children spend much of their day in the sea, diving for

food. They are uniquely adapted to this job – because they can see underwater.

And it turns out that with a little practice, their unique vision might be

accessible(可以使用的;可以获得的)to any young person.

In 1999, Anna Gislen at the University of Lund, in Sweden was investigating

different aspects of vision, when a colleague suggested that she might be

interested in studying the unique characteristics of the Moken tribe. “I’d been

sitting in a dark lab for three months, so I thought, ‘yeah, why not go to Asia

instead’,” says Gislen.

Gislen and her six-year old daughter travelled to Thailand and

integrated(融入，综合) themselves within the Moken communities, who mostly lived on

houses sat upon poles. When the tide came in, the Moken children splashed around

in the water, diving down to pick up food that lay metres below what Gislen or

her daughter could see. “They had their eyes wide open, fishing for clams,

shells and sea cucumbers, with no problem at all,” she says.

Gislen set up an experiment to test just how good the children’s underwater

vision really was. The kids were excited about joining in, says Gislen, “they

thought it was just a fun game.”

The kids had to dive underwater and place their heads onto a panel. From

there they could see a card displaying either vertical(垂直的)or

horizontal(水平的)lines. Once they had stared at the card, they came back to the

surface to report which direction the lines travelled. Each time they dived

down, the lines would get thinner, making the task harder. It turned out that

the Moken children were able to see twice as well as European children who

performed the same experiment at a later date.

What was going on? To see clearly above land, you need to be able to

refract(折射)light that enters the eye onto the retina(视网膜). The retina sits at

the back of the eye and contains specialised cells, which convert(转变)the light

signals into electrical signals that the brain interprets as images.

Light is refracted when it enters the human eye because the outer cornea(眼角膜)

contains water, which makes it slightly denser than the air outside the eye. An

internal lens refracts the light even further.

When the eye is immersed(沉浸)in water, which has about the same density as the

cornea, we lose the refractive power of the cornea, which is why the image

becomes severely

blurred(使……模糊).(当眼睛浸入水中，水的浓度与眼角膜相当，因而失去眼角膜的折射功能，于是映像就变得非常模糊。)

Gislen figured that in order for the Moken children to see clearly

underwater, they must have either picked up some adaption that fundamentally

changed the way their eyes worked, or they had learned to use their eyes

differently under

water.(Gilsen推想，摩肯族孩子能在水下有清晰的视力，要么因为他们经过某种适应，从根本上改变了眼睛的工作机理，要么因为他们学会了如何在水下以不同的方式使用眼睛。)

She thought the first theory was unlikely, because a fundamental change to

the eye would probably mean the kids wouldn’t be able to see well above water. A

simple eye test proved this to be true – the Moken children could see just as

well above water as European children of a similar age.

It had to be some kind of manipulation(操控)of the eye itself, thought Gislen.

There are two ways in which you can theoretically improve your vision

underwater. You can change the shape of the lens – which is called accommodation

– or you can make the pupil(瞳孔) smaller, thereby increasing the depth of

field.

Their pupil size was easy to measure – and revealed that they can constrict

their pupils to the maximum known limit of human performance. But this alone

couldn’t fully explain the degree to which their sight improved. This led Gislen

to believe that accommodation of the lens was also involved.

“We had to make a mathematical calculation to work out how much the lens was

accommodating in order for them to see as far as they could,” says Gislen. This

showed that the children had to be able to accommodate to a far greater degree

than you would expect to see underwater.

“Normally when you go underwater, everything is so blurry(模糊的)that the eye

doesn’t even try to accommodate, it’s not a normal reflex,” says Gislen. “But

the Moken children are able to do both – they can make their pupils smaller and

change their lens shape. Seals and dolphins have a similar adaptation.”

Gislen was able to test a few Moken adults in the same way. They showed no

unusual underwater vision or accommodation – perhaps explaining why the adults

in the tribe caught most of their food by spear fishing above the surface. “When

we age, our lenses become less flexible, so it makes sense that the adults lose

the ability to accommodate underwater,” says Gislen.

（转第二页）