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posted by janrinok on Sunday September 08 2019, @10:33AM   Printer-friendly
from the mermen-and-mermaids dept.

Arthur T Knackerbracket has found the following story:

Unlike most people, the children of a Thailand tribe see with total clarity beneath the waves – how do they do it, and might their talent be learned?

Deep in the island archipelagos on the Andaman Sea, and along the west coast of Thailand live small tribes called the Moken people, also known as sea-nomads. 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 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 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 or horizontal 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 light that enters the eye onto the retina. The retina sits at the back of the eye and contains specialised cells, which convert 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 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 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.

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.

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 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 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.

[...] Unfortunately, the children in Gislen’s experiments may be the last of the tribe to possess the ability to see so clearly underwater. “They just don’t spend as much time in the sea anymore,” she says, “so I doubt that any of the children that grow up these days in the tribe have this extraordinary vision.”


Original Submission

 
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  • (Score: 0) by Anonymous Coward on Monday September 09 2019, @03:41PM

    by Anonymous Coward on Monday September 09 2019, @03:41PM (#891720)

    It's not even fuzzy though. I don't get it.

    When I was a kid, I grew up on a fresh water lake. We spent a LOT Of time in the water, in the summer. Endless kids, playing games, you name it.

    I never closed my eyes when under water. None of my friends did, either. We could easily see plants, animals, fish, everything, without issue. It looked different, surely... but, it wasn't super blurry or fuzzy or hard to see.

    Hell, I could easily *hear* underwater too. Hear people talking above the water, although that was much quieter. We'd sometimes yell at each other underwater, like "get him" or whatever.. and it was easily understood.

    I could swim underwater for minutes.... but what use would that be, without seeing? I mean, if you're down there looking for crabs or shellfish or oysters or whatever, if you can't see them, what's the point.

    This seems to me, to be something that's 100% normal, but kids that grew up away from a body of water just never learned *could* be done, and any adult could learn like learning to ride a bike, or horse (but less skilled than if picked up as a kid...)

    Anyhow. Weird. This is right up there, with people being surprised that animals, and birds, listen to birds and alert calls.. something I learned at the age of, oh I dunno, 4 or 5?!