The ‘sea gypsy’ children of Southeast Asia have a incredible ability to see clearly underwater at depths of up to 75ft. Like dolphins, they appear to be able to spot small items, such as clams, beneath the waves without much difficulty.
Scientists believe the skill isn’t a genetic trait, but something that occurs with practice – and they say any child could learn to have such extraordinary vision.
According to an in-depth report in the BBC, she recently went back to the same tribe and found that the young children she studied, now in their late teens, still have the ability to see underwater.
But she believes the adults may have lost that ability as many of them no longer need to dive for food.
To discover how the sea gypsies could spot such small objects underwater, Gislen compared the vision of children from the Moken with that of European children on holiday in Southeast Asia.
Her team asked the children between 8-13 years old to look at gratings – black and white stripes – of various widths while they were underwater.
‘The children were asked to dive down and then come up and tell us which way these gratings were oriented,’ Lund told Reuters Health several years ago.
If they managed to correctly identify one pattern underwater, we then used a finer grating – thinner stripes – until the child made mistakes, which meant he or she could no longer see the pattern.’
The researchers determined that the Moken children could see twice as well underwater as their European counterparts.
Gislen said she believes this is mostly down to practice, because the Moken children swim and dive so much.
The researchers examined all the children’s eyes on shore and determined that there was no physical difference between the two groups.
Gislen noticed that the Moken children constricted their pupils when diving, similar to the shrinking of the aperture in a camera.
‘In optical terms,’ she explained, ‘we say that the focal depth is improved when the aperture is smaller.’
When diving, the European children’s pupils expanded – likely a response to dimmer light underwater, Gislen said.
But a person can also constrict their pupils if they are bringing something into focus, Gislen said.
What is interesting with the Moken children, Gislen said, is that they accommodate all through their dive.
This should be strenuous for them, but they are able to do so effortlessly.
The BBC reports that in unpublished work, Gislen recently tested the same children that were in her original experiment.
The Moken children, now teenagers, still have their unique vision. The adults, however, were too shy to be tested.
But Gislen suggests that the adults would have lost their ability to see underwater.
‘The adult eye just isn’t capable of that amount of accommodation,’ she told the BBC.
Today many Moken have opted for new jobs on the mainland.
Even those still living off the sea have become more sedentary in recent decades with Moklen families building houses along island coasts, using them as a base from which to trawl the ocean.
With their lifestyle changing dramatically following the 2004 tsunami in the Indian Ocean, Gislen says the latest generation could be the last to have such extraordinary vision.