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12 December 2013 1:00 pm ,
Vol. 342 ,
Evolutionary biologists have long studied how the Mexican tetra, a drab fish that lives in rivers and creeks but has...
Victorian astronomers spent countless hours laboriously charting the positions of stars in the sky. Such sky mapping,...
In an ambitious project to study 1000 years of sickness and health, researchers are excavating the graveyard of the now...
Stefan Behnisch has won awards for designing science labs and other buildings that are smart, sustainable, and...
The iconic 125-year-old Lick Observatory on Mount Hamilton near San Jose, California, is facing the threat of closure...
Recent results from the Curiosity Mars rover have helped scientists formulate a plan for the next phase of its mission...
A new, remarkably powerful drug that cripples the hepatitis C virus (HCV) came to market last week, but it sells for $...
In pretoothbrush populations, gumlines would often be marred by a thick, visible crust of calcium phosphate, food...
- 12 December 2013 1:00 pm , Vol. 342 , #6164
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Sea Travelers See Better
13 May 2003 (All day)
Divers know that all sorts of equipment is necessary to function underwater, including goggles to correct water-warped vision. But researchers have found that some Southeast Asian seafaring people can see underwater very clearly without such corrective devices. They push their eyes to the very limit of human perception.
Human eyeballs are filled with a watery fluid, so they have almost the same refractive index as water itself. Thus light coming into the eye isn't bent in the same way when underwater as on land. The unfocused light rays reduce clarity by about two-thirds. But certain Southeast Asian nomads dive and swim without eye protection and still manage to harvest small camouflaged shells, clams, and sea cucumbers. In order to find out their secret, a team of researchers from Lund University and the Institute of Clinical Neuroscience in Mölndal, both in Sweden, went to Thailand and Burma to study the Moken tribe.
On land, Moken children had the same visual acuity as a group of vacationing European children. Underwater, the Moken children could see about two times better than the European children, according to tests using grids with varying fineness. The researchers observed that Moken children could control the size of their pupils, constricting them underwater to the smallest diameter humanly possible--about 2 millimeters--whereas the European children's pupils opened slightly, the researchers report in the 13 May issue of Current Biology. Smaller pupils improve resolution, focusing light rays like the tiny opening in the front of a pinhole camera. According to the researchers' calculations, the Moken children also change the shape of their lenses with their eye muscles to focus even better.
Such so-called accommodation may be a genetically inherited trait useful for people who rely on the sea for food. But more likely, the response is learned, says Anna Gislén of the Lund team. "It is a surprise," says Tom Cronin of the University of Maryland, Baltimore County. "You would expect ... that [human] vision wouldn't change much from place to place." The children, he says, are accommodating "as well as anyone can do it." Gislén and her co-workers are training European children now to see if they can learn the same techniques.
Anna Gislén's Web page
Underwater eyes in animals
UNESCO Surin Islands Project: Indigenous Peoples and Parks
When underwater, Moken children can see grids more than three times finer than this one.