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For the Eyes Only


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Part I

If you fumbled for your reading glasses to see these words or are peering at the page at arm’s length, you already know that age is not kind to vision. In most settings young eyes trump old ones. So it was a surprise when a group of vision researchers found that in one contest, aging eyes always win: motion detection.

To learn about changes in the older brain, psychology doctoral candidate Lisa Betts and her colleagues at McMaster University in Ontario tested young college students against people in their sixties and seventies on how quickly they noticed the sideways movement of vertical bars on a computer screen. Students do terribly, says Betts. They leave in frustration, but “the older observers come out and say, ‘That was easy.’ ”

Their success seems to be a by-product of changes in brain chemistry that usually make older people worse at a task, says psychology researcher Allison Sekuler. The youthful brain filters out unimportant details of a cluttered scene, a process called inhibition. Older brains seem to lose this ability, possibly because they have lower levels of g-aminobutyrate, or GABA, one of the chemicals brain cells use for communication. GABA and other inhibitory neurotransmitters tell cells to slow down or stop sending messages. “They act like traffic cops,” says Sekuler. That’s why children, who have high levels of GABA, are much better at “Where’s Waldo?” than their grandparents, she says. Future work may suggest research to find pharmaceuticals to improve vision. “We are hoping drug studies will show that you can turn old brains young and vice versa,” says Sekuler.

She questions, however, the need to alter the system too much. Seniors have an advantage when it comes to assessing a group or tracking its movement—following a whole hockey team, for example, rather than a specific player. “The way we think about it,” Sekuler says, “is that the older people see the forest, and the younger ones see the trees.”

Jessa Forte Netting

Part II

Scientists have known for years that swordfish, tuna, and sharks have a special system that circulates warm blood to their eyes. “It’s like a heating blanket,” says biologist Kerstin Fritsches of the University of Queensland, Australia. Its purpose, though, had eluded researchers until Fritsches recently led a team to “good swordfish water” north of Hawaii. They found that when swordfish warm their eyes 18 to 27 degrees Fahrenheit above ocean temperature, they are able to see movement 10 times faster. This helps the fish spot and catch dinner.

The team dissected the grapefruit-size eyes of 10 swordfish and then tested the response of their retinas to flashes of light at various temperatures. The retinas could pick up fast movement more easily as they warmed up. “The biochemical processes responsible for converting light to electrical nerve signals depend on temperature,” says Eric Warrant, a vision expert at the University of Lund in Sweden, who helped conduct the on-deck experiments.

Fritsches speculates that the heating organ, located in a muscle near the eye, allows swordfish to expand their habitat. “Interestingly enough,” she says, “the swordfish has the largest heater organ [compared with tuna and sharks], and it goes into the coldest waters.”

Anne Casselman

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