- WASHINGTON (AP) -- Bat sonar is so much better than anything devised by
human technology that the cave-dwelling creatures seem to flaunt it.
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- "The bats were essentially turning
to us and thumbing their noses," researcher James Simmons of Brown
University said of tests aimed at challenging bats sonar ability.
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- Simmons experiments, reported in Monday's
issue of Proceedings of the National Academy of Science, are aimed at improving
the Navy's sonar to help detect mines under water.
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- Sonar systems send out a sound and then
listen for the echo to bounce back. The time it takes to return tells how
far away something is and in which direction. A major factor is the ability
to differentiate between two echoes that arrive at almost the same time.
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- At the wavelengths under study, electronic
sonar can differentiate between echoes about 12 millionths of a second
apart. With a lot of work, that can be cut to 6 millionths to 8 millionths
of a second, Simmons said.
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- "Bats do 2 to 3 (millionths of a
second) relatively easily," Simmons said. "That's the part that's
little distressing."
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- Being able to separate such sounds means
the bats could tell the difference between objects just 3/10ths of a millimeter
apart -- about the width of a pen line on paper.
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- In the experiment, the bats were sitting
on a platform in a familiar situation, he noted. They probably don't do
as well at night, chasing insects through the trees.
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- "They seem to be fat and happy all
the time, which means they are intercepting their targets," though,
Simmons observed. "The things they do are shocking."
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- To succeed in such chases, bats need
to be able to differentiate sounds 10 millionths of a second apart, Simmons
explained in a telephone interview. "We'd have to do a lot of work
to match what they're doing so easily."
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- While they're still trying to determine
why bats are so much better than human technology, they have begun experiments
to record bats' brain cell activity as they process sounds.
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- And Simmons is working on tweaking naval
sonars, both in listening for return sounds and in processing that information,
to make them a bit more like bats.
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- Dolphins also use sonar, and some have
been trained by the Navy to help find mines. But Simmons said it isn't
practical to do experiments on dolphins. Working with bats, on the other
hand, he hopes to learn ways to improve both underwater sonar and airborne
radar.
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- In Simmons' experiments, the bats are
trained to differentiate sounds with large gaps between them, getting a
reward of mealworms for each correct decision. Then the timing of the sounds
is shortened to test the bats' response.
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- "They cooperate in these experiments.
... They perform very fast," Simmons said. In an experiment, the bat
makes its decision about the sound and then runs forward to get the mealworm.
"They don't fly off; they just sit there and go right to it,"
he said.
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- Working with Simmons on the project were
Michael Ferragamo, now at Gustavus Adolphus College, and Cynthia Moss,
now at the University of Maryland.
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