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Maligned, misunderstood, and unappreciated, bats are relegated to Halloween fright or to such put-downs as "bats in the belfry." They are, in fact, an evolutionary marvel, capable of eating up to 600 insects an hour and of teaching us how to build ever-better radar.

Proceedings of the National Academy of Sciences.

Recent research conducted in the "bat lab" at Brown's Walter S. Hunter Laboratory suggests that these flying mammals are even more remarkable than earlier thought. Working with big brown bats collected from local attics, Professor of Biology and Neuroscience James Simmons and colleagues found that a bat's brain can resolve the timing of echoes for sonar images up to three times more sharply than previously thought and much better than conventional man-made equipment. The results of the study were published in the October 13

Simmons and fellow researchers Michael Ferragamo '94 Ph.D. and Cynthia Moss '86 Ph.D. also suggest that bats may be a dolphin's best friend. Because the study's findings may lead to the development of better sonar, they are of particular importance to the U.S. Navy, which relies on both man-made sonar and the sonar of trained dolphins to detect distant or obscure objects, particularly mines. "The idea," says Simmons, "is to use our results to build a sonar system that would find these mines without the need of dolphins or divers."

Bats primarily "view" their environment through sonar, sending out high-frequency sound waves and registering returning sounds, or echoes, from surrounding objects, ranging from buildings to bugs. Depending upon its size, an object bounces back a varying spectrum of reflected echoes, and it is this spectrum that the bat uses to achieve fine time resolution.

The researchers propose that bats process sonar echoes in a more sophisticated way than was suspected, probably to allow the animals to use echolocation for more tasks than just catching insects. In experiments at the bat lab on Waterman Street, the animals separately perceived and processed overlapping echoes at delays as close together as two microseconds. "Using the same sounds as the bat," Simmons says, "the best man-made sonar equipment can only process echo delays arriving five to ten microseconds apart."

The bats' fine-tuned sonar also allowed them to resolve echo-reflecting points on an object a mere three-tenths of a millimeter apart, a spacing the width of a pen line on a sheet of paper. Simmons and his colleagues have begun experiments to record the neural make-up of this superior resolution.





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