Bats navigating cluttered environments distinguish between echoes elicited by two closely successive broadcasts by focusing on the lowest frequencies, a study finds. Bats locate objects by emitting ultrasonic sounds called broadcasts, which contain frequencies ranging from 25 kHz to 110 kHz, and listening to the returning echoes. Occasionally, an initial broadcast elicits a long-delay echo reflected from a distant object, and a closely successive broadcast triggers a short-delay echo from a nearby object. However, both echoes reach the bat's ears at nearly the same time. James Simmons and colleagues describe how bats deal with the potential ambiguity in matching the echo to the correct broadcast. The authors trained four big brown bats to broadcast sonar sounds, which triggered loudspeakers placed on either side to deliver distinct simulated echoes consisting of various frequencies. To receive a reward, the bats had to approach the loudspeaker that delivered an echo simulating a nearby, insect-sized virtual object. Only the lowest broadcast frequencies of 25-30 kHz were necessary and sufficient for echo perception. The results explain how bats navigating cluttered environments easily distinguish between echoes elicited by two closely successive broadcasts. The authors note that only the second broadcast contains the lowest frequencies, and bats essentially ignore the faraway object represented by a long-delay echo elicited by the first broadcast. According to the authors, biologically inspired solutions could address the major challenge of designing radar and sonar systems that perform well in cluttered environments.
Article #20-01105: "How frequency hopping suppresses pulse-echo ambiguity in bat biosonar," by Chen Ming, Mary E. Bates, and James A. Simmons.
MEDIA CONTACT: James Simmons, Brown University, Providence, RI; tel: 401-863-1542; e-mail: james_simmons@brown.edu
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Proceedings of the National Academy of Sciences