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Fig. 1. Spectrograms of sonar sounds emitted by a big brown bat in target-detection
tasks while wideband random noise of different amplitudes was delivered from a
loudspeaker (Simmons et al.,
1974). In response to the noise, the bat lengthens its FM sweeps,
which have a curvilinear shape and tail down to a shallow sweep around
22–28 kHz (arrow). Its detection performance remains approximately
constant in ambient conditions and in –40 to –10 dB noise, but it
declines to chance in 0 dB noise.