コウモリのエコーロケーションにおける信号妨害の低減戦略

抄録

Bats emit ultrasonic vocalizations through their mouths or nostrils, listen to echoes returning from surrounding objects, and reconstruct three-dimensional images to navigate in the dark. To perform the reconstruction, bats compare their original emission with returning echoes that have been changed by the surroundings. In natural environments, echolocating bats receive various sensory inputs, including insect echoes, clutter echoes, and pulses and echoes from other bats, which must create a complex acoustic situation. Here, we discuss how bats extract own faint echoes in the presence of noise, by focusing on three similar but different situations; auditory masking, clutter interference, and jamming. Sensitivity to faint echoes is maintained after intense pulse emission, by contraction of middle ear muscles during emission. Echoes from off-axis objects could be "defocused" by comparing spectral features in the pulses and echoes. In the presence of conspecifics, bats increase the intensity and duration of pulses to improve the signal-to-noise ratio of their own echoes. They also regulate spectrotemporal features of pulses to separate their own echoes from sounds of conspecifics. Some of the adaptations made by bats may have future engineering applications for radar or sonar systems.