Bats have remarkable echolocation capabilities to detect prey in darkness. While it is clear how bats do this for prey that is isolated, moving, or noisy, their ability to find still and quiet prey within clutter has remained a mystery. A video published by the ChiRoPing group shows the gleaning bat Micronycteris microtis capturing a still dragonfly specimen sitting on a leaf surface. While hovering over the dragonfly, the bat's wings exert air forces that cause the dragonfly wings to deflect in synchrony with the bat's wing beats. This paper illustrates that echoes from such deflecting wings vary in both amplitude and time-of-flight, producing robust echo cues that permit prey detection, even when the prey is embedded within clutter. Experiments with a dragonfly specimen mounted on a leaf driven by periodic air puffs produced wing deflections that were sensed with sonar pulses. Results demonstrate that echo variations synchronized with periodic air puffs are easily distinguishable from surrounding clutter, even when clutter produces the first echoes. These results suggest a strategy that bats can employ to detect still and silent prey embedded within cluttered environments.

Blind humans echolocate nearby targets by emitting palatal clicks and perceiving echoes that the auditory system is not able to resolve temporally. The mechanism for perceiving near-range echoes is not known. This paper models the direct mouth-to-ear signal (MES) and the echo to show that the echo enhances the high-frequency components in the composite MES/echo signal with features that allow echolocation. The mouth emission beam narrows with increasing frequency and exhibits frequency-dependent transmission notches in the backward direction toward the ears as predicted by the piston-in-sphere model. The ears positioned behind the mouth detect a MES that contains predominantly the low frequencies contained in the emission. Hence the high-frequency components in the emission that are perceived by the ears are enhanced by the echoes. A pulse/echo audible sonar verifies this model by echolocating targets from 5 cm range, where the MES and echo overlap significantly, to 55 cm. The model predicts that unambiguous ranging occurs over a limited range and that there is an optimal range that produces the highest range resolution.

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Some blind humans echolocate by emitting palatal clicks and processing echoes, even when there is temporal emission/echo overlap (EEO). Our previous work indicates that high frequencies in the emission that travel directly to the ears are attenuated and, when high frequencies are heard, they come from target echoes. Binaural processing of these high frequency components in the EEO signals provide target range and bearing. Our experiments with 3D-printed parabolic pinnae and a speaker emitter indicate that while the high frequency components are important for object classification, the low frequencies in the emission provide more robust bearing localization because pinna diffraction effects are reduced. Classifying targets with EEO signals requires analysis in the power spectral domain because of the phase insensitivity of hearing. The power spectrum Fourier inverse estimates the autocorrelation function of the target reflector sequence. Robust autocorrelation estimates occur when the emission and echo contain comparable energies. Our experiments demonstrate that the echo energy varies with target type (e.g., planar or cylindrical) and the optimum range for classification depends on the target and itself forms a target classification feature.