Coordination of bat sonar activity and flight for the exploration of three-dimensional objects.

The unique combination of flight and echolocation has opened the nocturnal air space as a rich ecological niche for bats. By analysing echoes of their sonar emissions, bats discriminate and recognize three-dimensional (3-D) objects. However, in contrast to vision, the 3-D information that can be gained by ensonifying an object from only one observation angle is sparse. To date, it is unclear how bats synchronize echolocation and flight activity to explore the 3-D shape of ensonified objects. We have devised an experimental design that allows creating 3-D virtual echo-acoustic objects by generating in real-time echoes from the bat's emissions that depend on the bat's position relative to the virtual object. Bats were trained to evaluate these 3-D virtual objects differing in their azimuthal variation of either echo amplitude or spectral composition. The data show that through a very effective coordination of sonar and flight activity, bats analyse an azimuthal variation of echo amplitude with a resolution of approximately 16 dB and a variation of echo centre frequency of approximately 19%. Control experiments show that the bats can detect not only these variations but also perturbations in the spatial arrangement of these variations. The current experimental paradigm shows that echolocating bats assemble echo-acoustic object information - acquired sequentially in flight - to reconstruct the 3-D shape of the ensonified object. Unlike previous approaches, the recruitment of virtual objects allows for a direct quantification of this reconstruction success in a highly controlled experimental approach.