Target ranging by echolocation in bats: Performance and mechanisms

Abstract

James Simmons’s early research on sonar ranging in echolocating bats generated two groundbreaking discoveries: (1) Bats compute object distance from the time delay between sonar calls and echoes, and they discriminate echo-delay differences in the microsecond range [Simmons, https://psycnet.apa.org/doi/10.1121/1.1913559 (1973)] and (2) A population of auditory neurons show facilitated and echo delay-tuned responses, a posited neural substrate of sonar ranging [Feng et al., https://10.1126/science.705350 (1978)]. These findings spawned decades of biosonar research around the world, and this talk will summarize three new findings on the mechanisms of sonar ranging in the big brown bat, Eptesicus fuscus. (1) Echo-delay tuned neurons in the midbrain of the free-flying bat show 3D spatial tuning to echoes from physical objects, and sonar-guided attention evokes sharper delay-dependent response areas and shifts to shorter echo delays. (2) Local field potential recordings from auditory midbrain neurons in the passively listening bat encode the time interval between call-echo pairs in the microsecond range, with accuracy dependent on signal duration and bandwidth. (3) A population of hippocampal CA1 neurons encodes the distance of sonar objects in bats as they track moving targets, and responses of hippocampal neurons depend on the production of sonar calls that yield echo returns.