Different forms of auditory-vocal feedback control in echolocating bats

Abstract

Auditory feedback from the animal’s own voice is essential during bat echolocation: to optimize signal detection, bats continuously adjust various call parameters in response to changing echo signals. Horseshoe bats exhibit a particularly well-developed form of auditory feedback. Their echolocation pulses are dominated by a constant frequency component that matches the frequency range they hear best. To maintain echoes within this “auditory fovea,” horseshoe bats constantly adjust their echolocation call frequency depending on the frequency of the returning echo signal. This Doppler-shift compensation behavior represents one of the most precise forms of sensory-motor feedback known. When examining the Lombard effect in horseshoe bats, we found that noise had different effects on call amplitude and frequency rises indicating different neural circuits and/or mechanisms underlying these changes. Both, amplitude and frequency rises were extremely fast and occurred in the first call uttered after noise onset, suggesting that, in contrast to Doppler-shift compensation, the Lombard effect did not require any auditory feedback. Bats also possess a large repertoire of communication calls, which differ greatly from those emitted during echolocation. We compared the variability of echolocation pulses and one common type of communication signal and found fundamentally different feedback mechanisms for echolocation and communication.