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. Auditory feedback seems also necessary for controlling many bat communication calls, although it remains unclear how auditory feedback control differs in echolocation and communication. We tackled this question by analyzing echolocation and communication in greater horseshoe bats, whose 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 (DSC) behavior represents one of the most precise forms of sensory-motor feedback known. We examined the variability of echolocation pulses emitted at rest (resting frequencies, RFs) and one type of communication signal which resembles an echolocation pulse but is much shorter (short constant frequency communication calls, SCFs) and produced only during social interactions. We found that while RFs varied from day to day, corroborating earlier studies in other constant frequency bats, SCF-frequencies remained unchanged. In addition, RFs overlapped for some bats whereas SCF-frequencies were always distinctly different. This indicates that auditory feedback during echolocation changed with varying RFs but remained constant or may have been absent during emission of SCF calls for communication. This fundamentally different feedback mechanism for echolocation and communication may have enabled these bats to use SCF calls for individual recognition whereas they adjusted RF calls to accommodate the daily shifts of their auditory fovea.
Highlights
Hearing one’s own voice is critical for the maintenance of stable vocalizations in humans and songbirds, even in adulthood after human speech and bird song have already been established
We recorded a total of 1754 RF and 4275 short constant frequency call (SCF) calls from 8 greater horseshoe bats (Table 1)
As in a previous characterization of the repertoire of social calls in horseshoe bats [11], we found that SCFs had on average less than half the duration of RF calls
Summary
Hearing one’s own voice is critical for the maintenance of stable vocalizations in humans and songbirds, even in adulthood after human speech and bird song have already been established (for review [1,2]). In addition to producing echolocation pulses, bats generate a large repertoire of social calls to communicate with one another [4,5,6,7,8,9,10,11,12,13,14] It appears that at least some of these communication signals are dependent on auditory feedback, as for example effects of vocal learning suggest [2,15,16,17]. Different types of vocalization appear to involve different subsystems of the brainstem vocal motor network [19] It is unclear, if the different vocal premotor networks receive different auditory feedback. The communication call we focused on here resembles an echolocation pulse but is much shorter (around 17 ms; SCFs) and produced only during social interactions [11]
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