Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

Insectivorous bats are ideally suited for the study of acoustically guided behaviour. Their echolocation system for orientation in space or for catching prey is adapted to transform acoustic information on the environment into appropriate motor programs for vocalisation, body orientation and flight movements. The orientation towards a sound or echo source involves the acoustical analysis of spatial co-ordinates. The echolocation calls are modified in their spectral and/or temporal organisation as a consequence of analysis of acoustical parameters in the echoes and thus adapted to the requirements of specific echolocation tasks.

Some species of bats yield a most challenging model for studying mechanisms of audio-vocal control. So-called long CF/FM bats(rhinolophid and mormoopid bats) with long constant frequency (CF) orientation calls terminated by a short frequency modulated (FM) portion stabilise the echo carrier frequency to a distinct value irrespective of movement induced Doppler-shifts. During this so-called Doppler shift compensation, the flight-speed induced shifts are analysed in the hearing system and fed back to the motor structures controlling the vocal output. The emitted frequency is appropriately decreased, so that the echo frequency is held just above the bat's resting frequency. This automatic frequency control system, although functionally well defined (Schnitzler, 1968, Schuller et al., 1974) is not well understood in its neuronal implementation. The transformation from acoustic frequency error to appropriate motor output command is still widely unknown.

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