Echolocation on the wing: perception and neural representation of echo-acoustic flow fields in bats

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Self motion induces correlated changes in the percept of our environment: This close link between action and perception has been extensively studied in the visual system, where linear motion induces the percept of a visual flow field. Visual flow-fields provide crucial information both about the spatial layout between objects and the distance of the assessor to these objects. However, this information can not only be gained visually: Echolocating bats, flying in complete darkness through highly cluttered 3D environments, are very likely to exploit echo-acoustic flow-field information for navigation: Previous work has highlighted the exceptional capabilities of bats, and underlying neural processes, to extract both spatial and temporal information from returning echoes for reconstructing 3D layouts of their environment and objects within. Perception and neural representation of the dynamical changes of spatio-temporal representation of space, i.e., the echo-acoustic flow field a bat will experience in flight are, however, largely unknown.This proposal aims to investigate the perceptual capabilities and neurophysiological basis of echo-acoustic flow-field analysis in bats. To this aim a combined psychophysical and electrophysiological approach is used: Bats will be trained on linear flight in a state-of-the-art wind tunnel and presented with virtual echo-acoustic flow fields, generated through complex spatio-temporal real-time processing and playback of sonar emissions produced by the bats in flight. As in visual flow-field research, recruiting virtual echo-acoustic flow fields allows for detailed, hypothesis-driven manipulation of the flow-field information and formal psychophysical assessment of the perceptual sensitivity of the bats to these manipulations.Complementing the psychophysical research, our recent electrophysiological work has shown that the well-known chronotopic arrangement in dorsal auditory cortex (i.e., the topographic representation of echo delay) co-varies with a systematic spatial tuning of the neurons. This co variation of the neural code for distance and azimuth supports an explicit neural code for echo acoustic flow fields. This proposal aims to evaluate the function of this candidate neural substrate with advanced stimulation- and recording techniques, applied first under anesthesia and subsequently in the awake and behaving animal in flight.