Coding of spatial and temporal frequency in bat biosonar

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The concept of spatial frequency, introduced in the pioneering work by Wiesel and Hubel into visual brain research, was instrumental in understanding how peripheral representations of objects are processed by the brain. Many studies have shown how well biosonar systems can replace or complement visual object perception but, despite a direct ecological relevance of spatial frequencies for echolocating bats, this parameter has not received any scientific attention in biosonar. Building upon psychophysical studies of bats hunting above water surfaces, both in the lab and in the field, we will test the hypothesis that bats can analyse both the spatial and temporal frequency patterns of natural water surfaces to identify disruptions thereof as possible prey. The experimental program starts out with two formal psychophysical detection experiments, quantifying perceptual sensitivity to spatial frequency and temporal frequency. On these foundations, masking along the spatial and temporal frequency axes will be investigated allowing for quantitative estimates of how-small prey-induced disruptions may be to be detectable by bats. These formal experiments are complemented with flight-room experiments where hunting sequences of biosonar specialists, Daubentons bats, are evaluated above a water surface where both spatial and temporal frequency of the water surface can be systematically manipulated. The proposed research will provide first insights into how a biosonar system solves these challenging tasks despite its lack of an explicit spatially arranged sensor array and its discontinuous temporal sampling.