Evidence for a spectral basis of texture perception in bat sonar

Bats obtain information about the structure of objects in the outside world from their echolocation signals, an extremely useful method when hunting non-flying prey in densely cluttered habitats, for example. Information about object structure is contained both in the time and in the spectral interference patterns of signals reflected from surfaces at different distances from the bat. I report here an experiment designed to test the extent to which bats use these two types of information. A 'phantom target' is generated by playing back to an echolocating bat signals that mimic the result of reflection from two planes set at different distances. The ability of the bat to discriminate between two such targets is investigated as a function of the separations of the planes. Several of the results do not fit the hypothesis that the bat simply uses time-delay information: the very small time difference that can be discriminated, the fall off in ability to discriminate planes at a particular separation and the symmetry of the discrimination ability measured in the frequency domain. The empirical data can best be fitted by a function based on spectral correlation.