Acoustic-Imaging Computations by Echolocating Bats: Unification of Diversely-Represented Stimulus Features into Whole Images

The echolocating bat, Eptesicus fuscus, perceives the distance to sonar targets from the delay of echoes and the shape of targets from the spectrum of echoes. However, shape is perceived in terms of the target's range proftle. The time separation of echo components from parts of the target located at different distances is reconstructed from the echo spectrum and added to the estimate of absolute delay already derived from the arrival-time of echoes. The bat thus perceives the distance to targets and depth within targets along the same psychological range dimension, which is computed. The image corresponds to the crosscorrelation function of echoes. Fusion of physiologically distinct timeand frequency-domain representations into a fmal, common time-domain image illustrates the binding of withinmodality features into a unified, whole image. To support the structure of images along the dimension of range, bats can perceive echo delay with a hyperacuity of 10 nanoseconds. Acoustic-Imaging Computations by Echolocating Bats 3