Echolocating big brown bats perceive sonar images that have distance, or target range, as their primary dimension. Distances to objects are determined from the delay of echoes, but the bat's images also depict the locations of reflecting points within each object as the basis for representing target shape. Echoes from parts of objects arrive so close together that that they overlap to form an interference spectrum, and the bat determines the separation of the target's parts from the frequencies of notches in this spectrum. However, the distance to each part of the object is depicted in the images by transforming the pattern of notches into true delay estimates. The objective of the proposed research is to understand how spectral information about the small time separations of echoes from different parts of the same object is bound with spike-timing information about the overall delay of echoes for the distance to the object as a whole. In the auditory cortex, this binding process is based on temporal coincidences between spikes representing overall delay independent of the echo spectrum and spikes representing the delay of echoes that have spectral notches, thus serving as a model for temporal feature binding as a general perceptual phenomenon. The project consists of behavioral experiments to measure the width of the bat's time windows for binding spectral delay estimates to temporal delay estimates and neuropsychological experiments to trace the movement of information about the echo spectrum from one delay to another using the same acoustic stimuli as in the behavioral experiments. A biologically realistic computational model of echo processing will be used as a tool for linking the behavioral and physiological findings. ? ?
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