Representation of target range in the sonar receivers of echolocating bats

Abstract

Echolocating bats can discriminate the range (echo arrival time) of simulated targets with accuracy predictable directly from the sonar waveforms down to the region where echo and noise powers are about equal. Detection and ranging performance are closely linked. Equivalence of performance in simultaneous- and successive-presentation procedures indicates that bats make absolute range judgments and store range images of targets for subsequent comparisons. Targets separated in range and/or angular direction are perceived as distinct events. Although target range is perceived noncoherently, target fine structure may be perceived coherently. Information about the occurrence and timing of transmitted sounds and echoes is conveyed in the time domain over frequency-specific primary auditory neurons and appears, still in the time domain, ascending the lateral lemniscus and in the inferior colliculus. Behavioral data suggest ultimate spatial “receptor-field” representation of range in the brain, so echo-timing information may be receded into range-specific neurons at or above the inferior colliculus. The data generally suggest that target range is processed by channels used for periodicity-pitch perception in nonecholocating animals. [Work supported by NSF.]