Echolocation: Processing of Range Information by Bats

Abstract

Echolocating bats of the species Eptesicus fuscus and Phyllostomus hastatus were trained to respond to the nearer of two targets in simultaneous discrimination experiments. The acuity of depth or range perception by sonar was measured on a series of range differences from 10 cm down to zero at absolute ranges of 30 and 60 cm. The minimum detectable range difference (75% threshold) was 11 to 13 mm for both species. The shapes of the range threshold curves corresponded roughly to the shapes of the envelopes of the autocorrelation functions of the sonar cries of the bats, even when the envelopes exhibited several maxima. The results suggest that these bats may extract range information from echoes by pulse compression. The matched filter for the sonar receiver may be a correlation network in the bat's auditory nervous system.