Sonic-Pulse Compression in Bats and People: A Comment

Abstract

Bats have been reported to be extremely resistant to noise jamming. Since they navigate on a sonar consisting of FM chirps, G. K. Strother suggested that their auditory system contains “collapsing filter” similar in principle to that used in chirp radars. This paper examines that possibility in more detail and reports on some informal experiments with people; the conclusion is reached that people do not have collapsing filters, and that bats very probably don't either. It is further concluded, on the basis of an analysis of basilar-membrane responses, that at the hair-cell level the time order in the stimulus is preserved and that the basilar membrane as a whole preserves the envelope structure of a complex stimulus. Concerning the question of why, then, the bat chirps, the suggestion is made that an FM signal acts as a feature-extracting probe signal, informing the bat not only of the location but also of the size, and possibly texture, of objects in its environment.