Quantitative effects of noise on sonar performance in bats

Abstract

In 1948 Pumphrey and Gold investigated the ability to distinguish between a periodic sequence of identical sinusoidal pulses and a second sequence in which alternate pulses were inverted. The ability to detect differences between these sequences led them to calculate the Q of an assumed resonance system representing the auditory filter or critical band. They concluded that the Q was of the order of 100 for the conditions of these experiments. A detailed analysis of the spectrum of the two pulse trains indicates the critical cue for the discrimination is a pitch cue as described by Hiesey and Schubert. This pitch cue is the result of a ripple in the power spectrum of the stimulus and can be related to the pitch of delayed and added noise, as studied by Bilsen and others. [This research was supported by the National Institutes of Health. ]

Jamming avoidance response of big brown bats in target detection

“…Spectrograms of sonar sounds emitted by a big brown bat in target-detection tasks while wideband random noise of different amplitudes was delivered from a loudspeaker (Simmons et al, 1974). In response to the noise, the bat lengthens its FM sweeps, which have a curvilinear shape and tail down to a shallow sweep around 22-28·kHz (arrow).…”

“…When searching for insects in open spaces at long range, big brown bats greatly lengthen the shallow-sweeping part of the first-harmonic from 28 down to 22·kHz, which boosts the energy in this band (Simmons et al, 1979;Surlykke and Moss, 2000). Fig.·1 (Simmons et al, 1974) shows the FM sweeps produced by a big brown bat in conditions of varying wideband noise during a target detection task. In response to the noise, the bat lengthens its FM sweeps.…”