Clutter Interference and the Integration Time of Echoes in the Echolocating Bat, 'Eptesicus fuscus'

摘要

The ability of the echolocating bat, Eptesicus fuscus, to detect a sonar target is affected by the presence of other targets along the same axis at slightly different ranges. If echoes from one target arrive at about the same delay as echoes from another target, clutter interference occurs and one set of echoes masks the other. Although the bat's sonar emissions and the echoes themselves are 2 to 5 msec long, echoes (of approximately equal sensation levels--around 15 db SL) only interfere with each other if they arrive within 200 to 400 microseconds of the same arrival-time. This figure is an estimate of the integration time of the bat's sonar receiver for echoes. The fine structure of the clutter-interference data reflects the reinforcement and cancellation of echoes according to the their time separation. When clutter interference first occurs, the waveforms of echoes already overlap for much of their duration. The masking effect underlying clutter interference appears specifically due to overlap not between raw echo waveforms, but between the patterns of mechanical excitation created when echoes pass through band-pass filters equivalent to auditory-nerve tuning curves. Keywords: Biosonar echolocation, Target ranging, Echo reception, Neural display , Target images. (AW)