The absence of spatial echo suppression in the echolocating bats Megaderma lyra and Phyllostomus discolor

Abstract

Acoustic orientation most often takes place in echoic environments. The mammalian auditory system shows a variety of specializations to suppress misleading spatial information mediated by echoes. Psychophysically these specializations are summarized as the precedence effect. This study investigates how echolocating bats deal with multiple reflections of their sonar emissions from different spatial positions. In a two-alternative, forced choice paradigm, a study was made of the extent to which the echolocating bats Megaderma lyra and Phyllostomus discolor spontaneously suppress the spatial information of a second reflection of their sonar emission. The delay between the first and the second reflection ranged between 0 and 12.8 ms. In general, M. lyra (five individuals) and P. discolor (two individuals) did not suppress the spatial information of the second reflection of their sonar emission, whatever the delay. Only one M. lyra showed significant suppression for delays between 0.8 and 3.2 ms. However, this suppression could not be confirmed in an exact repetition of the experiment. The current data indicate that although bats may be able to suppress the spatial information of a second reflection, this is not their default mode of auditory processing. The reason for this exceptional absence of spatial echo suppression may lie in the shorter time constants of cochlear processing in the ultrasonic frequency range and the strong influence of cognitive components associated with the ;precedence effect'.