Segregating signal from noise through movement in echolocating bats

Mor Taub,Yossi Yovel

doi:10.1038/s41598-019-57346-2

Abstract

Segregating signal from noise is one of the most fundamental problems shared by all biological and human-engineered sensory systems. In echolocating bats that search for small objects such as tiny insects in the presence of large obstacles (e.g., vegetation), this task can pose serious challenges as the echoes reflected from the background might be several times louder than the desired signal. Bats’ ability to adjust their sensing, specifically their echolocation signal and sequence design has been deeply studied. In this study, we show that in addition to adjusting their sensing, bats also use movement in order to segregate desired echoes from background noise. Bats responded to an acoustically echoic background by adjusting their angle of attack. Specifically, the bats in our experiment used movement and not adaptation of sensory acquisition in order to overcome a sensory challenge. They approached the target at a smaller angle of attack, which results in weaker echoes from the background as was also confirmed by measuring the echoes of the setup from the bat’s point of view. Our study demonstrates the importance of movement in active sensing.

Highlights

Our work was motivated by a study by Siemers and Schnitzler (2004) that showed that bats can capture tethered insects in close proximity to an echoic background[20]
The same individual can sometimes forage in open spaces with no or few background echoes and other times forage in highly echoic environments such as dense vegetation
Even bats that only forage in open spaces, often roost in caves or crevices, and must routinely deal with highly echoic environments. In all of these situations, bats must be able to detect prey, obstacles and landing locations, a task that becomes very difficult when moving in highly echoic settings in which the background echoes are often louder than the target’s echoes[11]

Summary

Introduction

Our work was motivated by a study by Siemers and Schnitzler (2004) that showed that bats can capture tethered insects in close proximity to an echoic background[20]. The bats in that experiment often approach the target from the side, which led us to hypothesize that they were adjusting their movement in addition to adjusting echolocation. We hypothesized that they will point their echolocation beam in a smaller angle relative to the background in order to reduce its echo. To test this idea we trained Pipistrellus kuhlii bats to search for and land on a platform while confronting them with different echoic situations. When faced with an acoustically echoic background (mimicking natural vegetation echoes), the bats adjusted their angle of attack in order to improve SNR as we confirmed by recording the echoes of the target and the background. Our results demonstrate the importance of movement in addition to echolocation for active sensing in bats

Methods

Results

Conclusion