Information-theoretic assessment of the peripheral dynamics in the biosonar system of horseshoe bats

Abstract

Horseshoe bat biosonar is characterized by a pronounced dynamics at the interfaces of ultrasound emission and reception: The bats can alter the shapes of their noseleaves and outer ears (pinnae) through muscular action while they are emitting or receiving biosonar signals. An information-theoretic analysis has been conducted to assess whether these non-rigid baffle motions could affect the ability of the bats' biosonar system to encode sensory information. This analysis was based on acoustic characterizations (beampatterns) obtained either through numerical predictions or from measurements of physical models. In total, four time-variant baffle shapes, for emission and reception, numerical and physical each, have been analyzed. The similarity of beampattern across different baffle shape conformations was quantified using normalized mutual information that was found to be <20% for distant stages. Hence, the changes in the baffle shapes were capable of providing different views of a biosonar environment. The information added by these views was found to enhance performance bounds for sonar estimation tasks related to target direction. In particular, it was found that the number of resolvable directions and the accuracy of direction-finding (as measured by the Cramer Rao lower bound) increased when beampatterns from across a sequence of shape conformation were combined.