Quantification of fast pinna motions in rhinolophid and hipposiderid bats

Abstract

As part of their biosonar behaviors, rhinolophid (family Rhinolophidae) and hipposiderid bats (family Hipposideridae) both show conspicuous motions of their outer ears (pinna). These motions coincide with pulse emission and echo reception in time and could hence have a functional relevance for the encoding of sensory information. However, a quantitative in-depth characterization of these motions is still needed to derive detailed hypotheses for their function. To accomplish this, dense sets of landmark points have been placed on the pinna to provide for dense spatial coverage of its surface over the course of a motion cycle. Occlusion-free stereo tracking of the landmarks was accomplished with an array of four high-speed video cameras. Customized methods based on motion prediction have been used to track landmark points across video frames. The results have been used to construct accurate, continuous estimates of pinna surface motion. These estimates reveal that the pinna surface is subject to heterogeneous patterns of displacements and velocities within each motion cycle. Experiments with simplified robotic reproductions to understand the acoustic implications of these pinna surface motions are currently in progress. Once the signal transformations that result from the pinna motions are understood, the question of functional relevance can be addressed.

A biomimetic soft robotic pinna for emulating dynamic reception behavior of horseshoe bats

“…Given the positioning of the elastomers along the back of the biomimetic pinnae, the different pinna deformation patterns obtained in the current work all resulted in opening or closing of the pinna aperture. This is qualitatively similar to the pinna deformations seen in rhinolophid [10] and hipposiderid bats [38]. However, it remains to be seen whether the differences that were created by the different activation patterns for the elastomers have an equivalent in the pinna deformations of bats.…”

Dynamic echo signatures created by a biomimetic sonar head

“…Additionally, adding more degrees of freedom to the robotic model, in particular the ears, could result in a more accurate robotic model to study the effects of pinnae motion. In horseshoe bats, there are about 20 individual muscles [21] which are likely to allow for significantly more complex motion patterns and conformation states than was possible with our current model of sonar head [19,20]. Further investigation is needed to see if this complex dynamics could improve the ability for a sensing system to detect a geometric object within a cluttered environment, namely foliage.…”

“…Recently, a similar dynamics has been described in a New World leaf-nosed bat (Phyllostomus discolor, [18]). Likewise, the outer ears (pinnae) that receive the ultrasonic echoes have been shown to be in motion during echo reception [19,20], actuated by a musculature that is even more intricate than that of the noseleaves [21].…”