Anupam K. Gupta

Lancet Dynamics in Greater Horseshoe Bats, Rhinolophus ferrumequinum

Echolocating greater horseshoe bats (Rhinolophus ferrumequinum) emit their biosonar pulses nasally, through nostrils surrounded by fleshy appendages (‘noseleaves’) that diffract the outgoing ultrasonic waves. Movements of one noseleaf part, the lancet, were measured in live bats using two synchronized high speed video cameras with 3D stereo reconstruction, and synchronized with pulse emissions recorded by an ultrasonic microphone. During individual broadcasts, the lancet briefly flicks forward (flexion) and is then restored to its original position. This forward motion lasts tens of milliseconds and increases the curvature of the affected noseleaf surfaces. Approximately 90% of the maximum displacements occurred within the duration of individual pulses, with 70% occurring towards the end. Similar lancet motions were not observed between individual pulses in a sequence of broadcasts. Velocities of the lancet motion were too small to induce Doppler shifts of a biologically-meaningful magnitude, but the maximum displacements were significant in comparison with the overall size of the lancet and the ultrasonic wavelengths. Three finite element models were made from micro-CT scans of the noseleaf post mortem to investigate the acoustic effects of lancet displacement. The broadcast beam shapes were found to be altered substantially by the observed small lancet movements. These findings demonstrate that—in addition to the previously described motions of the anterior leaf and the pinna—horseshoe bat biosonar has a third degree of freedom for fast changes that can happen on the time scale of the emitted pulses or the returning echoes and could provide a dynamic mechanism for the encoding of sensory information.

Bat Noseleaves as an Inspiration for Smart Emission Baffle Structures

Baffle shapes are commonly used in engineered devices to interface sound sources with the free field. Examples are acoustic horns seen in megaphones and horn-loaded loudspeakers. Typical for these devices are simple, static shapes that serve primarily an impedance-matching function. Diffracting baffles linked to a sound source are also common in the biosonar system of bats. In particular in bat groups that emit their ultrasonic pulses nasally, the nostrils are always surrounded by some baffle shape. This is the case across several large and diverse bat families such as horseshoe bats (Rhinolophidae), Old World leaf-nosed bats (Hipposideridae), and New World leaf-nosed bats (Phyllostomidae). However, biosonar baffles differ from their technical counterparts in two important ways: They typically have a much greater geometrical complexity and they are capable of non-rigid shape changes over time. Although simple horn shapes can be found in the noseleaves of many bat species, they are rarely as plain and regular as in megaphones and other technical applications of acoustical horns. Instead, the baffles are broken up into several parts that are frequently augmented with intricate local shape features such as ridges, furrows, and spikes. Furthermore, we have observed that in species belonging to the horseshoe bats and the related Old World leaf-nosed bats these local shape features are often not static, but can undergo displacements as well as non-rigid deformations. At least some of these dynamic effects are not passive byproducts of e.g., sound production or exhalation, but due to specific muscular actuation that can be controlled by the animals. To study these intricate, dynamic baffles as inspirations for smart structures, we have recreated the degrees of freedoms that Old World leaf-nosed bats have in deforming their noseleaves in a digital model using computer animation techniques. In its current form, our model has 6 degrees of freedom that can be used to test interactions between different motions using actuation patterns that occur in life as well as patterns that have not been observed, but could aid understanding. Because of the high-dimensional parameter space spanned by the different degrees of freedom, a high-performance computing platform has been used to characterize the acoustic behavior across a larger number of deformed no seleaf shapes. A physical test bed is currently under construction for implementing baffle motions that have been found to result in interesting changes of the acoustic device characteristics and could hence be of use to engineering applications.Copyright

Estimating Parameters in Complex Systems with Functional Outputs: A Wavelet-Based Approximate Bayesian Computation Approach

We consider a family of parameter estimation problems involving functional data. In these problems, the relationship between functional data and the underlying parameters cannot be explicitly specified using a likelihood function. These situations often occur when functional data arises from a complex system and only numerical simulations (through a simulator) can be used to describe the underlying data-generating mechanism. To estimate the unknown parameters under these scenarios, we introduce a wavelet-based approximate Bayesian computation (wABC) approach that is likelihood-free and computationally scalable to functional data measured on a dense, high-dimensional grid. The proposed approach relies on near-lossless wavelet decomposition and compression to reduce the high-correlation between measurement points and the high-dimensionality. We adopt a Markov chain Monte Carlo algorithm with a Metropolis-Hastings sampler to obtain posterior samples of the parameters for Bayesian inference. To avoid expensive simulations from the simulator in the approximate Bayesian computation, a Gaussian process surrogate for the simulator is introduced, and the uncertainty of the resulting sampler is controlled by calculating the expected error rate of the acceptance probability. We motivate our approach and demonstrate its performance using the foliage-echo data generated by a sonar simulation system. Our Bayesian posterior inference provides the joint posterior distribution of all underlying parameters, which is otherwise intractable using existing analytical methods.

Horseshoe bat inspired reception dynamics embed dynamic features into speech signals

Horseshoe bats can alter the shape of noseleaves and outer ears (pinnae) at the time of emission and reception of biosonar pulses. The shape changes are a result of specific muscular action and significantly change the emission and reception beams by a spatial redistribution of energy in mainlobe and sidelobes. Here, we explore the potential of embedding dynamic features into the speech signals by means of bat inspired reception dynamics to improve the speech recognition accuracy and speaker localization. For this analysis, a digit dataset with 11 U.S. English speakers was recorded through a robotic setup that mimics pinna dynamics as observed in bats. The utterances were obtained through open-source speech corpora and amplitude modulated (carrier frequency: 55 kHz) to shift to ultrasonic band. These utterances were then re-recorded through the dynamic pinna set up and later demodulated to extract the original signal. It was found that reception dynamics have been able to enrich the speech signals with dy...

An approximate model for foliage echoes to study biosonar function in natural environments

Natural environments are difficult for current engineered sonars but apparently easy for at least some species of echolocating bats. To better understand the information that foliage echoes provide for biosonar-based sensing, an approximate model of foliage echoes has been developed. The model simplifies the scattering problem through two key assumptions: (i) multi-path scattering was neglected and (ii) all leaves were assumed to be circular disks. Due to the latter, the parameters of the model were reduced to the number of the disks, their positions, sizes, and orientations. The exact far-field scatter from a disk (i.e., simplified leaf) in response to planar incident waves can be obtained by summation over an infinite series of spheroidal wave functions. To reduce the calculation time, the scattered field has been approximated by exponential, polynomial, and cosine fitting functions that also depend on the disk parameters. This allows the simulation of echoes from 100 leaves in 20 s on a standard PC. The model was able to reproduce the echo waveforms from dense and sparse foliages qualitatively. The model should thus be well suited for generation of large echo datasets to explore the existence and utilization of statistical invariants in the echoes from natural environments.

Evidence for a possible functional significance of horseshoe bat biosonar dynamics

The periphery of the biosonar system of horseshoe bats is characterized by a conspicuous dynamics where the shapes of the noseleaves (structures that surround the nostrils) and the outer ears (pinnae) undergo fast changes that can coincide with pulse emission and echo reception. These changes in the geometries of the sound-reflecting surfaces affect the device characteristics, e.g., as represented by beampatterns. Hence, this dynamics could give horseshoe bats an opportunity to view their environments through a set of different device characteristics. It is not clear at present whether horseshoe bats make use of this opportunity, but there is evidence from various sources, namely, anatomy, behavior, evolution, and information theory. Anatomical studies have shown the existence of specialized muscular actuation systems that are clearly directed toward geometrical changes. Behavioral observations indicate that these changes are linked to contexts where the bat is confronted with a novel or otherwise demandi...

Biosonar dynamics in horseshoe and old-world leaf-nosed bats

Horseshoe bats (family Rhinolophidae) have evolved a capable biosonar system to allow the pursuit of prey amid dense vegetation that produces large amounts of clutter echoes. Horseshoe bats have long been known to employ dynamic effects such as Doppler effect compensation and large-scale rotations of their pinnae to realize these capabilities. Recent research has produced evidence of even more pervasive dynamical biosonar properties in horseshoe bat biosonar as well as in the related Old World leaf-nosed bats (family Hipposideridae). On the emission side, these animals employ elaborate baffle shapes that surround the exit points of their ultrasonic pulses (nostrils). During echolocation, multiple parts of these noseleaves such as the anterior leaf and the lancet in horseshoe bats are set in motion, typically in synchrony with pulse emission, hence creating a time-variant channel for the exiting wave packets. Similarly, the pinnae which diffract the incoming echoes on the reception side are frequently in m...

Static and dynamic control of emission beamwidth in horseshoe bats

Horseshoe bats (family Rhinolophidae) emit their ultrasonic biosonar pulses nasally with their nostrils surrounded by baffle structures known as “noseleaves.” The noseleaves are often characterized by intricate local shape details such as flaps, ridges, or furrows. Furthermore, some of these structures are capable of undergoing non-rigid shape changes over time. One part of the horseshoe bat noseleaf that has both static local shape features as well as a time dynamics is the lancet, a vertical projection on the top of the noseleaf. The most striking static shape features of the lancet are half-open cavities (furrows) and the most obvious in-vivo motion of the lancet is a rotation in the distal-proximal about the base of the lancet. In the present work, the acoustic effects of the furrows and the distal-proximal rotation of the lancet were studied in three individuals of the Greater Horseshoe bat (Rhinolophus ferrumequinum) using numerical methods. The lancet furrows were always found to act as beam-focusi...