Article

A numerical study of the role of the tragus in the big brown bat.

The Maersk Institute, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.
The Journal of the Acoustical Society of America (Impact Factor: 1.65). 01/2005; 116(6):3701-12. DOI: 10.1121/1.1815133
Source: PubMed

ABSTRACT A comprehensive characterization of the spatial sensitivity of an outer ear from a big brown bat (Eptesicus fuscus) has been obtained using numerical methods and visualization techniques. Pinna shape information was acquired through x-ray microtomography. It was used to set up a finite-element model of diffraction from which directivities were predicted by virtue of forward wave-field projections based on a Kirchhoff integral formulation. Digital shape manipulation was used to study the role of the tragus in detailed numerical experiments. The relative position between tragus and pinna aperture was found to control the strength of an extensive asymmetric sidelobe which points in a frequency-dependent direction. An upright tragus position resulted in the strongest sidelobe sensitivity. Using a bootstrap validation paradigm, the results were found to be robust against small perturbations of the finite-element mesh boundaries. Furthermore, it was established that a major aspect of the tragus effect (position dependence) can be studied in a simple shape model, an obliquely truncated horn augmented by a flap representing the tragus. In the simulated wave field around the outer-ear structure, strong correlates of the tragus rotation were identified, which provide a direct link to the underlying physical mechanism.

1 Bookmark
 · 
784 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Significant effort has been devoted to designing clustering algorithms that are responsive to user feedback or that incorporate prior domain knowledge in the form of constraints. However, users desire more expressive forms of interaction to influence clustering outcomes. In our experiences working with diverse application scientists, we have identified an interaction style scatter/gather clustering that helps users iteratively restructure clustering results to meet their expectations. As the names indicate, scatter and gather are dual primitives that describe whether clusters in a current segmentation should be broken up further or, alternatively, brought back together. By combining scatter and gather operations in a single step, we support very expressive dynamic restructurings of data. Scatter/gather clustering is implemented using a nonlinear optimization framework that achieves both locality of clusters and satisfaction of user-supplied constraints. We illustrate the use of our scatter/gather clustering approach in a visual analytic application to study baffle shapes in the bat biosonar (ears and nose) system. We demonstrate how domain experts are adept at supplying scatter/gather constraints, and how our framework incorporates these constraints effectively without requiring numerous instance-level constraints.
    IEEE Transactions on Visualization and Computer Graphics 12/2012; 18(12):2829-2838. · 1.90 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The biosonar beampatterns found across different bat species are highly diverse in terms of global and local shape properties such as overall beamwidth or the presence, location, and shape of multiple lobes. It may be hypothesized that some of this variability reflects evolutionary adaptation. To investigate this hypothesis, the present work has searched for patterns in the variability across a set of 283 numerical predictions of emission and reception beampatterns from 88 bat species belonging to four major families (Rhinolophidae, Hipposideridae, Phyllostomidae, Vespertilionidae). This was done using a lossy compression of the beampatterns that utilized real spherical harmonics as basis functions. The resulting vector representations showed differences between the families as well as between emission and reception. These differences existed in the means of the power spectra as well as in their distribution. The distributions were characterized in a low dimensional space found through principal component analysis. The distinctiveness of the beampatterns across the groups was corroborated by pairwise classification experiments that yielded correct classification rates between [Formula: see text] and [Formula: see text]%. Beamwidth was a major factor but not the sole distinguishing feature in these classification experiments. These differences could be seen as an indication of adaptive trends at the beampattern level.
    The Journal of the Acoustical Society of America 06/2014; 135(6):3613. · 1.65 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Reliable animal head-related transfer function (HRTF) estimation procedures are needed for several practical applications, for example, to investigate the neuronal mechanisms of sound localization using virtual acoustic spaces or to have a quantitative description of the different localization cues available to a given animal species. Here, two established techniques are combined to estimate an animal's HRTF from photographs by taking into account as much morphological detail as possible. The first step of the method consists in building a three-dimensional-model of the animal from pictures taken with a standard camera. The HRTFs are then estimated by means of a rapid boundary-element-method implementation. This combined method is validated on a taxidermist model of a cat by comparing binaural and monaural localization cues extracted from estimated and measured HRTFs. It is shown that it provides a reliable way to estimate low-frequency HRTF, which is difficult to obtain with standard acoustical measurements procedures because of reflections.
    The Journal of the Acoustical Society of America 05/2014; 135(5):2534. · 1.65 Impact Factor

Full-text

Download
18 Downloads
Available from