Meeting Abstract
P1.102 Monday, Jan. 4 A Role for Outer Ear Features in the Ability of Bats to Localize Sound? PERRIN, Gregory E.*; WANG, Fuxun; MüLLER, Rolf; GRASSO, Frank W.; BioMimetic and Cognitive Robotics Lab, Brooklyn College, CUNY, Brooklyn, NY; School of Physics, Shandong Univ., Jinan, China; Dept. Mechanical Engineering, Virginia Tech Danville, VA gregory.e.perrin@gmail.com
The ability to localize sources of acoustic signals is important in the majority of terrestrial animals and the diversity of sophisticated neural-acoustic information-processing mechanisms to support it has received intense attention. The diversity of ear shapes seen across mammals has received less attention and its functional significance is poorly understood. Echolocating bats rely on acoustic signal-processing and across species show a wide diversity of ear-shapes. We explored the impact of simple, geometric features of ear shape on the directivity of single model ears by building scaled, physical models. We recorded sounds received inside these model ears (at the ear canal) and mapped the sensitivity to broadband signals delivered to equidistant positions along a hemisphere around the ear. Geometric features included pinna shape (degree of ellipse eccentricity, conic section depth), surface features such as flaps and ridges, as well as the size and orientation of larger structures such as the tragus. The dimensions of the model ears and the wavelengths of sound used were scaled to match those of typical echolocating bat species. The results showed frequency-swept fan-beams which could encode the vertical location of a sound-source as a function of frequency. Simulation studies with geometrically similar, idealized ears produced comparable results. These findings support the hypothesis (advanced elsewhere) that such variations in ear structure may convey sound localization information to the bat’s brain in a way that complements the well-studied horizontal localization mechanisms produced by computation of inter-aural delay in the bat’s brainstem.
