Monaural and binaural spectral cues created by the external ears of the pallid bat

Abstract

The acoustic properties of external ears transform the spectra of incident sound in a location-dependent manner, and provide monaural and binaural spectral information used in 2-dimensional localization. Human studies suggest that binaural spectral differences, and spectral peaks and notches in monaural transfer functions, may all provide spatial information. This study examined the acoustic properties of the pallid bat ear to determine directionality, interaural intensity differences, spectral peaks and notches in transfer functions, as well as acoustic gain. The pallid bat is a gleaning bat that uses passive sound localization to find prey, and echolocation for general orientation. It is capable of very accurate passive sound localization, and the primary focus of this study was to determine the spectral cues that might support this localization acuity. Results show that the external ears of this bat create spectral maxima and minima that vary systematically with azimuth and elevation. The monaural spectral cues resemble those reported in humans and cats, and suggest that similar spectral cues are used across taxa. The ears also create robust interaural spectral differences that vary systematically with both sound azimuth and elevation. These monaural and binaural spectral cues may provide the basis for the 1° angular resolution apparent in it this bat's passive sound localization performance.