BackgroundMany bats vocalizing through their nose carry a prominent noseleaf that is involved in shaping the emission beam of these animals. To our knowledge, the exact role of these appendages has not been thoroughly investigated as for no single species both the hearing and the emission spatial sensitivities have been obtained. In this paper, we set out to evaluate the complete spatial sensitivity of two species of New World leaf-nosed bats: Micronycteris microtis and Phyllostomus discolor. From an ecological point of view, these species are interesting as they belong to the same family (Phyllostomidae) and their noseleaves are morphologically similar. They differ vastly in the niche they occupy. Comparing these species allows us to relate differences in function of the noseleaf to the ecological background of bat species.Methodology/Principal FindingsWe simulate the spatial sensitivity of both the hearing and the emission subsystems of two species, M. microtis and P. discolor. This technique allows us to evaluate the respective roles played by the noseleaf in the echolocation system of these species. We find that the noseleaf of M. microtis focuses the radiated energy better and yields better control over the emission beam.ConclusionsFrom the evidence presented we conclude that the noseleaves serve quantitatively different functions for different bats. The main function of the noseleaf is to serve as an energy focusing mechanism that increases the difference between the reflected energy from objects in the focal area and objects in the periphery. However, despite the gross morphological similarities between the noseleaves of the two Phyllostomid species they focus the energy to a different extent, a capability that can be linked to the different ecological niches occupied by the two species.

Region of highest sensitivity, HRTF patterns, and IID patterns are shown to be in good agreement with earlier experimental measurements on other specimens of the same bat species, i.e., the differences are within the interspecies variability range. Next, it is argued that the proposed simulation method offers distinct advantages over acoustic measurements on real bat specimens. To illustrate this, it is shown how computer manipulation of the virtual morphology model allows a more detailed comprehension of bat spatial hearing by investigating the effects of different head parts on the HRTF. From this analysis it is concluded that for this species the pinna has a significantly larger effect on the HRTF and IID patterns than the head itself. This conclusion argues in favor of a series of recent simulation studies based on pinna morphology only [R. Muller, J. Acoust. Soc. Am. 116, 3701-3712 (2004); Muller et al., ibid 119, 4083-4092 (2006)].

This paper presents an advanced bio-inspired binaural sonar sensor capable of localizing reflectors in 3D space with a single reading. The technique makes use of broadband spectral cues in the received echoes only. Two artificial pinnae act as complex direction-dependent spectral filters on the echoes returning from the ensonified reflector. The “active head-related transfer function” (AHRTF) is introduced to describe this spectral filtering as a function of the reflector angle, taking into account the transmitter radiation pattern, both pinnae and the particular sonar head geometry. 3D localization is performed by selecting the azimuth—elevation pair with the highest a posteriori probability, given the binaural target echo spectrum. Experimental 3D localization results of a ball reflector show that the AHRTF carries sufficient information to discriminate between different reflector locations under realistic noise conditions. In addition, experiments with more complex reflectors illustrate that the AHRTF dominates the echo spectrum, allowing 3D localization in the presence of spectrum distortions caused by unknown reflector filtering. These experiments show that a fairly simple sonar device can extract more spatial information about realistic objects in its direct surroundings than is conventionally believed.

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