Simulated head related transfer function of the phyllostomid bat Phyllostomus discolor

This paper presents a calculation of the head related transfer function (HRTF) for the frontal hemisphere of the phyllostomid bat Phyllostomus discolor using an acoustic field simulation tool based on the boundary element method. From the calculated HRTF results, binaural interaural intensity differences (IIDs) are derived. The results: 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. Müller, J. Acoust. Soc. Am. 116, 3701-3712 (2004); Müller, ibid 119, 4083-4092 (2006)].