Simulation of the Binaural Environmental Transfer Function for Gerbils Using a Boundary Element Method

The auditory system relies on spectral notches in the binaural environmental transfer function (BETF) as cues for localization of sources in the median plane. Experiments have shown that the BETF for gerbils in free space, regularly termed the head related transfer function (HRTF), contains a single notch in the ultrasonic range, while the BETF for a gerbil standing on a solid surface contains several notches at much lower frequency due to comb-filtering effects. In this research, the BETF for a model gerbil geometry is computed using a boundary element method (BEM). A parallel implementation of the BEM that includes the CHIEF regularization scheme is applied. The gerbil's BETFs for various source elevations and distances in the free-field and in the presence of a solid surface are computed. Comparisons with gerbil HRTF measurements show good agreement. The reflection due to the solid surface is shown to provide an acoustic cue for source elevation as well as source distance. It is demonstrated that the full variation of the BETF with source location can only be captured through a simulation that can account for both the solid surface and the gerbil and their combined influence on the sound field.