title: Range dependent characteristics in the head-related transfer functions of a bat-head cast: part 2. Binaural characteristics.
abstract: Further innovations in bio-inspired engineering based on biosonar systems, such as bats, may arise from more detailed understanding of the underlying acoustic processes. This includes the range-dependent properties of bat heads and ears, particularly at the higher frequencies of bat vocalizations. In a companion paper Kim et al (2012 Bioinspir. Biomim.), range-dependent head-related transfer functions of a bat head cast were investigated up to 100 kHz at either ear (i.e. monaural features). The current paper extends this to consider range-dependent spectral and temporal disparities between the two ears (i.e. binaural features), using experimental data and a spherical model of a bat head to provide insights into the physical basis for these features. It was found that binaural temporal and high-frequency binaural spectral features are approximately independent of distance, having the effect of decreasing their angular resolution at close range. In contrast, low-frequency binaural spectral features are strongly distance-dependent, such that angular sensitivity can be maintained by lowering the frequency of the echolocation emission at close range. Together with the companion paper Kim et al, we speculate that distance-dependent low-frequency monaural and binaural features at short range might help explain why some species of bats that drop the frequency of their calls on target approach while approaching a target. This also provides an impetus for the design of effective emissions in sonar engineering applied to similar tasks.
authors.affiliation: Institute of Sound and Vibration Research, University of Southampton, SO17 1BJ, UK. suyeon.kim@exergydevices.co.uk
authors.forename: S
authors.initials: S
authors.lastname: Kim
authors.forename: R
authors.initials: R
authors.lastname: Allen
authors.forename: D
authors.initials: D
authors.lastname: Rowan
mesh_terms: D000818:Animals; D032701:Biomimetics / Q000379:methods*; D002370:Casts, Surgical; D002685:Chiroptera / Q000502:physiology*; D003198:Computer Simulation; D004215:Distance Perception / Q000502:physiology*; D004455:Echolocation / Q000502:physiology*; D006257:Head / Q000502:physiology; D008954:Models, Biological; D011825:Radar; D014828:Vocalization, Animal / Q000502:physiology*