Abstract
We implement a new algorithm to model acoustic wave propagation through and around a dolphin skull, using the k-Wave software package [1]. The equation of motion is integrated numerically in a complex three-dimensional structure via a pseudospectral scheme which, importantly, accounts for lateral heterogeneities in the mechanical properties of bone. Modeling wave propagation in the skull of dolphins contributes to our understanding of how their sound localization and echolocation mechanisms work. Dolphins are known to be highly effective at localizing sound sources; in particular, they have been shown to be equally sensitive to changes in the elevation and azimuth of the sound source, while other studied species, e.g. humans, are much more sensitive to the latter than to the former. A laboratory experiment conducted by our team on a dry skull [2] has shown that sound reverberated in bones could possibly play an important role in enhancing localization accuracy, and it has been speculated that the dolphin sound localization system could somehow rely on the analysis of this information. We employ our new numerical model to simulate the response of the same skull used by [2] to sound sources at a wide and dense set of locations on the vertical plane. This work is the first step towards the implementation of a new tool for modeling source (echo)location in dolphins; in future work, this will allow us to effectively explore a wide variety of emitted signals and anatomical features.
Highlights
Most literature concerned with the evolution of sound localization postulates that this task is accomplished by means of several well established auditory cues, at least in mammals [3, 4]
We employ our new numerical model to simulate the response of the same skull used by [2] to sound sources at a wide and dense set of locations on the vertical plane
In order to be close to the experimental set-up in [2] and since one of the goals of this study is to investigate the mechanism by virtue of which the elevation of a sound source is determined, in the following we shall position numerical sources on the median plane, at a range of different elevations
Summary
Most literature concerned with the evolution of sound localization postulates that this task is accomplished by means of several well established auditory cues, at least in mammals [3, 4]. The binaural or interaural timeor phase-difference (ITD or IPD): the delay between the arrival time of a sound at the two ears. The binaural or interaural intensity or level difference (IID or ILD): the difference in the intensity of a sound, as perceived at the two ears. The locus of sources that can be associated to a given ITD and/or ILD is a cone, sometimes dubbed the “cone of confusion” [4]. Since humans and other species are known to distinguish different sources within such a cone, a third psychoacoustic cue must exist. It is clear from the physics of acoustic-wave propagation that the same signal interacts differently with our anatomy
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