Pseudo-spectral model of elastic-wave propagation through toothed-whale head anatomy, and implications for biosonar

TL;DR

This study models elastic wave propagation in toothed whale heads using a pseudo-spectral scheme, revealing how their anatomy enables precise biosonar localization despite lacking external pinnae.

Contribution

It introduces a 3D elastic wave model of toothed whale heads based on CT scans, demonstrating the role of internal anatomy in biosonar source localization.

Findings

Wave propagation is accurately captured at specific frequencies and scales.

Whale head anatomy facilitates source localization through reverberation analysis.

The model explains biosonar capabilities without external pinnae.

Abstract

The sound-localization and, in particular, biosonar system of toothed whales is exceptionally performant. How this is achieved is not clear, given that: (i) toothed whales have no pinnae; (ii) while their auditory pathways have been studied in detail, no specific feature apparently replacing the pinna has been identified. In this study, we employ a pseudo-spectral time domain (PSTD) numerical scheme to model three-dimensional elastic wave propagation through a toothed-whale head including soft tissues. Computed tomography (CT) scans were utilized to build a three-dimensional velocity-density model of the specimen's head, parametrized on a high-resolution $1.11$ mm voxel grid. We first validate our wave propagation solver, identifying a range of frequencies and spatial scale lengths where the PSTD scheme captures the complexities of elastic wave propagation through toothed-whale anatomy. We next focus on the toothed whale's ability to locate sources on the median plane, where the role of anatomy is crucial. A 45 kHz central frequency burst (dolphin-like click) was modeled and directed at elevation angles from $-90^\circ$ to $+90^\circ$ in $5^\circ$ steps along the midsagittal plane. We find that the incoming sound can be localized, via correlation, from the reverberated portion of the time-domain waveforms recorded at the tympano-periotic complex locations.