2D/3D Dolphin Bioacoustical Modeling.
Comments, suggestions, and/or questions are welcomed
regarding any portion of the research described here. Email the
author at email@example.com
Simple models of the dolphin echolocation
Click on the link below for an (unfinished) draft
of an article on models of dolphin echolocation signal emission.
I am hoping that readers will find this draft interesting enough
to send their comments and suggestions. This article proposes a
simple 3-component acoustical model of the dolphin forehead that
appears to explain a great many features of dolphin echolocation
signals. The acoustical behavior of each model component is illustrated
using simulation movies and examples of model input-output signals
Note: This article contains an introduction to dolphin
forehead anatomy and a brief description of dolphin echolocation
signals. Readers who are not familiar with dolphin anatomy and/or
echolocation signal characteristics may wish to read this introduction
before downloading the next article on 2D computer modeling of dolphin
echolocation beam formation.
I have not yet replaced the figures with thumbnails,
so the HTML page with all figures may take several minutes to download
(if you are using a modem).
HTML version of draft (~1 Mbyte including all figures):
Click here to
The following figure is from the above article draft.
Figure 1. Diagram of selected common dolphin
head tissues from the above article. [Figure adapted from Aroyan
2D Modeling of acoustic beam formation
in the common dolphin, Delphinus delphis.
The article below describes how 2D bioacoustic modeling
was used to study sonar beam formation by the forehead tissues of
the common dolphin. This article describes the methods and summarizes
the results of my MS thesis research. Click on the link below for
a PDF file.
Aroyan JL, Cranford TW, Kent J, Norris KS (1992) Computer modeling
of acoustic beam formation in Delphinus delphis. J. Acoust.
Soc. Am. 92:2539-2545.
It has been established that some
dolphins possess well-developed acoustic orientation (echolocation)
and information gathering abilities, though substantially less is
known about the system of sound generation and beam formation. Dolphins
use a narrowly focused sound beam which emanates from the forehead
and rostrum during echolocation. The primary objectives of this
study were to simulate the effects of anatomical structure on beam
formation, and to test the viability of various hypothetical sound
source locations. Outlines from parasagittal x-ray CT scans were
used to construct a 2-D model of the head of the common dolphin,
Delphinus delphis. Finite difference techniques were used
to simulate sound propagation through tissues modeled as inhomogeneous
fluids. Preliminary simulations confirm that beam formation results
primarily from reflection off of the skull and the skull-supported
air sac surfaces. For the frequencies tested, beam angles best approximate
those measured by experimental methods for a source located in a
region of the model referred to as the monkey lip/dorsal bursae
(MLDB) complex. The results suggest that: 1) the skull and air sacs
play the central role in beam formation; 2) the geometry of reflective
tissue is more important than the exact acoustical properties assigned;
3) a melon velocity profile of the magnitude tested is capable of
mild focusing effects; and 4) experimentally observed beam patterns
are best approximated at all frequencies simulated when the sound
source is placed in the vicinity of the MLDB complex. © 1992
Acoustical Society of America.
Article PDF file (file size 700 Kbyte): Click
here to view.
The following figure illustrates a simulation result
described in the above article.
Figure 1. A 2D computer simulation
of sound production in the common dolphin. The model of the dolphin's
head is indicated by a dotted outline. The yellow region represents
the fatty melon tissues, the blue regions indicate skull bones,
and the black regions are the nasal air sacs included in the head
model. Sonar pulses from a spot (just beneath the uppermost air
sac) below the dolphin's blowhole reflect and refract through these
structures. The lines around the dolphin's head represent the direction
and intensity of sound waves emitted from the model. Most of the
acoustic energy is emitted in a forward and slightly upward-directed
beam in this 100kHz simulation. The emitted field was collected
at the ring of points surrounding the model and compared to the
measured beam patterns of live dolphins for several different tissue
and source models. Graphic © 1992
Acoustical Society of America.
3D Modeling of biosonar emission
in Delphinus delphis.
The article below describes the use of 3D acoustic
modeling to study sonar signal emission by the forehead tissues
of the common dolphin. This research investigated several aspects
of the signal emission process in this animal, including the location
of the source tissues, focusing by the melon tissues, the focal
properties of the skull, and the overall focal characteristics of
the complete head of the dolphin. The methods described are more
involved than the earlier 2D simulations, and include a novel approach
to modeling the acoustic parameters of mammalian tissues based on
x-ray CT data. This article appeared as part of a chapter contributed
to Vol. 12 of the Springer Handbook of Auditory Research series.
It summarizes the biosonar emission methods and results of my PhD
Aroyan JL, McDonald MA, Webb SC, Hildebrand JA, Clark D, Laitman
JT, Reidenberg JS (2000) "Acoustic Models of Sound Production
and Propagation." In: Au WWL, Popper AN, Fay RR (eds), Hearing
by Whales and Dolphins. New York: Springer-Verlag, pp. 409-469.
Measurements of the acoustic field of echolocating dolphins have
demonstrated that dolphins emit a rapid series of pulses in a narrowly
focused beam that emanates from the forehead and rostrum. Despite
application of a variety of experimental techniques, the exact mechanisms
involved in the generation, emission, and reception of delphinid
biosonar signals have remained conjectural. Advances in the methodology
of bioacoustic simulations have led to powerful combinations of
techniques capable of addressing questions that have proven difficult
to resolve experimentally. Aroyan (1996) combined methods for 3D
acoustic simulation and extrapolation with a novel approach to the
mapping of acoustic tissue parameters from x-ray CT data. These
techniques, applied to models of the forehead and lower jaw tissues
of the common dolphin, Delphinus delphis, allowed sound propagation
within the modeled tissues to be studied in detail. The first part
of the current chapter discusses the methods of investigation and
presents several results concerning the location of the biosonar
signal source tissues, the acoustical consequences of forehead asymmetry
in D. delphis, and the roles of the skull, air sacs, and
soft tissues (including the melon) in beam formation.
3D Modeling of hearing in Delphinus
The article below appeared in the December 2001 issue
of JASA. This article summarizes the hearing simulation portion
my PhD research, describing how 3D bioacoustic modeling was used
to investigate pathways of hearing and directional sound reception
in the common dolphin. Similar approaches could be used to investigate
hearing mechanisms in many other marine mammals. The article notes
in conclusion a number of potential refinements and/or extensions
of the techniques that may be useful in future applications.
Please email me (contact link below) for additional
information. I would be delighted to work with sincere collaborators
in applying these techniques to other marine mammals.
Aroyan JL (2001) Three-dimensional modeling of hearing in Delphinus
delphis. J. Acoust. Soc. Am. 110(6), 3305-3318.
Physical modeling is a fertile approach to investigating sound
emission and reception (hearing) in marine mammals. A method for
simulation of hearing was developed combining three-dimensional
acoustic propagation and extrapolation techniques with a novel approach
to modeling the acoustic parameters of mammalian tissues. Models
of the forehead and lower jaw tissues of the common dolphin, Delphinus
delphis, were created in order to simulate the biosonar emission
and hearing processes. This paper outlines the methods used in the
hearing simulations and offers observations concerning the mechanisms
of acoustic reception in this dolphin based on model results. These
results include: 1) The left and right mandibular fat bodies were
found to channel sound incident from forward directions to the left
and right tympanic bulla and to create sharp maxima against the
lateral surfaces of each respective bulla; 2) The soft tissues of
the lower jaw improved the forward directivity of the simulated
receptivity patterns; 3) A focal property of the lower jaw pan bones
appeared to contribute to the creation of distinct forward receptivity
peaks for each ear; 4) The reception patterns contained features
that may correspond to lateral hearing pathways. A fast
lens mechanism is proposed to explain the focal contribution of
the pan bones in this dolphin. Similar techniques may be used to
study hearing in other marine mammals. © 2001 Acoustical
Society of America.
Article draft PDF file (approx. 1.4 Mbyte):
Click here to view.
The PDF file is actually an author proof of the above
article. The color figure resolution has been reduced to minimize
file size, but the content is otherwise the same as a reprint.
Incidentally, several "puzzling" results
of the hearing simulations decribed in the above article have turned
out to be supported by more detailed experimental measurements with
live dolphins. For example, the simulations indicate that as frequency
decreases, the directions of peak hearing sensitivity drop down
from the forward horizon to point (at 12.5 kHz) in lateral-ventral
directions for each ear. It now appears that this frequency dependence
is actually supported in principle by recent jaw-phone sensitivity
data for a bottlenose dolphin [see Brill RL, Moore PWB, Helweg DA,
Dankiewicz LA (2001) "Investigating the Dolphin's Peripheral
Hearing System: Acoustic Sensitivity About the Head and Lower Jaw,"
SPAWAR Technical Report No. 1865]. A pdf file of Brill et al.'s
report is available at the web site:
The hearing simulations also showed the same left-right
side asymmetry as Brill et al.'s experimental data. Unfortunately,
Brill et al.'s report was released (to the general public) after
I submitted my final draft, and I did not have an opportunity to
discuss these correlations in the article.
3D Modeling of hearing in Delphinus delphis
-- Additional Results
Full model (D. delphis) simulated hearing
receptivity plots for frequencies
12.5 kHz, 25 kHz, and 75 kHz.
(PDF file approx. 2.0 Mb).
This section under construction please check back soon.
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