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CHAPTER 1
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INTRODUCTION
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Inter- and intra-individual variation in earprints
1.1 General introduction and goal of research
The value ofthe external ear –also called auricle or pinna –as a means ofidentification
was recognized centuries ago.It has been studied and described as part ofprocedures to
establish the identity of criminals and victims of crimes and accidents (Bertillon,1885;
Hoogstrate et al.
,2001;Hunger and Hammer,1987;Iannarelli,1964;Swift and Rutty,2003),
or to prove paternity (Schade,1954; Tillner,1963).Not only the auricle itself showed
potential for establishingthe identityofcriminals,but also its prints (Dubois,1988;Hammer,
1986;Hirschi,1970a,
b;Kennerley,1998a,
b;Van der Lugt,2001,Pasescu and Tanislav,
1997).W hen perpetrators ofcrimes listen at,for instance,a door or window before breaking
and entering,oils and waxes on their ears leave prints that can be made visible using
techniques similar to those used when lifting fingerprints.These prints appear characteristic
for the ears that made them.
The majorityofscenes ofcrime where earprints are discovered involve burglaries.M ore
rarely,cases concern sexual offences or murder cases (Van der Lugt,1997;Kennerley,
1998a).A historical case in the Netherlands is described by Dubois (1988).He reveals how
earprints became part of the evidence used to convict the suspect of an armed robbery.
According to a survey carried out by the Rotterdam Police,in 15 % ofdomesticburglaries,
forensiccrime scene investigations showed the presence oflatent earprints (Cor van der Lugt,
personal communication).The percentage differs greatly per region,as it is not common
policy to actively search for earprints.In absence ofa national database,the chance ofan
earprint leading to a potential suspect,or the prospect oflinking different cases ofburglaries
to one burglar,depends greatlyon the effort –and memory–ofthe investigatingpolicemen.
Among the goals ofthe ‘FearID’research project are the development ofa system for
the recovery of seemingly similar earprints from a database,and the standardisation and
harmonisation ofprocedures to detect,recover,lift and record earprints.Presumably,this will
improve the practical implementation ofearprints in forensic research.The preparation ofa
training database and the dissemination ofresults through workshops and presentations are
intended to raise awareness among police authorities and consequently promote the
incorporation of a search for earprints as a standard procedure in technical forensic
investigations.
14
Introduction
Apart from practical implementation matters remains the issue of uniqueness. We
cannot prove that no two ears are alike. It is a working assumption, comparable to the
assumption that no two people have a similar pattern of ridges and furrows on their fingers.
But presumed uniqueness of ears does not guarantee uniqueness of prints, as many ears are
only partly imprinted due to differences in elevation of the various parts. So the question that
needs to be addressed is whether there is enough variation in earprints to be able to distinguish
between prints of different ears. An attendant complication is that not even two prints of the
same ear are exactly alike. Differences in the way prints are left, or the material they are left
on, may cause variation in prints by a single ear. The feasibility of earprint individualization,
therefore, depends not only upon the amount of variation in prints of different ears (interindividual), but also upon that which occurs in prints of a single ear (intra-individual).
To justify the claim that we can match an earprint uniquely to an ear, we must establish
that the print resembles other prints from the same ear more than it resembles prints from
another ear. We may attempt to do so by analysing multiple prints from a large sample of ears,
comparing inter-individual variation with intra-individual variation over a suitable set of
measurable features. An experimental feature set is suitable only if the inter-individual
variation is significantly greater than the intra-individual variation. For such a comparison, we
may use, for instance, cluster analysis or formal concept analysis (Dr. M. Ingleby, University
of Huddersfield, UK, personal communication). The outcome of this analysis will be
probabilistic. This means that we may estimate the probability of encountering seemingly
indistinguishable prints from different ears.
Prior to performing such an analysis, acquiring insight in the variability of the various
features in multiple prints originating from the same ear is of paramount importance. When
may discrepancies between prints be considered potential intra-individual variation, and when
should they be regarded as inter-individual variation? In order to understand the limits of
intra-individual variation, we first need to recognize the matters that cause it. A difference in
the amount of force that is applied by the ear to the surface during listening, for instance, is
one factor known to influence the appearance of the earprint. But how variable is applied force
during listening, and in turn, how variable are the resulting prints?What will affect the force
that is applied during listening?Will a burglar press his ear harder to a door or window when
he is eavesdropping near a busy railroad track as compared with when the environment is
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Inter- and intra-individual variation in earprints
relatively silent? Does applied force, and therefore the appearance of an earprint that was left
on a crime-scene, vary depending on whether there was noise coming from inside the house or
not?
Other factors to be considered for potential sources of intra-individual variation are, for
instance, the duration of the listening time and the amount of secretions that are present on the
ear. Are earprints affected by the time of day a person has listened or by outside temperatures?
Furthermore, to what extent does the material the print is left on influence its appearance? And
to what extent do the materials used to lift and secure it? Lastly, how stable are the features of
the actual live ear? The imprint of a newly acquired piercing or the outline of an additional
crease in the skin in front of the ear may be recognized as possible sources of intra-individual
variation in earprints. In addition, dimensions of the imprinted features may change because
the auricle itself increases in size throughout adult life. If the matching system to be designed
would base its classification at least partly on these dimensions, it would help to know just
how much the auricle may grow within a certain period of time, and moreover, if the various
parts of the auricle expand equally. Is it mainly the earlobe that stretches? Or does the
cartilaginous part of the auricle expand to a similar extent?
Such basic questions must be addressed before embarking upon a study of earprints
aimed at determining the extent of inter- and intra-individual variation. The answers will allow
us to make informed decisions regarding the circumstances under which earprints should be
collected. A study of earprint variation that includes a number of prints from each of many
ears – collected under varying conditions known to influence their appearance – will
eventually enable us to determine the boundaries to ‘natural’ variation in prints by a single ear.
It will allow the extraction of features that are sufficiently stable for a classification system
that is capable of distinguishing between inter- and intra-individual variability. Finally, it will
permit an informed estimation of the probability that two prints originate from the same ear.
1.2 Morphology of the external ear
(Excerpt from Meijerman et al., 2002)
In order to recognize the various components that make out an earprint one first needs
to familiarize oneself with the anatomy of the auricle. It is generally ovoid in form, with its
16
Introduction
larger end directed upward. Its lateral surface is irregularly concave, directed slightly forward,
and presents many ridges and grooves that serve to pick up sounds. It is made up of elastic
cartilage, connective tissue and skin, with muscular attachments in the back. The skin
overlying the lateral surface adheres firmly to the perichondrium, which carries the blood
supply to the cartilage. The medial surface however is attached more loosely. The auricularis
posterior muscle is surrounded by fibroareolar tissue, which adds to the flexibility of the ear.
An overview of the morphology of the external ear is provided in Fig. 1.1.
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helix
auricular tubercle
triangular fossa
anterior crus of anthelix
crus of helix
anterior notch
anterior knob (of tragus)
tragus
superior crus of anthelix
scaphoid fossa
cymba conchae
anthelix (stem)
cavum conchae
posterior auricular furrow
antitragus
intertragic notch
lobule
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Fig. 1.1 Morphology of the external ear.
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The crus of helix divides the largest concavity, the concha, into the cymba conchae
superiorly and the cavum conchae inferiorly. The cavum conchae extends into the external
acoustic meatus. The notch inferior to the crus of helix is the anterior notch (incisura anterior
helicis). Very occasionally the crus of helix divides, and another ridge runs superiorly. Schade
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Inter- and intra-individual variation in earprints
(1954) called this supernumerary ridge crus cymbae, after Quelprud (1934) (Fig. 1.2a). Schade
further noted that incidentally a similar ridge can be found in the lower part of the concha. He
called this ridge crus cavi.
Posterior and superior to the concha is a prominent ridge:the anthelix (erroneously also
called antihelix in literature). It is divided superiorly into two crura:crus superior (upper crus)
and crus anterior (also called crus inferior or lower crus). The two crura define a shallow
depression:the triangular fossa (fossa triangularis, also called fossa digitalis). At times, a third
crus of the anthelix is present, running from the crus superior to the supero-posterior part of
the helix. This crus is called crus posterior, or also crus tertium (Fig. 1.2b). The depression
between the anthelix and the helix is the scaphoid fossa, also called scapha or fossa
navicularis.
Anterior to the entrance to the external acoustic meatus lies a prominent cartilaginous
process, the tragus. At times, the tragus has a forked appearance. The superior tubercle of a
forked tragus (or tuberculum supratragicum) also appears in literature as the anterior knob.
Opposite the tragus, and separated from it by the intertragic notch (incisura intertragica), is
another prominent tubercle:the antitragus. The antitragus is an extension of the anthelix, and
is separated from the latter by a depression called the posterior auricular furrow (sulcus
auriculae posterior), also known as the oblique furrow (sulcus obliquus).
Note. Appendix I contains a list of definitions for the gross anatomical features of the
external ear.
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a
b
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Fig. 1.2 External ear showing crus cymbae (a) and crus posterior anthelicis (b).
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18
Introduction
1.3 Variability of the external ear
(Excerpt from Meijerman et al., 2002)
A great amount of variation is found in the morphology of all anatomical structures, and
ears are no exception. Variation in the anatomical structures of the ear, their position,
elevation or indent, will affect the print left by a given ear. It is, however, by no means
necessary to try to ‘recreate’ in our minds a 3-dimensional structure from the 2-dimensional
print in order to be able to individualize a print, as we may compare a print with other prints
and not with the ear itself. Also, variation in ear morphology does not automatically lead to a
similar amount of variation in earprints. It is nonetheless very informative to know the extent
of variation in ear morphology, as it will enable us to interpret the features of a print, and
facilitate the recognition of variation in prints made by the same ear from those made by
different ears. In addition, knowledge on the frequency at which different ‘printable’
morphological structures occur may allow a prediction of the significance of an imprinted
feature.
Several authors have described and/or classified the variation in morphology of the
external ear (e.g., Hunger and Leopold, 1978; Imhofer, 1906; Van der Lugt, 2001; Oepen,
1970, 1976; Olivier, 1969; Schade, 1954; Södermann and O’Connell, 1962; Tillner, 1963). In
the following text, different structures and classifications of their forms are treated. When
available, the frequency at which the various forms are reported to occur is provided.
Peculiarities and anomalies are also discussed.
General form of the external ear
The overall shape of the auricle is determined by the contour of the helix and of the
lobule. A common way of classifying the shape of the auricle is by defining it as either ‘oval’,
1
‘round’, ‘rectangular’ and ‘triangular'
.
1
According to the definitions provided by Van der Lugt (2001) the oval ear is longer than it is wide, the width
being maximal at the centre. It has a rounded top and bottom. The round ear is almost as long as it is wide. It
also has a rounded top and bottom. The rectangular ear is longer than it is wide, with a rectangular top and
bottom. Both ends are almost as wide as halfway down the ear. The triangular ear is longer than it is wide, with a
rounded top that is wider than the bottom.
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Inter- and intra-individual variation in earprints
The oval shape appears to be most common. Van der Lugt (2001) found 68.7% of
examined (male) ears to be oval, and Iannarelli (1989) 65% (both sexes). For triangular ears a
frequency of 21.9 % was observed by Van der Lugt, and 30% by Iannarelli. For rectangular
ears this was respectively 9.1% and 3%, and for round it was 0.3% and 2%. When taking the
shape of the earlobe into account, the ear may be further classified as ‘kidney-shaped’ (oval
with an unattached earlobe) or ‘shaped as half of a heart’ (oval with attached earlobe). Hunger
and Hammer (1987) classified the shape of the ear as ‘elliptical’ (32.2%), ‘oval’ (59.1%),
‘quadrangular’ (3.2%) or ‘triangular’ (5.5%) (no definitions provided). Hildén (1929)
compared human ears to those of other primates, suggesting that in 0.96% of cases humans
may exhibit the ‘macaque form’ (pointed supero-posteriorly; Fig. 1.3a) of the ear and in
1.98% of cases the ‘cercopithecus form’ (pointed superiorly; Fig. 1.3b).
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a
b
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Fig. 1.3 Uncommon shapes of the external ear:the macaque form (a) and the cercopithecus form (b).
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Length and width of the auricle
Length (or height) and width of the ear may be determined according to various
standards. In Meijerman et al. (2004b) the following procedure was used. The distance
between the most superior point of helix and the most inferior point of the earlobe on lines
parallel to the ear base (the auricular attachment to the head) determines the length of the
auricle. Width of the auricle is determined by the greatest distance between the ear base and
20
Introduction
the posterior part of the helix, on a line perpendicular to the ear base.
Sexual dimorphism is evident in measurements of length and width of the auricle.
Among males and females belonging to the same age group, males exhibit higher values for
both auricle length and width (Ito et al., 2001; Meijerman et al., 2004b). Measurements of
auricle length and width have also been used by various authors to explore differences
between populations. The work of Vorobev has been cited in Gerasimov (1940) and Van der
Lugt (2001). Vorobev studied ear length differences and suggested that different populations
display different phenotypes, hence different averages for ear dimensions. Similarly, Farkas
(1994) measured length and width of ears of various populations in a series of studies aimed
at recognizing populational differences necessary for facial reconstruction in plastic surgery.
The studies conducted by Farkas included Afro Americans, Chinese and North American
Caucasians. It was observed that ears of different ethnic populations varied in overall
proportions.
Physiognomic Ear Index
In addition to simply measuring ear length and width, these can be put in relation to
one another as to give what is called the Physiognomic Ear Index (EI), which provides an
immediate reference of the proportions of the ear in a single value. It is calculated by the
following formula: EI = (Width * 100) / Length. The index provides – to some extent –
information about the shape of the ear, but not about its contours. Hrdlicka (1920, cited in
Farkas and Munro, 1987) emphasized the greater importance of indices over absolute
measurements when comparing various groups of people or populations. The ear index has
therefore been used to classify the overall shape of the ear into narrow (EI<60), medium
(60<EI<65) and wide (EI>65) (Facchini, 1988). According to Topinard (1885), the EI is
relatively low among Caucasians as compared with African, Polynesian and Micronesian
populations. This indicates that Caucasian ears are comparatively long and narrow.
Helix
The curve of both the outer and inner rim of the helix may vary almost endlessly.
Particularly the inner rim may exhibit characteristic notches and acute angles. Oepen (1970)
studied ears of 500 males and 500 females and found the inner rim to have multiple notches in
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Inter- and intra-individual variation in earprints
one or both ears in 12.6% of the males and 18% of the females. The degree of rolling (or
inward folding) of the helix varies greatly as well, and may be classified as either strong,
normal, weak or not rolled at all. Depending upon how the rim is rolled or folded, the lateral
surface of the helix will be flat or convex or even concave.
Helix width may also vary greatly, both among various different ears and within the
helix of a single ear. As differences between the various regions of the helix are great, the
helix is best divided into sections when describing its variation. Commonly the helix is
subdivided into a superior and an inferior part (also called cauda helicis). This division is
useful for comparing the local degree of inward rolling of the helix, as the lower end of the
cartilage in the helix is partially separated from the main body of cartilage (Fig. 1.4), and the
degree of inward rolling of the helix in these sections is often quite different. Unfolded parts
are characteristic: Oepen (1970) found the superior part to be unrolled in one or both ears of
2% of the examined males and in 0.2% of the females. The inferior part was unrolled in one
or both ears of 6% of the males and 17.8% of the females. Oepen further noted the occurrence
of a notch in the outer margin of the helix between the superior and inferior parts. It was
observed in one or both ears of 11.8% of the males and 7.6% of the females.
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2
3
1
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Fig. 1.4 Cartilago auricularis and part of os temporale.
1. Os temporale (temporal bone); 2. cartilaginous part of the auricle; 3. cauda helices.
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22
Introduction
A special characteristic of the helix is the presence or absence of an auricular tubercle,
also known as Darwinian tubercle or Darwinian nodule. This tubercle is positioned posterosuperiorly, and may be very conspicuous and characteristic. It may be pointed or more
rounded, and it can be positioned on the inner edge, outer edge, or both, or even on the lateral
surface (Fig. 1.5). Keith (1901) illustrated the diversity of forms of this tubercle by stating
that “between every type distinguished there occurs a chain of intermediate forms”.
Hildén (1929) found that the tubercle occurs more frequently on the right side than on the left
side, and also more frequently in males than in females. More rarely, two or even more
tubercles are present. Oepen (1970) provided numbers for the occurrence of various forms of
the auricular tubercle. A very pronounced auricular tubercle occurred one-sided in only 0.2%
of the examined males. It was not observed in any of the females. A presence of two smaller
auricular tubercles occurred in one or both ears of 5.6% of the males and 4.8% of the females.
The one-sided occurrence of three auricular tubercles was noted in 0.2% of the males
and 0.4% of the females.
Tubercles are also frequently found on the superior part of the helix. Oepen (1970)
observed them on one or both ears of 9.4% of the males and 4.4% of the females. They may
be very characteristic. Finally, Geyer (1928) and Jürgens (1961) described a ribbon-like, flat
helix: the helix taeniata.
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Fig. 1.5 Various forms of the auricular tubercle.
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Anthelix
The anthelix also exhibits a vast amount of variation. The anthelix can be flat or
pronounced, wide or narrow (or anything in between), more elevated than the helix, or less
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Inter- and intra-individual variation in earprints
elevated. The superior section is usually divided into two crura: crus superior and crus
anterior (also called crus inferior). The superior and anterior crura of the anthelix define the
triangular fossa. This area varies in size depending on the curve and width of the two crura.
The curvature of each of the sections of the anthelix varies greatly, as does the elevation of
the various sections. Oepen (1970) found the superior crus to be flat (one- or both-sided) in
7.8% of the males and 4% of the females.
At various places, knobs may occur, particularly in the inferior section, the stem of the
anthelix. Oepen (1970) observed a knob at the anthelix stem in one or both ears of 19.2% of
the males and 11.2% of the females. A knob at the anterior crus was observed in 0.2% of the
females and none of the males. A knob at the superior crus occurred in 1% of the males and
none of the females. A knob at the junction into crura was found in 0.8% of the males and
0.2% of the females.
The presence of a third crus, running from the crus superior toward the supero-posterior
part of the helix (see Fig. 1.2b), may further be characteristic. Oepen found this additional
crus, known as crus posterior, in one or both ears of 2% of the males and 0.6 % of the
females. Imhofer (1906) found it in 1% of the studied ears of both sexes, and Tillner (1963) in
1% (males) and 1.4% (females) of the ears.
Scaphoid fossa
The anthelix and helix define the scaphoid fossa, also known as scapha. It can be wide
or narrow, and may taper toward the earlobe, or broaden. It can be short or long. Oepen
(1970) observed that when the scaphoid fossa broadens toward the earlobe, or when it has an
angular (ventral) apex, the posterior auricular fossa is often deep. She found the scaphoid
fossa to broaden in 35.4 % of the males and 37.4% of the females. A scaphoid fossa with an
angulated apex occurred in 18.2 % of the males and 13.6% of the females.
Crus helicis, crus cymbae and crus cavi
The helix is continued in the concha as the crus of the helix, dividing the concha in an
upper and lower half. The crus helicis can be to a greater or lesser extent elevated, curved, and
oblique. It may also give rise to additional crura. Several authors (Oepen, 1976; Quelprud,
1934; Schade, 1954; Tillner, 1963) made note of the occurrence of a ridge running from the
24
Introduction
crus of the helix toward the anterior crus of the anthelix. This ridge, the crus cymbae, is often
found to be only one-sided. Quelprud found this crus in 5 to 6% of the people, Tillner in
1.03%, while Loeffler (1940) did not encounter it at all. Cor van der Lugt, during his
extensive study of ears and earprints of the Dutch population, did not encounter it either
(personal communication). Schade (1954) quoted Loeffler (1940) in saying that the
occurrence of this feature varies greatly between different geographic regions. He furthermore
introduced the crus cavi, a ridge that also runs from the crus of helix, but through the lower
part of the concha. Schade did not provide information regarding its frequency.
Tragus, antitragus and intertragic notch
Oepen (1976) provided the following classification for the different forms: simple,
spherical, flat or with a second protuberance. The latter form, the ‘forked tragus’, was
observed by Imhofer (1906) in approximately 21% of 500 studied ears. The second (superior)
protuberance is called anterior knob. The tragus may be arched outward, or more inward, and
it can be smaller or larger than, or of equal size to, the antitragus. Excepting the forked type,
the antitragus may be similarly characterized. It can further be categorized as either horizontal
or oblique.
The tragus and antitragus define the intertragic notch. This notch can be wide or narrow,
and is classified by Schade (1954) as either V-shaped, U-shaped, horseshoe-shaped, angulated
or arched. The edges may be flat or swollen, and may give rise to a lobular furrow. A furrow
originating at the intertragic notch was noted in 26.6% of the studied males and in 21.4% of
the females by Oepen (1970).
Anterior notch
The tragus (with or without the anterior knob) and the crus of the helix define the
anterior notch, which may be more or less pronounced.
Concha
The tragus, antitragus, anthelix and crus of the helix together define the shape of the
concha. The concha may be deep or shallow, large or small, round or square. The relative
sizes of cavum conchae and cymba conchae may be classified as cavum smaller than cymba
25
Inter- and intra-individual variation in earprints
or cymba smaller than cavum.
Posterior auricular furrow
This is a depression between the antitragus and the anthelix, which may be absent or
present, deep or shallow, and oblique to various degrees. Oepen (1970) found a very deep
posterior auricular furrow in 22.8% of the males examined and in 11.4% of the females.
Lobule
Much variation is found in the length and shape of the lobule (earlobe), as well as the
extent to which it is attached to the head (free, totally attached, or anything in between). Van
der Lugt (2001) recognized 4 shapes of the lobule: round, triangular, square and lobed.
Hunger and Leopold (1978) and Hunger and Hammer (1987) refer to this division similarly as
arched, triangular, square and tongue-shaped. Schade (1954) recognized six forms, dividing
the triangular lobule into the following: ‘attached, rounded’, ‘attached, straight’ and ‘attached,
tapering to the cheek’ (See Fig. 1.6).
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a
d
b
e
c
f
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Fig. 1.6 Various forms of the lobule: unattached, tongue-shaped (a), unattached, arched (b), attached, square (c),
attached, triangular, rounded (d); attached, triangular, straight (e); attached, triangular, tapering to the cheek (f).
___________________________________________________________________________
Attached earlobes were seen in 10%-26% of different German populations by Schäffer
(1892-1893). Hildén (1922) recorded attached earlobes in 35% of the population of the island
Runö (now part of Estonia). Van der Lugt (2001) studied the occurrence of the various forms
26
Introduction
of the earlobe as well, and found the ‘round' earlobe (similar to ‘unattached, arched’ (b) in
Fig. 1.6) to occur in 63.6% of 1000 studied (male) ears, the ‘triangular’ earlobe (including
type d, e and f in Fig. 1.6) in 22.6%, the ‘lobed’ earlobe (similar to ‘unattached, tongueshaped’ (a) in Fig. 1.6) in 9%, and finally the ‘square’ earlobe (resembling ‘c’ in Fig. 1.6, but
unattached) in 4.8%. Hunger and Hammer (1987) recorded percentages of 38.8 (arched), 31.8
(tongue-shaped), 15.3 (triangular) and 14.1 (square).
An unusual form, the lobe inclus was depicted by Jürgens (1961). In this form, the
auricular attachment (or ear base) curves more or less abruptly to the front. According to
Jürgens it is found particularly in persons of multiethnic descent.
Peculiarities, minutiae and anomalies
Furrows may be very characteristic. They are often present in the lobe, tragus and the
pre-auricular area. Moles, freckles, as well as an irregular skin structure may also be
distinctive. The occurrence of pre-auricular appendages and (pre-) auricular sinuses, also
called auricular pits or fistulae auris congenitae, may be very characteristic as well.
Appendages and sinuses are skin tags and depressions or tubes respectively. (Pre-) auricular
sinuses may indicate abnormal embryological development of the auricular hillocks, whereas
pre-auricular appendages may be due to accessory hillocks (Sadler, 2003). Appendages may
usually be found anterior to the tragus, while sinuses more often occur on, or close to, the
anterior margin of the ascending limb of the helix.
Tillner (1963) quoted percentages of occurrence of auricular sinuses for groups of
various descent: European: 0.036-1.7%; African: 4.5%; Japanese: 7.8%; Asian: 10-14%.
Ewing (1946) noted auricular sinuses in 0.9% of 3500 studied British men. In the majority of
these men (77%) it occurred unilaterally; 90% of the 0.9% concerned a sinus at the margin of
the helix. Tillner found auricular sinuses in 1.16% of a group of 2322 persons of both sexes.
Like Ewing, he concluded that the majority of these sinuses occurred unilateral and close to
the anterior margin of the helix, but he did not provide statistics. Tsuchiya and Nagashima
(1998) provided data on a limited group of 45 Japanese children. In this group sinuses
occurred unilateral in 62.2% of the cases. Sinuses at the margin of the helix were found in 36
cases (80%). In seven cases the sinus was situated on the crus of helix and in five cases in the
pre-auricular region. Three of these cases had two sinuses on one side. Tillner (1963) further
27
Inter- and intra-individual variation in earprints
mentioned the occurrence of congenital cleft earlobes and earlobes with holes, resembling
pierced earlobes. Both phenomena are rare.
1.4 Recognizing the representations of gross anatomical features in an earprint
An earprint is a two-dimensional reproduction of the parts of the auricle that touch a
surface, like the print of a stamp. Unlike in a regular stamp, the elevation and the flexibility of
the various structures of the auricle vary. Due to this fact, the imprint of some morphological
structures will appear in the overall earprint, but some may not, or only partly. This all
depends on the position and elevation of each morphological structure in relation to the
position and elevation of the other structures. Imprinted features in prints of different ears
may therefore not only differ in shape and size, but also in relative intensity, or they may be
absent from a print. Absence of the imprint of (part of) a gross anatomical feature from a print
may therefore also be informative regarding the origin of the print. Fig. 1.7 shows three
examples of left-earprints, in which imprints of the various gross anatomical features are
indicated. Depressed areas of the ear show as voids in the print. In the first and third prints,
features of the external ear are almost completely imprinted. In the second print they have a
very patchy appearance.
Anatomical features most frequently found in a print are the helix, anthelix, tragus and
antitragus. If visible, the imprint of the helix will be the most peripheral part of the earprint. It
may be continuous or interrupted. The imprint of the anthelix usually runs parallel to the
imprint of the helix. At times, the imprints of the helix and anthelix are connected in the
posterior section of the print. The imprint of the anthelix may have one or more branches
extending from its upper area. It is frequently continuous with the imprint of the antitragus
and varies greatly in shape. Extensions from the upper area of the imprint of the anthelix are
called anthelix branches. Not all branches of the anthelix are necessarily imprints of actual
crura of the anthelix. An inferior branch (extending downwards) may for instance result from
the inner margin of the anthelix-stem, or from a knob at the junction of the superior and
anterior crura. For convenience we do not distinguish between branches on the basis of their
origin. Branches may extend anteriorly, superiorly, posteriorly or inferiorly.
The imprint of the tragus can be seen as an extension projecting distally from the pre-
28
Introduction
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________________________________________________________________
Fig.1.7 Examples of left-earprints in which imprints of the various anatomical features are indicated.
1. helix; 2. crus of helix; 3. anthelix; 4. anterior branch of anthelix; 5. superior branch of anthelix; 6. inferior
branch of anthelix; 7. tragus; 8. antitragus; 9. (outline of) intertragic notch; 10. lobe; 11. apex of schaphoid fossa;
12. auricular tubercle.
___________________________________________________________________________
auricular area. The projection produces a curve that may range from pointed to shallow. It
may also occur as a separate patch. The imprint of the antitragus is situated inferior to the
imprints of anthelix and tragus. It may appear as a separate patch, but it may also be
continuous with the imprints of tragus, lobe and/or antitragus. The notch linking the tragus
and antitragus imprints the outline of the intertragic notch. Its shape may vary. If the tragus
and antitragus imprints are not connected, traces of this notch may still be visible.
Features that are less often imprinted include the earlobe and (a large part of) the crus of
helix. If present, the imprint of the lobe is the most inferior extension of the earprint whose
anterior point may attach to the imprinted pre-auricular area. It is frequently incomplete and
varies greatly in shape. If the crus (root) of helix is imprinted, it is usually only the beginning
of its continuation into the helix imprint that is visible. Rarely, a small patch of the posterior
part of the crus of helix is imprinted as well, often continuous with that of the anthelix. In Van
29
Inter- and intra-individual variation in earprints
der Lugt (2001) a print is depicted in which the entire crus of helix is imprinted. This print
was made while using excessive force. A complete imprint of the crus of helix as such is
thought to occur unlikely in a functional print, i.e., a print resulting from the act of listening.
The entire outline of the concha is usually not visible in a print, and the same can be said
for the outline of the scapha. At times, however, the outline of the – often characteristically
shaped – inferior apex of the scapha is clearly imprinted. Finally, a crus cymbae, which is
already a rare feature in the actual auricle, is even less likely to be found in a print because of
its low elevation. Part of the pre-auricular region is, however, often represented in a print, and
may provide valuable information.
Note: When describing and comparing the various components of an earprint in which
the imprints of two or more of the gross anatomical features are connected, it may be useful
to have an agreement on where to put the boundaries of each of the features involved.
Appendix III provides directions for the transitions between the gross features zones in
earprints.
1.5 Materials and methods
A list of the images used to illustrate this thesis is provided as appendix IV.
Acknowledgments of sources are provided with this list.
Details on materials and methods used during the various studies are outlined in the
appropriate chapters of this thesis. In this section, some general remarks are made on the
manner of collecting the earprints that were used for the various studies.
All prints but those of the identical twins (chapter 9) and those used when exploring
the effect of the amount of oily substances present on the ear (chapter 7) were collected using
a preliminary version of the FearID listening box. This apparatus had a weight scale2
incorporated in one of its surfaces. The surface of the weight scale served as the listening
surface, enabling the measurement of (perpendicular) force applied by the ear during
listening. Loudspeakers were placed on the inside of sound box, making it possible to supply
2
LUTRON GM5000; accuracy 0.3% + 1d (specifications by manufacturer).
30
Introduction
sound during a listening effort. After the sound box had been adjusted for the appropriate
height, the subject was asked to approach the sound box and to listen for sound.
Latent prints were enhanced with ‘Special Silver’ fingerprint powder 3 – referred to as
aluminium powder in the remainder of this text – using a brush made of squirrel hair. Prints
were secured using black gelatine lifters. These lifters comprised of three separate layers: a
removable transparent plastic cover over a layer of low tack gelatine with a backing of white
rubberised linen. Firstly, the transparent top layer was removed, after which the gelatine layer
was applied onto the powdered earprint. The lifter – now having the fingerprint powder
adhered to it – was removed from the listening surface and the transparent top layer was
placed back on the gel to protect the print. Prints were scanned at 600 dots per inch, using a
Hewlett Packard ScanJet 7400c.
When collecting the earprints used for the study of variation in earprints of identical
twins (chapter 9), and those used when exploring the effect of the amount of oily substances
present on the ear (chapter 7), an acetate sheet was attached to a hard (metal) vertical surface.
This acetate sheet served as listening surface. After subjects were asked to listen, the acetate
sheet was dusted, and prints were secured in the same manner as described above.
Prints that were used for the studies mentioned in chapters 2, 3 and 8 were collected by
Ruud van Basten (Police Academy of the Netherlands). Cor van der Lugt (Police Academy of
the Netherlands) collected the prints used for the studies described in chapters 7 and 9. For the
study described in chapter 6, prints were collected by Cor van der Lugt and Ruud van Basten
(Police Academy of the Netherlands), Marta Giacon and Francesca De Conti (University of
Padova, Italy), and Zale Johnson (Centrex National Training Centre, UK).
1.6 Chapter outline
Chapter 2 contains the results of a literature study into the classification and
individualization of earprints. Results from this literature study were combined with results
from a preliminary study of earprints and suggestions for future research.
In chapters 3 to 7, various (potential) causes of intra-individual variation are addressed.
Chapter 3 contains a study into the effect of the level and frequency of the target sound and
3
Manufactured by BVDA International BV, Haarlem, the Netherlands.
31
Inter- and intra-individual variation in earprints
the level of ambient noise on the force that is applied by the ear to the surface when listening.
In chapter 4, the effect of presence or absence of a target sound on the force applied by the ear
is explored. Chapter 5 contains a study aimed at determining the rate of growth of the external
ear during adult life in order to evaluate the extent to which the anatomical features may shift
position in earprints with passing time. In chapter 6, it is investigated whether the duration of
listening affects the size and intensity of the imprinted surface. Chapter 7 contains the results
of a study to test whether the amount of oily substances that is present on the ear affects the
size and intensity of the imprinted surface.
Chapter aims to provide insight into the level of detail to which prints are compared. We
show for five individuals (examples of) the variation that may occur between different prints
of the same ear.
In chapter 9, realistic intra-individual variation is compared with a very small degree of
inter-individual variation, i.e., that in earprints of identical (monozygotic) twins. A possible
method for the classification of earprints is suggested. This method may be applied to design
an automatic matching system, and to calculate the match likelihood for any two prints.
Chapter 10 discusses the use of earprints in forensic investigations. This chapter
provides an overview of literature on the practical use of earprints as well as a summary of the
results from previous chapters. It contains the concluding remarks.
As several chapters comprise of manuscripts that were either published or submitted for
publication, unavoidably some essentials of the introduction may return in some of the
chapters.
32