P3 .

5;: VI

...... 3.: ,
_

at:

.
, -
5*.”
..
...

 

_ nx

.‘Sv

.....s. «:1...
51/ .. K

. nut
hum
. st...

2'
A"

,.'.

'Sy‘h
'fi .
JJ

 

I
v

4

19%!
-.’:I 3
327:};

..\|.

.59.:

can. xmnm»

 

11.3.33...
A ‘9: 22..
It; $.15.
v.
a
\L
1.
r!

1'.

a-..» d .....1

giéfifigéa .

.w,...m....u«v , ,4
. s fl _ fiéggfif m . .

 

)1- TI”,
lJ'J)

.‘ a My
r 1 . f ,
J I :3 C/ V

V"

“mamas”
MICHIGAN STA
EAST LANSING, MICH 48824-1048

This is to certify that the
thesis entitled

THE EFFECTS OF SYMMETRICAL DECORATIONS
ON THE ATTRACTIVENESS OF
FACES AND ABSTRACT DESIGNS

presented by

Rodrigo Andres Cérdenas

has been accepted towards fulfillment
of the requirements for the

 

M.A. degree in Department of Anthropologl

 

 

/ V Major’Professor’s Signature

W/av /0 2003'“
I I J

Date

MSU is an Affirmative Action/Equal Opportunity Institution

 

PLACE IN RETURN BOX
to remove this checkout from your record.

TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

DATE DUE

DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE EFFECTS OF SYMMETRICAL DECORATIONS
ON THE ATTRACTIVENESS OF
FACES AND ABSTRACT DESIGNS
By

Rodrigo Andre's Cérdenas

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
MASTER OF ARTS
Department of Anthropology

2005

ABSTRACT

THE EFFECTS OF SYMMETRICAL DECORATIONS ON THE ATTRACTIVENESS
OF FACES AND ABSTRACT DESIGNS

By

Rodrigo Andres Cardenas

Physical symmetry enhances physical attractiveness in several species. A
proposed explanation of this effect is that symmetry is a phenotypic indicator of
biological fitness. Another explanation is that it is a by—product of object recognition
mechanisms. Throughout the world, symmetrical designs are also common in face and
body painting as well as in the decorative arts. In three experiments, I asked whether
attractiveness could also be enhanced by symmetrical decoration. In Experiments 1 and 2,
subjects were shown photographs of pairs of human faces and instructed to choose the
more attractive face in each pair. The photographs were of physically symmetrical and
asymmetrical faces decorated with either symmetrical or asymmetrical designs. As
indexed by the number of times they were chosen, symmetrical faces were judged to be
more attractive than asymmetrical faces; adding asymmetrical designs to symmetrical
faces decreased their attractiveness; and adding symmetrical designs to asymmetrical
faces increased their attractiveness. In Experiment 3, subjects made Similar choices from
pairs of non-representational designs taken from several cultures and modified in shape,
coloration, and orientation of design features. Symmetrical designs again were judged to
be more attractive. The results are interpreted as partial support for the fitness hypothesis
and suggest that the same mechanisms underlying the judgment of physical attractiveness

also underlie cultural practices of face painting and non-representational art.

ACKNOWLEDGEMENTS

This work would not have been possible without the support and encouragement
of many people. Preliminary versions of this work were discussed with Alfredo Prieto,
Karen Miller, Tom Carr and Julio Cano. I am always grateful for stimulating discussions
with them. I thank the helpful recommendations and inspiring questions raised by my
committee members Dr. David Dwyer and Dr. Norm Sauer. I am especially thankful to
Lauren Harris for the many hours he has dedicated helping me to improve this thesis, for
the always stimulating discussions, and of course, for the free coffee and wine.

A I am especially indebted to my wife Karen Miller for her support, encouragement
and inspiring ideas.

Quiero agradecer muy especialmente a mis padres, Pedro Cardenas y Yanett
Carcamo, y mis abuelos, Tadec Carcamo y Edith Espafia, por todo el apoyo y entusiasmo
que siempre me han brindado.

I also thank Juan Carlos Soto, Salvatore Cirillo, the Instituto de la Patagonia, and
the Universidad de Magallanes, Chile, for their assistance in Experiment 1.

This work was supported by a grant from the Cognitive Science Program at
Michigan State University, and conference presentations of this work were possible
thanks to the financial support of the department of Anthropology at Michigan State

University.

iii

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................. vi
LIST OF FIGURES .......................................................................................................... vii
INTRODUCTION .............................................................................................................. 1
THE BIOCULTURAL BASIS FOR PREFERENCE FOR SYMMETRY IN ART .......... 4
Animal Ornaments and the Theory of Sexual Selection ................................................. 8
Human Ornaments ........................................................................................................ 10
Fitness and F luctuating Asymmetry ............................................................................. 14
What is Symmetry? ....................................................................................................... 15
Symmetry Detection ..................................................................................................... l7
Symmetry and Orientation ........................................................................................ 18
Location in the Visual Field ...................................................................................... 20
Parallel or Serial Process .......................................................................................... 20
Does Symmetrical Decoration Enhance Attractiveness? .............................................. 22
EXPERIMENT 1: DOES SYMMETRICAL DECORATION ENHANCE FACIAL
ATTRACTIVENESS? ...................................................................................................... 24
Subjects ......................................................................................................................... 25
Materials and Methods .................................................................................................. 25
Faces ......................................................................................................................... 25
Experimental Conditions .......................................................................................... 26
Procedure .................................................................................................................. 29
Results ........................................................................................................................... 29
Discussion............................ ......................................................................................... 32

EXPERIMENT 2: DOES SYMMETRICAL DECORATION ENHANCE

ATTRACTIVENESS IN FACES WITH IDENTICAL SKIN TEXTURE? .................... 34
Subjects ......................................................................................................................... 35
Questionnaire ............................................................................................................ 35
Sexual Orientation and Country of Origin ................................................................ 37
SES and Art Capital .................................................................................................. 37
Materials and Methods .................................................................................................. 42
Faces ......................................................................................................................... 42
Experimental Conditions .......................................................................................... 43
Procedure .................................................................................................................. 46
Results ........................................................................................................................... 46
SES and Art Capital .................................................................................................. 46
High-Asymmetry Group ........................................................................................... 46
Low-Asymmetry Group ............................................................................................ 48
Across Experiments 1 and 2 ..................................................................................... 49

iv

Discussion ..................................................................................................................... 50

EXPERIMENT 3: SYMMETRY PREFERENCES WITH NON-

REPRESENTATIONAL DESIGNS ................................................................................ 51
Subjects ......................................................................................................................... 52
Materials and Methods .................................................................................................. 52

Designs ...................................................................................................................... 52
Experimental Conditions .......................................................................................... 52
Procedure .................................................................................................................. 54
Results ........................................................................................................................... 54
Discussion ..................................................................................................................... 56

CONCLUSIONS AND GENERAL DISCUSSION ......................................................... 57
Receiver Bias ................................................................................................................ 5 7
Good Genes ................................................................................................................... 59
Extended Phenotype ...................................................................................................... 61

Future Studies ........................................................................................................... 61

REFERENCES ................................................................................................................. 65

LIST OF TABLES

Table 1. Subjects’ family income compared to Michigan family income. ....................... 38

Table 2. Subjects’ family educational attainment compared to Michigan population ...... 39

Table 3. Subjects’ number of art courses taken ................................................................ 40
Table 4. Subjects’ self-expected art test performance ...................................................... 40
Table 5. Subjects’ report on the number of art items they own ........................................ 41

LIST OF FIGURES

Figure 1. The four types of symmetry in the plane. .......................................................... 16
Figure 2. Examples of stimuli used in symmetry detection research ................................ 18

Figure 3. Experiment 1. Design of symmetrical and asymmetrical faces by manipulation
of symmetry of face and symmetry of paint. ............................................................ 27

Figure 4. The effect of symmetry of paint on facial attractiveness. Mean number of
symmetrical and asymmetrical faces judged as more attractive in Conditions 1, 2,
and 3 (8 trials for each condition). ............................................................................ 30

Figure 5. The effect of symmetry of paint on facial attractiveness. Interaction between
same-opposite sex of face (sex of subject compared to sex of face being judged) and
experimental conditions (Conditions 1 and 2) in the mean number of symmetrical
faces chosen across 4 trials (scores for asymmetrical faces are not shown but are in
the same direction as the scores for symmetrical faces). .......................................... 31

Figure 6. Experiment 2. Design of symmetrical and asymmetrical faces with synthetic
skin texture by manipulation of symmetry of face and symmetry of paint. ............. 44

Figure 7. The effect of symmetry of paint on facial attractiveness. Mean number of
symmetrical faces chosen as more attractive in each condition (8 trials / condition).
Conditions 1, 2, and 3 consisted of faces painted with either high-asymmetry or low-

asymmetry designs. ................................................................................................... 47

Figure 8. Experiment 3. Abstract designs whose symmetry was manipulated according to
three experimental conditions: Shape, Coloration, and Orientation. ........................ 53

Figure 9. Mean number of designs chosen in each condition by male and female subjects.
................................................................................................................................... 55

vii

INTRODUCTION
“. . .the eye prefers symmetry or figures with some regular recurrence.
Patterns of this kind are employed by even the lowest savages as ornaments;
and they have been developed through sexual selection for the adornment of
some male animals.”
Charles Darwin, The Descent of Man and Selection in Relation to

sax,1882,p.93.

People all over the world willingly transform the human face and body, through
the use of decoration and ornamentation, into something more appealing, something
closer to an ideal type. Certainly it was this behavior that inspired Charles Darwin in the
passage quoted above as well as Franz Boas (1955) when Boas wrote, “aesthetic pleasure
is felt by all members of mankind” (p. 9). Indeed, the decorative arts and body adornment
are broadly acknowledged as universal features of mankind and as hallmarks of “modern
human behavior” (e.g., Mithen, 1996; Henshilwood et al., 2002; Power, 1999), and
among their most striking and common features is the use of symmetrical designs (e. g.,
for body adornment: Boas, 1955; Brain, 1979; Ebin, 1979; Gusinde, 1982; for decorative
arts: Gombrich, 1984; McManus, 2002; Washburn & Crowe, 1988; Weyl, 1952).

This common use of and implied preference for symmetry in face and body
painting and the decorative arts could be acquired through cultural processes, but that
cannot be the whole story. One reason is that many cultures showing the preference are
temporally and geographically isolated (Levi-Strauss, 1963). Another reason is that

symmetry is perceptually salient in human visual processing as indicated by its rapid and

accurate detection in adults (Julesz, 1971; Evans et al., 2000; Tyler, 2002; Wagemans,
1999; Wenderoth, 1994), its prominence in memory (Attneave, 1955; Deregowski, 1972),
and its high signal value even for infants (Bomstein et al., 1981). Preference for
symmetry also appears to be unaffected by learning (Rentschler et al., 1999; Washburn &
Humphrey, 2001). Finally, facial symmetry has the same effect in a variety of cultures: to
enhance physical attractiveness (Grammer & Thomhill, 1994; Hume & Montgomerie,
2001; Jones et al., 2001; Koehler et al., 2002; Little et al., 2001; Mealy et al., 1999;
Penton-Voak et al., 2001; Perrett et al., 1999; Rhodes et al., 1998, 2001a,b). Collectively,
the evidence suggests that the preference for symmetry, while perhaps acquirable through
cultural processes, is rooted more fundamentally in our evolutionary history. If so, it
further suggests that the preference is an adaptive trait, perhaps related to sexual selection
just as Darwin proposed.

Given the ubiquity of symmetrical designs, the salience of symmetry in vision, its
effects on physical attractiveness, and the possibility that the preference is adaptive, the
question is whether symmetrical designs, namely, decoration in the form of facial paint,
can enhance facial attractiveness, that is, make faces more attractive than they would be
otherwise, and, likewise, whether symmetry also can enhance the attractiveness of
abstract, or non-representational, designs. To find out, I conducted three experiments, the
first two with faces, the third with abstract designs.

In this thesis, I begin by discussing the conceptual framework behind this work in
the context of current research in the anthropology of art. After that, I discuss research on

the perception of symmetry. I then describe the three experiments and discuss the results

as they bear on three different explanations for symmetry preference. Finally, in the

conclusions, I propose new questions to be addressed in future research.

THE BIOCULTURAL BASIS FOR PREFERENCE FOR SYMMETRY IN ART

Like all species, human beings are biological organisms functionally shaped
through evolution. Functional design implies that biological systems are endowed with
physiological structures designed to enhance their own survival and reproductive success.
Such structures could in fact embody cognitive architectures for perceiving and
processing information, and, therefore, be tuned to allow organisms to interact effectively
with their environment. As neuroscience research has shown, understanding the
physiological characteristics and functional design of such structures is critical for
understanding behavior.

Despite the growing body of evidence for the role of physiological structures in
behavior, modern anthropology has not been much concerned with understanding how
such structures can affect cultural behavior. This lack of concern is partly due to how
cultural phenomena are studied by the dominant paradigm in social sciences, the so-
called “Standard Social Science Model” (Tooby & Cosmides, 1992). This paradigm
assumes that culture is a social construction determined historically by contextual social
factors and that there are no relevant evolutionary forces or psychological mechanisms
that contribute significantly to cultural behavior (an expression of Durkheim’s claim that
society is a sui generis reality). As a logical derivation from this assumption, the
paradigm conceptualizes the human mind as a ‘black box’ (Locke’s tabula rasa), an
unbounded, unbiased learning machine (Sperber & Hirschfeld, 2004) whose functional
design is not relevant for understanding cultural behavior.

This rationale has led anthropologists to focus exclusively on cultural differences

across societies, leaving practically unexplored the similarities or universals of human

behavior and their role in cultural dynamics. Many findings, however, cast doubt on the
validity of the standard social science model. As mentioned above, there is growing
evidence in neuroscience that the physiological structures that embody cognitive
architectures are critical for understanding human behavior. Comparative neuroanatomy
has Shown the relationship between neurological structures and the presence or absence
(and degree of development) of cognitive skills in different species. Neuroscience,
including cognitive neuro-psychology, also has shown that normal behavior is disrupted
when certain structures are damaged, and developmental studies have Shown behavioral
correlates between the development of physiological structures and the development of
behavior.

The standard social science model has also substantially influenced the
anthropological study of art. Even though art is ubiquitous in human societies, few
attempts have been made by modern anthropology to examine the possible biological
basis of art. Instead, anthropologists pay closer attention to the particularities of aesthetic
behavior within each culture and predominantly to the meanings and values that artistic
objects convey within a society, that is, the particularities of the social context that
apparently gives rise to certain decorative patterns. Although the standard social science
model acknowledges that our common human physiology can lead to universal features
in the way people perceive decorative patterns, such features are excluded a priori from
anthropological analysis.

Jeremy Coote (1992), for instance, argues that perception is a process in which
“cultural factors play a dominant role;” in other words, “perceptions are cultural

phenomena” (p. 247). As one may expect, however, Coote is not specific about where to

draw the line where “physiological perception” ends and “cultural perception” begins. He
proposes that the most fundamental motivation of the anthropology of art is to understand
how artists and viewers see art.

In a similar vein, Howard Morphy (1994) argues that “the analysis of the objects
must be framed in terms of their place and meaning within the producing culture” (p.
655). He recommends that the anthropological analysis of art should focus on the analysis
of form, namely, “Shape, componential structure and material composition”, as a “point
of entry” to understand art and other aspects of a given culture. For Morphy, many of the
physical properties of objects can be apprehended cross-cultmally, but the most critical
aspect is to recognize the “non-material attributes” of objects, the ones that “presuppose
cultural knowledge” (p. 673).

In general, the underlying assumption of such arguments is that it is possible to
separate physiology from culture, to somehow depurate culture from biology, and that
semantics and knowledge cannot be shaped by our cognitive architectures and mental
mechanisms. This dichotomizing between biology and culture leads to the
disembodirnent of cultural behavior.

In recent years, there has been movement against the standard social science
model as shown in increasing interest in understanding how evolved cognitive
architectures Shape cultural behavior. By framing questions about cultural practices in
evolutionary biological terms, this perspective promises to shed new light on the nature
of cultural behavior. In the case of art, for instance, we could ask: Is art unique to
humans? Why is art so pervasive across cultures? What evolutionary forces and

processes, if any, have contributed to set off and shape human art?

Such questions have been particularly intriguing to evolutionists concerned with
the survival value of human behavioral traits. Some of them regard art as a more or less
wasteful activity with no survival, or adaptive, value, merely a by-product of other
sophisticated mental faculties for information-processing (e.g., Pinker, 1997). But if art
was Shaped by sexual selection, then it is also possible that it has a direct adaptive value
(Darwin, 1882; Zahavi, 1978; Zahavi & Zahavi, 1997; Miller, 2000, 2001). In other
words, an adaptive fimctional design may underlie aesthetic preferences where beauty
and ugliness correlate with survival and reproductive success (Thomhill, 1998).

Thus, instead of separating biology and culture into separate domains, to
understand cultural behavior, biology and culture can be integrated into a biocultural
perspective, one that draws on convergent evidence from different scientific disciplines to
provide an integrated view of human behavior in an evolutionary context.

One possible way to achieve this integration is through use of the fiamework proposed in
1963 by the Dutch ethologist Nikolaas Tinbergen. Tinbergen proposed that animal
behavior could be studied by asking four types of complementary questions about an
organism’s behavior:

- How does it work? This question addresses the mechanistic causes of behavior, in
other words, how a particular stimulus affects an organism’s nervous system.

- How did it develop? This question addresses the developmental or ontogenetic causes
of behavior, that is, how the mechanisms responsible for behavior develop in an
organism.

- Why does it exist? This question addresses the selective advantage of the behavior.

- Why did it evolve? This question focuses on phylogeny, that is, on the evolutionary
history of the behavior.

The first two questions are called “proximate” questions: they are the “how”
questions, meaning that they ask how mechanisms work and develop in the lifespan of an
organism, without looking directly at evolutionary processes. The last two questions are
“ultimate”, or “why” questions, which involve evolutionary and historical thinking. Thus,
we could ask about decorative patterns: How does a particular pattern or design affect the
nervous system of a given organism? When does the organism develop the perceptual
mechanisms required for perception of the designs? For example, are they age specific?
Why is the behavior functional, or adaptive, for the organism, in other words, what are its
benefits? Finally, how did this behavior come about in the course of evolution?

The strength of this conceptual framework is that it considers all levels of
explanation as complementary and not as mutually exclusive. It therefore avoids the
simple dichotomy between nature and culture given that any behavior is supported by

biological mechanisms.

Animal Ornaments and the Theory of Sexual Selection
In the animal kingdom, decorative patterns are common, as they identify the
species and often also an individual’s sex and age (Zahavi, 1978). A possible explanation
for the evolution of animal ornaments is that they evolved from sexual selection
pressures.
Darwin proposed the theory of sexual selection, which critics regard as its most
original contribution to evolutionary theory, in 1871. He recognized that, contrary to the

predictions of natural selection, many animal traits were detrimental to survival. To solve

this puzzle, Darwin came to realize that organisms not only strive to survive but to
reproduce, so that they may evolve traits that enhance their reproductive fitness even at
the cost of their personal survival. He coined the term “sexual selection,” therefore, to
designate the type of selection produced by the differential success of given physical and
behavioral phenotypes for acquiring mates. According to Darwin, sexual competition for
mates occurs in at least two forms: in the form of fights among rivals of the same sex
(intra-sexual selection) and in the form of mate choice, that is, in the capacity of
individuals of one sex to attract mates of the other sex (inter-sexual selection). Darwin
proposed that fights between rivals leads to the evolution of traits, such as weapons, that
enhance the capacity for defeating rivals in agonistic competition, and that mate choice
leads to the evolution of ornaments to attract mates.

Although the theory of sexual selection is a centerpiece of Darwin’s view of
evolution, it remained largely ignored and discredited until the 1970’s (Cronin, 1991;
Anderson, 1994). During the centennial commemoration of the publication of Darwin’s
book on sexual selection, new seminal work on sexual selection appeared. Trivers (1972),
for instance, proposed that differences in mating behavior, such as the tendency of
females to choose mates and of males to court mates, result from differences in parental
investment: females invest more resources than males in raising their offspring. Several
other ideas, such as the handicap principle, and new intellectual paradigms, such as
sociobiology, also raised interest in sexual selection (Miller, 1998).

Among the hypotheses proposed for the evolution of ornaments are the “runaway

sexual selection”, the “good-genes hypothesis”, and the “sensory bias hypothesis”.

The runaway hypothesis, introduced by R. A. Fisher (1930), proposes that sexual
selection could originate when females arbitrarily became attracted to some trait in males.
Males with the preferred trait will be more successful reproducing, and females with the
preference will have more attractive male offspring. Over generations, sexual selection
would favor more extreme developments of the trait until equilibrium is reached because
the males’ survival is compromised.

The good-genes hypothesis, however, proposes that the attractive male trait is an
indicator of mate quality, so that attractive mates have a better genotype for survival. One
of the proposed good-genes hypotheses, the handicap principle, introduced by A. Zahavi
in 1975, suggests that signals are not selected because they enhance survival but because
they enhance the reliability of the message signaled. When it comes to mate quality, a
Signal can be reliable only if it is so costly for survival that poor-quality mates would not
be able to fake it (because their survival is compromised), that is, when it become a
handicap for its bearer.

The third hypothesis, the sensory bias, or receiver’s bias, hypothesis, proposes
that mate selection occurs thanks to a pre-existent sensory bias in females that leads to
the evolution of more extreme signals in males (e.g., brighter colors, louder calls), in
other words, without a necessary genetic correlation between a preference and trait

(Ryan, 1998).

Human Ornaments
Like animal ornaments, human ornaments serve many purposes, some of them
unique to humans. Indeed, the cultural selection and transmission of decorative patterns

in a given population can operate at a much faster rate than the time required for

10

biological patterns to spread in a population (e. g., fashion compared to birds’ feather
coloration). Moreover, culture can quickly change not only the structure of a particular
ornament but its meaning as well.

Across cultures humans have undergone brutal pain and spent conspicuously
precious time and resources with the aim of adorning their bodies. Potentially harmful
procedures of body modification are well known and documented, such as scarification,
tooth removal, tooth-chipping or filing, foot binding, piercing, and reshaping skulls and
limbs. These practices can lead to a number of health problems, such as infectious
diseases (particularly in geographic areas with high pathogen prevalence) or the
disruption of normal physiological processes. The corset, for instance, designed to
reshape the waist and abdomen, can lead to pulmonary disease and cause varicose veins
because it restricts the return of blood from the legs (Brain, 1979, p.81).

Cosmetic decoration, of course is not unique to pre-industrial societies. Indeed, in
industrial economies the resources spent on cosmetics are in no way diminished, as
illustrated by the current economic success of the “beauty industry”. The beauty industry
represents a $160-billion-a-year global business with an estimated annual growth of 7%,
which is more than twice the rate of the developed world’s GDP (Anon. 2003, p.71).
Americans, for instance, spend more each year on beauty that they do on education.

But what is the benefit of such costly behavior? Even though body decoration
may serve physiological needs, such as protecting the Skin with paint against cold
weather (e.g., among the Thompson Indians of North America), body decoration serves

social communication. Indeed, humans have developed an enormous variety of

11

decorative designs that either lack any direct physiological function or are
physiologically harmful but that serve social communication.

The communicative functions of body adornment are copiously documented in
the ethnographical literature. Body adornment has been described as encoding
cosmovision, or links to the supernatural world, warfare, mourning, marital status,
physiological processes, age, social adscription, social inequalities (status, rank, property
in the case of slavery), emotional states, for good luck, and for recovering from illness.
Body decoration can became a tangible medium for making objective abstract concepts,
such as social differences and religious ideas, and also as a way to enact a worldview.

As mentioned earlier, body adornment is widespread. Bobbi Low (1979) surveyed
a sample of 138 societies from the Human Relations Area Files and found that all
practiced some form of ornamentation, even those with a subsistence economy. The
survey also revealed some sex differences in ornamentation, Showing a tendency for
female ornamentation to signal sexual availability (pubertal or marital status), while male
ornamentation tended to signal rank and puberty, but seldom marital status (p. 486).

Similarly, an unpublished survey on 60 preindustrial societies shows that women
are more likely than men to use body paint as a form of adornment (Alford, 1996). In
about one-half of preindustrial societies, men and women are equally decorated, in 8%
men are more decorated, and in 38% women are more decorated. The expression of rank
through adornment, however, is more common for men (43%) than for women (13%).

Not all designs resemble a culturally standardized system of communication, and
often that is the case with body ornamentation aimed at enhancing attractiveness.

According to the ethnographical record, attractiveness can be enhanced in a number of

12

ways. For instance, in his survey of the Tiv of Central Nigeria, Bohannan (1956) found
that most decoration is cosmetic and that beauty can be achieved only when it is painful,
through scarification. As Bohannan’s informant stated: “of course it is painful. What girl
would look at a man if his scars had not cost him pain?” (p. 121).

Age is also encoded in ornaments aimed to enhanced attractiveness. Among the
Tiv, scarification style changes from one generation to the next, and young women’s
preference for young instead of old men is expressed in their preference for new types of
facial marking (Bohannan, 1956).

Health is also related to attractiveness and encoded in body ornamentation. That is
the case, for instance. for the Ommura of Eastern Highlands, Papua New Guinea, who
signal health by adding pig fat to their body paintings to make them shine (Johnson,
2001 ). Body decoration can also signal health in more subtle ways. A survey of cross-
cultural data on scarification showed that stomach scarification could act as a signal of
female mate quality in societies with high prevalence of pathogens (Singh & Bronstand,
1997). The analysis showed that pathogen prevalence predicts female stomach
scarification independent of polygyny, famine, and social class stratification, and that the
relationship is not evident for males.

The resources expended in enhancing one’s attractiveness are not without social
consequences. Attractiveness is valued in many societies and particularly by men (Buss,
1989). At least in Western societies, attractive people are perceived, for example, as more
intelligent and, perhaps partly for that reason, receive better grades and jobs (e.g.,

Zebrowitz et al., 2002).

13

Fitness and Fluctuating Asymmetry

In this thesis, I am interested in the frequent use of symmetrical designs in body
decoration. Recent research suggests that symmetry can enhance attractiveness in many
species by reflecting stability in development. In nature, no “bilaterally symmetrical”
organism is perfectly symmetrical. Every creature instead shows what in biology is called
“fluctuating asymmetry”, small and random deviations from perfect symmetry of
bilaterally symmetrical traits (Ludwig, 1932). Across a population, these deviations are
normally distributed about a mean of zero (Swaddle, 2003; Palmer & Strobeck, 2003).

Because both sides of the body share the same genotype and are exposed to the
same effects of the environment, it is hypothesized that fluctuating asymmetry reflects an
organism’s capacity to cope with developmental noise (e. g., metabolic rates,
concentration of regulatory molecules, diffusion, thermal noise, and rates of cell division,
cell growth, and cell death) (Palmer & Strobeck, 2003). In other words, morphological
differences in body sides are believed to be due to the interaction between random forces
perturbing development and mechanisms that reverse or stabilize development
(developmental instability) (Lens etal., 2002). Therefore, the degree of symmetry is now
typically used as a measure of an organism’s developmental precision, that is, how
closely an organism’s structure approaches its expected phenotype for a given genotype
and environment (Palmer & Strobeck, 2003). Fluctuating asymmetry therefore may serve
as an indicator of fitness (Maller, 1992; Maller & Thomhill, 1998).

F luctuating asymmetry has been found to affect mate selection in a number of
species in a variety of environmental setting, including arboreal, terrestrial and aquatic,

which suggest that fluctuating asymmetry plays the same role irrespective of the different

14

visual demands required in different environments. However, not all research on
fluctuating asymmetry shows a consistent relationship between fitness and fluctuating
asymmetry: some show a clear relationship, others Show weak relationships (trait or
taxon specific), and still others Show no relationship at all. These discrepant findings
- could be attributed to differences in the methodology used (fluctuating asymmetry is
usually very subtle, around 1% or less of the size trait), or they could mean the
relationship does not exist, but it is important to note that the idea is under current debate
(Swaddle, 2003).

Thus, if fluctuating asymmetry is indeed a clue to fitness used for selecting mates,
animals should be very good (or at least better than chance levels) at detecting it. Most
symmetry detection studies have been with humans (Swaddle, 1999). The general

findings of such studies are reviewed in the next section.

What is Symmetry?

The word symmetry is used in a wide range of intellectual domains —such as
music, biology, and physics— to describe several kinds of patterns, a characteristic that
has contributed the typical polysemy of the term symmetry. In art and design, for
instance, symmetry loosely refers to ‘balance’ or to the effect of the artwork’s elements
being evenly distributed across a picture (therefore, it does not mean that identical
elements are distributed across a picture). In music, conversely, it refers to a number of
compositional patterns such as contrapuntal operations, for example, canon, counterpoint
(operations common in Bach’s music), and mirror chords. In this thesis, however, I use

the term following its mathematical definition, according to which symmetry occurs

15

when an object (a shape or pattern) is identical to a transformed copy of it. Four types of
symmetry can be identified according to the type of transformation (Figure 1):

- Reflectional symmetry, also known as mirror or bilateral symmetry, occurs when the
object iS copied or reflected across a plane (the object is “flipped” over a line).

- Rotational symmetry occurs when the object is rotated around a center point.

- Translational symmetry occurs when an object is moved a given distance parallel to a
plane (its orientation is not altered).

- Glide-reflection is a combination of reflection in a plane and movement a given

distance parallel to that plane.

 

 

 

Reflectional

 

 

 

 

C

”VRotational WI, ‘. l

 

Glide-reflection

 

 

 

 

Translational

 

Figure 1. The four types of symmetry in the plane.

16

In the following section I review some findings from visual science on how

humans detect symmetry.

Symmetry Detection

As Pascal defined it, symmetry is “what is perceived at a glance”. Understanding
symmetry’s ubiquitous salience for the visual system has motivated studies on the
detection of symmetry since the early days of visual science (e. g., Mach, 1959).

Despite the diversity of methods used to study how humans detect symmetry,
most studies assume that the underlying perceptual and cognitive processes are directly
reflected in people’s accuracy (“error rate”) and decision time (“reaction time”) in
determining whether or not a given figure (stimulus) is symmetrical. It is possible,
therefore, to examine how people detect symmetry by measuring changes in their
performance associated with changes in the structure of the stimuli (e. g., number of
elements comprising the design, coloration, shape, and orientation), changes in their time
of presentation (e. g., 100 milliseconds, or until symmetry is detected), as well as with
changes in where the stimulus is presented in the visual field, for example, in the area
where the person is looking (fixation, centered at the fovea) or outside that area
(eccentricity).

Typically the stimuli correspond to clot patterns or shapes, like those depicted in

Figure 2.

17

 

Figure 2. Examples of stimuli used in symmetry detection research.

Most studies have focused only on how people detect reflectional symmetry. The
results show that people are remarkably accurate and fast, particularly when the axis of
symmetry is oriented vertically. Although research on symmetry detection shows several
consistent findings, certain findings have puzzled researchers for decades, and, as a
result, there is no current unifying theory (Wagemans, 1995, 1997). In what follows I

briefly review some of the main finding in this research.

Symmetry and Orientation
Studies comparing pe0ples’ performance at detecting mirror symmetry with other
kinds of symmetry have found that mirror symmetry is perceptually more salient than
rotational or translational symmetry (and therefore glide-reflection) (Julesz, 1971;
Corballis & Roldan, 1974; Royer, 1981; Baylis & Driver, 1994; Wagemans et al., 1993).
Performance at detecting symmetry changes depending on how the axis of
symmetry is oriented (e. g., vertical, horizontal, diagonal). People are best at detecting

vertical symmetry (90°), then horizontal symmetry (0°, 180°), then symmetry whose axis

18

is oriented at the main oblique diagonals (45°, 135°), and then any other orientation
(Mach, 1959; Julesz, 1971; Barlow and Reeves, 1979; Wenderoth, 1994).

One factor that might explain why vertical symmetry is perceptually salient is the
structure of the visual world. Analyses of large samples of images of real world scenes
(indoor, outdoor, and natural scenes) have shown that the vertical and horizontal
orientations are the most prevalent (Switkes et al., 1978; Coppola et al., 1998). This
finding has been suggested as the basis of the “oblique effect” (Coppola et al., 1998):
better discrimination of visual stimuli oriented horizontally or vertically compared to
stimuli oriented obliquely (Appelle, 1972). The neurological correlates of the oblique
effect suggest that the salience of vertical symmetry is hardwired: cortical cell
populations responsive to vertical stimuli are more abundant than cells tuned to
horizontal or oblique orientations (Beh & Latirner, 1997; Hubel & Wiesel, 1968; Li etal.,
2003), and vertically and horizontally symmetrical patterns Show a different pattern of
brain activity than the activity produced by oblique axis orientations (Beh & Latirner,
1997). However, the oblique effect does not explain why people are also better at
detecting symmetry oriented at 45° and 135° over other orientations.

Additionally, the advantage of detecting vertical symmetry over any other
orientation appears to be due not only to a fixed neural architecture but also to people’s
attentional strategies (Wagemans, 1997). Wenderoth (1994), for instance, showed people
a set of figures whose axis of symmetry ranged from 0° to 90° and from 90° to 180°,
meaning that the mean of the distribution of orientations was not a vertical axis. He found
that people were not better at detecting vertical symmetry but instead were faster and

more accurate detecting symmetry around the axis of symmetry that was more likely to

19

occur (the one representing the mean of the frequency distribution of the stimulus set).
Similarly, Pashler (1990) found that people were faster at detecting non-vertical
symmetry when cued about the figure’s orientation that they were going to see. These
studies Show that people’s attentional strategies are important for understanding their
performance at detecting symmetry at different orientations.

Thus, although it is not completely clear why symmetry at certain orientations is
more salient to the visual system, it seems clear that evolved neural architectures and

attentional strategies are orchestrated for understanding the structure of the visual world.

Location in the Visual Field
Reflectional symmetry is detected faster and more accurately when the axis of
symmetry is at fixation, that is, directly located where the eyes are focused (centered at
fovea). However, the effect seems less critical for closed shapes than for dot patterns.
People are faster and more accurate at discriminating symmetry when the figure’s
elements are near the axis of symmetry, or midline (Julesz, 1971, Bruce & Morgan, 1975;
Barlow & Reeves, 1979; Jenkins, 1982), as well as near the edge or outline of the figure

(Barlow & Reeves, 1979).

Parallel or Serial Process

The salience of symmetry has led some researchers to hypothesize that symmetry
is perceived in a parallel rather than a serial process (Wagemans, 1999). To perceive
symmetry as a serial process means that the detection time is proportional to the number
of elements comprising the stimulus because every feature-point of the design needs to be
examined individually and independently of other points in the design. Consequently,

increasing the number of feature-points comprising a design would increase the time

20

required to determine the symmetry of a design. In a parallel process, on the other hand,
detection of symmetry occurs independently of the number of elements comprising a
design, for that symmetry can be determined at the same speed even when the number of
elements increases.

Recent research suggest that people use a parallel process for extracting general
features of the stimulus but use a serial, or point-by-point, process for comparing more
detailed features. This is suggested by a study Showing that small perturbations of a
symmetric display are not readily perceived (Huang & Pashler, 2002).

Additionally, when research is conducted with figures with multiple features to be
checked for symmetry (e. g., several colors), that is, figures more complex than
monochromatic figures (dots and lines), the results Show that people cannot judge
simultaneously the symmetry of more than one feature or dimension of a figure (Morales
& Pashler, 1999; Huang & Pashler, 2002). For instance, when Shown a figure with two
colors (two features), people first judge the symmetry of one color and then the symmetry
of the other color (Morales & Pashler, 1999). The same is found for other features, such
as two shapes comprising the design (Huang & Pashler, 2002). These results corroborate
the view that attentional mechanisms are needed when judging symmetry.

In sum, although there is no unified theory of how people perceive symmetry,
research on symmetry detection shows that symmetry is a very salient feature of the
visual system and that people are quite proficient at detecting symmetry, particularly
when it is oriented vertically and centered at the fovea. Symmetry detection research also

demonstrates the importance of attention. The salience of symmetry covers the entire

21

human lifespan, as indicated by its salience for infants (Bomstein et al., 1981; Fisher et

al., 1981), but it seems to decline for adults over 60 years old (Herbert et al., 2001).

Does Symmetrical Decoration Enhance Attractiveness?

As previously noted, although the preference for symmetry may be due to cultural
factors, in the traditional sense of the word, many findings suggest that this cannot be the
whole story. As also noted, many species Show a preference (or a distinctive behavior)
for symmetry and humans are endowed with a visual system tuned to detect symmetry
fast and accurately. Thus, it is possible that symmetrical decorations are very common
across cultures because humans are endowed with perceptual mechanisms very sensitive
to symmetry detection that affect the way designs are produced and judged around the
world, such as the use of specific colors, contrast and patterns in order to enhance the
display of symmetrical designs. However, if symmetry signals fitness, then people, along
with having perceptual mechanisms tuned to detect symmetry efficiently, would have
different perceptual biases in how symmetry affects the attractiveness of mate-relevant
compared to mate-irrelevant stimuli.

To address such possibilities I performed three experiments to test the hypothesis
that symmetrical decoration also enhances the attractiveness of faces (Experiments 1 and
2) and geometric designs (Experiment 3). I was particularly interested in investigating
whether people actually prefer symmetry when judging decorated faces and geometric
designs that were manipulated according to general properties for symmetry detection in
vision (color, shape and orientation of design features) and according to the stimulus’s
relevance for mate choice (same or opposite sex as their own). Although studies find that

people judge symmetry to be more attractive than asymmetry, no study has been

22

conducted to determine whether other factors relevant for symmetry detection, such as
orientation and color, are also attractive. This issue was addressed in Experiment 3.

If the preference for symmetry has a biological basis, the preference ought to be
universal, that is, people from all societies Should Show similar preferences toward such .
stimuli. Demonstrating such universality, however, was not the goal of this work. Instead
it was to investigate whether people show biases toward stimuli that were manipulated, as
just mentioned, according to mate-relevancy and the properties for symmetry detection in
vision.

The first experiment tested undergraduate subjects from the city of Punta Arenas,
Southern Chile. Due to possible methodological Shortcomings in the manipulation of
images of that study, I conducted a second experiment with American undergraduates at
Michigan State University using an improved methodology for image manipulation.
Along with assessing the validity of the first study’s findings, it also addressed additional
questions that had emerged in the course of carrying out the first study. Given their
methodological differences, these studies cannot be regarded as providing for a cross-
cultural comparison of symmetry preferences. Additionally, although there are social
differences between American and Chilean students, both societies have many
commonalities such as being industrial-westem societies exposed to Western mass media
and capitalist patterns of consumption. Thus, although comparing the populations is
informative, it is not conceived as a critical test of the cross-cultural validity of either the

experiment or the findings.

23

EXPERIMENT l: DOES SYMMETRICAL DECORATION ENHANCE FACIAL
ATTRACTIVENESS?

Given the effect of symmetry on attractiveness and its possible adaptive function,
its salience in vision, and the ubiquity of symmetrical designs in face and body
ornamentation, Experiment 1 was designed to test the hypothesis that symmetrical designs,
in the forrrr of facial paint, can enhance facial attractiveness.

If facial attractiveness can be enhanced by symmetrical paint, the effect could
either depend on or be independent of the attractiveness of the faces themselves. For
instance, symmetrical paint could enhance the attractiveness of symmetrical faces by
making the symmetrical features more salient and therefore more easily perceived; it
could enhance the attractiveness of asymmetrical faces by making their asymmetrical
features look more symmetrical; and it could enhance attractiveness independently of
facial features by enhancing the attractiveness of all faces, whatever their degree of
zwynnneny.

If the preference for symmetry is adaptive and related to sexual selection, then
enhancement effects also could depend on the sex of the person judging the faces as well
as the sex of the faces being judged. The literature on symmetry provides several
examples of a sex-related effect, including reports that symmetry affects attractiveness
judgments more strongly for faces of the opposite than the same sex as the person
judging the faces, in other words, for faces that are mate-relevant (Little etal., 2001;
Penton-Voak et al., 2001), and that for both men and women, ratings of perceived health
are more strongly correlated with symmetry of opposite- than same-sex faces (Jones et

al., 2001).

24

To address these different possibilities, men and women were asked to judge the
attractiveness of symmetrical and asymmetrical faces (as indexed by facial features) of

both sexes decorated with either symmetrical or asymmetrical facial paint.

Subjects
The subjects were undergraduate students from the Universidad de Magallanes,
Chile: 20 men (18-25 years old) and 20 women (18-26 years old). Subjects were recruited
from public areas of the university during the months of June and July of 2002. All
signed a consent form. All procedures were approved by the Michigan State University

Committee on Research on Human Subjects.
Materials and Methods

Faces

The faces were produced from digital images of 16 faces, all of young adults (8
male and 8 female), all with naturally asymmetrical facial features, selected from the AR
Database (Martinez & Benavente, 1998). All were frontal view faces with “neutral”
expression, standard illumination, and a resolution of 768 by 576 pixels and 24 bits of
depth. Faces were resized, translated, and rotated to a standard center position.

Following the method used by Rhodes et al. (1998), each image was manipulated
to produce 16 faces with symmetrical features. The procedure was as follows: from each
of the original asymmetrical 16 faces, two chimeric faces (mirror reflections of the face’s
right and left sides) were created. Each pair of chimeric faces was then “averaged” into a
new face by manually placing 145 points on each chimera to indicate to a morphing-
sofiware, WinMorph 3.01, the location of the facial features to be averaged. This

procedure yielded 16 new “average faces” with perfectly symmetrical features. Finally,

25

using Corel PHOTO-PAINT 9, each new face was manually retouched to have the same
hairstyle, visible clothing, and skin texture as the original face. Together, the 16
symmetrical faces and the 16 original faces gave a total of 32 faces.

To each of the 32 faces, two designs of facial paint were manually applied with
Corel PHOTO-PAINT 9, one symmetrical, the other asymmetrical, using a reference-
mask containing the pixel coordinates of the areas to be painted on each face. The
symmetrical design consisted of a central white square on the bridge of the nose and a
black horizontal stripe on each check with a white circle to the outside. To produce the
asymmetrical design, the stripe and circle were vertically displaced on one side by 3mm
(10 pixels). By this method, 64 faces with facial paint were produced, 32 asymmetrical

and 32 symmetrical.

Experimental Conditions

A within-subjects design was used with the variables symmetry of paint (two
levels: symmetrical paint, asymmetrical paint), symmetry of face as indexed by facial
features (two levels: symmetrical features, asymmetrical features), and sex of face
relative to sex of subject (two levels: same-sex, opposite-sex). Combining the variables of
symmetry of paint and symmetry of face, two experimental conditions were defined as

Shown in Figure 3.

26

CONDITION 1

 

    

Symmetrical Asymmetrical
Face with Face with
Symmetrical Asymmetrical
Paint Paint
CONDITION 2
Symmetrical Asymmetrical
Face with Face with
Asymmetrical Symmetrical
Paint Paint
CONDITION 3
Symmetrical Asymmetrical
Face Face
(undecorated) (undecorated)

 

Figure 3. Experiment 1. Design of symmetrical and asymmetrical faces by

manipulation of symmetry of face and symmetry of paint.

In Condition 1, a symmetrical face decorated with symmetrical paint (face A) was
paired with an asymmetrical face decorated with asymmetrical paint (face C). In
Condition 2, an asymmetrical face with symmetrical paint (face D) was paired with a
symmetrical face with asymmetrical paint (face F).

To control for possible interaction effects of individual faces and experimental
conditions (e. g., the possibility that symmetry of paint affects the attractiveness of ‘face
x’ in Condition 1 but not in Condition 2, and vice versa for ‘face y’), the subjects were
divided into two groups so that each face appeared as Condition 1 for one group and as
Condition 2 for the other.

To check whether, as in prior reports, faces with symmetrical features are judged
as more attractive, a control condition, Condition 3, was added, consisting of pairs of
unpainted symmetrical and asymmetrical faces (faces J and K). This condition also was
used to provide a base line against which to compare the effect of symmetry of paint on
subjects’ judgments.

Each of the three conditions consisted of 8 trials, so that each subject judged a
total of 24 face-pairs. The 8 trials included 4 trials of 4 different pairs of male faces and 4
trials of 4 different pairs of female faces. Total preference scores for each condition (i.e.,
the total number of judgments, or choices, of the more symmetrical face of each pair as
the more “attractive”) therefore could range from 0 to 8 (0-4 for face-pairs of the same
sex as the subject and 0-4 for face-pairs of the opposite sex as the subject). Across
conditions for both groups of subjects, the faces comprising each pair were left-right
counterbalanced for position of the faces with symmetrical and asymmetrical features and

for position of the faces with symmetrical and asymmetrical paint.

28

Procedure

Subjects were instructed to “choose the face that is physically more attractive in
each pair of faces”. Before starting, subjects were given 5 practice trials using faces with
and without facial paint (no faces from the experimental set were included). Faces were
presented on a LCD screen (215 x 285 mm) of a laptop computer. Subjects triggered the
image presentation by a key—press and advanced the series of images at their own pace,
without time limits. Subjects were tested individually in an empty, quiet room at the

university, and all completed the session in about 10 minutes.

Results

The results are summarized in Figure 4. They showthat for Condition 3, the
control condition with unpainted faces, symmetrical faces were preferred, or judged to be
more attractive, than asymmetrical faces, as indicated by the finding that the mean
number of symmetrical faces chosen was significantly greater than chance (5.8 > 4) [t(39)
= 3.56, P = 0.001]. A mixed factorial AN OVA showed that, although men and women
alike chose symmetrical faces mere, the margin of preference was greater for wOmen
([F(l ,3 8) = 4.588, P = 0.04]), and that for all subjects the preference score was unrelated
to the sex of the face [F(1,38) = 1.639, P = 0.21] or to whether it was the same as or
different from the sex of the subject [F (1,38) = 0.02, P = 0.89].

For Conditions 1 and 2, the experimental conditions with painted faces, a mixed
factorial ANOVA showed a significant effect across conditions for the variable symmetry
of paint [F(1,38) = 6.769, P = 0.01], indicating that symmetrical faces with symmetrical
paint were the most attractive (mean preference = 6.2); that applying an asymmetrical

design to a symmetrical face decreased its attractiveness (mean preference = 4.8); and

29

that asymmetrical faces with symmetrical paint (Condition 1) were more attractive (mean
preference = 3.2) than asymmetrical faces with asymmetrical paint (mean preference =
1.97). Symmetrical paint alone, however, did not guarantee that a face would be judged
as the more attractive. In condition 2, the mean preference score for symmetrical faces
still exceeded chance (4.8 vs. 4.0; [t(39) = 2.278, P = 0.02]), indicating that when faces
were painted, the degree of symmetry of their physical features still influenced the

subjects’ judgments.

8 _
[I symmetrical
[:I asymmetrical

C

d)

8 6 -

.C

O

(I)

8

..‘E

9—

S 4 -

o

.D

E

3

C

C

8

2 2 ‘
0 _

 

 

 

Condition 1 Condition 2 Condition 3

Figure 4. The effect of symmetry of paint on facial attractiveness. Mean
number of symmetrical and asymmetrical faces judged as more attractive
in Conditions 1, 2, and 3 (8 trials for each condition).

Finally, as shown in Figure 5, neither the sex of the subject nor whether it was the
same as or different from the sex of the faces influenced the faces’ perceived

attractiveness (no main effect for sex of subject [F(1,38) = 0.294, P = 0.59] and no

30

interactions between sex of subject and sex of face [F(1,3 8) = 0.01, P = 0.92], and this
was so whether the face painting was symmetrical or asymmetrical [F(1,3 8) = 0.228, P =
0.63]). Symmetrical paint, however, enhanced facial attractiveness more for faces of the
opposite than the same sex as the subject (significant interaction between the variable
symmetry of paint, sex of subject, and sex of face [F(1,3 8) = 4.19, P = 0.04]), and this

was equally true for the male and female subjects.

 

 

 

 

4
T a Opposite-Sex of subject

0:, a Same-Sex as subject
8
.r:
o
a 3 -
o
.59
TD
.9
‘55
E 2 ‘ — -chance
E
>.
m
3
cf)
‘5
:i 1 ‘
C
c
(D
a)
E

O _

 

 

Condition 1 Condition 2

Figure 5. The effect of symmetry of paint on facial attractiveness.
Interaction between same-opposite sex of face (sex of subject compared to
sex of face being judged) and experimental conditions (Conditions 1 and
2) in the mean number of symmetrical faces chosen across 4 trials (scores
for asymmetrical faces are not shown but are in the same direction as the

scores for symmetrical faces).

31

Discussion

The results are consistent with a wide range of studies showing that more
symmetrical faces are more attractive than less symmetrical faces (Grammer & Thomhill,
1994; Hume & Montgomerie, 2001; Mealy et al., 1999; Scheib et al., 1999; Jones et al.,
2001; Koehler et al., 2002; Little et al., 2001; Penton-Voak et al., 2001; Perrett et al.,
1999; Rhodes et al., 1998, 2001a, b). They also Show that facial attractiveness can be
enhanced by symmetrical facial paint and reduced by asymmetrical facial paint. This
appears to be the first experimental demonstration of this effect. Finally, they show that,
whether the paint is symmetrical or asymmetrical, subjects’ judgments are more affected
by feature symmetry, and more for faces of the opposite than the same sex as their own.
Feature symmetry, therefore, appears to be more influential than paint symmetry on
perceived attractiveness, especially of opposite-sex faces. In sum, the results show that
symmetry’s effect on attractiveness varies with respect to the symmetry of face and that
the effect is modulated by the combination of sex of the subject and sex of the face being
judged.

For this experiment, it is possible that the method of producing symmetrical faces
yielded faces with smoother skin texture than the original face, meaning that the manual-
retouching method did not sufficiently reduce the differences in skin texture between the
original and symmetrical faces. If so, preferences for symmetrical faces might have been
confounded with preferences for faces with smoother skin texture. Even if that happened,
it probably did not weaken the obtained effects of the symmetrical facial paint on
attractiveness because symmetrical faces were manipulated in the same way across

experimental conditions, meaning that the changes in the attractiveness of symmetrical

32

faces can be attributed only to the concomitant changes in the symmetry of paint. Still, to
be sure, a second experiment was conducted, Experiment 2, to see whether the results
remained the same for faces with identical skin texture.

The second experiment also provided an opportunity to ask whether facial
attractiveness would be affected even when the difference between the asymmetrical and
symmetrical facial paint conditions is smaller than the difference in Experiment 1.
Defining the level of asymmetry in Experiment 1 as “high”, two levels were created in
Experiment 2, one “high”, matching the level in Experiment 1, and one “low”, with half

that level.

33

EXPERIMENT 2: DOES SYMMETRICAL DECORATION ENHANCE
ATTRACTIVENESS IN FACES WITH IDENTICAL SKIN TEXTURE?

Experiment 2, therefore, tested the effects of symmetrical decoration found in
Experiment 1, using an improved method for the manipulation of facial features, and also
tested the idea that the effect of symmetry on attractiveness varies according to the degree
of asymmetry of decorations.

To find out whether symmetrical facial paint affects the perceived attractiveness
of faces with identical skin texture, a synthetic skin texture was produced for each pair of
faces (original and symmetrical face) by blending the left and right chimeras (mirror
faces) of each original face. Using WinMorph 3.01, this skin texture was remapped
(warped) to fit the facial features of the original face and its symmetrical version. As just
noted, to compare the effect of degree of difference in symmetry on perceived
attractiveness, two levels of asymmetrical designs were created, one matching that in
Experiment 1, one with half that level.

The subjects also were asked to provide information about their socioeconomic
status, art capital, and sexual orientation. The purpose was to provide descriptive
information about the subjects and not to address the question of whether such variables
affect symmetry preferences or not. This is because the primary question was whether
symmetrical decoration affects facial attractiveness, and not whether socio-structure
influences aesthetic preferences. Socioeconomic variables were chosen because they are
normally used to provide a raw indicator of how socio-structural variables affect

behavior. Art capital was included because education and art training are relevant factors

34

of aesthetic preferences, particularly since modern art favors asymmetrical forms (or

forms other than bilateral symmetry).

Subjects
The high-asymmetry group included 20 men (20-23 years old) and 20 women
(18-23 years old); the low-asymmetry group included 20 men (18-24 years old) and 20
women (18-22 years old). All subjects were undergraduate students at Michigan State
University recruited from undergraduate psychology and linguistic classes during the
Spring semester of 2004. All signed a consent form and received class credit for
participating. All procedures were approved by the Michigan State University Committee

on Research on Human Subjects.

Questionnaire

Sexual orientation. Given than symmetry may be used for choosing mates,
subjects were also asked about their self-perceived sexual orientation, so to provide a
basis for categorizing the stimuli as either mate-relevant or mate-irrelevant. Subjects were
asked to identify themselves as heterosexual, homosexual or bisexual. I

Country of origin. To provide information about the place of origin and residence
of subject, they were also asked to indicate the country and city were they were born as
well as the place where they have lived most of their lives.

Socioeconomic status. Socioeconomic status (SES) is traditionally used to
indicate the position of an individual or group within a social stratification system.
Different indicators are used, some better than others depending on the social field being

studied (health research for instance). Here, because the goal was to provide a raw

35

description of the subjects, descriptors of income, level of education, and occupation
were used.

Given that undergraduate students normally are in the process of acquiring a more
stable SES (e.g., they are acquiring new Skills that will affect their future income, they
may or may not be economically dependent on their parents), I also asked for information
about their family SES, including, parents’ income, level of education as well as
occupation. Globally, these indicators provide a raw estimate of household position
(number of people living at home, geographic or residence area, or other possible
indicators of wealth were not identified). Therefore, in this study, resources are combined
with prestige-based measurements. These multiple indicators were included because of
the reported tendency among people in the United States to not respond to questions
about income, especially if their income is high (Krieger, Williams, & Moss, 1997,
p.358).

Questions were formulated and answers were tabulated to match similar
information asked in the United States 2000 census, so as to facilitate comparison of the
student sample with characteristics of the Michigan population.

Art capital. I use the term “art capital” to indicate how people’s conventional art
training and interest in arts may affect their preference for symmetry. Thus, questions
were asked about formal art training (art courses taken), how knowledgeable the subjects
feel in art (how well they expect they will do in a general art test), and their interest in art
(e.g., how frequently they visit art museums, number of art books owned, art works

owned, how frequently they produce art work).

36

Sexual Orientation and Country of Origin

With respect to sexual orientation, 78 people (97.5%) reported that they were
heterosexual, 1 person identified herself as bisexual, and one person identified himself as
homosexual. Seventy-two subjects were born in the United States and lived most of the
time in Michigan (90%), while 4 (5%) lived in another state, and 4 (5%) were born

outside the US.

SES and Art Capital

Family income (see Table 1) was measured by summing subjects’ income with
their parents' income. Ten subjects did not report family income. The median family
income of the sample is almost double that of the median family income of Michigan,
and also shows a distribution skewed toward high-income levels.

The data on educational attainment (see Table 2) shows that the education level of
the subject families was also higher than that for the average Michigan resident of 25
years old or older.

Most subjects (55%) reported not having any formal art training (see Table 3). For
those with art training, most of had 1 high school class (32.5%), and some had more than
1 high school course or 1 college level course (10%). Only 2 subjects reported having
more than 1 art college class.

It not surprising, therefore, that most students did not feel competent in art history
(see Table 4). When asked "If right now you were given an exam on art history (e.g.,
painters, styles), how do you think you would do?" most people reported that they

expected to do poorly (82.5%).

37

Table 1. Subjects’ family income compared to Michigan family income.

 

 

 

 

Subjects Michigan
Income N % N %
Less than $10,000 0 0 123,861 4.8
$10,000 to $14,999 0 0 91,412 3.5
$15,000 to $24,999 2 2.86 249,241 9.6
$25,000 to $34,999 1 1.43 292,656 11.3
$35,000 to $49,999 5 7.14 434,128 16.8
$50,000 to $74,999 12 17.14 608,663 23.5
$75,000 to $99,999 11 15.71 366,946 14.2
$100,000 to $149,999 20 28.57 287,956 11.1
$150,000 to $199,999 9 12.86 70,576 2.7
$200,000 or more 10 14.29 65,873 ' 2.5
Total 70
Median family income 100,000 53,457

 

38

Table 2. Subjects’ family educational attainment compared to Michigan

population

 

 

 

 

S’s Mother S’s Father Subject MI
Educational Level N % N % N % %
Less than 9‘h grade — — - - — — 4.7
9th to 12th grade, no
diploma — — — — — - 11.9
High school
graduate 26 32.5 21 26.25 — — 31.3
Some college, no
degree 5 6.25 l 1.25 69 86.25 23.3
Associate degree 8 10 5 6.25 6 7.5 7
Bachelor's degree 29 36.25 30 37.5 5 6.25 13.7
Graduate or
professional degree 12 15 23 28.75 8.1

 

39

Table 3. Subjects’ number of art courses taken

 

 

 

 

 

Number of art courses N %
None 44 55
1 High school course 26 32.5
1 college or more than 1 high school course 8 10
More than 1 college course 2 2.5
Total 80 100
Table 4. Subjects’ self-expected art test performance

Self-expected art

test performance N %

Poor 66 82.5

Good 12 15

Very Good 2 2.5

Excellent 0 0

Total 80 100

 

40

Another potential indicator of subjects' interest in art is the number of art-related
items they own.(see Table 5). I therefore asked subjects to report the number of original
artworks they had at home (e. g., paintings), the number of art reproductions (e. g., poster
of paintings), and the number of art reference items (e. g., books, videos). The sample
showed that most people did not own any such items, particularly original artwork, and

when they owned such materials, they had only a few items.

Table 5. Subjects’ report on the number of art items they own

 

 

 

Original Art Reprotllitrction Art References
Amount N % N % N %
0 43 53.75 23 28.75 33 41.25
1-4 22 27.5 23 28.75 27 33.75
5-10 11 13.75 26 32.5 14 17.5
More than 10 4 5 8 10 6 7.5

 

In sum, the sample represented a population with a social status relatively higher
than the mean social status of Michigan as indicated by income levels and family
educational attainment. The survey also shows that most people perceived themselves as
not very knowledgeable about art history and that they have not invested considerable

economic capital or time in acquiring art items or formal education in art.

41

Materials and Methods
As in Experiment 1, subjects were asked to judge the attractiveness of
symmetrical and asymmetrical faces of both sexes decorated with either symmetrical or
asymmetrical facial paint. The subjects were divided into two groups: a high-asymmetry
group judged faces with high-asymmetry designs, and a low-asymmetry group judged

faces with low-asymmetry designs.

Faces

Thirty-two faces (16 male and 16 female) were selected from the AR Database
and then resized, translated, and rotated to a standard center position. The facial features
and skin texture of each face were manipulated using methods similar to those described
elsewhere (Perrett et al., 1999; Rhodes et al., 2001b). First, the position of facial features
of each original face was recorded by manually placing 304 reference points on each
image. For each original face, left and right chimeras were created, and, using a computer
script, 304 points were placed on each chimeric face. A morphing software, Winmorph
3.01, used this information to produce 32 synthetic skin textures by averaging (morphing)
each pair of chimeric faces. The software then produced 32 asymmetrical faces by
remapping (warping) each synthetic skin texture to fit the asymmetrical features of each
original face (as indicated by the 304 reference points). A symmetrical version of each
face was created with an additional computer script that calculated the average position
(x, y) of feature points of each original face, and then used this information to remap the
synthetic skin to fit the symmetric (averaged) facial features. All symmetrical and

asymmetrical faces were manually retouched to have the same hairstyle and visible

42

clothing. This process yielded ‘32 faces with asymmetrical features and 32 faces with
symmetrical features.

To each of the 64 faces, three designs of facial paint were applied: symmetrical,
high asymmetry, and low asymmetry. As in Experiment 1, these designs were created
using a reference-mask containing the pixel coordinates of the areas to be painted in each
face. To produce designs with high asymmetry, the black horizontal stripe and white
circle were again displaced on one side of the design by 3 mm (10 pixels); to produce
designs with low asymmetry, the same elements were displaced by 1.5 mm (5 pixels).
This method yielded 192 faces: 64 with symmetrical designs. 64 with low-asymmetry
designs, and 64 with high-asymmetry designs.

Experimental Conditions

Subjects in the high-asymmetry and low-asymmetry groups were asked to judge

faces that had been manipulated according to three experimental conditions as shown in

Figure 6.

43

Symmetrical
Face with
Symmetrical
Paint (A)

Asymmetrical
Face with
Symmetrical
Paint (D)

Asymmetrical
Face with
Symmetrical
Paint (G)

Symmetrical

(undecorated)

CONDITION 1

ECONDITION 2

CONDITION 3
G H l

    

Asymmetrical
Faces with
Asymmetrical

(a: low 0: high)

Symmetrical
Faces with
Asymmetrical

Paint
(E: low. F: high)

Asymmetrical
Faces with
Asymmetrical

(H. low I. high)

Asymmetrical

(uandecorated)

Figure 6. Experiment 2. Design of symmetrical and asymmetrical faces

with synthetic skin texture by manipulation of symmetry of face and

symmetry of paint.

In Condition 1, a symmetrical face decorated with symmetrical paint (face A) was
paired with an asymmetrical face decorated with asymmetrical paint (face B in the low-
asymmetry group, face C in the high-asymmetry group). In Condition 2, an asymmetrical
face with symmetrical paint (face D) was paired with a symmetrical face with
asymmetrical paint (face E-low or face F-high). Because all pairings in Experiment 1
were of symmetrical and asymmetrical faces, a check was made to see whether
symmetrical facial paint enhances the attractiveness of faces with the same degree of
symmetry. To do this, a new condition, Condition 3, was added, which paired an
asymmetrical face with symmetrical paint (face G) with the same asymmetrical face with
asymmetrical paint (face H-low or face I-high).

As in Experiment 1, as a control for possible interaction effects of individual faces
and experimental conditions, the subjects were divided into two subgroups, so that each
face appeared as Condition 1 for one subgroup and as Condition 2 for the other.
Condition 3 stimuli were identical for both subgroups. For the low-asymmetry group a
control condition, Condition 4, was added, consisting of pairs of undecorated
symmetrical and asymmetrical faces (faces J and K). Because a different technique was
used in Experiment 2 to manipulate the symmetry of facial features, this control condition
provided a new base line against which to compare the effect of symmetry of paint on
subjects’ judgments.

Each of the 4 conditions consisted of 8 trials (4 trials of male faces and 4 trials of
female faces), so that each subject in the high-asymmetry group judged a total of 24 face-
pairs, and each subject in the low-asymmetry group judged a total of 32 face-pairs. Total

preference scores for each condition therefore could range from 0 to 8 (0-4 for same-sex

45

pairs and 0-4 for opposite-sex pairs). Stimulus presentation was left-right

counterbalanced for symmetry of face, symmetry of paint, and sex of faces.

Procedure

Subjects were instructed to “choose the face that is physically more attractive in
each pair of faces.” Before starting, subjects were given 5 practice trials of faces with and
without facial paint. Faces were presented on a LDC screen (216 x 285 mm) of a laptop
computer. I designed a computer interface for stimulus presentation and data recording.
Subjects triggered the image presentation with a mouse-click under the face they
considered more attractive and advanced the series of images at their own pace, without
time limits. Their answers were automatically recorded in a database. Subjects were
tested individually in a quiet room at the university and completed the session in about 15

minutes. Additionally, they filled out a brief questionnaire.
Results

SES and Art Capital
Although the information collected was intended only for descriptive purposes, it
is important to notice that socioeconomic status, and art capital were not correlated with

subject’s preferences (P>0.05).

High-Asymmetry Group

The results are summarized in Figure 7. For Conditions 1 and 2 in the high-
asymmetry group, a two-way repeated measures AN OVA showed a significant effect for
symmetry of paint [F (1 ,3 8) = 17.65, P < 0.001], indicating that symmetrical paint
enhanced attractiveness while asymmetrical paint decreased attractiveness, to the extent

that symmetrical faces were no longer preferred when decorated with asymmetrical paint

46

([t(39) = -0.36, P = 0.72]). Symmetrical paint also affected the attractiveness of male

faces more than female faces [F (1,38) = 10.05, P = 0.003]; and this was true both for

men’s and women’s judgments across conditions [F (1 ,3 8) = 0.179, P = 0.675].

 

@ high-asymmetry
[III] low-asymmetry

 

 

 

 

 

 

 

 

 

 

— — — .3 -- -- chance

 

;
1
4LT
L
L
' r51 I
g

'0

’o

.3:

0 0
0.0:

0

.v
0
0
.0

0

v '
o o.
o

0..
e. .0

0

0
0

’o

0

v
.0

’0

’0
o
.0

'
o 0
0’0.
.0

0
0
.0

0
0

0
0

0

0
0

O

0
0

'2

N
v .
0....
9.9.0
o o o

o

.e'o
o

0 O

.0

0
0
.0

.0

O

’0

’0

.0

.0

.'

.0
0
O

:0
o

o
o

O

0
0
0
0
0

Mean number of symmetrical faces chosen

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

h----- xxx x

 

O _. I ..-—hint

Conditiont Condition2 Condition 3 Condition 4

Figure 7. The effect of symmetry of paint on facial attractiveness. Mean
number of symmetrical faces chosen as more attractive in each condition

(8 trials / condition). Conditions 1, 2, and 3 consisted of faces painted with

either high-asymmetry or low-asymmetry designs.

For Condition 3, which paired an asymmetrical face with symmetrical paint with
the same asymmetrical face with asymmetrical paint, the results Showed that
asymmetrical faces with symmetrical paint were considered more attractive [t(3 9) =

. 4.913, P < 0.001]. Finally, a repeated measures ANOVA showed that whether the sex of

47

each pair of faces was the same as or different from the sex of the subject did not

influence their perceived attractiveness [F(1,39) = 0.687, P = 0.412].

Low-Asymmetry Group

For the low-asymmetry group, the results for Condition 4 (undecorated faces)
showed that symmetrical faces were more attractive than asymmetrical faces (mean
preference for symmetrical faces was greater than chance [t(39) = 5.631, P < 0.001]), and
a mixed factorial ANOVA showed that the score was not affected by sex of face [F (1 ,3 8)
= 0.693, P = 0.41], sex of subject [F(1,38) = 2.875, P = 0.09], or by whether sex of faces
was the same as or different from sex of subject [F (1,38) = 0.354, P = 0.55].

For Conditions 1 and 2, a mixed factorial ANOVA Showed a significant effect for
symmetry of paint [F(1,3 8) = 3.785, P = 0.05], indicating that symmetrical faces with
symmetrical paint were more attractive (mean preference = 5.45) than asymmetrical faces
with asymmetrical paint (mean preference = 2.55) and that applying an asymmetrical
design to a symmetrical face decreased its attractiveness (mean preference = 4.75)
compared to an asymmetrical face with a symmetrical design (mean preference = 3.25).
Neither sex of subject [F(1,3 8) = 0.286, P = 0.59] nor whether sex of faces was the same
as or different from sex of subject [F(1,3 8) = 0.27, P = 0.87] influenced the faces’
attractiveness, and there were no interactions between sex of face and symmetry of paint
[F(1,3 8) = 0.695, P = 0.41] or between symmetry of paint, sex of face, and sex of subject
[F(1,38) = 0.315, P = 0.57]. The analysis also showed that the number of female
symmetrical faces preferred fluctuated more across Conditions 1 and 2 than the number

of male symmetrical faces [F(1,38) = 7.873, P = 0.008].

48

For Condition 3, the results showed that asymmetrical faces with symmetrical
paint were not considered significantly more attractive than the same faces with
asymmetrical paint (mean number of faces with symmetrical paint preferred, 4.43, was
not significantly greater than the number expected by chance [t(39) = 1.752, P = 0.088]).
A mixed factorial AN OVA showed that attractiveness judgments were not significantly
affected by sex of face [F (1,38) = 2.567, P = 0.11], sex of subject [F(1,38) = 0.857, P =
0.36], or by whether sex of face was the same as or different fi'om sex of subject [F(l ,3 8)

= 0.137, P = 0.71].

Across Experiments 1 and 2

A comparison of the judgments of the subjects in the low asymmetry group in
Experiment 2 with the Chilean students in Experiment 1 Showed no significant difference
in judgments of faces without paint [F(1,76) = 3.084, P = 0.08]. It did, however, Show
that women chose symmetrical faces more often than men [F(1,76) = 7.4, P = 0.008]. No
other interactions were significant.

Judgments were also similar for both samples when judging faces with paint, such
that male attractiveness tended to be affected more than female attractiveness by the
symmetry of the paint [F(1,76) = 5.44, P = 0.02]. This effect also was greater, but not
significantly, for the American students in Experiment 2 [F(1,76) = 4.15, P = 0.06].

When comparing all groups in both experiments, the only significant interaction
preserved was between the sex of the face and the symmetry of the paint, indicating again
that male faces were affected more than female faces by the symmetry of the paint

[F(1,114) = 13.69, P < 0.001].

49

Discussion

The results of Experiment 2 confirm again that faces with more symmetrical
facial features are judged as more attractive. They also confirm the finding from
Experiment 1 that facial attractiveness is enhanced by symmetrical facial painting and
reduced by asymmetrical facial painting. All other things being equal, they also suggest
that the smoother skin texture of the faces in Experiment 1 had a minor (but not
statistically significant) effect on facial attractiveness, given that the mean number of
choices of symmetrical faces without paint was only slightly higher in Experiment 1 than
in Experiment 2.

The results also Show that the influence of symmetry of paint on attractiveness is
modulated by the degree of asymmetry of the designs. This was seen in Condition 3,
where attractiveness was significantly affected in the high asymmetry condition but not in
the low asymmetry conditions (although faces with symmetrical paint were chosen more
often than faces with asymmetrical paint).

Finally, the experiments showed that the magnitude of the effect of decoration on
attractiveness depends in the sex of the face, indicating that male faces were affected
more by symmetrical decoration. These findings, however, differed from those in

Experiment 1 and therefore must be regarded with caution.

50

EXPERIMENT 3: SYMMETRY PREFERENCES WITH NON-
REPRESENTATIONAL DESIGNS

In the Introduction I noted the widespread use of symmetrical designs in the
decorative arts as one piece of evidence that the preference for symmetry has an
evolutionary basis. Studies also find a positive relation between the perceptual salience of
symmetrical designs and the aesthetic preference for these designs (Eisenman & Gellens,
1968; Jacobsen & Héfel, 2001; Rentschler et al., 1997; Washburn & Humphrey, 2001)
and between bilateral symmetry about a vertical axis (i.e., left-right symmetry), the kind
most salient to the human visual system (Wenderoth, 1994; Evans et al., 2000), and
preference for bilaterally symmetrical stimuli. The preference, furthermore, does not
seem to change after training (Rentschler et al., 1999; Washburn & Humphrey, 2001),
which suggests an a priori and stable preference for symmetry. That symmetry is
perceptually salient, however, does not necessarily mean that it will always enhance
attractiveness. For instance, under some circumstances, asymmetry might be preferred
because, being visually less redundant than symmetry, it looks more “complex” (Berlyne,
1971; Krupinski & Locher, 1988).,

If the design of the visual system is sufficient to account for the preference for
symmetry, one would not expect symmetry to be preferred when the stimuli are not
salient to ‘bottom-up’ mechanisms of symmetry detection. In Experiment 3, I tested this
prediction by examining adults’ preferences for abstract designs varying in three kinds of
symmetry: shape, color, and axis of symmetry. If bottom-up mechanisms can fully
account for the preference, I can predict the following: a) because symmetrical stimuli are

detected fast and accurately, stimuli with symmetrical shape should be preferred to

51

stimuli with asymmetrical shape; b) because color is not tuned to symmetry detection
(Morales & Pashler, 1999), preferences for symmetrically colored stimuli should be
random; and c) because left-right, or vertical, symmetry is most salient to the visual
system, stimuli with a vertical axis of symmetry should be preferred to stimuli of any

other orientation.

Subjects
The subjects were undergraduate students from Michigan State University: 20
men (18—24 years old) and 20 women (18-22 years old). These individuals comprised the
low-asymmetry group in Experiment 2, and the tests with abstract designs were
administered in the second part of that experiment. All procedures were approved by the

Michigan State University Committee on Research on Human Subjects.
Materials and Methods

Designs

The designs were digital images of geometric designs from several non-western
cultures (e.g., Aonikenk, Navajo, Yoruba). Using vector-based illustration software,
Corel Draw 9, I produced a symmetrical and an asymmetrical version of the same design
(totalling 800 X 570 pixels). Their positions in the display were counterbalanced across

the experiment.

Experimental Conditions

Three experimental conditions were defined as shown in Figure 8:

52

 

CONDITION 1 SHAPE

 

 

 

 

Symmetrical Asymmetrical

Shape Shape
CONDITION 2 COLORATION

Symmetrical Asymmetrical

Coloration Coloration
CONDITION 3 ORIENTATION

Vertical Non-vertical

Axis Axis

 

 

 

 

Figure 8. Experiment 3. Abstract designs whose symmetry was
manipulated according to three experimental conditions: Shape,

Coloration, and Orientation.

Condition 1: Shape. Designs with symmetrical Shape compared to designs with
asymmetrical shape.

Condition 2: Coloration. Designs with symmetrical color compared to designs
with asymmetrical color.

Condition 3: Orientation of symmetrical design features. Designs with vertical
axis of symmetry compared to designs with non-vertical axis of symmetry (45° and 135°).

Each condition consisted of 10 trials, so that each subject judged a total of 30
pairs of designs. For each condition, subjects received a score from 1 to 10 to indicate the

number of symmetrical designs chosen as more attractive.

Procedure

Subjects were instructed to “choose the design that is more attractive in each pair
of designs.” Before starting, practice trials were given with 3 pairs of designs (these trials
did not include any designs from the experimental set). Again, no time limits were set; all
subjects triggered the image presentation by a key press and were tested individually in a

quiet room at the university.

Results
Men’s and women’s preferences did not significantly differ fi'om each other
across the three conditions ([F(1,38) = 0.58, P = 0.81] or for interaction between sex of
subject and experimental condition [F(1,38) = 0.544, P = 0.46]). The men’s and
women’s scores, therefore, were combined for further statistical analyses. The results are

summarized in Figure 9.

54

In Condition 1, designs with symmetrical shape were judged to be more attractive
than designs with asymmetrical shape (the mean number of designs with symmetrical
shape preferred, 6.93, was greater than expected by chance [t(39) = 6.976, P < 0.001]).

In Condition 2, symmetrically-colored designs were judged to be more attractive
than asymmetrically-colored designs (the mean number of symmetrically-colored designs
preferred, 7.6, was greater than expected by chance [t(39) = 8.34, P < 0.001]).

In Condition 3, designs with a vertical axis of symmetry were chosen as more
attractive than designs with a non-vertical axis of symmetry (the mean number of designs
with vertical axis of symmetry preferred, 7.1, was greater than expected by chance [t(39)

= 6.121, P < 0.001]).

10 -i
8 E] male
8 female
'5 8
in
C
‘9 %
(I)
o .
'D ’I
a 6
E t— — chance
E
F 4
'5 .
S I
E .
3 a
C 2
c f
m J
g J

0 ""'

 

 

 

 

 

 

 

 

Condition1 Condition2 Condition3

Figure 9. Mean number of designs chosen in each condition by male and

female subjects.

55

Discussion

The results of Condition I confirm prior findings that stimuli with symmetrical
shape are seen as more attractive (Eisenman & Gellens, 1968; J acobsen & H6fel, 2001;
Rentschler et al., 1997; Washburn & Humphrey, 2001). They also are compatible with
the profuse use of symmetrical design in the decorative arts across cultures (Washburn &
Crowe, 1989). The results of Condition 3 Show that designs with a vertical axis of
symmetry were preferred over designs with a non-vertical axis of symmetry, which
suggests that the preference for symmetry is compatible with the. design of the visual
system. Finally, the results of Condition 2 Show that even though color, unlike
monochromatic stimuli, is not tuned to symmetry detection, color symmetry does
Significantly enhance attractiveness. In combination, the results suggest that mechanisms
of symmetry detection affect visual preferences but do not totally constrain the preference
for symmetry and that other mechanisms also contribute. There is independent support
for this view in lateralization studies using ERP (Evoked-Related Potential). Jacobsen
and Htifel (2001) found that although the separate acts of perceiving symmetry and
judging the attractiveness of symmetry were strongly correlated, aesthetic judgments
were associated with a more pronounced right-hemispheric lateralization of neural

activity than was the perception of symmetry per se.

56

CONCLUSIONS AND GENERAL DISCUSSION

All together, the results show that symmetry enhances the attractiveness not only
of faces per se and of faces decorated with symmetrical paint but also of artistic-cultural
products like those seen in the decorative arts. They also show that the effect of
symmetrical face-paint is weaker for female faces and that symmetry enhances
attractiveness even in stimuli that do not fit the apparent design of visual mechanisms of
symmetry detection.

If the results support the hypothesis that the preference for symmetry has roots in
our evolutionary history, the next question is: Is the preference adaptive, that is, a direct
product of selective forces, or is it a by-product of other adaptations? At least three
hypotheses address this question: the ‘receiver bias’ hypothesis, according to which the
preference is a by-product, and the ‘good genes’ and ‘extended phenotype’ hypotheses,
according to which it is a direct product of selective forces. Although my experiments
were not specifically designed to test these hypotheses, I shall note to what extent the

results, along with other findings, fit the predictions that can be derived from each one.

Receiver Bias
According to the ‘receiver bias’ hypothesis (Enquist & Arak, 1994; Johnstone,
1994; Enquist & Johnstone, 1997), preference for symmetry is a by-product of the
common properties of biological systems of recognition, so that symmetry becomes
perceptually salient when the mean of a population of stimuli with random fluctuating
asymmetries corresponds to a symmetrical stimulus. Preference for symmetry therefore
emerges from a generalization process (Enquist & Johnstone, 1997; Jansson et al., 2002),

which helps recognition systems identify objects in different positions and orientations.

57

As such, symmetry does not signal ‘fine-grained details’ such as the quality of a potential
mate (Enquist et al., 2002).

There is broad support for the receiver bias hypothesis. Simulations using
artificial neural networks show that a preference for symmetry emerges when the network
has been exposed to asymmetry (J ohnstone, 1994, Enquist & Arak, 1994); domestic fowl
choose novel symmetrical stimuli after repeated exposure to asymmetrical stimuli
(Jansson et al., 2002); and humans find ‘average faces’ and ‘average non-face’ stimuli
attractive. In this last group of experiments, the face and non-face stimuli were
composites with symmetrical features produced by blending many exemplars
superimposed on each other (Halberstadt & Rhodes, 2000; 2003; Langlois & Roggrnan,
1990; Langlois et al., 1994; Rhodes et al., 1999).

Even though the attractiveness scores for symmetry and averageness are
correlated, averageness and symmetry contribute independently to facial attractiveness
(Rhodes et al., 1999), and attractive average stimuli do not have to be symmetrical (see
Halberstadt & Rhodes, 2003). Nor is the relationship between averageness, familiarity,
and attractiveness constant across stimuli. A study by Halberstadt and Rhodes (2003)
suggests that averageness has a stronger effect on attractiveness when people judge
biological as opposed to non-biological stimuli (it remains significant after partialling out
the effect of familiarity only when people judge biological stimuli). Finally, Little and
Jones (2003) have shown that preferences for symmetrical faces are stronger for upright
than for inverted faces, indicating that preference for symmetrical faces is not constant

across orientations.

58

The results of Experiments 1 and 2 show that, even though symmetrical
decoration in faces enhances facial attractiveness, the effect depends on the sex of the
face (stronger for same-sex faces in Experiment 1 and stronger for male faces across
experiments). The receiver-bias hypothesis would not predict this diminishing of the
effect for men or women, but it does predict the findings in Experiment 3, where subjects
showed a preference for symmetrical over asymmetrical geometric designs, a preference
that may be irrelevant for mate-choice (but see the “extended phenotype” hypothesis
below). However, the premise of the hypothesis that a preference for symmetry emerges
as a result of generalization implies that the preference depends strongly on visual
experience. The subjects in Experiment 3 preferred symmetry in designs that were
presumably unfamiliar, but because their familiarity was not assessed beforehand, we

cannot be sure.

Good Genes

According to the “good genes” hypothesis, the symmetry of morphological traits
reliably signals an animal’s fitness. Because environmental stressors such as parasites and
mutations can produce morphological asymmetries, the symmetry of a given phenotype
can indicate an individual’s capacity to cope with such environmental stressors (its
developmental instability). Thus, individuals who use this information in mate selection
would increase their offsprings’ chances of survival. By this hypothesis, symmetrical
faces are preferred because they Signal stable development and, therefore, high mate
quality.

Support for the ‘good genes’ hypothesis comes from studies on several species

showing that individuals with symmetrical features have greater reproductive success

59

(Mcller & Thomhill, 1998), that symmetrical faces are attractive (Grammer & Thomhill,

1994; Rhodes et al., 1998, 2001a,b; Mealy et al., 1999; Perrett et al., 1999; Hume &
Montgomerie, 2001; Jones et al., 2001; Little et al., 2001; Penton—Voak et al., 2001;
Koehler et al., 2002), that facial symmetry is positively correlated with perceived health
(Jones et al., 2001), and that symmetry’s influence on attractiveness varies according to
the sex of the subjects and the sex of the faces (Jones et al., 2001; Little et al., 2001;
Penton-Voak et al., 2001).

Not all findings, however, support the hypothesis (e.g., Koehler et al., 2002), and
it appears that the relationship between morphological asymmetries, genes, and
environmental stressors is taxon- and trait- specific (Swaddle, 2003).

This hypothesis, however, does not address the question of why symmetry is also
preferred in decorative art. One possibility is that the adaptive value of detecting
symmetry in potential mates generalizes to other objects (Little & Jones, 2003). If facial
symmetry signals developmental stability and if symmetrical facial decoration does not
signal fitness (or is a less reliable indicator of fitness), the ‘good genes’ hypothesis also
might account for the greater importance of facial morphology in judgments of female
faces, namely, that female faces are less affected by decoration because, in general, their
physical features are more important for assessing their quality as mates (or as
competitors for mates). Clearly, further studies are needed to address the reliability and
nature of the proposed interaction between a generalized preference for symmetry in
mate-irrelevant stimuli and a specific preference for morphological symmetry in mate-

relevant faces.

60

Extended Phenotype

According to the extended phenotype hypothesis, symmetrical art, instead of
being mate-irrelevant, signals the fitness of the artist on the premise that perfectly
symmetrical designs are hard to produce (Miller, 2000; Miller, 2001; Zahavi, 1978;
Zahavi & Zahavi, 1997). Because I did not ask the subjects in any of the three
experiments, “Who is the best artist?”, I could not directly test this hypothesis. But if it is
correct, then, for example, in the case of Experiments 1 and 2, the artist’s skill in
applying the facial paint cannot have been the only basis for the perception of facial
attractiveness. First, whether decorated or not, faces with symmetrical features were
perceived as more attractive than asymmetrical faces. Second, the effect of symmetrical
paint, rather than being constant across faces, depended on the sex of the face and the sex
of the subject.

As mentioned, symmetrical decoration does not completely outweigh the
influence of symmetrical facial features. Given that, on average, asymmetrical faces tend
to benefit the most from symmetrical decoration, symmetrical decoration seems to act as
a ‘handicap’ for symmetrical faces (Zahavi, 1978; Zahavi & Zahavi, 1997) because only
symmetrical faces can afford to have their competitors enhance their attractiveness with
symmetrical paint and still be considered more attractive overall. If symmetrical facial
features indicate biological fitness, the results suggest that they can reliably communicate

the fitness of the sigrraler.

Future Studies
The finding that symmetrical decoration enhances physical attractiveness opens a

number of questions for future studies:

61

 

Decoration and Location Eflects. Further research needs to be conducted to
determine whether or not the effect of symmetry is dependent on the specific kind of
decoration used in this study, in other words, whether the effect can be replicated with
other kinds of designs. In this regard, new studies should address the question of whether
the location of the designs has different effects on attractiveness; for instance, is
decoration in the region of the eyes more important that decoration in other regions of the
face? Relatedly, are the effects of facial decoration also found in body decoration?

Individual Diflerences. From the standpoint of evolutionary theory, variation is
integral to evolutionary change so that it would be expected that the degree of symmetry
would vary in any population of faces. To the extent that symmetry contributes to facial
attractiveness, some faces will be intrinsically more attractive than others. In the same
way, some individuals might be affected more by facial symmetry than others. In the
current study, for instance, 10% of the subjects who were asked to judge faces without
paint (n=80) did not Show a preference for symmetrical faces. Similarly, about 28% of
the total number of subjects (n=120) did not follow the tendency showed by the rest of
the subjects when judging decorated faces; that is, they chose symmetrical faces more
often when decorated with asymmetrical paint that when decorated with symmetrical
paint. Besides the possibility of measurement error (e. g., individuals who for one reason
or another were not fully involved in the task, so that their answers are not entirely
trustworthy), such variability indicates the need for studying individual differences
systematically. It is possible, for instance, that the preference for symmetry partly
depends on self-perceived attractiveness (e.g., less attractive people might place less

emphasis on facial attractiveness for mate selection).

62

Sexual Orientation. The more general question of individual orientation raises the
more specific question about sexual orientation. For this Study, I asked subjects about
their self-perceived sexual orientation so as to provide a basis for categorizing the face
stimuli as either mate-relevant or mate-irrelevant. All but two subjects, one man and one
woman, identified themselves as heterosexual. This number precluded any systematic
assessment of the role of sexual orientation on symmetry preference, but this might be a
promising area for further research on the premise that if symmetry is a factor, sexual
orientation would be relevant for the categorization task. For example, if for a male
homosexual, only the male face would be mate-relevant, then symmetry in a male face
might be expected to be more salient than symmetry in a female face with respect to
judgments of attractiveness.

Further exploration of the role of symmetry in mate choice is also necessary. An
interesting question, for instance, is whether the preference changes over the menstrual
cycle given that mate selection strategies would be expected to differ according the
female’s fertility status. Finally, future research must address the limits of the
effectiveness of symmetry on attractiveness, that is, is symmetry always more attractive?
if so, why are “beauty marks” often asymmetrical?

In sum, the results show that adults prefer symmetrical faces and abstract designs
and that symmetrical decoration enhances facial attractiveness, that is, that the preference
for symmetry extends to the cultural products of facial paint and the decorative arts. This
does not mean that all types of face painting or decorative art will tend to be symmetrical;
certain types, such as those used for mourning or warfare, probably do not have the

enhancement of physical attractiveness as their goal. The results do suggest, however,

63

that when that is the goal, the designs will tend to be symmetrical. They also suggest that
even though symmetrical art is very common, the preference for symmetrical facial
features is more likely to be constant than the preference for symmetrical art.

If the biological fitness hypothesis is correct, the results provide indirect evidence
for the influence of evolutionary biases towards symmetry and for the effect of such
biases on cultural practices. Further indirect support for the hypothesis will require
showing that, like the perception of attractiveness of other physical traits (Yu & Shepard,
1998; Marlowe & Wetsman, 2001), the results are replicable across cultures. The
comparability of results for Experiment 1 with Chilean subjects and Experiment 2 with

American subjects is a small step in this direction.

64

REFERENCES

Alford, R. (1996). Adomment. In D. Levinson & M. Ember (Eds) Encyclopedia of
cultural anthropology. (pp. 7-9). New York: Henry Holt & Company.

Andersson, MB. (1994). Sexual selection. Princeton, NJ: Princeton University Press.

Anon. (2003). Special Report: Pots of prorrrise - The beauty business. The Economist.
London: May 24, Vol.367, Issue 8325.

Appelle, S. (1972). Perception and discrimination as a function of stimulus orientation -
oblique effect in man and animals. Psychological Bulletin, 78 (4), 266-278.

Attneave, F. (1955). Symmetry, information, and memory for patterns. American Journal
of Psychology, 68, 209-222.

Barlow, H.B., & Reeves, BC. (1979). The versatility and absolute efficiency of detecting
nrirror symmetry in random dot displays. Vision Research, I 9, 783-793

Baylis, G., & Driver, J. (1994). Parallel computation of symmetry but not repetition
within single visual shapes. Visual Cognition, 1, 377-400.

Beh, H.C., & Latimer, CR. (1997). Symmetry detection and orientation perception:
Electrocortical responses to stimuli with real and implicit axes of orientation,
Australian Journal of Psychology, 49, 128-133.

Berlyne, D. (1971). Aesthetics and psychobiology. New York: Appleton-Century-Crofts,
Meredith Corporation.

Boas, F. (1955). Primitive art. New York: Dover Publications.
Bohannan, P. (1956). Beauty and scarification amongst the Tiv. Man, 56, 117-121.

Bomstein, M., Ferdinasen, K., & Gross, C. (1981). Perception of symmetry in infancy.
Developmental Psychology, 1 7, 82-86.

Bourdieu, P. (1984). Distinction: A social critique of the judgment of taste (R. Nice,
Trans.) Cambridge, Mass.: Harvard University Press. (Original work published
1979)

Bourdieu, P. (1986). The Forms of Capital. In J. Richardson (Ed.) Handbook of theory
and research for the sociology of education (pp. 241—25 8). New York: Greenwood
Press.

Brain, R. (1979). The decorated body. New York: Harper & Row.

65

Bruce, V., & Morgan, M. (1975). Violations of symmetry and repetition in visual
patterns. Perception, 4, 239-249.

Buss, D.M. (1989). Sex differences in human mate preferences: Evolutionary hypotheses
tested in 37 cultures. Behavioral and Brain Sciences, 12, 1-49.

Coote, J. (1992). ‘Marvels of everyday vision’: The anthropology of aesthetics and the
cattle-keeping Nilotes. In J. Coote & A. Shelton (Eds.) Anthropology, art, and
aesthetics (pp. 245-73). Oxford: Clarendon Press.

Coppola, D.M., Purves, H.R., McCoy, A.N., & Purves, D. (1998). The distribution of
oriented contours in the real world. Proceedings of the National Academy of Science,
95 (7), 4002-6.

Corbalis, C., & Roldan, E. (1974). On the perception of symmetrical and repeated
patterns. Perception and Psychophysics, 16, 136-142.

Cronin, H. (1991). The ant and the peacock: altruism and sexual selection fiom Darwin
to today. Cambridge; New York: Press Syndicate of the University of Cambridge.

Darwin, C. (1882). The descent of man and selection in relation to sex (2nd ed.). London:
John Murray.

Deregowski, J. (1972). The role of symmetry in pattern reproduction by Zambian
children. Journal of Cross-C ultural Psychology, 3, 303-307.

Ebin, V. (1979). The body decorated. London: Thames & Hudson.

Eisenman, R., & Gellens, H. (1968). Preference for complexity-sirnplicity and symmetry-
asymmetry. Perceptual and Motor Skills, 26, 888-890.

Enquist, M., & Arak, A. (1994). Symmetry, beauty, and evolution. Nature, 3 72, 169-172.

Enquist, M., & Johnstone, R. (1997). Generalization and the evolution of symmetry
preferences. Proceedings of the Royal Society of London, Series B: Biological
Sciences, 264, 1345-1348.

Enquist, M, Ghirlanda, S., Lundqvist, D., & Wachtrneister (2002). An ethological theory
of attractiveness. In G. Rhodes & L. Zebrowitz (Eds), Facial attractiveness:
Evolutionary, cognitive, and social perspectives. Advances in Visual Cognition, Vol.
1 (pp. 127-151). Westport, CT: Ablex.

Evans, C., Wenderoth, P., & Cheng, K. (2000). Detection of bilateral symmetry in
complex biological images. Perception, 29, 31-42.

Fisher, C., Ferdinandsen, K., & Bomstein, M. H. (1981). The role of symmetry in infant
form discrimination. Child Development, 52, 457-462.

66

Fisher, R.A. (1930). The genetical theory of natural selection. Oxford: Clarendon Press.

Gombrich, E. (1984). The sense of order: A study in the psychology of decorative art.
Ithaca, New York: Cornell University Press.

Grammer, K., & Thomhill, R. (1994). Human (Homo sapiens) facial attractiveness and

sexual selection: the role of symmetry and averageness. Journal of Comparative
Psychology, 108 (3), 233-242.

Grammer, K., Fink, B., Moller, A., & Thomhill, R. (2003). Darwinian aesthetics: sexual
selection and the biology of beauty. Biological Review, 78, 385-407.

Gusinde, M. (1982). Los indios de T ierra del F uego: Los Selk'nam. Buenos Aires: Centro
Argentino de Etnologia Americana.

Halberstadt, J., & Rhodes, G. (2000). The attractiveness of nonface averages:
implications for an evolutionary explanation of the attractiveness of average faces.
Psychological Science, I 1, 285-289.

Halberstadt, J ., & Rhodes, G. (2003). It’s not just average faces that are attractive:
computer-manipulated averageness makes birds, fish, and automobiles attractive.
Psychonomic Bulletin & Review, 10, 149-156.

Henshilwood, C.S., d’Errico, R, Yates, R., Jacobs, Z., Tribolo, C., Duller, G.A.T.,
Mercier, N., Sealy, J.C., Valladas, H., Watts, 1., & Wintle, AC. (2002). Emergence

of modern human behaviour: middle stone age engravings from South Africa.
Science, 295, 1278-1280.

Herbert, A.M., Overbury, 0., Singh, J., & Faubert, J. (2001). Aging and bilateral
symmetry detection. Journal of Gerontology: Psychological Sciences, 5 7B (3), 241 -
245.

Huang, L., & Pashler, H. (2002). Symmetry detection and visual attention: A “binary-
map” hypothesis. Vision Research, 42, 1421-1430.

Hubel, D.H., & Wiesel, TN. (1968). Receptive fields and functional architecture of
monkey striate cortex. Journal of Physiology, 195 (1), 215-43.

Hume, D., & Montgomerie, R. (2001). Facial attractiveness signals different aspects of
‘ ‘quality” in women and men. Evolution and Human Behavior, 22, 93-112.

Jacobsen, T., & Hiifel, L. (2001). Aesthetic electrified: and analysis of descriptive
symmetry and evaluative aesthetic judgment processes using event-related brain
potentials. Empirical Studies of the Arts, 1 9, 177-190.

Jansson, L., Forknam, B., & Enquist, M. (2002). Experimental evidence of receiver bias
for symmetry. Animal Behavior, 63, 617-621.

67

Jenkins, B. (1982). Redundancy in the perception of bilateral symmetry in dot textures.
Perception and Psychophysics, 32, 443-448.

Johnson, R. (2001). The anthropological study of body decoration as art: collective
representations and the somatization of affect. Fashion Theory, 5 (4), 417-434.

Johnstone, R. (1994). Female preference for symmetrical males as a by-product of
selection for mate recognition. Nature, 372, 172-175.

Jones, B.C., Little, A.C., Penton-Voak, I.S., Tiddeman, B.P., Burt, D.M., & Perrett, DJ.
(2001). Facial symmetry and judgments of apparent health: support for a “good

genes” explanation of the attractiveness-symmetry relationship. Evolution and
Human Behavior, 22, 417-429.

J ulesz, B. (1971). Foundations of cyclopean perception. Chicago: University of Chicago
Press.

Koehler, N., Rhodes, G., & Simmons, L. (2002). Are human female preferences for
symmetrical male faces enhanced when conception is likely? Animal Behavior, 64,
233-238.

Krieger, N., Williams, D.R., & Moss, NE. (1997). Measuring social class in US public
health research: concepts, methodologies, and guidelines. Annual Review of Public
Health, 18, 341-78.

Krupinski, E., & Locher, P. (1988). Skin conductance and aesthetic evaluative responses
to nonrepresentational works of art varying in symmetry. Bulletin of the
Psychonomic Society, 26, 355-358.

Langlois, J.H., & Roggrnan, LA. (1990). Attractive faces are only average.
Psychological Science, I , 1 15-121.

Langlois, J.H., Roggrnan, L.A., & Musselrnan, L. (1994). What is average and what is
not average about attractive faces? Psychological Science, 5, 214-220.

Lens, L., Van Dongen, S., Kark, S., & Matthysen, E. (2002). Fluctuating asymmetry as
an indicator of fitness: can we bridge the gap between studies? Biological Review,
77, 28-3 8.

Levi-Strauss, C. (1963). Structural anthropology. New York: Basic Books.

Li, 8., Peterson, M.R., & Freeman, RD. (2003). Oblique effect: A neural basis in the
visual cortex. Journal of Neurophysiology, 90, 204-217.

68

Little, A.C., Burt, D.M., Penton-Voak, I.S., & Perrett, DJ. (2001). Self-perceived
attractiveness influences human preferences for sexual dimorphism and symmetry in

male faces. Proceedings of the Royal Society of London, Series B: Biological
Sciences, 268, 39-44.

Little, A.C., & Jones, BC. (2003). Evidence against perceptual bias views for symmetry
preferences in human faces. Proceedings of the Royal Society of London, Series B:
Biological Sciences, 270 (526), 1759-1763.

Locher, P., & Nodine, C. (1989). The perceptual value of symmetry. Computers &
Mathematics with Applications, 17, 475-484.

Low, BS. (1979). Sexual selection and human ornamentation. In N. Chagnon & W. Irons
(Eds) Evolutionary Biology and Human Social Behavior: An Anthropological
Perspective (pp. 462-486). North Scituate, Mass: Duxbury Press.

Ludwig, W. (1932). Das rechts-links problem im tierreich und beim menschen. Berlin:
Springer-Verlag.

Mach, E. (1959). The analysis of sensations, and the relation of the physical to the

psychical. (C.M. Williams, Trans.) New York: Dover Publications (Original work
published 1886).

Marlowe, F., & Wetsman, A. (2001). Preferred waist-to-hip ratio and ecology.
Personality and Individual Diflkrences, 30, 481-489.

Martinez, A.M., & Benavente, R. (1998). The AR Face Database. CVC Technical Report
24, Universitat Autonoma de Barcelona.

Mealy, L., Bridgestock, R., & Townsend, G. (1999). Symmetry and perceived facial
attractiveness. Journal of Personality and Social Psychology, 76, 151-158.

McManus, C. (2002). Right hand, left hand: The origins of asymmetry in brains, bodies,
atoms and cultures. Cambridge, MA: Harvard University Press.

Miller, GP. (1998). How mate choice shaped human nature: A review of sexual selection
and human evolution. In C. Crawford & D. Krebs (Eds.), Handbook of evolutionary
psychology: Ideas, issues, and applications (pp. 87-129). Mahwah, N.J.: Lawrence
Erlbaurn.

Miller, GR (2000). The mating mind: How sexual choice shaped the evolution of human
nature. New York: Doubleday.

Miller, GP. (2001). Aesthetic fitness: How sexual selection shaped artistic virtuosity as a

fitness indicator and aesthetic preferences as mate choice criteria. Bulletin of
Psychology and the Arts, 2, 20-25.

69

Mithen, S. (1996). The prehistory of the mind: The cognitive origins of art, religion and
science. London: Thames & Hudson.

Morales, D., & Pashler, H. (1999). No role for colour in symmetry perception. Nature,
399,115-116.

Mallet, AP. (1992). Female swallow preference for symmetrical male sexual ornaments.
Nature, 35 7, 23 8-240.

Mallet, A.P., & Thomhill, R. (1998). Bilateral symmetry and sexual selection: a meta-
analysis. American Naturalist, 151, 174-192.

Morphy, H. (1994). The anthropology of art. In T. Ingold (Ed.) Companion encyclopedia
of anthropology: Humanity, culture & social life (pp. 648-685). London: Routledge.

Morales, D. & Pashler, H. (1999). No role for colour in symmetry perception. Nature,
399,115-116.

Palmer, A.R., & Strobeck, C. (2003). F luctuating asymmetry analyses revisited. In M.
Polak (Ed.) Developmental instability: Causes and consequences (pp. 279-319).
New York: Oxford University Press.

Pashler, H. (1990). Coordinate frame for symmetry detection and object recognition.
Journal of Experimental Psychology: Human Perception and Performance, 1 6, 150-
163.

Penton-Voak, I.S., Jones, B.C., Little, A.C., Baker, 8., Tiddeman, B., Burt, D.M., &
Perrett, DJ. (2001). Symmetry, sexual dimorphism in facial proportions and male
facial attractiveness. Proceedings of the Royal Society of London, Series B:
Biological Sciences, 268, 1617-1623.

Perrett, D.I., Burt, D.M., Penton-Voak, 1., Lee, K., Rowland, D., & Edwards, R. (1999).
Symmetry and human facial attractiveness. Evolution and Human Behavior, 20, 295-
307.

Pinker, S. (1997). How the mind works. New York: Norton.

Power, C. (1999). ‘Beauty magic’: the origins of art. In R. Dunbar, C. Knight & C. Power
(Eds), The evolution of culture: An interdisciplinary view. (pp. 92-112). New
Brunswick, NJ: Rutgers University Press.

Rentschler, I., Jiittrrer, M., Unzicker, A., & Landis, T. (1999). Innate and learned
components of human visual preference. Current Biology, 9, 665-671.

Rhodes, G., Proffrtt, F., Grady, J., & Sumich, A. (1998). Facial symmetry and the
perception of beauty. Psychonomic Bulletin & Review, 5 (4), 659-669.

70

Rhodes, G., Sumich, A., & Byatt, G. (1999). Are average facial configurations attractive
only because of their symmetry? Psychological Science, 10, 52-58.

Rhodes, 6., Yoshikawa, S., Clark, A., Lee, K., McKay, R., & Akamatsu, S. (2001a).
Attractiveness of facial averageness and symmetry in non-Western cultures: In
search of biological based standards of beauty. Perception, 30, 611-625.

Rhodes, G., Zebrowitz, L., Clark, A., Kalick, S.M., Hightower, A., & McKay, R.
(2001b). Do facial averageness and symmetry signal health? Evolution and Human
Behavior, 22, 31-46.

Rikowski, A., & Grammer, K. (1999). Human body odour, symmetry and facial
attractiveness. Proceedings of the Royal Society of London, Series B: Biological
Sciences, 266, 869-874.

Royer, F. (1981). Detection of symmetry. Journal of Experimental Psychology: Human
Perception and Performance, 7(6), 1 186-1210.

Ryan, M. (1998). Sexual selection, receiver biases, and the evolution of sex differences.
Science, 281, 1999-2003.

Scheib, J .E., Gangestad, S.W., & Thomhill, R. (1999). Facial attractiveness, symmetry
and cues of good genes. Proceedings of the Royal Society of London, Series B:
Biological Sciences, 266, 1913-1917.

Singh, D., & Bronstad, PM. (1997). Sex differences in the anatomical locations of
human body scarification and tattooing as a function of pathogen prevalence.
Evolution and Human Behavior, 18 (6), 403-416.

Sperber, D., & Hirschfeld, LA. (2004). The cognitive foundations of cultural stability
and diversity. Trends in Cognitive Sciences, 8 (1), 40-46.

Swaddle, J. (1999). Visual Signaling by asymmetry: a review of perceptual processes.
Philosophical Transactions of the Royal Society of London, Series B: Biological
Sciences, 354, 1383-1393.

Swaddle, J. (2003). Fluctuating asymmetry, animal behavior, and evolution. Advances in
the Study of Behavior, 32, 169-205.

Switkes, E., Mayer, M.J., & Sloan, J .A. (1978). Spatial frequency analysis of the visual
environment: anisotropy and the carpentered environment hypothesis. Vision
Research, 18 (10), 1393-9.

Thomhill, R. (1998). Darwinian aesthetics. In C. Crawford & D. Krebs (Eds) Handbook
of evolutionary psychology: Ideas, issues and applications (pp. 543-572). Mahwah,
NJ: Lawrence Erlbaurn Associates.

71

Thomhill, R., & Gangestad, SW. (1999). Facial attractiveness. Trends in Cognitive
Science, 3, 452-460.

Tinbergen, N. (1963). On the aims and methods of ethology. Zeitschrififi'ir
T ierpsychologie, 20, 410-463.

Tooby, J ., & Cosmides, L. (1992). The psychological foundations of culture. In J.
Barkow, L. Cosmides & J. Tooby (Eds) The adapted mind: Evolutionary psychology
and the generation of culture (pp. 19-136). NY: Oxford University Press.

Trivers RL (1972) Parental Investment and Sexual Selection. In B. Campbell (Ed)
Sexual selection and the descent of man, 1871-1971 (pp. 136-179). Chicago: Aldine.

Tyler, C.W. (Ed.). (2002). Human symmetry perception and its computational analysis.
Mahwah, NJ: Lawrence Erlbaum Associates.

Wagemans, J ., Van Gool, L., Swinnen, V., & Van Horebeek, J. (1993). Higher-order
structure in regularity detection. Vision Research, 33, 1067-1088.

Wagemans, J. (1995). Detection of visual symmetries. Spatial Vision, 9, 9-32.

Wagemans, J. (1997). Characteristics and models of human symmetry detection. Trends
in Cognitive Sciences, 1 (9), 346-352.

Wagemans, J. (1999). Parallel visual processing in symmetry perception: normality and
pathology. Documenta Ophthalmologica, 95, 359-370.

Watson, P., & Thomhill, R. (1994). F luctuating asymmetry and sexual behavior. Trends
in Ecology and Evolution, 9(1), 21-25.

Washburn, D. (1999). Perceptual anthropology: the cultural salience of symmetry.
American Anthropologist, 101 (3), 547-562.

Washburn, D., & Crowe, D. (1988). Symmetries of culture: Theory and practice of plane
pattern analysis. Seattle, WA: University of Washington Press.

Washburn, D., & Humphrey, D. (2001). Symmetries in the mind: production, perception,
and preference for seven one-dimensional patterns. Visual Arts Research, 70, 57-68.

Wenderoth, P. (1994). The salience of vertical symmetry. Perception, 23, 221-236.
Weyl, H. (1952). Symmetry. Princeton, New Jersey: Princeton University Press.

Yu, D., & Shepard, G. (1998). Is beauty in the eye of the beholder? Nature, 396, 321-
322.

72

Zahavi, A. (1975). Mate selection - A selection for a handicap. Journal of Theoretical
Biology, 53, 205-213.

Zahavi, A. (1978). Decorative patterns and the evolution of art. New Scientist, 80, 182-
1 84.

Zahavi, A., & Zahavi, A. (1997). The handicap principle: A missing piece of Darwin 's
puzzle. New York: Oxford University Press.

Zebrowitz, L.A., Hall, J .A., Murphy, N.A., & Rhodes, G. (2002). Looking smart and
looking good: Facial cues to intelligence and their origins. Personality and Social
Psychology Bulletin, 28, 238-249.

73

‘ F ' ‘a‘I: ‘ 1

.- III‘IITIIIVIT‘III‘I

I ‘1‘ ‘I‘rl

   

IIIIIIIIIIIIIIIIIIIIIIII