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Gender differences in the motivational processing of facial beauty

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卷:
39
年:
2008
语言:
english
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10
DOI:
10.1016/j.lmot.2007.09.002
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Available online at www.sciencedirect.com

Learning and Motivation 39 (2008) 136–145
www.elsevier.com/locate/l&m

Gender differences in the motivational
processing of facial beauty q
Boaz Levy a, Dan Ariely b, Nina Mazar b, Won Chi a,
Scott Lukas a, Igor Elman a,*
a
Department of Psychiatry, Behavioral Psychopharmacology Research Laboratory,
McLean Hospital/Harvard Medical School, 115 Mill Street, Belmont, MA 02478-9106, USA
b
Program in Media Arts and Sciences and Sloan School of Management,
Massachusetts Institute of Technology, Cambridge MA, USA

Received 12 July 2007; received in revised form 29 August 2007
Available online 26 November 2007

Abstract
Gender may be involved in the motivational processing of facial beauty. This study applied a
behavioral probe, known to activate brain motivational regions, to healthy heterosexual subjects.
Matched samples of men and women were administered two tasks: (a) key pressing to change the
viewing time of average or beautiful female or male facial images, and (b) rating the attractiveness
of these images. Men expended more effort (via the key-press task) to extend the viewing time of the
beautiful female faces. Women displayed similarly increased effort for beautiful male and female
images, but the magnitude of this effort was substantially lower than that of men for beautiful
females. Heterosexual facial attractiveness ratings were comparable in both groups. These findings
demonstrate heterosexual specificity of facial motivational targets for men, but not for women.
Moreover, heightened drive for the pursuit of heterosexual beauty in the face of regular valuational
assessments, displayed by men, suggests a gender-specific incentive sensitization phenomenon.
Ó 2007 Elsevier Inc. All rights reserved.
Keywords: Reward; Reinforcement; Sex; Motivation; Men; Women; Male; Female; Incentive sensitization;
Heterosexual

q
*

This work was supported by Grant D.A. #017959 (I.E.) from the National Institute on Drug Abuse.
Corresponding author. Fax: +1 617 8553711.
E-mail addre; ss: ielman@partners.org (I. Elman).

0023-9690/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved.
doi:10.1016/j.lmot.2007.09.002

B. Levy et al. / Learning and Motivation 39 (2008) 136–145

137

According to Darwin’s sexual selection theory (Darwin, 1871), gender differences in
mating strategies and effort reflect adaptive natural selection processes, derived from conflicting motivations for maximizing the number of fertilized women by the abundant
sperm vs. entrusting a limited egg supply to the fittest men. Thus, women tend to search
for men with social dominance and material goods (Sadalla, Kenrick, & Vershure, 1987),
whereas men pursue physiological qualities that indicate fertility, including large breasts,
prominent buttocks, and wide pelvises (Buss, 1989; Buss & Schmitt, 1993; Cunningham,
1986; Senior, 2003; Symons, 1979). The motivational appeal of these exaggerated fertility
symbols, depicted in the figures of ancient Eastern goddesses of fertility (e.g., Babylonian
Ishtar) and still permeating some cultures, has, however, been sublimated over time into
more subtle ideals of health and facial beauty (Rhodes, 2006).
Much of the prior research on the motivational role of beauty in mating gender differences is based on self-report measures and ratings of preferences, while fundamental motivational drives to pursue heterosexual beauty have not yet been methodically assessed
using rigorous scientific paradigms. For this purpose, it is critical to develop a solid theoretical framework along with accurate measurements of motivated behavior.
Germane here, Berridge and Robinson (2003) advanced a theory that integrates new
neurobiological insights into the brain reward system with psychological aspects of motivation. In this model, the authors distinguish between the desirability of reward and emotional experience. The former is defined by the extent to which a particular reward is
wanted, whereas the latter refers to the subjective experience of pleasure or pain. Rewards
that are ‘‘liked’’ (e.g., evoke pleasure) may not always be desired or ‘‘wanted’’, as in the
case of sexual pursuit of a physically attractive partner in situations where destructive consequences are likely to ensue.
Psychological aspects of ‘‘wanting’’ and ‘‘liking’’ are purportedly mediated via distinct
neurobiological pathways, which play different roles within the motivational and reward
system. The mesolimbic dopaminergic system may thus be particularly involved in what
Berridge and Robinson (2003) term the ‘‘incentive salience’’ of reward, which refers to
the ‘‘wanting’’ process by which an organism determines the motivational value of a particular object beyond the emotional experience it evokes. Normally objects with high
incentive salience are deemed to capture greater attention resources and lead to expenditure of greater behavioral effort relative to available alternatives of lower motivational
value. ‘‘Liking’’ is conveyed to the frontotemporal cortical structures (Berridge, 2003; Kelley, 2004) via distinct opioid neurotransmission within the scattered network of subcortical
and brain stem nuclei (Saper, Chou, & Elmquist, 2002).
It has been proposed that some psychopathological conditions (to name a few: substance use disorders, psychosis and Parkinson’s disease) with excessive release of- and/
or sensitivity to dopamine in the ‘‘wanting’’ system may be associated with aberrant salience attribution, that is to say, incentive sensitization (Berridge, 2006; Elman, Borsook,
& Lukas, 2006; Kapur, 2003). For example, in the form of irresistible urges to seek and
consume drugs despite their diminished hedonic qualities, incentive sensitization is particularly conspicuous in patients with substance use disorders (Kalivas & Volkow, 2005).
However, healthy people may be as well disproportionably sensitized to various stimuli
including spiders, snakes, crowds, flights, closed spaces, and many others. In this regard,
men could motivationally process heterosexual beauty with heightened incentive salience
and, given potentially pathological aspects of this motivational state (Kernberg, 1995),
with incentive sensitization.

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The purpose of the present study was to determine whether male sex is associated with
increased motivational value of heterosexual beauty. We applied a ‘‘mating opportunity
mindset’’-inducing (Wilson & Daly, 2004) facial paradigm that was originally developed
by Ariely, Breiter, and Etcoff (Aharon et al., 2001) and was later used by Elman and colleagues (Elman et al., 2005). In this paradigm, participants (1) can either increase or
decrease the viewing time of each of the faces by pressing designated keys on the keyboard
and (2) rate the attractiveness of human faces that appear on a computer screen. In this
way, an objective marker of operant behavior or a motivational value conceptualized as
effort expended to pursue beauty (in units of computer key presses) and reflective of internal state can be related to conscious and subjective valuation of beauty’s esthetics. Thus,
our facial paradigm distinguishes between ‘‘wanting’’ (i.e., number of key presses as a measurement of motivational value) aspects of motivation from ‘‘liking’’ (i.e., ratings of
attractiveness indicating subjective valuation of esthetics).
The value of using the key-press and the ratings tasks is a more conclusive interpretation of the findings. Matching increments on both tasks’ measurements with regard to
beauty will support the intuitively obvious incentive salience attribution to the objects that
are consciously experienced as beautiful (Berridge, 2006). On the other hand, increased
key-press numbers without corresponding increases in the attractiveness ratings will suggest incentive sensitization mechanisms (Berridge, 2006; Evans et al., 2006). With these
considerations in mind, it was hypothesized that, in comparison to men, women will have
similar ratings of heterosexual beauty, but decreased key-press responses to this stimulus.
Additionally, given greater bisexual interest among heterosexual women vs. men (Chivers
& Bailey, 2005; Diamond, 2003), we expected to find in the former group increased attractiveness ratings and motivation for viewing beautiful female images.
Methods
Participants
For clarity of presentation, study participants are referred to as ‘‘men’’ and ‘‘women’’
and facial images as ‘‘male’’ and ‘‘female’’. Study subjects comprised healthy individuals,
as determined by the Structured Clinical Interview for DSM-IV-TR Axis I Disorders
(SCID-I/NP; First, Spitzer, Gibbon, & Williams, 2002). Their self-reported heterosexual
status was confirmed with the Klein Sexual Orientation Grid (KSOG; Klein, Sepekoff,
& Wolf, 1985) that assessed the sexual self (attraction, fantasy, and behavior), the sexual
orientation (emotional preference, social preference, and heterosexual or homosexual lifestyle), and the self-identification using the Likert-type scale raging from 1 (‘‘hetero or
other sex only’’) to 7 (‘‘same sex or gay only’’) as applying to the present, past, or ideal.
No subject expressed a greater than ‘‘2’’ rating i.e., ‘‘other sex/hetero mostly’’ on any of
the KSOG items.
Men (n = 18) and women (n = 17) groups were matched with respect to age (within 3–4
year range), ethnicity (11 Caucasian, 4 African-American; 2 Hispanic and 1 Asian vs. 11
Caucasian; 3 African-American; 2 Hispanic and 1 Asian) and years of education (within
2–3 year range). According to the SCID-I/NP, no subject met criteria for current or lifetime substance abuse or dependence. Women were studied in the midfollicular phase of
their menstrual cycle. All subjects gave written informed consent for participation after
the procedures had been fully explained.

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139

Stimuli
Subjects were presented with 80 nonfamous human faces that were selected from print
media and classified according to pilot test results in the following four categories of 20
each: average female, beautiful female, average male, and beautiful male. The pictures
were digitized at 600 dpi in 8-bit grayscale, spatially downsampled, and cut to fit in an oval
‘‘window’’ sized 310–350 pixels wide by 470 pixels high using Photoshop 4.0 software
(Adobe Systems). Examples of categorical facial images used as visual stimuli are presented in Fig. 1.
Procedures
There were two tasks administered in separate runs: a key-press task, followed by an
image attractiveness rating task. For each run, faces were presented in two blocks by gender. The order of the gender blocks was counterbalanced across subjects. Within each gender block, the average and beautiful faces were presented intermingled, in random order.
For the key-press task, subjects were informed that the entire task duration was fixed
and independent of their actions but that they could control the viewing time of each individual picture. The default viewing time for an individual facial image was 4 s. However,
subjects could either increase or decrease this time by up to 4 s (depending upon the frequency of the key presses) by alternately pressing a keyboard’s ‘‘n’’ and ‘‘m,’’ or ‘‘z’’ and
‘‘x’’ keys, respectively. The former key presses were scored as positive and the latter as negative. The average of these values for the 20 pictures in each of the four facial categories
yielded a subject’s ‘‘net’’ key presses for each category. In addition, each subject’s total key
presses, i.e., absolute number of key presses, regardless of whether scored positive or negative, during the entire experiment were calculated for use as a covariate.
During the subsequent rating task, the subject rated the attractiveness of the same faces
on a visual analog scale ranging from 0 ‘‘not attractive at all’’ to 100 ‘‘very attractive.’’ The
averages for the 20 pictures in each of the four facial categories yielded a subject’s attractiveness rating for each facial category.
Statistical analyses
Data were analyzed using the statistical package Statistica (StatSoft, Inc., Tulsa, OK).
T tests for independent samples were conducted to compare demographic variables. To

Fig. 1. Examples of categorical facial images used as visual stimuli.

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B. Levy et al. / Learning and Motivation 39 (2008) 136–145

determine effects of beauty and gender on attractiveness assessments and quantified measures of beauty motivation, i.e., computer key presses, a two-factor analysis of variance
(ANOVA), with Gender (men and women) as a between-subjects factor and Face type
(average female, beautiful female, average male, and beautiful male) as a within-subjects
factor was conducted. When group-by-time interactions were significant, post-hoc Newman–Keuls t tests were performed to determine differences in subjects’ responses to the
facial stimuli. Group data were summarized as mean (M) ± standard deviation (SD).
All analyses were two-tailed, and a p value < .05 defined statistical significance.

Attractiveness (mm)

100

men (N=18)
women (N=17)

80
60
40
20
0
20

Number of Key Presses

15

10
5

0
-5
-10

Average
female

Beautiful
female

Average
male

Beautiful
male

Stimulus
Fig. 2. Facial attractiveness ratings by men and women study participants and their performance on the keypress task. Data are presented as mean (SD). The ordinate represents the distance on the visual analog scale of
attractiveness, measured in millimeters. Rating data were analyzed with one-way ANOVA, using gender as the
grouping factor, and Face Type as the within-subjects factor and post-hoc Newman–Keuls t tests. Key-press data
were analyzed with ANCOVA using gender as the grouping factor, Face Type as the within-subjects factor and
the absolute total key presses as the covariate; Newman–Keuls t tests were used for post-hoc comparisons.

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141

Results
Men and women groups were similar with respect to age [M = 28.7, SD = 8.4 vs.
M = 25.0, SD = 3.3; t(33) = 1.60, p = .10] and years of education [M = 15.7, SD = 1.5
vs. 15.8 , SD = 1.5; t(33) = 0.20, p = .84)]. Fig. 2 displays the rating and net key-press
data for each category. Overall, the two groups did not differ in the attractiveness ratings
[group effect: F(1, 33) = 2.92, p = .10], but beautiful faces’ ratings significantly exceeded
those of the average faces [Faces Type effect: F(3, 99) = 127.90, p < .0001] with men rating
significantly lower male beauty [Group by Face Type interaction: F(3, 99) = 15.21,
p < .0001]. Post-hoc Newman–Keuls t tests revealed accordingly no group differences in
the ratings of beautiful females (p = .87) or of heterosexual beauty images (i.e., beautiful
females’ ratings by men and beautiful males’ ratings by women; p = .71) and significantly
lower ratings of beautiful male images in the men group (p = .005). Men rated beautiful
males significantly higher (p < .001) than average males and females, while women gave
male and female beauty similar (p = .51) ratings that significantly (p = .0001) exceeded
those of the average images.
Significant [t(33) = 2.18, p = .04] men [M = 11.1, SD = 6.2] and women [M = 6.93,
SD = 5.1] group differences were detected in the total number of key presses (i.e., absolute
number of key presses, regardless of whether scored positive or negative, during the entire
experiment). To ascertain that group differences in the net key presses for facial categories
did not merely reflect a group difference in general key-press activity, absolute total key
presses were used as a covariate in the key-press data analysis. The ANCOVA results
yielded a significant group (i.e., Gender) by Face Type interaction [F(3, 96) = 7.47,
p = .0002], with post-hoc Newman–Keuls t tests showing a higher number of key presses
in the male group for beautiful females (p = .002). Men exerted significantly greater
(p = .0001) effort (in the unit of computer key-press) to view beautiful female vs. beautiful
male faces; this difference was not detected in the women group (p = .90). Men’s mean
number of key presses for beautiful females was significantly higher than for any other
facial category (p = .0001), and no other significant differences in men’s key presses were
found (p > .90).
Discussion
The results of the current study provide empirical laboratory-based evidence for the
motivational value of beauty. Our interpretation that the observed gender differences
are related to motivational drives of the viewers (Senior, 2003) rather than to social acceptance or desirability of prolonged viewing behavior towards opposite sexes is supported by
recent work demonstrating stronger fMRI activations within motivational/reward regions
by female than by male faces for heterosexual men and by male than by female faces for
heterosexual women (Ishai, 2007; Kranz & Ishai, 2006; O’Doherty et al., 2003). Moreover,
a neuroimaging study employing the same visual stimuli in men only indicated that the key
presses, but not the esthetic ratings, were paralleled by activation of distinct brain regions
of motivational and reward circuitry (Aharon et al., 2001).
Our data contrast, however, with a prior report on facial beauty processing by healthy
subjects (Kranz & Ishai, 2006). In groups of heterosexual men and women (n = 10, each),
Kranz and Ishai (2006) observed similar visual processing time and attractiveness ratings
of male and female faces. In the present study, men found beautiful male faces less attrac-

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tive than beautiful female faces, with corresponding increases in the viewing times of the
latter. These contrasting data might be accounted for by differences in the study design,
such as categorical vs. visual analog types of attractiveness rating scales and passive visual
processing vs. operant assessments of motivational effort employed by our study.
The present data render the dissociation between assessments of attractiveness and quantified measures of reward valuation, which the authors, respectively, referred to as ‘‘liking’’
and ‘‘wanting’’ (Aharon et al., 2001), gender specific. Specifically, the results of the rating
task qualitatively paralleled those for the key presses (i.e., corresponding increases in both
measures) only in the women group. Furthermore, healthy men rated beautiful female faces
as highly attractive as healthy women did for beautiful males, but they expended more than
quadruple the effort to increase the viewing times of these same faces. This group difference
was not explained by the overall level of key-press activity. Our findings are therefore consistent with the conclusions that (1) men assess the attractiveness of heterosexual beautiful faces
similarly but derive greater motivational drive (assessed operantly) from viewing them; in
other words, in comparison to women, men ‘‘wanted’’ female beautiful faces more then could
be explained by their esthetic attributes; and (2) the neural system identified for ‘‘wanting’’ in
preclinical studies (Berridge & Robinson, 2003) may be the same system, sensitized in men,
for processing female beauty stimuli.
Human sexuality is a broad phenomenon, integrating a complex system of interrelated
biological, societal and psychological aspects, each of which exhibits a unique role within
the context of sexual behavior. Although it is tempting to suggest that motivational sensitization in men for pursuit of women represents a biology-based phenomenon, similar to
exaggerated (relative to hedonic effects) drug ‘‘wanting’’ or craving in addicts (Kalivas &
Volkow, 2005), the paradigm employed does not allow us to firmly conclude that. For
instance, it remains unclear whether the present findings are a product of innate and/or
learned motivation to pursue facial beauty. Moreover, recent work in homosexual individuals has demonstrated that the response to faces is modulated by sexual preference, but
not necessarily by gender per se (Ishai, 2007; Kranz & Ishai, 2006). Hence, it would be
revealing to perform a follow-up study in homosexuals to examine whether the effect of
gender would reverse in this case, or some more complex pattern would emerge.
Another unanswered question raised by this experimental design concerns motivational
targets that are more ‘‘wanted’’ by women than by men. Masculine beauty does not seem
to be one, as heterosexual women’s virtually identical responses to both male and female
faces is also seen in other behavioral (e.g., reaction time, valuational assessments and motivational effort) and neuronal (amplitude of the fMRI signal in the orbitofrontal cortex)
manifestations (Bray & O’Doherty, 2007; Kranz & Ishai, 2006). An alternative target
could be parental investment in care giving and in maximizing offspring survival, particularly in the context of the mother–infant diad (Depue & Morrone-Strupinsky, 2005; Taylor et al., 2000). A prospective survey of 1450 children born with defects revealed the
decisive role played by esthetic appearance in the creation and maintenance of mothers’
emotional bonds with biological children (Weiss, 1994). In this study, almost 70% of children abandoned by their parents carried a conspicuous flaw in their appearance that was
neither life threatening nor affected intellectual development; only 7% of abandoned children had a serious internal organ (e.g., heart and kidneys) defect. This report underscores
the motivational power of beauty and supports the hypothesis that, akin to heterosexual
beauty in men, infants’ esthetic appearance may be a potent motivational enhancer for
women, expressed as incentive sensitization to this stimulus.

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143

If the hypothesis of normative incentive sensitization is further supported, an important
focus for future research will be to determine whether this phenomenon generalizes
beyond beauty to other motivational targets (e.g., food and money). Further research is
also needed to determine gender differences in the neural substrate underlying incentive
sensitization processes and how it may be involved in psychopathologies characterized
by gender-specific courses, such as schizophrenia, substance use disorders, and major
depression.
An additional issue to consider here, given the predictable preference and pursuit of
physically attractive individuals, is that motivational and esthetic aspects of beauty are
two closely related concepts. Although disentangling these ‘‘original attributes of the
sexual object’’ (Freud, 1946) can be a daunting task (Finlayson, King, & Blundell,
2006), the rationale for the use of our paradigm, juxtaposing subjective esthetic valuations to a physical activity, construed to reflect subliminal internal states, is built upon
several lines of neuroimaging and clinical data, including evidence that independently
of the tasks’ nature, passive viewing of faces activates both motivational and valuational neural pathways, resulting in differential response patterns to sexually preferred
images (Aharon et al., 2001; Kranz & Ishai, 2006), along with differential effects of psychopathology on the performance on these tasks (Elman et al., 2005). Nonetheless,
introduction of additional paradigms, targeting other subjective aspects of ‘‘liking’’
responses (Berridge, 2006; Finlayson et al., 2006; Wilson & Daly, 2004; Winkielman,
Berridge, & Wilbarger, 2005) than the ones captured by this study may complement
our findings.
In conclusion, the data presented here suggest both similarities and differences with
regard to processing of beauty by both genders. Healthy men and women displayed similar
perception of heterosexual facial attractiveness, with men providing lower ratings for
beautiful males. In addition, men expended substantially greater motivational effort for
viewing beautiful female images than women for beautiful males. At the same time,
women increased the viewing time of both beautiful male and female faces, whereas
men concentrated on the beautiful females only. Gender differences in the processing of
average faces were not apparent. These data suggest various degrees of facial beauty’s
motivational value. While, regardless of an image’s gender, it appears to be a motivationally salient stimulus for women, men could be incentively sensitized to female beauty.
These data call for further research aimed at understanding the distinctive features of
motivational systems in men vis-à-vis those of women and their potential role in healthy
functioning and in psychopathology.
Acknowledgment
The authors thank Dr. Alumit Ishai for her insightful comments on the manuscript.
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