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Gender and Sexual Orientation Differences in Sexual Response to Sexual
Activities Versus Gender of Actors in Sexual Films
Meredith L. Chivers
Centre for Addiction and Mental Health
Michael C. Seto and Ray Blanchard
Centre for Addiction and Mental Health and University
of Toronto
In this study, the authors investigated the hypothesis that women’s sexual orientation and sexual
responses in the laboratory correlate less highly than do men’s because women respond primarily to the
sexual activities performed by actors, whereas men respond primarily to the gender of the actors. The
participants were 20 homosexual women, 27 heterosexual women, 17 homosexual men, and 27 hetero-
sexual men. The videotaped stimuli included men and women engaging in same-sex intercourse, solitary
masturbation, or nude exercise (no sexual activity); human male–female copulation; and animal (bonobo
chimpanzee or Pan paniscus) copulation. Genital and subjective sexual arousal were continuously
recorded. The genital responses of both sexes were weakest to nude exercise and strongest to intercourse.
As predicted, however, actor gender was more important for men than for women, and the level of sexual
activity was more important for women than for men. Consistent with this result, women responded
genitally to bonobo copulation, whereas men did not. An unexpected result was that homosexual women
responded more to nude female targets exercising and masturbating than to nude male targets, whereas
heterosexual women responded about the same to both sexes at each activity level.
Keywords: sexual arousal, sexual orientation, gender differences, vaginal photoplethysmography, penile
plethysmography
Female and male sexual orientation are not parallel phenomena.
Gender differences in the correlates of sexual orientation have
been reported across several lines of research, including birth
order, age of pubertal onset, heritability (see Mustanski, Chivers,
& Bailey, 2002, for a review), and the development, temporal
stability, and exclusivity of same- and opposite-gender sexual
experiences and attractions (Bailey, Dunne, & Martin, 2000; Di-
amond, 2000a, 2000b, 2005; Laumann, Gagnon, Michael, &
Michaels, 1994; Savin-Williams & Diamond, 2000). Gender dif-
ferences are not unique to sexual orientation, however, and have
been observed in many aspects of sexuality; for example, large
differences on measures of masturbation incidence and attitudes
about casual sex and small to moderate differences in other aspects
of sexual behavior, such as age at the time of first intercourse and
number of sexual partners, have been reported (Oliver & Hyde,
1993).
In recent research, another gender difference in relation to
sexual orientation, having to do with sexual response patterns
when participants are presented with sexual stimuli (see Chivers,
2005, for a review), has been identified. One expects sexual
responses (in terms of subjective and genital sexual arousal) to
sexual stimuli depicting male targets or female targets to reflect a
person’s sexual orientation. This expectation is correct for men:
Heterosexual men show greater sexual responses to depictions of
women than to depictions of men, whereas gay men show the
converse pattern. In contrast, both heterosexual and lesbian women
respond substantially to both depictions of women and depictions
of men.
The sexual psychophysiology research on this gender differ-
ence and sexual orientation difference in sexual response is
described in greater detail in the next section. Some definitions
are required, however, before proceeding. In this article, sexual
stimuli that depict content that corresponds with a person’s
stated preferences are described as preferred; stimuli depicting
anything else are described as nonpreferred. Thus, in regard to
sexual orientation, the preferred stimuli for heterosexual men
and homosexual women depict women, whereas the preferred
stimuli for homosexual men and heterosexual women depict
men. A pattern of sexual response that is significantly greater to
one’s preferred category of sexual stimuli is considered
category-specific (i.e., the responses demonstrate specificity).
Significant sexual responding to both preferred and nonpre-
ferred sexual stimuli is considered nonspecific.
Meredith L. Chivers, Law and Mental Health Program, Centre for
Addiction and Mental Health, Toronto, Ontario, Canada; Michael C. Seto
and Ray Blanchard, Law and Mental Health Program, Centre for Addiction
and Mental Health, and Department of Psychiatry, University of Toronto,
Toronto, Ontario, Canada.
Part of this article was presented at the 32nd Annual Meeting of the
International Academy of Sex Research, Amsterdam, the Netherlands, in
July 2006. Financial support was provided by a Social Sciences and
Humanities Research Council of Canada postdoctoral fellowship grant
awarded to Meredith L. Chivers. We thank Teresa Grimbos for her assis-
tance with recruiting participants. We also thank James Cantor, Martin
Lalumie`re, and Kenneth Zucker for their helpful comments on earlier
versions of this article, and we are grateful to the study participants.
Correspondence concerning this article should be addressed to Meredith
L. Chivers, Law and Mental Health Program, Centre for Addiction and
Mental Health, 1001 Queen Street West, Toronto, Ontario M6J 1H4,
Canada. E-mail: meredith_chivers@camh.net
Journal of Personality and Social Psychology Copyright 2007 by the American Psychological Association
2007, Vol. 93, No. 6, 1108–1121 0022-3514/07/$12.00 DOI: 10.1037/0022-3514.93.6.1108
1108
Specificity of Sexual Response
Male Specificity
Men show category-specific sexual responding. Multiple studies
have shown that male genital responses (recorded, in terms of
changes in penile circumference or volume, with phallometry) are
greater to preferred categories of sexual stimuli with regard to the
gender of persons depicted (e.g., Freund, 1963; Mavissakalian,
Blanchard, Abel, & Barlow, 1975; Sakheim, Barlow, Beck, &
Abrahamson, 1985; Tollison, Adams, & Tollison, 1979) or the age
of persons depicted (e.g., Blanchard, Klassen, Dickey, Kuban, &
Blak, 2001; Seto, Lalumie`re, & Blanchard, 2000). The specificity
of male genital response is sufficiently robust that phallometric
measurement of penile responses are used in forensic evaluations
of individuals who might deny their sexual preferences, as in the
case of male sex offenders who wish to avoid being diagnosed
with pedophilia (for a review, see Seto, 2004). In nonforensic
contexts, men’s self-reported sexual arousal is category-specific,
such that men report their greatest subjective response to their
preferred gender (e.g., Chivers, Rieger, Latty, & Bailey, 2004;
Mavissakalian et al., 1975).
Female Nonspecificity
Female genital responses, however, appear to be nonspecific. A
series of studies has shown that both heterosexual and lesbian
women show substantial increases in genital sexual arousal (re-
corded, in terms of vaginal vasocongestion, with vaginal photo-
plethysmography) to both preferred and nonpreferred stimuli with
regard to the gender of the persons depicted (Chivers et al., 2004;
Chivers & Bailey, 2005; Laan, Sonderman & Janssen, 1995;
Steinman, Wincze, Sakheim, Barlow, & Mavissakalian, 1981;
Wincze & Qualls, 1984). In other words, both heterosexual and
lesbian women show substantial genital responses both to stimuli
depicting women and to stimuli depicting men, and thus, patterns
of genital arousal are only weakly related to a woman’s sexual
orientation. Self-reported sexual arousal is somewhat category-
specific because women report greater sexual arousal to their
preferred sexual stimuli, but they also report some sexual arousal
to nonpreferred sexual stimuli (Chivers et al., 2004; Chivers &
Bailey, 2005; Laan, Sonderman, & Janssen, 1995; Schmidt, 1975).
As an illustration, Chivers et al. (2004) found that women showed
very similar genital responses to films of female–female, female–
male, or male–male intercourse, whereas their subjective re-
sponses were significantly greater to the category that corre-
sponded to their sexual orientation (i.e., female–male or male–
male intercourse for heterosexual women and female–female
intercourse for lesbian women). Men assessed in these same stud-
ies demonstrated significantly greater genital and self-reported
sexual arousal to films depicting their preferred gender (female–
female intercourse for heterosexual men and male–male inter-
course for homosexual men).
Chivers and her colleagues (Chivers & Bailey, 2005; Chivers et
al., 2004; Suschinsky, Lalumie`re, & Chivers, 2007) have system-
atically addressed alternative explanations for the consistent find-
ing of female nonspecificity. They showed that vaginal photo-
plethysmography is specific to sexual arousal and is therefore not
elicited by nonsexually arousing stimuli (Suschinsky et al., 2007;
see also Laan, Sonderman, & Janssen, 1995) and that vaginal
photoplethysmography can detect category-specific responding in
male-to-female transsexuals with surgically constructed vaginas
(Chivers et al., 2004). Further, they demonstrated that women’s
nonspecific sexual arousal is not explained by limited variability in
genital responses: Women show significant increases in vaginal
vasocongestion both to preferred and nonpreferred sexual stimuli
(Chivers et al., 2004; Chivers & Bailey, 2005).
The ability to genitally respond to sexual stimuli that do not
correspond to one’s sexual orientation suggests that female genital
responding is flexible. Flexibility refers to a pattern of intraindi-
vidual variability in sexual preferences, attitudes, and behaviors
(see Baumeister, 2000, for a review). For example, women are
more likely to experience and express same-sex attractions and
less likely to engage in exclusively heterosexual or homosexual
contacts (Bailey et al., 2000; Kinsey, Pomeroy, & Martin, 1948,
Kinsey, Pomeroy, Martin, & Gebhard, 1953; Laumann et al., 1994;
Rust, 1992), and women’s sexual identities show less temporal
stability than men’s (Bell, Weinberg, & Hammersmith, 1981;
Diamond, 2000a, 2000b, 2005; Kinnish, Strassberg, & Turner,
2005; Savin-Williams & Diamond, 2000).
The research conducted to date has suggested there is a gender
difference in the specificity of genital response, such that male
sexual responding is category-specific, whereas female sexual
responding is nonspecific. This gender difference is clearest in
studies that have directly compared male and female participants
on the same sexual stimuli (e.g., Chivers et al., 2004; Chivers &
Bailey, 2005). It is not known, however, why this gender differ-
ence exists: Why do women, but not men, show a genital response
to nonpreferred sexual stimuli? This leads to two even more
fundamental questions: What makes a sexual stimulus sexual? Do
the features that make a stimulus sexual differ for men and
women?
The Critical Features of Sexual Stimuli
Some investigators have suggested that sexual meaning is as-
cribed when viewing sexual stimuli and that this sexual meaning,
in turn, activates subjective and genital responses (Van Lunsen &
Laan, 2004). Surprisingly little is known, however, about what
specific features of sexual stimuli are critical to sexual meaning
and then to sexual response. In studies reporting nonspecific gen-
ital response in female participants, researchers used films por-
traying nude individuals engaged in sexual activity, which is a
common depiction in sexually explicit, commercially available
pornography. But what features of these films evoke genital re-
sponses? Is it the actors’ gender-typical physical characteristics,
such as breasts, vulva, or penis? Is it the movements associated
with sexual activity? Is it the explicitness of the sexual activity,
which can range from kissing and caressing to oral sex to inter-
course? We review the relevant research on gender and sexual
activity cues next.
Gender Cues
Both heterosexual and gay men demonstrate both self-reported
and genital sexual arousal to images of a nude person of their
preferred gender who is not engaged in any sexual activity (e.g.,
Mavissakalian et al., 1975; Tollison et al., 1979). There have been
few comparable studies of women, however. Laan and Everaerd
1109
GENDER AND SEXUAL ORIENTATION DIFFERENCES
(1995) found no significant increases in women’s subjective or
genital responses to pictures of male or female figures whether the
actors were nude or semiclothed. Other studies using pictures of
nude figures also suggested that actor gender cues are not suffi-
cient to elicit reports of sexual arousal from heterosexual women
(e.g., Knoth, Boyd, & Singer, 1988). None of these studies in-
cluded groups of lesbian women, however, so the importance of
gender cues with regard to female sexual orientation has not yet
been examined.
Sexual Activity Cues
There is evidence that heterosexual women’s sexual responses
are influenced by the explicitness of depictions of sexual activity,
with more explicit depictions eliciting greater self-reported and
genital sexual arousal. For example, Laan, Everaerd, van der
Velde, and Geer (1995) found that women’s sexual responses
increased as they viewed films of heterosexual couples engaging in
increasingly explicit sexual activities, ranging from kissing and
caressing to undressing, breast stimulation, manual stimulation of
the genitals, and then to cunnilingus and penile–vaginal inter-
course. This finding was replicated by Both, Boxtel, Stekelenburg,
Everaerd, and Laan (2005) using films of low (kissing), moderate
(caressing), and high (penile–vaginal intercourse) sexual explicit-
ness.
Other studies have shown that both women and men demon-
strate significantly greater genital responses to films depicting
penile–vaginal intercourse than to films depicting a man and
woman kissing and caressing (Suschinsky et al., 2007; Winzce,
Venditti, & Mavissakalian, 1980). Among men, Gaither and Plaud
(1997) showed that heterosexual men’s self-reported and genital
sexual arousal were greater to depictions of penile–vaginal inter-
course than to depictions of oral sex.
Self-report data are also germane. Kelley and Musialowski
(1986) found that women’s self-reported sexual arousal ratings are
more influenced by variation in sexual activity, whereas men’s
ratings are more influenced by variation in actor characteristics.
Ellis and Symons (1990) examined the content of sexual fantasies
and found that men are more likely to fantasize about the physical
characteristics of the imagined sexual partner, whereas women are
more likely to fantasize about the psychological characteristics of
the imagined sexual partner and the details of the sexual interac-
tions.
In a more direct test of the hypothesis that sexual activity is a
more salient sexual feature for women, Chivers and Bailey (2005)
reported that women demonstrate genital responses to stimuli
depicting sexual activity but no plausible sexual partner. To de-
termine whether features of sexual activity alone could produce a
sexual response in women, these investigators examined women’s
and men’s sexual responses to films depicting heterosexual, gay,
or lesbian couples engaging in oral and penetrative sex, as well as
a film of female and male bonobo chimpanzees (Pan paniscus)
engaging in repeated penile–vaginal penetration. The women pro-
duced genital responses to the mating bonobos that were larger
than their responses to a nonsexual control stimulus depicting
landscapes but significantly smaller than their responses to the
films depicting human couples; at the same time, women did not
report feeling any sexual arousal to the bonobo film. In contrast,
men showed no subjective or genital responses to the bonobo film.
Current Study
The gender difference in specificity of genital response may
reflect a more fundamental gender difference in the importance of
different features of ostensibly sexual stimuli. For men, the most
important features may be cues of actor gender, whereas for
women, the most important features may be cues of sexual activ-
ity. This hypothesis cannot be tested by reanalyzing extant data
because previous studies have used film clips of couples engaging
in sexual activity (Chivers et al., 2004; Chivers & Bailey, 2005;
Laan, Sonderman, & Janssen, 1995; Suschinsky et al., 2007). For
example, Chivers et al. (2004) presented films that depicted les-
bian, gay, or heterosexual couples engaged in oral and penetrative
sex acts and argued that the lesbian and gay stimuli were infor-
mative because they were homogeneous with regard to the gender
of the actors (i.e., only depicting women or only depicting men).
These films, however, confound actor gender and sexual activity.
In addition, depictions of lesbian, gay, or heterosexual sex may
have different sexual meanings depending on the sexual orienta-
tion of the viewer, which may in turn affect sexual response. For
example, watching films depicting two men engaged in intercourse
may be more taboo for heterosexual viewers than watching films
depicting two women engaged in intercourse, given that lesbian
sex is a common theme in mainstream, commercially available
pornography. For lesbian or gay viewers, watching a man and
women engaged in intercourse may not be taboo, given the com-
mon representations of heterosexual sex in mainstream media. To
determine whether female sexual response to preferred and non-
preferred actors is truly nonspecific and is not an artifact of the
sexual stimuli that were used in the previous studies, one must
examine women’s sexual arousal to stimuli that disentangle actor
gender from sexual activity.
In the present study, we sought to clarify the relationships
among sexual orientation, gender, and sexual response by present-
ing homosexual and heterosexual men and women with stimuli
depicting men or women engaged in different levels of sexual
activity. By using an experimental design that completely crossed
actor gender (male target[s] vs. female target[s] depicted) and
sexual activity (none/exercise vs. masturbation vs. intercourse), we
examined the relative effects of actor gender and sexual activity
cues on the sexual responses of women and men.
The first objective, therefore, was to address two novel ques-
tions regarding the relationship between sexual orientation and
sexual response, which focus on women because of the counter-
intuitive findings that have been reported to date. These were as
follows: (a) Are women’s sexual responses category-specific when
women are presented with stimuli depicting a solitary male target
or a solitary female target, consistent with their stated sexual
orientation? and (b) Are women’s sexual responses related to the
amount of sexual activity depicted in a stimulus, ranging from
none (in the case of nude individuals exercising) to masturbation to
sexual intercourse? The second objective was to replicate Chivers
et al.’s (2004) results showing women’s genital responses do not
differentiate among stimuli depicting male–male, female–female,
or female–male intercourse, whereas men’s genital responses do.
The third objective was to replicate Chivers and Bailey’s (2005)
results in which women, but not men, show a significant genital
response to a nonhuman stimulus depicting bonobos engaging in
penile–vaginal intercourse.
1110
CHIVERS, SETO, AND BLANCHARD
Method
Participants
We recruited women and men via advertisements posted on a
student employment website at a local university, placed in a local
gay weekly newspaper, and posted in a monthly e-newsletter for
lesbian women. The inclusion and exclusion criteria were as fol-
lows: Participants who are between the ages of 18 years and 40
years; are able to read and write English fluently; have no history
of sexual response difficulties; have no history of mental illness or
substance abuse; have no current use of medications or contracep-
tives known or suspected to influence sexual functioning (i.e.,
psychotropics, neuroleptics, hormones, antihypertensives, or cold/
allergy medications; see Meston & Frolich, 2000); have no active
sexually transmitted disease; have a stated sexual preference for
women or for men; and for women, are not pregnant and have a
regular menstrual cycle.
There were 205 women who responded to the advertisement: 93
declined participation or did not respond further after receiving
more information about the study, 58 were not eligible to partic-
ipate, 54 were eligible to participate and scheduled an appoint-
ment, and 49 of the eligible women attended the experimental
session. There were 120 men who responded to the advertisement:
46 declined participation or did not respond further after receiving
more information about the study, 20 were not eligible to partic-
ipate, 54 were eligible to participate and scheduled an appoint-
ment, and 47 of the eligible men attended the experimental session.
All participants received $50 for their time and expenses.
Apparatus and Materials
Data acquisition. All psychophysiological responses were
sampled and recorded with a Limestone Technologies Data-
Pac_USB system (Limestone Technologies, Kingston, Ontario,
Canada). The Limestone software and hardware were installed on
a Pentium Dell desktop computer (Dell Canada Inc., North York,
Ontario, Canada).
Self-reported sexual response. While watching the experimen-
tal stimuli, women and men manipulated a virtual gauge (i.e., an
electronic representation of a bar) to continuously report their
subjective state of sexual arousal, defined as their “state of mental
or emotional sexual arousal” on a scale from 0% (no sexual
arousal) to 100% (most sexual arousal ever felt, sexual arousal
associated with orgasm). Participants raised and lowered the vir-
tual gauge, presented on a computer monitor adjacent to the sexual
stimulus, using a keypad attached to the armrest of a comfortable
reclining chair.
Female genital response. Women’s genital responses were
assessed with vaginal photoplethysmography (Sintchak & Geer,
1975). The alternating current component of the vaginal photopl-
ethysmograph signal, vaginal pulse amplitude (VPA), was selected
as the dependent measure for this study. VPA represents the phasic
changes in vaginal blood flow associated with each heartbeat, such
that higher amplitudes reflect greater vaginal vasocongestion. In-
creases in VPA are specific to sexual response (Laan, Everaerd, &
Evers, 1995; Suschinsky et al., 2007). The photoplethysmograph
signal was sampled at a rate of 10 samples per second, band-pass
filtered (0.5 Hz to 10 Hz), and digitized (40 Hz). VPA was
measured as peak-to-trough amplitude for each vaginal pulse.
Movement artifacts were detected by visual inspection of the
waveforms and removed prior to further data preparation and
analysis.
Male genital response. Men’s genital response was measured
with a mercury-in-rubber strain gauge, a reliable and valid method
of measuring changes in penile circumference (see Janssen &
Geer, 2000). The signal was sampled at a rate of 10 samples per
second, low-pass filtered (to 0.5 Hz), digitized (40 Hz), and
transformed into millimeters of change in circumference. The
gauge was calibrated over six 5-mm steps between each participant
session, consistent with Janssen’s (2002) recommendation.
Experimental stimuli. The experimental stimuli consisted of
18 film clips that were 90 s and that were presented with sound,
representing nine stimulus categories: control (landscapes accom-
panied by relaxing music), nonhuman sexual activity (bonobos or
Pan paniscus mating), female nonsexual activity (nude exercise),
female masturbation, female–female intercourse (cunnilingus and
vaginal penetration with a strap-on dildo), male nonsexual activity
(nude exercise), male masturbation, male–male intercourse (fella-
tio and anal intercourse), and female–male copulation (cunnilingus
and penile–vaginal intercourse). Participants saw two exemplars of
each stimulus category. All of these clips were excerpted from
commercially available films.
The exercise clips featured solitary nude women or men en-
gaged in a form of exercise such as yoga, calisthenics, or walking.
Masturbation films featured solitary nude women or men stimu-
lating their genitals manually. Exercise and masturbation films
were presented with background music, whereas the human inter-
course stimuli were presented with the sounds (music and sexual
vocalizations) that originally accompanied the films. The nonhu-
man film was presented with nonhuman primate vocalizations and
nature sounds in lieu of the original voice-over narration. The
intercourse, control, and nonhuman films were identical to those
used by Chivers et al. (2004) and by Chivers and Bailey (2005),
except the films were abbreviated to 90 s from 120 s. A 3-min film
with nonsexual content (depictions of landscapes and buildings)
was used as an adaptation stimulus.
Self-Report Measures
Sexual orientation. Participants were classified as heterosex-
ual or homosexual on the basis of their self-assessment on the
Kinsey Sexual Attraction Scale (Kinsey, et al., 1948; Kinsey et al.,
1953). Individuals who rated their sexual attractions as predomi-
nantly toward opposite-gender persons were classified as hetero-
sexual (score equal to or lower than 2 on a scale from 0 to 6), and
those rating their sexual attractions as predominantly toward same-
gender persons (score equal to or greater than 4 on the same scale)
were classified as homosexual. By this measure of sexual orien-
tation, 20 homosexual women, 29 heterosexual women, 17 homo-
sexual men, and 30 heterosexual men participated in the study.
In the rest of this article, we refer to women with predominantly
or exclusively same-gender sexual preferences as homosexual, not
lesbian, because many of these women did not identify as such: Of
the 20 homosexual women we recruited, 11 identified as lesbian,
1 identified as bisexual, and 7 identified as queer; the remaining
woman did not label her sexual identity. Men with predominantly
or exclusively same-gender sexual preferences are described as
homosexual for the same reason: Of the 17 homosexual men we
1111
GENDER AND SEXUAL ORIENTATION DIFFERENCES
recruited, 15 identified as gay, 1 identified as bisexual, and 1
identified as queer. We also wished to avoid confusing sexual
identity with sexual orientation (see Mustanski, Chivers, & Bailey,
2002).
Although interesting results have been reported in sexual psy-
chophysiology studies of bisexual-identified male participants (see
Rieger, Chivers & Bailey, 2005), we opted to exclude men or
women who reported equal sexual attraction to both genders to
maximize the clarity of the research design with respect to the
category-specificity of gender preferences.
Personal information. Participants completed items assessing
their age, romantic relationship status, sexual relationship status,
education, household income, ethnicity, and employment status.
Homosexual women were significantly older, F(1, 48) ⫽ 21.52,
p ⬍ .0001, were less ethnically diverse,
2
(3, N ⫽ 47) ⫽ 9.60, p ⫽
.02, and were more likely to be employed full time,
2
(3, N ⫽
47) ⫽ 23.27, p ⬍ .0001, than heterosexual women. No significant
differences were observed between heterosexual and homosexual
men.
Procedure. Potential participants responded to advertise-
ments; they were screened for eligibility and were scheduled to
attend testing sessions that were predominantly held in the late
afternoon or early evening. All participants were asked to refrain
from the following prior to testing: (a) sexual activity of any type
for 24 hr, (b) physical exercise of all types for 1 hr, because
sympathetic nervous system arousal due to exercise potentiates
genital responses (Meston & Gorzalka, 1996), and (c) use of
alcohol or recreational drugs on the day of testing. At the testing
session, all participants indicated that they had complied with these
requests. Participants were seated in a comfortable recliner and
assessed individually in a dimly lit, private room. A standard
computer monitor was placed approximately 1.5 m away at eye
level. Participants received instruction on using the genital gauge
and then fitted the gauge themselves in private. The experimenter
(Meredith L. Chivers) instructed participants to sit as still as
possible, to pay full attention to the films, to not manipulate their
genital responses (e.g., by contracting their pubococcygeal mus-
cles), and to not touch their genitals during testing. Participants
watched the adaptation film and then the 18 experimental stimuli.
The stimuli were separated by return-to-baseline intervals so that
the participant’s genital response could return to a pretrial baseline.
The duration of these interstimulus intervals varied, averaging
approximately 3 min. While watching the films, participants re-
ported their subjective sexual response, using the keypad to ma-
nipulate the virtual gauge. Participants completed distraction tasks
during the interstimulus intervals (e.g., counting backward from a
starting number by groups of 7, reading aloud from a neutral-
content magazine article) and, after the sexual arousal assessment,
completed questionnaires regarding their sexual interests, sexual
experience, and sexual functioning.
Data Exclusion Criteria
Participants were excluded from the data analysis if there were
problems with genital data acquisition, the participants’ genital
responses did not reach a minimum threshold, or they could not be
classified as heterosexual or homosexual. Data from 2 women
were excluded because these women experienced vaginal muscle
contractions during testing that resulted in unreliable VPA signals.
The remaining women (n ⫽ 47) demonstrated a 0.5 standard
deviation or greater increase in their maximum genital response to
any sexual stimulus, relative to their response to the control films,
and were therefore included in the data analysis (see Chivers et al.,
2004, for further details). Data were excluded from 2 men who
exhibited little penile response during the testing session (defined
a priori as less than 2.5 mm change in penile circumference to any
sexual stimulus; see Kuban, Barbaree, & Blanchard, 1999). Data
from 1 man were excluded because he reported gender identity
confusion and an uninterpretable Kinsey scale score. The remain-
ing men (n ⫽ 44) all showed at least a 2.5 mm increase in penile
circumference and a 0.5 standard deviation or greater increase in
maximum genital response to any sexual stimulus, relative to their
response to the control films.
Data Reduction and Analysis
Change in genital response was calculated by subtracting pre-
trial baseline genital response from mean genital response to each
experimental stimulus. (Pretrial baseline was established during
the 5–10 s interval recorded while the participant was completing
pretrial questions; these questionnaire data are not presented in this
article). The resulting change scores were standardized within
subjects (i.e., ipsatized). Standardization of responses within sub-
jects controls for individual differences in responsivity and max-
imizes the discriminative validity of genital arousal assessment
(see Harris, Rice, Quinsey, Chaplin, & Earls, 1992, regarding
phallometric data). Mean values for self-reported sexual arousal,
expressed as the percentage increase from pretrial baseline values,
were used in the analysis. Mean subjective and genital responses to
each stimulus category were then calculated by averaging over the
two exemplars of each category.
Results
In the following section, we first examine the genital responses
of the female participants and then examine the genital responses
of the male participants, to compare the relative effects of sexual
activity cues and actor gender cues. We then examine the effects
of these different kinds of cues on self-reported sexual arousal for
female participants and then for male participants. We further
analyze the data to examine the category-specificity of women’s
and men’s subjective and genital responses, to replicate the major
finding reported by Chivers et al. (2004). Finally, we examine the
responses of women and men to the nonhuman stimulus depicting
bonobos mating, to replicate the major finding reported by Chivers
and Bailey (2005).
Effects of Sexual Activity and Gender
Genital Responses
Female participants. Figure 1 presents the mean genital re-
sponses for heterosexual and homosexual women. Women’s vag-
inal responses were predicted to vary with the amount of sexual
activity depicted in the stimulus; that is, women were predicted to
show their highest genital responses to intercourse, to show inter-
mediate responses to masturbation, and to show their lowest re-
sponses to films of nude men or women engaging in exercise (i.e.,
no sexual activity). As a test of this hypothesis, mean vaginal
1112
CHIVERS, SETO, AND BLANCHARD
responses to male exercise, male masturbation, male–male inter-
course, female exercise, female masturbation, and female–female
intercourse were submitted to a 2 ⫻ 2 ⫻ 3 mixed-design analysis
of variance (ANOVA): The two repeated factors were Stimulus
Activity (exercise, masturbation, intercourse) and Stimulus Gender
(female, male), and the between-subjects factor was participant
Sexual Orientation (homosexual, heterosexual).
A main effect of Stimulus Activity, F(2, 90) ⫽ 54.82, p ⬍ .001,
p
2
⫽ .55, was found. Planned contrasts showed that masturbation
elicited significantly greater vaginal responses than exercise, F(1,
45) ⫽ 43.78, p ⬍ .001,
p
2
⫽ .49, and couples engaging in sexual
intercourse elicited significantly greater vaginal responses than
masturbation, F(1, 45) ⫽ 62.23, p ⬍ .001,
p
2
⫽ .58. These results
support the hypothesis that women’s vaginal responses vary with
the sexual activity depicted, with more explicit sexual activity
eliciting stronger responses.
Exercise films depicted no sexual activity, so vaginal responses
to these films were not expected to be significantly greater than
responses to control stimuli; however, paired t tests showed that
women’s vaginal responses to female exercise were significantly
greater than responses to the control stimulus, t(46) ⫽ 6.43, p ⬍
.001, d ⫽ 1.24 (Dunlap, Cortina, Vaslow, & Burke, 1996). Re-
sponses to male exercise, however, were not significantly different
from the response to the control stimulus, t(46) ⫽ – 0.56, p ⫽ .58,
d ⫽ 0.10.
Women’s vaginal responses to solitary nude persons exercising
or masturbating were predicted to be equal across male and female
sexual stimuli, consistent with previous findings regarding the
nonspecificity of women’s vaginal responses with regard to actor
gender. Instead, a significant interaction was found between Sex-
ual Orientation and Stimulus Gender, F(1, 45) ⫽ 4.41, p ⫽ .04,
p
2
⫽ .09: Homosexual women showed greater vaginal responses to
female stimuli than to male stimuli and, therefore, exhibited
category-specific genital responding to these films. Heterosexual
women experienced similar vaginal responses to male and female
sexual stimuli and therefore demonstrated a nonspecific pattern of
genital response.
Two-tailed paired t tests between control films and male exer-
cise, masturbation, and intercourse films were conducted to deter-
mine whether homosexual women showed significant vaginal re-
sponses to male stimuli. Homosexual women had significantly
greater responses to male–male intercourse films than to control
films, t(19) ⫽ 4.95, p ⬍ .001, d ⫽ 1.82, but did not show
significantly greater responses to male exercise, t(19) ⫽ 0.59, p ⫽
.57, d ⫽ 0.14, or to masturbation films, t(19) ⫽ 1.68, p ⫽ .11, d ⫽
0.67, compared with the control films. This result suggests that a
category-specific pattern of genital response can be observed in
women, but only among those who report a predominantly or
exclusively homosexual orientation and only when they are pre-
sented with sexual stimuli that are less intense or explicit (nude
figures or solitary figures masturbating).
Male participants. Figure 2 presents the mean genital re-
sponses for heterosexual and homosexual men. Mean penile re-
sponses to male exercise, male masturbation, male–male inter-
course, female exercise, female masturbation, and female–female
intercourse were submitted to a 2 ⫻ 2 ⫻ 3 mixed-design ANOVA.
As in the previous analysis, the two repeated factors were Stimulus
Activity (exercise, masturbation, intercourse) and Stimulus Gender
(female, male), and the between-subjects factor was participant
Sexual Orientation (homosexual, heterosexual).
A significant three-way interaction among Stimulus Gender,
Stimulus Activity, and Sexual Orientation was observed, F(2,
84) ⫽ 32.76, p ⬍ .001,
p
2
⫽ .44. The three-way interaction
indicates that both heterosexual and homosexual men exhibited
significantly greater penile responses to their preferred sexual
stimuli than to their nonpreferred sexual stimuli, F(1, 42) ⫽
111.84, p ⬍ .001,
p
2
⫽ .73, and greater penile responses as the
intensity of the preferred sexual stimulus increased, F(2, 84) ⫽
49.92, p ⬍ .001,
p
2
⫽ .54. In other words, men’s penile responses
were category-specific, and the effect of sexual activity was mostly
limited to the preferred category of sexual stimuli (females exer-
Figure 1. Heterosexual and homosexual women’s mean genital response,
in z scores, to all categories of stimuli. Error bars represent the 95%
confidence interval for the mean. E ⫽ exercise; M ⫽ masturbation; I ⫽
intercourse; C ⫽ control; NH ⫽ nonhuman; FM I ⫽ female–male inter-
course.
1113
GENDER AND SEXUAL ORIENTATION DIFFERENCES
cising, masturbating, or engaging in sexual intercourse for hetero-
sexual men; males exercising, masturbating, or engaging in sexual
intercourse for homosexual men).
Two-tailed paired t tests between men’s genital responses to the
control films and men’s genital responses to each level of sexual
activity featuring the nonpreferred gender were conducted sepa-
rately for heterosexual and homosexual men, to determine whether
men showed significant penile responses to nonpreferred sexual
stimuli. Heterosexual men had significant increases in penile re-
sponses to the male–male intercourse, t(26) ⫽ 2.36, p ⫽ .03, d ⫽
0.67, but not to the male masturbation, t(26) ⫽ .91, p ⫽ .37, d ⫽
0.22, or exercise films, t(26) ⫽ –1.16, p ⫽ .26, d ⫽ 0.19. Homo-
sexual men showed an increase in penile responses to female–
female intercourse that approached statistical significance, t(16) ⫽
2.02, p ⫽ .06, d ⫽ 0.67, but not to female exercise, t(16) ⫽ 1.46,
p ⫽ .16, d ⫽ 0.29, or to masturbation films, t(16) ⫽ 0.93, p ⫽ .37,
d ⫽ 0.43. Thus, the sexual activity presented in the intercourse
films was sufficiently intense to generate an increase in genital
response to nonpreferred sexual stimuli in both heterosexual and
homosexual men.
Subjective Responses
Female participants. Figure 3 presents the mean self-reported
sexual arousal for heterosexual and for homosexual women. Mean
subjective responses to male exercise, male masturbation, male–
male intercourse, female exercise, female masturbation, and
female–female intercourse were submitted to a 2 ⫻ 2 ⫻3 mixed-
design ANOVA that was identical to the ANOVAs described for
genital responses.
Women’s self-reported sexual responses were predicted to vary
with the amount of sexual activity depicted in the stimulus. As
expected, there was a significant main effect of Stimulus Activity,
F(2, 90) ⫽ 25.39, p ⬍ .001,
p
2
⫽ .36. There was also a significant
interaction between Stimulus Gender and Stimulus Activity, F(2,
90) ⫽ 5.85, p ⫽ .004,
p
2
⫽ .12. All women reported significantly
greater sexual arousal to masturbation than to exercise films, F(1,
45) ⫽ 27.18, p ⬍ .001,
p
2
⫽ .38, and to intercourse than to
masturbation films, F(1, 45) ⫽ 5.97, p ⫽ .02,
p
2
⫽ .12. The effect
of sexual activity was significantly different, however, for homo-
sexual and heterosexual women’s subjective responses to inter-
course and masturbation films, F(1, 45) ⫽ 6.08, p ⫽ .02,
p
2
⫽ .12.
Heterosexual women reported greater sexual arousal to male mas-
turbation than to male–male intercourse, whereas homosexual
women were more sexually aroused by male–male intercourse
than by male masturbation.
Women’s subjective responses were expected to be category-
specific. There was a significant main effect for Stimulus Gender,
F(1, 45) ⫽ 26.22, p ⬍ .001,
p
2
⫽ .37, and a significant two-way
interaction between Stimulus Gender and Sexual Orientation, F(1,
45) ⫽ 7.10, p ⫽ .01,
p
2
⫽ .14. All women reported greater
subjective responses to the female films; however, homosexual
women rated these films as significantly more arousing than het-
erosexual women did (M ⫽ 21.25 vs. M ⫽ 14.65, respectively),
and heterosexual women rated the male stimuli as significantly
more arousing than homosexual women did (M ⫽ 9.93 vs. M ⫽
6.30). Heterosexual women’s subjective responses were not
category-specific because they reported greater response to female
stimuli than to male stimuli; homosexual women’s subjective
responses were somewhat category-specific because they reported
greater sexual arousal to female stimuli than to male stimuli, but
they also reported some sexual arousal to male stimuli.
Male participants. Figure 4 presents the mean subjective re-
sponses for heterosexual and homosexual men. Mean continuous
self-report of sexual arousal was submitted to a 2 ⫻ 2 ⫻ 3
mixed-design ANOVA, as in the previous analyses.
Men’s subjective sexual responses were expected to be
category-specific and were expected to show an effect of sexual
activity. The three-way interaction among Stimulus Gender, Stim-
Figure 2. Heterosexual and homosexual men’s mean genital response, in
z scores, to all categories of stimuli. Error bars represent the 95% confi-
dence interval for the mean. E ⫽ exercise; M ⫽ masturbation; I ⫽
intercourse; C ⫽ control; NH ⫽ nonhuman; FM I ⫽ female–male inter-
course.
1114
CHIVERS, SETO, AND BLANCHARD
ulus Activity, and Sexual Orientation was significant, F(2, 84) ⫽
20.22, p ⬍ .001,
p
2
⫽ .33, and supported these predictions. As
with their genital responses, heterosexual men and homosex-
ual men reported significantly greater sexual arousal to stimuli
that depicted their preferred gender, F(1, 41) ⫽ 61.59, p ⬍ .001,
p
2
⫽ .60, and their subjective responses generally showed a
sexual activity effect for their preferred gender, F(2, 84) ⫽
38.12, p ⬍ .001,
p
2
⫽ .48. Heterosexual men, however, re
-
ported similar increases in sexual arousal to female–female
intercourse and female masturbation (M ⫽ 24.10 vs. M ⫽
23.59, respectively).
Concordance Between Genital and Subjective Sexual
Arousal
The agreement between genital and self-reported sexual arousal
(concordance) was computed for each participant, across all 18
stimuli, for a total of 18 pairs of data points per participant. Mean
change in subjective or genital sexual response, in standardized
units, was used as the dependent variable. Mean subjective– genital
correlations were computed by calculating the Pearson correlation
coefficient for each participant, z transforming the correlation,
calculating the mean z-transformed correlation for each of the four
Figure 4. Heterosexual and homosexual men’s mean self-reported sexual
responses, in percentage increase from baseline, to all categories of stimuli.
Error bars represent the 95% confidence interval for the mean. E ⫽
exercise; M ⫽ masturbation; I ⫽ intercourse; C ⫽ control; NH ⫽ nonhu-
man; FM I ⫽ female–male intercourse.
Figure 3. Heterosexual and homosexual women’s mean self-reported
sexual responses, in percentage increase from baseline, to all categories of
stimuli. Error bars represent the 95% confidence interval for the mean. E ⫽
exercise; M ⫽ masturbation; I ⫽ intercourse; C ⫽ control; NH ⫽ nonhu-
man; FM I ⫽ female–male intercourse.
1115
GENDER AND SEXUAL ORIENTATION DIFFERENCES
gender by sexual orientation groups, and back-transforming the
resulting mean to a Pearson correlation coefficient.
These correlations were large for heterosexual and homosexual
men, r(27) ⫽ .82 and r(17) ⫽ .85, respectively. The correlations
for heterosexual and homosexual women were lower, r(27) ⫽ .56
and r(20) ⫽ .58, respectively, but were higher than are typically
found; in a recent meta-analysis of studies that have examined
concordance, an average correlation of .30 for women and .68 for
men was found (Chivers, Seto, Lalumie`re, Laan, & Grimbos,
2005). However, the correlations obtained in the present study
were quite similar to those reported by Chivers et al. (2004), .48
for women and .88 for men, and did not differ across sexual
orientation for either women or men.
Replication of the Gender Difference in Category-
Specificity
To compare category-specific responding in this sample with
the results of Chivers et al. (2004), we computed a male–female
difference score by subtracting responses to the female stimuli
from responses to the male stimuli, across each sexual activity
(exercise, masturbation, intercourse) and type of response (genital,
self-reported). A more positive difference score indicates greater
response to male stimuli, whereas a more negative difference score
indicates a greater response to female stimuli. Correlations be-
tween the resulting difference scores and Kinsey Sexual Attraction
ratings (reverse coded for women, such that high ratings indicate
greater attraction to men) were calculated to provide estimates of
category-specificity with regard to gender (see Table 1); in other
words, the correlations indicate the extent to which participants’
Kinsey ratings corresponded to their subjective and genital re-
sponse.
The correlation values that were obtained are very similar to
those reported by Chivers et al. (2004): For female participants, the
correlations between self-reported arousal and sexual orientation
were significant and positive, whereas correlations between genital
arousal and sexual orientation were not statistically significant. For
male participants, both genital sexual arousal and self-reported
sexual arousal were strongly and significantly correlated with
sexual orientation. Correlations obtained for male participants
were significantly greater than were those obtained for female
participants for both genital and self-reported sexual responses to
all categories of sexual stimuli.
Replication of a Gender Difference in Response to
Nonhuman Stimuli
Chivers and Bailey (2005) reported that heterosexual female
participants showed a significant increase in vaginal responses to
depictions of bonobo chimpanzee copulation, compared with re-
sponses to control films, but did not report increased subjective
sexual arousal to the nonhuman films. Male participants did not
show any subjective or penile response to the films of bonobos
mating.
Paired t tests comparing participants’ mean sexual responses
with the nonhuman and control films were conducted for women
and men separately, collapsing across sexual orientation, to deter-
mine whether the present study replicated these results. For
women, there was a significant vaginal response, t(46) ⫽ 2.10, p ⫽
.04, d ⫽ 0.38, but no increase in self-reported sexual arousal,
t(46) ⫽ 1.16, p ⫽ .25, d ⫽ 0.19. For men, there was no significant
increase in either penile responses, t(43) ⫽ 0.37, p ⫽ .71, d ⫽
0.05, or subjective responses, t(42) ⫽ 1.50, p ⫽ .14, d ⫽ 0.17.
Thus, the present study replicated the main finding reported by
Chivers and Bailey (2005) in a new sample of women and men.
Discussion
Summary
The results of the present study were consistent with our hy-
potheses. Sexual activity was a stronger determinant of women’s
sexual response than was the gender of the actor(s) in the sexual
films, whereas for men, actor gender was a stronger determinant of
their sexual responses. The response patterns of homosexual and
heterosexual men were essentially mirror images of each other,
with both their subjective and penile responses corresponding to
their preferred gender. There was a significant effect of sexual
activity on male sexual responses, but primarily for their preferred
gender. A different pattern of results was found for heterosexual
and homosexual women. Heterosexual women’s subjective and
vaginal responses varied as a function of sexual activity but not
actor gender, whereas homosexual women’s sexual responses var-
ied as both a function of sexual activity and actor gender. The
effects of actor gender cues and sexual activity cues are summa-
rized and discussed in the following sections.
Table 1
Within-Group Correlations Among Male–Female Difference Scores and a Continuous Measure of Sexual Orientation, for Each Type
of Sexual Activity and Sexual Response
Sample
Genital response Self-reported response
Exercise Masturbation Intercourse Exercise Masturbation Intercourse
Female participants .23 .22 .24 .42
**
.55
***
.36
*
Male participants .64
***
.78
***
.83
***
.74
***
.77
***
.74
***
z
a
⫺2.41
**
⫺3.79
***
⫺4.35
***
⫺2.32
*
⫺1.85
*
⫺2.64
**
a
Fisher’s z-test for the significance of the difference between female participants’ correlations and male participants’ correlations (Cohen & Cohen, 1983).
*
p ⬍ .05.
**
p ⬍ .01.
***
p ⬍ .001.
1116
CHIVERS, SETO, AND BLANCHARD
The Critical Features of Sexual Stimuli
Gender cues. There was a significant effect of gender cues on
the subjective and genital responses for both heterosexual and
homosexual men but not for heterosexual women. Unlike previous
studies, homosexual women in the present study showed category-
specific vaginal responding to depictions of solitary male targets or
female targets exercising or masturbating but showed nonspecific
responding to depictions of couples engaged in intercourse.
It is possible that the specificity of homosexual women’s vag-
inal responses is overwhelmed by a sexual activity effect when the
stimuli are sufficiently intense; this would explain the nonspeci-
ficity of homosexual women’s sexual responses when they are
presented with explicit films of couples engaging in intercourse
(Chivers et al., 2004; Chivers & Bailey, 2005; Laan, Sonderman,
& Janssen, 1995; Wincze & Qualls, 1984). It is interesting to
observe in this context that explicit depictions of sexual inter-
course are also sufficiently intense to elicit a small genital response
to nonpreferred actors in men; heterosexual men produced a sig-
nificant increase in penile response to depictions of two men
engaged in intercourse, whereas homosexual men produced a
response, which approached statistical significance, to depictions
of two women engaged in intercourse. This finding has been
reported by other investigators (e.g., Mavissakalian et al., 1975;
Sakheim et al., 1985; Steinman et al., 1981; Wincze & Qualls,
1984). These penile responses to nonpreferred stimuli, however,
were much less than the penile responses to depictions of the
preferred gender, even when no sexual activity was shown (nude
exercise).
As a group, women reported greater sexual arousal to stimuli
depicting female targets than to stimuli depicting male targets.
This seems counterintuitive, yet it is consistent with past sexual
psychophysiology research. Both lesbian and heterosexual women
report greater sexual arousal to stimuli depicting female targets
(heterosexual or lesbian couples) than to stimuli depicting only
male targets (Chivers et al., 2004; Chivers & Bailey, 2005; Stein-
man et al., 1981; Wincze & Qualls, 1984). Why would women
report greater sexual arousal to female targets, especially when, for
heterosexual women, female targets are not of the preferred gen-
der? One possible explanation is that women identify with the
depicted female targets. Approximately 30 years ago, Symons
(1979) proposed that men and women differ in their responses to
visual sexual stimuli, whereby men attend to the physical charac-
teristics of actors and women identify with the actors, imagining
themselves in the sexual interaction. Symons suggested that
women would experience greater sexual arousal (he did not dis-
tinguish between subjective or genital response) to films that
depict women because these films would allow women to identify
with the female actor. Consistent with this idea, women’s self-
reported sexual arousal is positively related to imagining oneself as
a participant in the sexual activities that are portrayed (Janssen,
Carpenter, & Graham, 2003).
The current study cannot directly address the merits of the
identification hypothesis regarding gender differences in sexual
responding. We believe, however, that this explanation is not
sufficient because it cannot explain why women respond subjec-
tively and genitally to films of two men having sexual intercourse
or why women respond genitally to films of bonobos mating.
Further research is needed on the appraisal and meaning of sexual
stimuli and on the relationship between these cognitive processes
and physiological sexual response.
Sexual activity cues. Our results replicate previous research in
which it was found that heterosexual women produced genital
responses that are related to the intensity of the sexual stimuli
(Laan, Everaerd, van der Velde, & Geer, 1995; Both et al., 2005).
Men also demonstrated this effect of sexual activity cues, but the
effect was primarily restricted to stimuli that depicted their pre-
ferred gender. Women, but not men, showed a small increase in
genital response to the nonhuman sexual stimulus, replicating the
results of Chivers and Bailey (2005), even though the length of the
film clip was 30 s shorter in the current study and though these
clips were presented twice rather than once. This suggests that
vaginal responding to nonhuman sexual activity is a reliable effect.
In a similar vein, homosexual women produced significant vaginal
responses to films of male targets engaged in sexual intercourse
and heterosexual women produced a significant vaginal response
to films of female targets masturbating; it seems that women can
become genitally aroused by cues of sexual activity, even when the
actors are of the nonpreferred gender (or species).
Consistent with previous studies, heterosexual women did not
show significant vaginal responses to nude male exercisers. This
result nicely illustrates the gender and sexual orientation differ-
ences in sexual responding, as homosexual women and both ho-
mosexual and heterosexual men do respond to depictions of a nude
person of their preferred gender, even when they are engaging in
a nonsexual activity like exercise. It is also consistent with re-
search that suggests heterosexual women report less interest than
men or lesbian women in visual sexual stimuli featuring nude
people of their preferred gender (Bailey, Gaulin, Agyei, & Gladue,
1994).
Although it was unexpected, heterosexual women did show
some sexual response to the solitary female exercisers. Although
the exercise films were selected to depict no sexual activity, some
aspect of these films was perceived as sexual by women, as
indicated by their small but significant subjective and genital
responses. We speculate that this responding may be a result of an
unforeseen confound in the exercise stimuli. As the women exer-
cised, their vulvas were sometimes exposed, for example, during
leg raises or certain stretches. The genitals of the men who exer-
cised were in plain view during the entire film presentation, but
their penises were flaccid. Seeing an exposed vulva is unusual
outside of sexually intimate situations, so women may have inter-
preted the sight of an exposed vulva as sexual. In contrast, seeing
a flaccid penis is not restricted to sexual situations, unlike seeing
an erect penis. If our speculation is correct, then we can expect no
sexual response from heterosexual women to a film of exercising
women who did not expose their vulvas and a significant sexual
response to depictions of exercising nude men with erect penises.
There is some support for the idea that an exposed vulva or an
erect penis are prepotent sexual stimuli from another line of
research: In a study of brain activation to images of erect penises
and engorged vulvas, Ponseti et al. (2006) found that both women
and men showed greater activation of the brain regions associated
with incentive motivation when viewing images of aroused geni-
talia of their preferred gender. It is unclear, however, whether this
pattern of neural activation reflects sexual arousal, as the research-
ers did not assess subjective or genital responses. Future sexual
psychophysiological research could test the prepotency of genital
1117
GENDER AND SEXUAL ORIENTATION DIFFERENCES
cues by presenting close-up images of genitals in different states
(e.g., exposed vulva vs. vulva obscured by pubic hair, flaccid penis
vs. erect penis).
Possible Explanations for the Gender Differences in the
Specificity of Sexual Responding
The nonspecificity of heterosexual female sexual responses and
the specificity of male sexual responses are congruent with re-
search in which other psychophysiological methodologies, such as
viewing time measures, electroencephalograms, or functional
magnetic resonance imaging were used to examine gender differ-
ences in the specificity of sexual responding (Costa, Braun &
Birbaumer, 2003; Costell, Lunde, Kopell, & Wittner, 1972; Ha-
mann, Herman, Nolan, & Wallen, 2003; Wallen, 2006; Wright &
Adams, 1999). For example, Wallen (2006) reported that hetero-
sexual men showed greater activation of brain areas associated
with sexual arousal to preferred, compared with nonpreferred,
sexual stimuli, whereas heterosexual women did not show this
differential activation. The general pattern of results from these
different lines of research is that men show significantly greater
responses to preferred than to nonpreferred stimuli, whereas
women do not. Below, we consider possible explanations for this
gender difference.
Excitation transfer. Why do women, but not men, show sub-
stantial genital responses to depictions of nonhuman copulation or
depictions of nonpreferred couples engaging in sexual intercourse?
One possibility is excitation transfer, whereby watching taboo or
nonpreferred sexual stimuli elicits greater general, nonsexual
arousal among women than among men and this general arousal is
interpreted as sexual arousal or facilitates sexual response (see
Meston & Frolich, 2003). Studies of women’s responses to sexual
fantasy, however, suggest that taboo themes are rated as less
sexually arousing than depictions of consensual genital sexual
contact (Meuwissen & Over, 1991), and measures of general
arousal, such as skin conductance, are not significantly correlated
with measures of sexual response during presentations of sexual
stimuli (Laan, Sonderman, & Janssen, 1995). Vaginal vasoconges-
tion is a specific response to sexual stimuli and is not elicited by
generally arousing films that evoke feelings of anxiety or exhila-
ration (Laan, Sonderman, & Janssen, 1995; Suschinsky et al.,
2007). It seems unlikely, therefore, that a gender difference in
excitation transfer can explain the gender difference in specificity
of sexual response.
Male inhibition of response. Category-specific responding in
men may occur because men inhibit their subjective and genital
responses to nonpreferred stimuli. There is evidence that men have
some voluntary control over their penile responding, and it is
possible that homophobia causes heterosexual men to inhibit their
sexual responses to depictions of men. However, preliminary
findings suggest it is unlikely that men inhibit sexual response to
nonpreferred stimuli: Adams, Motsinger, McAnulty, and Moore
(1992) demonstrated that men are able to reduce but not increase
their responses to nonpreferred sexual stimuli, whereas Safron et
al. (2007) did not observe activation in brain areas associated with
suppression of sexual arousal (i.e., right superior frontal and an-
terior cingulate cortices, see also Beauregard, Le´vesque, & Bour-
gouin, 2001) when gay and heterosexual men viewed nonpreferred
sexual stimuli. We also note that men do demonstrate moderate
increases in genital responding to films of their nonpreferred
gender target engaged in sexual intercourse; therefore, the differ-
ence in women’s and men’s sexual arousal patterns is one of
degree rather than kind.
Female flexibility. Another possibility is that nonspecificity of
female vaginal responding—across different levels of sexual ac-
tivity for heterosexual women and for depictions of intercourse for
homosexual women—may be a manifestation of greater female
flexibility. Another example of female flexibility in sexuality is the
relatively modest agreement between continuously assessed sub-
jective and genital sexual arousal observed across sexual psycho-
physiology studies that report data for both measures (Chivers et
al., 2005). As we mentioned in the introduction, there is also
evidence that women have greater flexibility in sexual attitudes,
sexual behaviors, and sexual preferences than do men (Baumeister,
2000). Nonspecificity of genital responding may therefore be part
of a broader pattern in female sexuality. Indeed, some have spec-
ulated that this pattern, in which one sex is categorical with respect
to their sexual interests whereas the other is more flexible, is
characteristic of mammalian species (Goy & Goldfoot, 1975);
among humans, women may be the more flexible sex.
Is Female Sexual Responding Automatic?
Flexibility in genital sexual responding may be related to the
automaticity of female genital arousal. It has been suggested that
vaginal responding is reflexively activated by sexual stimuli
(Chivers, 2005; Laan & Everaerd, 1995). Genital response pre-
cedes subjective sexual arousal (Lake Polan et al., 2003), can be
observed within seconds of the onset of a sexual stimulus (Laan &
Janssen, 2007), and can occur in the absence of subjective sexual
arousal (Chivers & Bailey, 2005). Reflexive vaginal responding
may have had fitness benefits for our female ancestors because
vaginal vasocongestion produces lubrication, which reduces the
likelihood of injury and subsequent infection during vaginal pen-
etration. Ancestral women who did not reflexively lubricate would
have been more likely to experience injuries or infections that
could have rendered them reproductively sterile or resulted in their
deaths. According to our research, seeing a nude person is not
sufficient to elicit a vaginal response among heterosexual women;
instead, depictions of sexual activity, either in the form of mas-
turbation or sexual intercourse or nonhuman mating, are necessary.
For homosexual women, whose sexual arousal patterns are less
female-typical, more intense depictions of sexual activity, such as
sexual intercourse, are necessary for reflexive vasocongestion to
occur when films do not portray their preferred gender of actor.
Sexual Orientation and Sexual Responding Among
Women
The difference between heterosexual women and homosexual
women in the specificity of their sexual responding can be viewed
as a difference in the threshold at which the effect of sexual
activity cues exceeds the effect of gender cues. Thus, homosexual
women are more male-typical than are heterosexual women in this
threshold, showing category-specificity to depictions of solitary
nude figures exercising or masturbating. Diamond (2005) has
distinguished between homosexual women with a more stable
lesbian sexual identity and those with a more fluid lesbian sexual
1118
CHIVERS, SETO, AND BLANCHARD
identity. It is possible that women with a more stable lesbian
sexual identity are even more category-specific in their sexual
responding; however, we were not able to test this hypothesis
because our sample of homosexual women was not assessed for
the temporal stability of their sexual identity. One could also
compare the sexual responding of homosexual women with an
exclusive attraction to other women versus those who also have
some attraction to men; between homosexual women with, versus
homosexual women without, a history of sexual contacts with
men; and between homosexual women who are more masculine
and those who are more feminine (e.g., Singh, Vidaurri, Zam-
barano, & Dabbs, 1999).
The reliable observation that heterosexual women’s sexual re-
sponses do not distinguish between depictions of female targets or
depictions of male targets does not mean heterosexual women are
bisexual in orientation. Heterosexual women do not identify as
bisexual, and they clearly do not make symmetrical choices re-
garding the gender of their sex partners, as evidenced by their
much greater involvement with men than with women and by their
reported preference for men in their sexual thoughts, fantasies, and
attractions. To conclude that women are bisexual on the basis of
their sexual responding overlooks the complexity and multidimen-
sionality of female sexuality.
Instead of a sexual orientation linked to sexual responding,
women’s romantic and sexual partner choices may be more influ-
enced by their emotional attachments (see Diamond, 2003). Dia-
mond suggested that the processes underlying romantic and affec-
tionate bonding are not intrinsically gendered (i.e., oriented toward
female targets or male targets) and, particularly among women,
have the capacity to kindle sexual desire. For an ostensibly het-
erosexual woman, sexual desire for another woman may emerge
from a close emotional relationship instead of from sexual attrac-
tion to and arousal by women. Self-report data on the development
of female sexual orientation support this proposition; women re-
port that social and emotional factors are more salient than sexual
arousal to the development of their sexual interests in the same
gender (Diamond, 2000a, 2000b) or opposite gender (Knoth,
Boyd, & Singer, 1988), whereas men indicate sexual arousal is
more salient than the other factors (Savin-Williams & Diamond,
2000). The current study demonstrates that female sexual re-
sponse, among heterosexual women, is also not intrinsically gen-
dered and that female sexual response may thus facilitate greater
flexibility of sexual expression.
Study Limitations
Volunteers for sexual psychophysiology research are not repre-
sentative of the general population (e.g., Morokoff, 1986;
Wolchik, Braver, & Jensen, 1985). Compared with the general
population, volunteers for sexual psychophysiology research re-
port more sexual partners, greater masturbatory and noncoital
sexual experiences such as oral sex, more liberal sexual attitudes,
less sexual inhibition, and more interest in and experience with
sexually explicit materials (Morokoff, 1986; Wolchik et al., 1983,
1985). The gender and sexual orientation differences reported in
this study, especially the nonspecificity of vaginal responses ob-
served among heterosexual women, may be limited to those indi-
viduals who volunteer for sexual psychophysiology research. If
this is correct, sexuality variables such as those listed above should
be related to the specificity of sexual responding. In a test of this
idea, however, Chivers et al. (2004) found no such relationships,
suggesting nonspecificity of genital response is not an artifact of a
recruitment bias among heterosexual women. Because the present
results converge with the results from studies that examined sexual
responses with the use of other assessment methodologies, we
believe the nonspecificity of heterosexual women’s vaginal re-
sponse is not restricted to our particular samples.
The present results pertain only to the processing of visual
sexual stimuli. The solitary stimuli portrayed only visual sexual
cues, as there were no sexual vocalizations (such as moans, sighs,
or grunts) accompanying the films of nude figures exercising or
masturbating. The films depicting intercourse, however, did in-
clude such sounds. It is possible that these vocalizations augment
sexual responses to the visual sexual stimuli, so that the effect of
sexual activity level cannot be attributed only to the visual cues
that were available. In men, there is some support for the idea that
such sounds matter, as Gaither and Plaud (1997) have demon-
strated that the addition of auditory cues of sexual activity signif-
icantly increased men’s self-reported and genital sexual arousal to
their preferred sexual stimuli. For women the addition of sexual
vocalizations does not appear to augment self-reported or genital
sexual arousal (Lake Polan et al., 2003). The confounding of visual
and auditory cues in our set of films depicting intercourse, how-
ever, does not explain why men show a category-specific pattern
of sexual response, whereas heterosexual women show a nonspe-
cific vaginal response.
Final Comments
Female and male sexual responding appear to be organized
differently in terms of the relative importance of sexual activity
and gender cues and in the level of agreement between subjective
responses and genital responses to sexual stimuli. A unique aspect
of our findings is that we directly observed a gender difference in
sexual responding by objectively measuring sexual arousal with
measures of genital vasocongestion. Oliver and Hyde (1993) noted
that the research they reviewed in their meta-analysis of gender
differences in sexuality relied on self-report, which meant it was
possible that their results might be explained by a gender differ-
ence in willingness to report sexual behavior. Genital sexual
arousal is less susceptible to respondent biases than is self-reported
sexual arousal.
The results of the present study add to a growing body of
research on the greater flexibility of women’s sexuality with
regard to sexual identity, same-sex attraction, and same-sex be-
havior (Bailey et al., 2000; Diamond, 2005; Kinsey et al., 1948,
1953; Laumann et al., 1994; Savin-Williams & Diamond, 2000).
This gender difference fits into a larger pattern among mammals,
in which one sex is categorical with respect to their same-sex
contacts versus their opposite-sex contacts, whereas the other is
more flexible (Goy & Goldfoot, 1975). It would be of great
theoretical interest in the study of sexuality to identify the factors
that determine which sex will be more flexible and to describe the
ontogenetic and phylogenetic development of sexual flexibility.
We also found evidence of a sexual orientation difference in
female sexual responses. Unlike heterosexual women, who
showed nonspecific subjective and vaginal responses with regard
to actor gender, homosexual women in the present study exhibited
1119
GENDER AND SEXUAL ORIENTATION DIFFERENCES
a mix of male-typical (category-specific genital arousal to solitary
nude figures exercising or masturbating) and female-typical re-
sponding (nonspecific genital arousal to couples engaged in inter-
course, lower agreement between subjective and genital measures
of sexual arousal). A similar pattern of results, whereby homosex-
ual women demonstrate both gender-typical and gender-atypical
traits has been reported in other domains, including mate prefer-
ences and choices, childhood gender nonconformity, and occupa-
tional preferences (Bailey et al., 1994; Bailey & Zucker, 1995;
Lippa, 2002).
Our results do not speak to the origins of the mixed pattern of
sexual responding among homosexual women, which could in-
clude genetic, neurohormonal, and sociocultural factors (see Mus-
tanski et al., 2002). Further sexual psychophysiology research on
the sexual responses of homosexual women and on distinguishing
lesbian subtypes—with the use of markers of neurohormonal ex-
posure, measures of socialization and sociocultural values, and
measures of other domains in which gender and sexual orientation
differences have been found— could contribute to our understand-
ing of the development of sexual orientation among women. Such
research could also shed more light on our more general under-
standing of human sexual arousal and processing of sexual stimuli.
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Received August 25, 2006
Revision received July 10, 2007
Accepted July 10, 2007 䡲
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