Meredith L. Chivers

A Sex Difference in the Specificity of Sexual Arousal

Sexual arousal is category-specific in men; heterosexual men are more aroused by female than by male sexual stimuli, whereas homosexual men show the opposite pattern. There is reason to believe that female sexual arousal is organized differently. We assessed genital and subjective sexual arousal to male and female sexual stimuli in women, men, and postoperative male-to-female transsexuals. In contrast to men, women showed little category specificity on either the genital or the subjective measure. Both heterosexual and homosexual women experienced strong genital arousal to both male and female sexual stimuli. Transsexuals showed a category-specific pattern, demonstrating that category specificity can be detected in the neovagina using a photoplethysmographic measure of female genital sexual arousal. In a second study, we showed that our results for females are unlikely to be explained by ascertainment biases. These findings suggest that sexual arousal patterns play fundamentally different roles in male and female sexuality.

A sex difference in features that elicit genital response

Previous research suggests that womens genital arousal is an automatic response to sexual stimuli, whereas mens genital arousal is dependent upon stimulus features specific to their sexual interests. In this study, we tested the hypothesis that a nonhuman sexual stimulus would elicit a genital response in women but not in men. Eighteen heterosexual women and 18 heterosexual men viewed seven sexual film stimuli, six human films and one nonhuman primate film, while measurements of genital and subjective sexual arousal were recorded. Women showed small increases in genital arousal to the nonhuman stimulus and large increases in genital arousal to both human male and female stimuli. Men did not show any genital arousal to the nonhuman stimulus and demonstrated a category-specific pattern of arousal to the human stimuli that corresponded to their stated sexual orientation. These results suggest that stimulus features necessary to evoke genital arousal are much less specific in women than in men.

Gender and sexual orientation differences in sexual response to sexual activities versus gender of actors in sexual films.

In this study, the authors investigated the hypothesis that womens sexual orientation and sexual responses in the laboratory correlate less highly than do mens 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 heterosexual 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.

Sexual Arousal Patterns of Bisexual Men

There has long been controversy about whether bisexual men are substantially sexually aroused by both sexes. We investigated genital and self-reported sexual arousal to male and female sexual stimuli in 30 heterosexual, 33 bisexual, and 38 homosexual men. In general, bisexual men did not have strong genital arousal to both male and female sexual stimuli. Rather, most bisexual men appeared homosexual with respect to genital arousal, although some appeared heterosexual. In contrast, their subjective sexual arousal did conform to a bisexual pattern. Male bisexuality appears primarily to represent a style of interpreting or reporting sexual arousal rather than a distinct pattern of genital sexual arousal.

A critical review of recent biological research on human sexual orientation.

Abstract This article provides a comprehensive review and critique of biological research on sexual orientation published over the last decade. We cover research investigating (a) the neurohormonal theory of sexual orientation (psychoneuroendocrinology, prenatal stress, cerebral asymmetry, neuroanatomy, otoacoustic emissions, anthropometrics), (b) genetic influences, (c) fraternal birth-order effects, and (d) a putative role for developmental instability. Despite inconsistent results across both studies and traits, some support for the neurohormonal theory is garnered, but mostly in men. Genetic research using family and twin methodologies has produced consistent evidence that genes influence sexual orientation, but molecular research has not yet produced compelling evidence for specific genes. Although it has been well established that older brothers increase the odds of homosexuality in men, the route by which this occurs has not been resolved. We conclude with an examination of the limitations of biological research on sexual orientation, including measurement issues (paper and pencil, cognitive, and psychophysiological), and lack of research on women.

Sex Differences in Patterns of Genital Sexual Arousal: Measurement Artifacts or True Phenomena?

Sex differences in patterns of sexual arousal have been reported recently. Men’s genital arousal is typically more category-specific than women’s, such that men experience their greatest genital arousal to stimuli depicting their preferred sex partners whereas women experience significant genital arousal to stimuli depicting both their preferred and non-preferred sex partners. In addition, men’s genital and subjective sexual arousal patterns are more concordant than women’s: The correlation between genital and subjective sexual arousal is much larger in men than in women. These sex differences could be due to low response-specificity in the measurement of genital arousal in women. The most commonly used measure of female sexual arousal, vaginal photoplethysmography, has not been fully validated and may not measure sexual arousal specifically. A total of 20 men and 20 women were presented with various sexual and non-sexual emotionally laden short film clips while their genital and subjective sexual arousal were measured. Results suggest that vaginal photoplethysmography is a measure of sexual arousal exclusively. Women’s genital responses were highest during sexual stimuli and absent during all non-sexual stimuli. Sex differences in degree of category-specificity and concordance were replicated: Men’s genital responses were more category-specific than women’s and men’s genital and subjective sexual arousal were more strongly correlated than women’s. The results from the current study support the continued use of vaginal photoplethysmography in investigating sex differences in patterns of sexual arousal.

A brief review and discussion of sex differences in the specificity of sexual arousal

Sex differences in human sexuality are plentiful and include physical, psychological, and psychophysiological variations (Geary, 1998). Examples include masturbation frequency (Oliver & Hyde, 1993), sex drive (Baumeister et al., 2001), habituation of sexual arousal to sexual stimuli (Laan & Everaerd, 1995a, b; O’Donohue & Geer, 1985), cognition (Geer & Bellard, 1996), self-reported arousal to sexual stimuli (Murnen & Stockton, 1997), and the concordance between genital and self-reported sexual arousal (Laan & Janssen, in press; Chivers et al., 2005), to name just a few. These examples suggest considerable variability between the sexes in various aspects of sexuality. However, most traditional models of sexual response (APA, 1994), sexual dysfunction (Barlow, 1986), and sexual orientation (Bem, 1996) are not sexspecific and, as such, may not adequately explain observed differences in male and female sexuality. As Symons’ (1979) quote suggests, undifferentiated models of sexuality run the risk of biasing observations and interpretations of sexual phenomena as deficits, excesses, etcetera depending on what standard is adopted. Recently, however, there has been a paradigm shift in thinking about female and male sexuality, and sex-specific models are emerging, e.g., the recent recommendations for revising the definition of female sexual dysfunction (Basson et al., 2003).

Phosphodiesterase Type 5 Inhibitors and Female Sexual Response: Faulty Protocols or Paradigms?

INTRODUCTION Phosphodiesterase type 5 inhibitors (PDE5), such as sildenafil, tadalafil, and vardenafil, have revolutionized the treatment of erectile dysfunction. Few successes, in contrast, have been reported for the use of these agents in treatment of sexual arousal problems in women. AIM To review research examining efficacy of PDE5 in women, critique the methods and models employed, and integrate the findings within a broader, gender-specific understanding of female sexual response. METHODS A conceptual and methodological review of all published studies examining PDE5 efficacy in female samples. MAIN OUTCOME MEASURES Study methods, populations, outcome measures, study results. RESULTS A total of 16 studies were reviewed. Studies using self-reported measures of sexual functioning showed mixed results whereas studies examining physiological effects of PDE5 on genital vasocongestion consistently report significant effects on genital sexual response. CONCLUSIONS The lack of efficacy of PDE5 treatment in women is likely attributable to gender differences in the concordance between physiological and psychological components of sexual response. Discordance between genital and subjective measures of sexual response in women may be augmented by PDE5 effects on genital vasocongestion in some populations, rendering successful treatment unlikely via pharmacological treatment alone.

Sexual orientation of female-to-male transsexuals: a comparison of homosexual and nonhomosexual types.

Homosexual and nonhomosexual (relative to genetic sex) female-to-male transsexuals (FTMs) were compared on a number of theoretically or empirically derived variables. Compared to nonhomosexual FTMs, homosexual FTMs reported greater childhood gender nonconformity, preferred more feminine partners, experienced greater sexual rather than emotional jealousy, were more sexually assertive, had more sexual partners, had a greater desire for phalloplasty, and had more interest in visual sexual stimuli. Homosexual and nonhomosexual FTMs did not differ in their overall desire for masculinizing body modifications, adult gender identity, or importance of partner social status, attractiveness, or youth. These findings indicate that FTMs are not a homogeneous group and vary in ways that may be useful in understanding the relation between sexual orientation and gender identity.

Toward Personalized Sexual Medicine (Part 2): Testosterone Combined with a PDE5 Inhibitor Increases Sexual Satisfaction in Women with HSDD and FSAD, and a Low Sensitive System for Sexual Cues

INTRODUCTION Low sexual desire in women may result from a relative insensitivity of the brain for sexual cues. Administration of sublingual 0.5 mg testosterone (T) increases the sensitivity of the brain to sexual cues. Sexual stimulation in the brain is necessary for phosphodiesterase type 5 inhibitor (PDE5i)-mediated increase in genital sexual response. Accordingly, a single dose of T+PDE5i might enhance sexual responsiveness, especially in women with low sensitivity for sexual cues. AIM To assess the hypothesis that treatment with on-demand use of T+PDE5i improves sexual functioning, particularly in women who suffer from Hypoactive Sexual Desire Disorder (HSDD) as the result of a relative insensitivity for sexual cues. METHODS In a randomized, double-blind, placebo-controlled, crossover design, 56 women with HSDD underwent three medication treatment regimes (placebo, T+PDE5i, and T with a serotonin receptor agonist; see also parts 1 and 3), which lasted 4 weeks each. In a participant-controlled ambulatory psychophysiological experiment at home (the first week of each drug treatment), physiological and subjective indices of sexual functioning were measured. In a bedroom experiment (the subsequent 3 weeks), sexual functioning was evaluated following each sexual event after the self-administration of study medication. Subjective evaluation of sexual functioning was also measured by weekly and monthly reports. MAIN OUTCOME MEASURES Subjective: sexual satisfaction, experienced genital arousal, sexual desire. Physiological: vaginal pulse amplitude. Cognitive: preconscious attentional bias. RESULTS T+PDE5i, as compared with placebo, significantly improved physiological and subjective measures of sexual functioning during ambulatory psychophysiological lab conditions at home and during the sexual events, in women with low sensitivity for sexual cues. CONCLUSIONS The present study demonstrated that on-demand T+PDE5i is a potentially promising treatment for women with HSDD, particularly in women with low sensitivity for sexual cues.