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Category-specificity and sexual concordance: the stability of sex differences in sexual arousal patterns.

Abstract: The sexual arousal patterns of men and women differ in two ways. First, men's genital arousal and self-reported sexual arousal are "category-specific" such that different stimuli elicit different degrees of arousal. Women's self-reported sexual arousal is, like men's, category-specific, but their genital arousal is "category-nonspecific", because they show similar genital responses to different sexual stimuli. Second, men's "sexual concordance", or the relationship between genital arousal and self-reported sexual arousal, is higher than women's. Although these sex differences are consistent across studies, there has been little research on the stability of these differences within the same sample. In the present study, 20 men and 18 women participated in two experimental sessions one month apart, in which they listened to sexual and nonsexual audiotaped narratives while their genital arousal and self-reported sexual arousal were measured. The expected sex differences were found in both sessions; men's genital arousal was more category-specific than women's, and their sexual concordance was higher than women's. Men and women did not show significantly different self-reported sexual arousal in either session. Correlational analyses revealed little stability for genital arousal category-specificity and sexual concordance at the individual level for women. Overall, the results suggest that the expected sex differences in sexual arousal patterns were stable across testing sessions. This finding lends additional support for the validity of such differences although further research is required to better understand the stability of sexual arousal patterns at the individual level.

Introduction

There are several features of a sexual stimulus that elicit genital arousal, self-reported sexual arousal, or both. Some of these features include the sex and age of persons shown in the stimulus and the kind of sexual activity depicted. Men's genital responses (as measured by changes in penile circumference or volume with penile plethysmography) tend to be differentially affected by these features, whereas women's genital responses (as measured by changes in vaginal blood flow with vaginal photoplethysmography) tend not to be (e.g., Blanchard, Klassen, Dickey, Kuban, & Blak, 2001; Chivers, Rieger, Latty, & Bailey, 2004; Chivers, Seto, & Blanchard, 2007; Suschinsky, Lalumiere, & Chivers, 2009; Suschinsky & Lalumiere, 2011). Thus, men exhibit a "category-specific" pattern of genital arousal and women exhibit a "category-nonspecific" pattern of genital arousal. For example, when presented with stimuli depicting partnered sexual activity between a man and woman, two men, or two women, gynephilic men (i.e., men with a sexual preference for women) show the most genital arousal to stimuli that depict women (e.g., Suschinsky et al., 2009), and androphilic men (i.e., men with a sexual preference for men) show the most genital arousal to stimuli that depict men (e.g., Chivers et al., 2004). Similarly, when presented with stimuli depicting children and adults, men without a history of sexual activity with children exhibit their highest genital arousal to stimuli involving adults, whereas men with a history of sexual activity with multiple children show their highest genital arousal to stimuli depicting children (e.g., Blanchard et al., 2001).

Laboratory research suggests that the sex of persons depicted in a sexual stimulus does not seem to have much influence on women's genital responses. For example, androphilic women show relatively equal genital arousal to stimuli depicting sexual activity between two men and stimuli depicting sexual activity between two women (e.g., Chivers et al., 2004). Gynephilic women display somewhat category-specific genital responses to low intensity sexual stimuli, in that they exhibit higher genital arousal to stimuli depicting a nude female exercising or a nude female masturbating relative to the equivalent male stimuli. Gynephilic women, however, show similar genital arousal to high intensity partnered sexual interactions between two men, two women, or a man and a woman. No one has assessed women's genital responses to stimuli depicting persons in different age categories (with the exception of one case study of a woman with multiple paraphilias who had a category-nonspecific genital arousal pattern; Cooper, Swaminath, Baxter, & Poulin, 1990).

Men's genital responses also vary depending on the type of sexual activity that is depicted. Men without a history of sexual aggression exhibit their highest genital responses to stimuli that depict consensual sexual activity and much less genital arousal to stimuli that depict non-consensual sexual activity (Lalumiere & Quinsey, 1994). Men with a history of sexual aggression exhibit, on average, similar genital arousal to stimuli that depict consensual and non-consensual sexual activity, but there are some sexually aggressive men who show the most arousal to non-consensual sexual stimuli (Lalumiere & Quinsey, 1993).

Only one published study has specifically investigated women's genital arousal in response to different partnered sexual activities of similar intensities. This study differed from other studies that have assessed sexual arousal to different partnered sexual activities (Laan, Everaerd, & Evers, 1995; Suschinsky et al., 2009) by holding the number of actors depicted and the amount of sexual content described constant across stimuli. Suschinsky and Lalumiere (2011) presented men and women with a variety of audio-stories while their genital arousal was assessed. The audio-stories described interactions between a man and a woman and varied based on three factors: expression of consent or non-consent on the part of the woman, presence or absence of sexual activity, and presence or absence of violence and injury to the woman. Unlike the men, the women showed relatively high and relatively equal genital arousal to the stimulus categories that contained sexual content, regardless of the presence of violence and injury or non-consent.

In contrast to documented sex differences in genital arousal patterns, both men and women exhibit a category-specific pattern of self-reported sexual arousal, in that they report different degrees of sexual arousal to different sexual stimuli. Androphilic and gynephilic men and women typically report their highest sexual arousal in response to stimuli that depict sexual partners who match their sexual preferences, and little to no arousal in response to stimuli depicting non-preferred sexual partners (e.g., Chivers et al., 2004). Although men and women do not exhibit different patterns of self-reported sexual arousal, they do exhibit different degrees of "sexual concordance", that is, the extent to which their genital arousal and self-reported sexual arousal are associated. Men have high correlations between their genital arousal and self-reported sexual arousal whereas women have positive but significantly lower correlations between their genital and self-reported sexual arousal (Chivers, Seto, Lalumiere, Laan, & Grimbos, 2010). Women's lower sexual concordance is not simply the result of their lower genital category-specificity--if women exhibit genital arousal to both preferred and non-preferred sexual stimuli, but only report sexual arousal in response to some sexual stimuli (e.g., preferred sexual stimuli), low correlations between genital and self-reported sexual arousal would be inevitable because self-reported arousal would only be elicited by some stimuli. Androphilic women still exhibit lower sexual concordance than men when presented with sexual stimuli that correspond with their sexual preferences (Suschinsky, Chivers, & Lalumiere, 2011; Wincze, Venditti, Barlow, & Mavissakalian, 1980). Women also show significantly lower sexual concordance than men when asked to focus on their physiological sensations by reporting their feelings of genital arousal, rather than overall feelings of sexual arousal (Chivers et al., 2010).

How stable are sexual arousal patterns?

The sex differences in genital category-specificity and sexual concordance appear to be valid phenomena in need of explanation, and not the result of measurement error. The validity of penile plethysmography as a measure of sexual arousal has been well-established for some time (for reviews, see Rosen & Beck, 1988; Janssen, Prause, & Geer, 2007; Zuckerman, 1971), and the validity of vaginal photoplethysmography has been established more recently (Laan et al., 1995; Suschinsky et al., 2009). This validity is reflected in the fact that increases in penile circumference (or volume) and in vaginal blood flow are only observed in response to sexual stimuli (Laan et al., 1995; Suschinsky et al., 2009; Zuckerman, 1971). Similarly, higher intensity sexual stimuli depicting partnered copulation elicit higher genital arousal in men and women than lower intensity sexual stimuli depicting solitary masturbation or two clothed people kissing and caressing each other (Chivers et al., 2007; Suschinsky et al., 2009).

Although the sex differences in sexual arousal patterns appear to be valid phenomena, in that they have been reported by different researchers for several years, little to no research has examined the stability or consistency of these differences. If the sex differences are consistent across testing sessions, their validity would be further supported and less likely to be the result of extraneous factors, such as experience with erotica, experience with sexual arousal, or comfort with the laboratory context. If these sex differences are not consistent across testing sessions and especially if the sex differences decrease over testing sessions, researchers must question their validity and possibly alter their experimental methodologies to incorporate multiple testing sessions.

The relatively few studies that have assessed sexual arousal over more than one testing session include an investigation of the test-retest reliability of penile plethysmography in men (Eccles, Marshall, & Barbaree, 1988; Farkas et al., 1979) and several studies on the effect of the menstrual cycle on women's sexual arousability (Hoon, Bruce, & Kinchloe, 1982; Meuwissen & Over, 1992; Schreiner-Engel, Schiavi, Smith, & White, 1981; Slob, Bax, Hop, Rowland, & Vender Werff ten Bosch, 1996). Some research suggests that men's sexual arousal patterns may actually become more discriminating over testing sessions. For example, Barbaree, Baxter, and Marshall (1989) presented 41 male university students and 60 incarcerated rapists with audio-stories of consensual and non-consensual sexual interactions over two testing sessions that took place at least 48 hours (but not more than a month) apart. A rape index (i.e., the summed penile responses to non-consensual stimuli divided by the summed penile responses to consensual stimuli) was calculated for each participant for each testing session. Barbaree et al. found that the rapists' rape indices were moderately correlated across testing sessions (Pearson r = .44), but that the students' rape indices were less correlated across testing sessions (Pearson r = .29). They noted that the students exhibited a greater degree of discrimination between the consensual and non-consensual stimuli during the second testing session, by showing greater arousal to consensual stories. To our knowledge, an equivalent study in women has not been conducted.

Sexual concordance, the degree of relationship between genital arousal and self-reported sexual arousal, has been assessed across testing sessions in men and women. With respect to men, Wormith (1986) presented a variety of slides depicting nude individuals of different ages and heterosexual couples engaging in sexual activity to three groups of incarcerated offenders; 12 had committed rape or attempted rape, 12 were pedophiles, and 12 were non-sex offenders. Subjects' genital arousal and self-reported arousal during exposure to the slides were assessed in two separate testing sessions given one week apart. Wormith reported a nearly significant between-session correlation for sexual concordance of .23 (p < .09), suggesting that the men's sexual concordance may have been somewhat stable.

Henson, Rubin, and Henson (1979) assessed genital arousal in eight women using vaginal photoplethysmography and labial thermistors across two testing sessions separated by at least seven days (the maximum number of days was not reported). The women were presented with an 11 minute erotic film that depicted heterosexual sexual behaviours. Participants were asked to report their genital sexual arousal once before the film began and once immediately after the film ended and also to retrospectively assess their arousal during the film and at two minute intervals in the ten minutes that followed the film. Henson et al. reported high correlations between genital arousal (as measured by both vaginal photoplethysmography and labial thermistors) and self-reported sexual arousal in both testing sessions (Session 1: r = .65 and r = .64; Session 2: r = .57 and r = .82 for the correlation between self-reported genital arousal and actual genital arousal measured by vaginal photoplethysmography and labial thermistors, respectively).

Heiman (1977; 1980) also assessed sexual arousal in two testing sessions. Heiman's (1977) study involved presenting 39 men and 59 women with audio stimuli depicting erotic, erotic-romantic, romantic, or neutral heterosexual content while their genital arousal was measured; self-reported arousal was assessed after each stimulus. Participants listened to the same stimuli in both sessions, which took place two weeks apart. The erotic and erotic-romantic stimuli elicited the highest genital arousal in both sessions. Although the author did not report the sexual concordance scores for each session, she did note that sexual concordance was somewhat higher in the first testing session. Heiman's (1980) other study included 27 married and 28 unmarried women who watched an erotic heterosexual film, listened to an erotic heterosexual tape, and fantasized while their genital arousal was measured; participants reported their feelings of arousal after each stimulus. Overall, genital responses were similar across sessions, in that the film elicited the most arousal in both sessions. There were some inconsistencies, however, because the unmarried women showed significantly higher genital arousal relative to the married women to the film and the tape in only the first session. Similarly, only the unmarried women showed significant sexual concordance, and this was true only in the first session.

Although Henson et al. 's (1979) and Heiman's ( 1977; 1980) research provided initial insight into assessing the consistency of sexual arousal patterns in women, their studies had several limitations in that regard. First, Henson et al. employed a very small sample to assess the consistency of sexual concordance across testing sessions. Second, it is unclear whether Henson et al. or Heiman controlled for menstrual cycle effects. This is a limitation because some research indicates that women's genital arousability changes across the menstrual cycle; for example, higher genital arousal responses have been reported at the follicular phase (Schreiner-Engel et al., 1981; Slob et al., 1996) and the luteal phase (Schreiner-Engel et al., 1981). However, other research did not find evidence of changes in genital responsiveness across the menstrual cycle (Hoon et al., 1982; Meuwissen & Over, 1992). Henson et al. reported that their testing sessions were separated by a minimum of seven days but it is unclear whether most (or any) of their participants were tested in the same phase of their menstrual cycle, and if not, whether menstrual cycle phase was taken into account in the analyses. Similarly, Heiman (1977) reported that the two sessions were two weeks apart, but Heiman (1980) did not describe the amount of time separating the testing sessions. Third, Henson et al. and Heiman presented the same heterosexual sexual stimuli in both sessions; thus, women's genital category-specificity was not assessed and it is unclear whether any changes in sexual concordance are the result of enhanced awareness, remembering the first session, or decreases in responding to the same stimulus resulting from habituation. Fourth, Henson et al. reported between-subjects correlations for sexual concordance, which may underestimate women's (and men's) degree of sexual concordance (Chivers et al. 2010); between-subjects correlations speak to the agreement between genital arousal and self-reported sexual arousal within a group of individuals, whereas within-subjects correlations speak to the agreement between genital arousal and self-reported sexual arousal within an individual (Geer & Janssen, 2000). Fifth, and most germane to the current study, Henson et al. and Heiman did not report between-session correlations to assess the stability of sexual concordance. No study has examined the stability of sex differences in genital category-specificity or sexual concordance.

In addition to Heiman's (1977; 1980) research suggesting that women's arousal patterns may change over testing sessions, there are other reasons to suspect that women's sexual arousal patterns may not be stable over time, or at least not as stable as men's. For example, experience may influence sexual arousal patterns. Pearson and Pollack (1997) found that women who had previous experience with erotic materials reported more feelings of overall sexual arousal and more genital sensations in response to a sexual film they watched in a laboratory (genital arousal was not directly assessed) compared to women who had no previous experience with erotic materials. Men report significantly more experience with erotic materials than women in terms of both frequency and the number of years that they have used erotic materials (Buzzell, 2005; Hald, 2006). Men also have more experience with masturbation in that they report more frequent masturbation and earlier age of first masturbation compared to women (Gerressu, Mercer, Graham, Wellings, & Johnson, 2008; Laumann, Gagnon, Michael, & Michaels, 1994; Oliver & Hyde, 1993; Petersen & Hyde, 2010). Given that women have less experience with both erotic materials and their genitals, it is possible that their sexual arousal patterns may change with experience. In other words, the low genital category-specificity and sexual concordance typically observed in women in the laboratory may change with experience with the unusual testing environment of the laboratory.

The current study

The purpose of the current study was to assess the stability of sex differences in sexual arousal patterns as well as the stability of sexual arousal patterns in general. We expected that men and women would exhibit different patterns of genital arousal for the first testing session; men were expected to exhibit a more category-specific pattern of genital arousal and higher sexual concordance than women. We also expected men and women to both exhibit a category-specific pattern of self-reported sexual arousal in the first testing session. Also, we expected that if the sex differences in genital category-specificity and sexual concordance are valid phenomena, there should be little change in the magnitude of the differences across the two testing sessions.

Methods

Participants

Individuals were eligible to participate if they met the following criteria: age 18-35 years; predominantly attracted to members of the opposite sex; sexually experienced (i.e., had engaged in partnered sexual activity defined as genital touching, oral sex, or sexual intercourse); had used erotic materials such as movies or magazines; fluent in English; and no history of mental illness, sexual dysfunction, or sexually transmitted infections. Twenty men and 25 women participated in the first session. Data from four women were excluded from data analysis because they failed to exhibit a genital response to any stimulus category that was greater than their genital response to the neutral stimulus category. Data from an additional three women were excluded because they did not attend the second testing session because of scheduling problems. Data from four men and six women (Session One only) were collected as part of a previously published study (Suschinsky & Lalumiere, 2011). All experimental procedures were approved by the university's Human Subject Research Committee and all participants were informed about the procedures and gave informed consent.

The mean ages for the men (N=20) and the remaining women (N = 18) were 24.5 years (SD = 5.2) and 21.6 years (SD = 2.9), respectively. All men and 89% of the women were Caucasian and the vast majority of men (95%) and women (94%) reported that they had either completed or were currently enrolled in postsecondary education. Slightly more than half of the men (65%) and women (67%) reported that they were in a romantic relationship of some sort. The majority of men (90%) and women (94%) reported that they were heterosexual, and the remaining participants reported that they were bisexual. Half of the women reported using hormonal contraceptives. The men were significantly older than the women, t(36) = 2.05, p = .048; there were no significant sex differences for any of the other biographic information, ps [greater than or equal to] .23.

Materials and measures

Audio stimuli

The audio narratives were identical to those reported by Suschinsky and Lalumiere (2011). The stimuli were 2-minute audio narratives told from a woman's perspective by a female narrator. Sexual narratives told from a woman's perspective produce genital arousal in both men (Lalumiere, Quinsey, Harris, Rice, & Trautrimas, 2003) and women (Suschinsky & Lalumiere, 2011). The narratives described an interaction between a man and a woman and followed a standard format that included: a few sentences to set the scene, a description of the initial contact between a man and a woman, the woman's reaction, the man's response, the woman's experience, the man's final acts, and the woman's final condition. The narratives varied based on the presence or absence of three features: consent (female consent and enjoyment versus refusal and displeasure); violence (injury and suffering versus none); and sexual content (sexual acts and nudity versus none). These three features were factorially crossed to yield eight stimulus categories, one of which was not used (no consent, no violence, no sex). There were five slightly different narratives for each stimulus category; for each session, two narratives were randomly selected from each category for each participant. One neutral and one consensual nonviolent sex narrative were presented at the beginning of each session to acquaint the participant with the research setting; data collected during these trials were not included in analyses. For each session, the remaining 14 narratives were presented in a quasi-random order for each participant, such that no two narratives from the same stimulus category were presented consecutively.

Genital measures

All psychophysiological data were collected using the same procedure as Suschinsky and Lalumiere (2011); the psychophysiological data were sampled continuously during each narrative using a Limestone Technologies Inc. (Kingston, ON) DataPac_USB and Preftest software, Version 10. Mercury-in-rubber strain gauges (D. M. Davis, New Jersey) were used to measure men's genital arousal. The signal was sampled at a rate of 10 samples/second, low-pass filtered (to 0.5 Hz), and digitized (40 Hz). The signal was transformed into mm of circumference. Baseline was captured at the beginning of each stimulus and the peak response corresponded to the highest circumference value during the stimulus presentation. The gauges were calibrated over six 5-mm steps for each participant. The gauges ranged in size from 75 mm to 100 mm; participants used the same size of gauge in both testing sessions.

Women's genital arousal was assessed with changes in vaginal pulse amplitude via a vaginal photoplethysmograph equipped with an orange-red spectrum light source (Technische Handelsonderneming Coos, The Netherlands). The photoplethysmograph signal was sampled at a rate of 10 samples/second, band-pass filtered (0.5 Hz to 10 Hz), and digitized (40 Hz). Baseline was captured at the beginning of each stimulus and the peak response corresponded to the largest peak-to-trough distance during the stimulus presentation. A piece of flexible silicone was attached to the cable 5 cm from the light detector; this placement device was used to control the depth and the orientation of the gauge (Laan et al., 1995). Participants used the same probe in both testing sessions. Movement artifacts were detected through visual inspection of the waveforms and artifacts were removed prior to data analysis for both the men's and women's data. The experimenter was blind to the stimulus content while inspecting the data.

Self-reported sexual arousal

Participants continuously rated their feelings of sexual arousal (defined as "How turned on did you feel?") during each narrative using a button press on a keypad. The button press manipulated a vertical bar that represented the individual's self-reported sexual arousal on a computer screen placed five feet away from the participant. Participants also used the keypad to report their sexual arousal after each narrative. Participants used a scale of 1 (no arousal) to 9 (maximum arousal) to report how sexually aroused they felt (i.e., their emotional state of arousal) and how sexually aroused their genitals felt.

Questionnaires

In Session One, participants answered a series of questionnaires assessing their biographic information, sexual orientation, and other traits not examined in this article.

Procedures

Screening and session one

Prospective participants responded to advertisements placed in a university newspaper and posters placed on a university campus. The first author responded to prospective participants either via telephone or email, at which time a description of the study and its procedures was provided. The researcher also provided the list of eligibility criteria (see above). Eligible participants booked an appointment for their first session; women's appointments were scheduled such that they did not participate while they were menstruating. Participants were asked to refrain from sexual activity of all types for 24 hours, physical exercise of all types for one hour (because exercise results in sympathetic nervous system arousal that can influence genital responses; Meston & Gorzalka, 1996), and using substances that may influence their physiological and psychological sexual arousal on the day of testing (e.g., alcohol, tobacco, caffeine, cold medications, and recreational drugs).

Participants were assessed individually. The female experimenter explained the details of the study and obtained consent. Participants were left alone in a dimly lit room to attach the strain gauge or insert the probe. The narratives were presented via headphones; participants were instructed to rate their sexual arousal continuously during each narrative and then after each narrative. The narratives were separated by inter-stimulus intervals of 30 - 300 seconds to allow a return to baseline. Following the psychophysiological assessment, participants completed a questionnaire package. Session One lasted between 2 and 2.5 hours. Participants were compensated with $50.

Session Two

On average, Session Two occurred 28 days after Session One (minimum = 27 days, maximum = 31 days); Session Two was scheduled to take place during the same time of day that Session One had occurred. Female participants were tested in the same phase of their menstrual cycle, as determined by the reverse counting method (Chen, 2005). Specifically, six women were tested in the two weeks immediately following their menstruation (i.e., pre-ovulatory and ovulatory phase). Eleven women were tested in the two weeks before their next menstruation was expected (i.e., post-ovulatory phase). Menstrual cycle phase could not be determined for one participant. Analyses were performed on women's data with menstrual cycle phase as a between-subjects factor, with no significant effect on genital arousal patterns, self-reported sexual arousal patterns, or sexual concordance.

Each male participant was yoked to a female participant, to ensure a similar passage of time between testing sessions. The psychophysiological assessment in Session Two followed a procedure identical to Session One, with the exception of the questionnaire package. Session Two lasted between 1 and 1.5 hours. Participants were compensated with $25 and debriefed about the purposes of the study.

Data preparation

Genital arousal and continuous self-reported sexual arousal scores were calculated by subtracting the trial baseline from the peak response for each narrative. Scores for the genital arousal data were then standardized within subjects across both sessions combined because the response output scales differ between men and women. Self-reported sexual arousal scores were not standardized. Category scores were computed separately for genital arousal and continuous self-reported sexual arousal by averaging the scores from the two narratives for each category for each session. A Kolmogorov-Smirnov test was performed on individual participants' genital arousal and continuous self-reported arousal scores for each session in order to compare the distribution of responses to all non-neutral stimuli against a theoretical uniform (i.e., flat) response distribution, with higher Z scores indicating that the pattern reflects a less uniform distribution (i.e., a more category-specific response pattern). The resulting Z scores were then averaged within each sex. As per Chivers et al.'s (2010) recommendation, for each session, sexual concordance was calculated within subjects using the genital arousal scores and post-stimulus self-reported overall feelings or emotional sexual arousal collected for the eight sexual stimuli only. Coercion Indices were calculated for genital and continuous self-reported sexual arousal using the sum of a participant's responses to consensual sexual activities (i.e., consenting sexual sadism and consenting sex) subtracted from the sum of that participant's responses to non-consensual sexual activities (i.e., sadistic rape and non-sadistic rape); positive scores indicate greater arousal to coercive or non-consensual sexual activities.

Results

The stability of genital arousal patterns

Figure 1 shows the standardized genital responses for men and women across the two testing sessions. The figure indicates that men were more genitally aroused by consenting, non-violent sex compared to the other stimulus categories, whereas women's genital arousal appeared to be much less affected by stimulus category. A 2 (session) X 7 (stimulus category) X 2 (sex of participant) analysis of variance (ANOVA) revealed that men's and women's overall genital arousal did not change over the testing sessions, F(1, 36) = 0.80,p = .38,112= 0.02. Session did not interact or stimulus category, F(6, 216) = 0.42, p = .86, [[eta].sup.2] = 0.01, sex, F(1, 36) = 0.58, p = .44, [[eta].sup.2]= 0.02, or with stimulus category and sex together, F(6, 216) = 1.07, p = .38, [[eta].sup.2] = 0.02. The ANOVA did reveal a significant interaction between stimulus category and the participants' sex, F(6, 216) = 7.63, p < .001, [[eta].sup.2] = 0.18. There was also a main effect of stimulus category, F(6, 216) = 76.27, p < .001, [[eta].sup.2] = 0.68. The results were effectively the same when age was used as a covariate. Overall, then, the results showed a sex difference in the category-specificity of genital arousal, and that difference did not vary by session.

Figure 2 shows the correlation between the Z scores obtained from the Kolmogorov-Smirnov analyses for genital arousal for the two testing sessions. A Pearson r correlation revealed that genital category-specificity scores were not significantly correlated across the two testing sessions (r = .37 and r = -.09 for men and women, respectively). We conducted a 2 (session) X 2 (sex of participant) ANOVA with the genital arousal Z scores as the dependent variable. There was no main effect of testing session, F(1, 36) = 0.02, p = .90, [[eta].sup.2] = 0.00, but there was a near significant interaction between testing session and sex, F(1, 36) = 3.98,p = .054, [[eta].sup.2] = 0.10. There was also a main effect of participant sex, F(1, 36) = 18.22, p < .001, [[eta].sup.2] = 0.34. One-way ANOVAs revealed that men's Z scores (M = 1.49, SD = 0.44 and M = 1.69, SD = 0.58 for Session One and Two, respectively) were significantly higher than women's Z scores (M= 1.18, SD = 0.47 and M = 1.00, SD = 0.32 for Session One and Two, respectively) for both testing sessions, ps < .05. Although men's Z scores increased and women's decreased across testing sessions, these changes were not significant in either sex, ps [greater than or equal to] 19. When age was used as a covariate, the interaction between testing session and participant sex was significant, F(1, 35) = 5.46, p = .025, [[eta].sup.2]= 0.14; all other results remained the same. Overall, men's genital responses were more category-specific than women's, and the sex difference was even larger for Session Two (Cohen's d = 1.53) than for Session One (Cohen's d = 0.68). For comparison, a d value of 0.2 to 0.3 is considered a small effect size, 0.5 medium, and 0.8 large (Cohen, 1988).

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

To further investigate the degree of change in genital category-specificity across testing sessions, we computed absolute difference scores by subtracting each participant's Kolmogorov-Smimov Z score for Session One from the corresponding score in Session Two. If women's genital arousal patterns were less stable than men's, women should have significantly larger difference scores than men. There was no significant difference between men's (M = 0.46, SD = 0.40) and women's (M = 0.46, SD = 0.40) degree of change in genital arousal specificity, t(36) = 0.018, p = .98, d = 0.00.

A Pearson r correlation indicated that Coercion Indices were not significantly correlated across sessions within men or women (r = .14 and r = -.02, ps [greater than or equal to] .55, respectively). A 2 (session) X 2 (sex of participant) ANOVA revealed that men's and women's relative genital arousal to non-consensual and consensual sexual stimuli did not change over the testing sessions, F(1, 36) = 0.71,p = .41, [[eta].sup.2] = 0.02. Session did not interact with participant sex, F(1, 36) = 0.14, p = .71, [[eta].sup.2] = 0.00. There was a main effect of sex, F(1,36) = 18.16,p < .001, [[eta].sup.2] = 0.34, with women having a higher Coercion Index overall (Session One: M = -0.78, SD = 1.20; Session Two: M = -0.42, SD = 1.18) relative to men (Session One: M = -2.07, SD = 1.57; Session Two: M = -1.93, SD = 1.45). The results were similar when age was covaried. These results are consistent with the results reported above, indicating that women's genital responses are less category-specific than men's in both sessions.

The stability of self-reported sexual arousal patterns

Figure 3 shows the distribution of continuous self-reported sexual arousal responses across the two testing sessions and suggests that both men and women reported they were most aroused by the consenting, non-violent sexual stimuli in both sessions. A 2 (session) X 7 (stimulus category) X 2 (sex of participant) ANOVA revealed no main effect of testing session, F(1,36) = 1.38,p = .24, [[eta].sup.2] = 0.04. Session did interact with stimulus category, F(6, 216) = 2.98,p = .008, [[eta].sup.2] = 0.08, but did not interact with the sex of participants, F(1, 36) = 0.03, p = .86, [[eta].sup.2] = 0.00, or with stimulus category and sex together, F(6, 216) = 0.68,p = .67, [[eta].sup.2] = 0.02. There was also a main effect of stimulus category, F(6, 216) = 92.66, p < .001, [[eta].sup.2] = 0.72. Men and women did not differ in their overall self-reported sexual arousal, F(1, 35) = 1.19, p = .28, [[eta].sup.2] = 0.03. When age was used as a covariate, all results remained the same, with one exception; the interaction between session and stimulus category was no longer significant, F(6, 210) = 1.77, p = .10, [[eta].sup.2] = 0.04. Overall, then, men and women did not show significantly different self-reported sexual arousal patterns for either session.

[FIGURE 3 OMITTED]

Figure 4 shows the correlation between the Z scores obtained from the Kolmogorov-Smirnov analyses for continuous self-reported sexual arousal across the two testing sessions. A Pearson r correlation revealed that men's and women's self-reported sexual arousal patterns were significantly correlated across the two testing sessions (r = .81 and r = .85, respectively); the results are consistent when controlling for age. We also conducted a 2 (session) X 2 (sex of participant) ANOVA with the self-reported arousal Z scores as the dependent variable. There was a main effect of session, F(1, 35) = 5.76, p = .022, [[eta].sup.2] = 0.14, with Session Two Z scores being higher (M = 1.95, SD = 0.82) than Session One Z scores (M = 1.76, SD = 0.70). There was no main effect of sex, F(1, 35) = 1.32, p = .26. When age was used as a covariate, there was no main effect of testing session, F(1, 34) = 0.06, p = .81, [[eta].sup.2] = 0.00. Overall, the patterns of self-reported sexual arousal were very consistent across sessions in both men and women.

Self-reported Coercion Indices were not significantly correlated across sessions in men (r = .20, p = .38), but they were in women (r = .59, p = .01). A 2 (session) X 2 (sex of participant) ANOVA revealed that men's and women's relative self-reported arousal to non-consensual and consensual sexual stimuli changed over the testing sessions, F( 1,36) = 6.48, p = .015, q2 = 0.15. Men's and women's Coercion Indices were significantly lower in Session One (M= -54.70, SD = 27.61 and M = -37.21, SD = 19.40, respectively) than Session Two (M = -39.72, SD = 27.90 and M = -27.75, SD = 26.82, respectively). Session did not interact with participant sex, F(1, 36) = 0.33, p = .56, [[eta].sup.2] = 0.00. Women's Coercion Indices were significantly higher than men's Coercion Indices, F(1, 36) = 4.60, p = .039, [[eta].sup.2] = 0.11. The results were similar when age was covaried. Overall, then, men's and women's relative self-reported preference for consensual sexual stimuli decreased over time, and men showed greater preference for consensual over non-consensual stimuli in comparison to women.

The stability of sexual concordance

Figure 5 shows the Pearson r correlation between the sexual concordance scores obtained in the two testing sessions. A 2 (session) X 2 (sex of participant) ANOVA with sexual concordance score as the dependent variable revealed a near significant main effect of session, F(1, 36) = 3.83,p = .058, [[eta].sup.2] = 0.10. Session did not interact with participants' sex, F(1, 36) = 0.91, p = .34, [[eta].sup.2] = 0.02. There was a main effect of sex, F(1, 36) = 47.86, p < .001, [[eta].sup.2] = 0.57. Men exhibited significantly higher sexual concordance scores than women in Session One (r = .57 and r = .37, respectively) and Session Two (r = .70 and r =. 18, respectively). There was no significant correlation between sexual concordance scores across testing sessions for men (r = .44, p = .06) nor women (r = -.20, p = .44). The results remained the same when age was covaried. Overall, men showed significantly higher sexual concordance than women, and this sex difference tended to be even larger in Session Two.

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

To investigate the degree of change in sexual concordance across testing sessions, we computed absolute difference scores by subtracting each participant's sexual concordance score for Session One from Session Two. If women's sexual concordance scores are less stable than men's, they should have higher difference scores than men. An independent samples t-test revealed that women's sexual concordance scores (M = .44, SD = .36) changed to a significantly greater degree than men's sexual concordance scores (M = .19, SD =. 18), t(36) = 2.67, p = .011, d = 0.92.

Discussion

In the present study, sex differences in genital category-specificity and sexual concordance were found in both testing sessions, and may have been even larger in the second session. Consistent with previous research (Chivers et al., 2004; Chivers et al., 2007; Suschinsky et al., 2009; Suschinsky & Lalumiere, 2011), men's genital arousal patterns were category-specific and tended to become even more specific over the two testing sessions (Barbaree et al., 1989). Women's genital arousal patterns were much less category-specific in both testing sessions, and tended to become less category-specific in the second session. Also consistent with previous research, men's and women's self-reported sexual arousal patterns were similar (Chivers et al., 2004; Chivers et al., 2007; Suschinsky et al., 2009; Suschinsky & Lalumiere, 2011). In both testing sessions, men and women exhibited a category-specific pattern of self-reported sexual arousal, and tended to become more category-specific in the second session. Also consistent with previous research, men had significantly higher sexual concordance scores than women (Chivers et al., 2010) in both testing sessions, with a tendency for a larger difference in the second session. Although the sex difference in genital category-specificity and sexual concordance was observed in both testing sessions, the correlational analyses revealed little stability at the individual level, especially in women.

The stability of sexual arousal patterns in men and women

Men's genital arousal, self-reported sexual arousal, and sexual concordance patterns were relatively stable across testing sessions. Interestingly, women's self-reported sexual arousal was stable across the testing sessions, but their genital arousal and sexual concordance were less stable. These results are consistent with previous research. Heiman (1977) reported that sexual concordance scores were slightly lower in the second testing session of her study, though no analyses were presented. Similarly, Heiman (1980) reported changes in sexual arousal patterns across testing sessions in her sample of married and unmarried women; the unmarried women showed significantly higher genital arousal to an erotic tape and film than married women, but this difference was only present in the first testing session. Similarly, sexual concordance was significant for the unmarried women only in the first session. Heiman's findings, in combination with the results of the current study, suggest that women's sexual arousal patterns may have less stability than men's sexual arousal patterns.

Given that individual women's self-reported sexual arousal patterns were relatively stable across the testing sessions, we are left to explain why their genital arousal patterns seem to vary across testing sessions. Men's genital responses are closely connected with their sexual preferences, such that men show varying degrees of genital arousal to different high and low intensity sexual stimuli that correspond with their preferred sexual partners and sexual activities. Women's genital responses are less closely connected with their sexual preferences, such that women show relatively equal degrees of genital arousal to high intensity sexual stimuli that depict both preferred and non-preferred sexual partners (Chivers et al., 2007) and sexual activities (Suschinsky & Lalumirre, 2011). The reflex-like onset of their genital responses in the presence of sexual stimuli (Suschinsky et al., 2011) supports one particular functional explanation for women's genital arousal patterns. The "preparation hypothesis" suggests that women's genital responses, as measured by changes in vaginal blood flow, should occur in the presence of any sexual stimulus, in order to induce lubrication (Levin, 2003), thus preparing women for sexual encounters (Chivers, 2005; Laan, 1994; Suschinsky & Lalumiere, 2011). Women's magnitude of genital response may not need to be consistent across testing sessions (or sexual encounters, for that matter), provided that there is enough of an increase in vaginal blood flow to induce lubrication. The preparation hypothesis thus suggests that the presence of genital arousal, rather than its magnitude, should be consistent across sessions in women.

We note that the degree of stability of sexual arousal patterns may still be related to sexual experience. Although we presented men and women with sexual stimuli at two different periods, it is possible that sexual arousal patterns are more associated with direct experience with one's genitals and the use of erotic material for sexual pleasure, rather than simple exposure. In general, women report masturbating and using erotic materials less frequently than men (e.g., Petersen & Hyde, 2010). Thus, it is possible that women who have more experience with their own sexual responses may have more stable patterns of sexual arousal.

Limitations of the study

Sampling

The sample of participants in the current study was rather limited in that the sample consisted primarily of Caucasian university students. The results cannot be generalized to other groups at this time. We note also the possibility of the well-known self-selection bias in sexual psychophysiological studies arising from the tendency of individuals willing to participate in sexual arousal studies to be more sexually experienced and less likely to report sex guilt (e.g., Strassberg & Lowe, 1995). If sexual experience is associated with greater or lower stability of sexual arousal patterns, this self-selection bias would be a concern for the generalizability of the results.

Measures of genital arousal

Another limitation of the current study involves the devices that we used to measure genital arousal in men. Although penile plethysmography and vaginal photoplethysmography are valid measures of genital arousal, they do not measure the same structures. It is possible that sex differences in genital category-specificity and sexual concordance (and stability thereof) reflect the differences in the measures used. Changes in genital temperature can be assessed in both men and women. To date, genital category-specificity has not been assessed with temperature or thermographic measures of genital arousal, but sexual concordance has (e.g., Henson et al., 1979; Kukkonen, Binik, Amsel, & Carrier, 2007; 2010). Chivers et al. (2010) noted that temperature measures of genital arousal do tend to yield higher sexual concordance scores in women, relative to vaginal photoplethysmography. Similarly, when men's and women's sexual concordance is assessed with thermographic measures, the sex difference can be eliminated (e.g., Kukkonen et al., 2007; 2010). Although thermographic measures are promising for the assessment of sexual concordance in men and women, these results must be interpreted with caution because some women still exhibit very low sexual concordance. All of the men in Kukkonen et al.'s (2010) study had positive sexual concordance scores, but 40% of the women had a sexual concordance score less than or equal to zero. Half of these women had significant negative correlations between their genital temperature and self-reported sexual arousal, and the remaining women reported no variability in their self-reported arousal, despite changes in their genital temperature, suggesting that they were less aware of their sexual arousal. Future research should assess genital arousal category-specificity and continue to assess sexual concordance with both blood flow and temperature measures to better understand sexual arousal patterns in men and women.

Stimuli

A limitation associated with the stimuli may be the fact that audio stimuli tend to elicit lower levels of genital arousal relative to film stimuli (e.g., Abel, Barlow, Blanchard, & Mavissakalian, 1975; Heiman, 1980). Four women were excluded from data analysis because they did not exhibit a genital response to any stimulus category that was larger than their response to the neutral stimulus category. Film stimuli may reduce the number of non-responder participants. Film stimuli may also reduce some ambiguity related to the stimulus content, potentially resulting in more stable patterns of sexual arousal within subjects. The stimuli in the current study all followed the same format (described above), thus possibly confusing participants. For example, participants may have expected any given stimulus to include sexual content, and slowly realized that no sexual activity would occur as the stimulus progressed. Film stimuli may be less ambiguous and easier for participants to interpret because they provide both audio and visual cues, thus resulting in potentially more stable sexual arousal patterns within subjects. Some of our stimuli also described relatively atypical sexual activities between male and female characters only. Future research could use interactions between different couples (e.g., two men, two women, and a man and woman) to assess the stability of sexual arousal patterns with respect to the gender of the actors depicted in the stimuli. We anticipate that the sex differences in sexual arousal patterns would be relatively stable with those stimuli.

Timing

A final limitation may involve the amount of time that passed between testing sessions. We tested participants approximately one month apart, to limit potential menstrual cycle effects on women's sexual arousability (Schreiner-Engel et al., 1980; Slob et al., 1996; but see Hoon et al., 1982; Meuwissen & Over, 1992). Most of the research that has investigated the stability of sexual arousal has looked at arousal patterns within a shorter period of time, such as one or two weeks (Barbaree et al., 1989; Heiman, 1977; Henson et al., 1979; Wormith, 1986). It is possible that the amount of time that passed between testing sessions was too long and that participants responded to the stimuli as if they were novel, thus reducing the impact of experience on arousal patterns. There is some evidence to suggest that men's genital responses habituate or decrease over multiple testing sessions (e.g., Plaud, Gaither, Amoto, Henderson, & Devitt, 1997), but it is unlikely that we would have found habituation in the current study because we used similar but different stimuli in each testing session. Future research could involve assessing the stability of sexual arousal patterns over shorter periods of time (e.g., days) while women are still in the same phase of their menstrual cycle, to assess the short-term effects of experience or exposure to sexual stimuli on genital arousal and sexual concordance.

Conclusions and future research questions

The results of the current study suggest that the sex differences in genital arousal category-specificity and sexual concordance are stable across testing sessions, and are thus valid phenomena. More research is required to further assess the stability (or lack thereof) of women's sexual arousal patterns at the individual level. The outcome of such research will have important implications for future research. If women's sexual arousal patterns are in fact stable across testing sessions, we can begin to investigate the development of sexual arousal patterns in men and women. We currently know very little about the development of sexual arousal patterns in either sex and questions remain. Is genital category-nonspecificity in women something that develops over time? Do men start out nonspecific and somehow learn genital specificity? We suspect both sexes begin with the female pattern of category-nonspecificity, and that boys, in the course of sexual differentiation, develop category-specificity. If that is not the case, is it possible that some environmental, social, or personal cues trigger genital nonspecificity in women? It would be worthwhile to examine such cues as frequency of being the target of courtship, the sex ratio of the social environment (a male-biased sex-ratio might be more likely to lead to sexual pressures), the age of the women, or a history of sexual assault.

We can ask similar questions about sexual concordance. Men do have significantly greater experience with their genitals and erotic material relative to women (Buzzell, 2005; Hald, 2006; Laumann et al., 1994; Oliver & Hyde, 1993; Petersen & Hyde, 2010). Although age does not seem to impact sexual concordance (e.g., Chivers et al., 2010), it is possible that actual experience rather than chronological age influences sexual concordance.

If it is shown sexual arousal patterns are not stable in women over time, this will have a significant impact on clinical applications and future research. In terms of clinical applications, it would be difficult to interpret changes in genital arousal following a therapeutic intervention, especially the lack of treatment-induced changes, if sexual arousal patterns prove to be relatively unstable in women. Similarly, experimental methodology may need to be altered if women's sexual arousal patterns are not stable over time. A more accurate pattern of sexual arousal may be obtained by collecting data over multiple testing sessions. Future research is required to better understand these issues.

Acknowledgements: We would like to thank the Social Sciences and Humanities Research Council of Canada and the Natural Sciences and Engineering Research Council of Canada for supporting this research. We would also like to thank Brittany Bannerman, Samantha Dawson, Meg Ebsworth, Grant Harris, Vernon Quinsey, and Michael Seto for helpful feedback on an earlier draft of this manuscript, as well as Mackenzie Becker for data entry.

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Kelly D. Suschinsky (1) and Martin L. Lalumiere (1)

(1) Department of Psychology, University of Lethbridge, Lethbridge, AB

Correspondence concerning this article should be addressed to Martin Lalumiere, Department of Psychology, University of Lethbridge, Lethbridge AB T1K 3M4. E-mail: martin.lalumiere@uleth.ca
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Author:Suschinsky, Kelly D.; Lalumiere, Martin L.
Publication:The Canadian Journal of Human Sexuality
Date:Sep 22, 2011
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