Sexual behavior and responsiveness to sexual stimuli following laboratory-induced sexual arousal.

Emotion can be construed as fundamentally an action disposition, a tendency to do something (Frijda, 1986; Lang, 1993). In this view emotions serve the satisfaction of goals and generate relevant action (such as fight-flight or approach). Sexual excitement, in this respect, does not deviate from other emotions: It serves to satisfy concerns and generates a tendency for sexual behavior (Everaerd, Laan, Both, & Spiering, 2001). From this viewpoint it follows that sexual excitement should incorporate sexual action tendencies and sexual action. To test this prediction, we investigated men's and women's sexual behavior following laboratory induced sexual excitement.

Laboratory studies on human sexual responses generally include measures of genital arousal and subjective sexual arousal. Overt sexual behavior is seldom measured. However, sexual activity may be a relevant variable to investigate in laboratory studies about sexual motivation. Incentive behavior consists of appetitive and consummatory responses and generally proceeds from the appetitive phase to the consummatory phase (Pfaus, 1999). Measuring appetitive and consummatory sexual behavior following laboratory visits offers the opportunity to study the relationship between physiological sexual arousal, subjectively experienced sexual arousal, and overt sexual activity in men and women. The inclusion of measures of overt sexual behavior in laboratory studies will provide a more complete picture of the generation of sexual action.

Incentive motivation theories state that approach behavior will be activated by appropriate incentives (Agmo, 1999; Bindra, 1974; Singer & Toates, 1987). Bindra (1974) introduced the concept of a central motive state, "a hypothetical set of neural processes that promote goal directed actions in relation to particular classes of incentive stimuli, for example, it promotes food seeking and eating in relation to food, or defensive fighting and escape in relation to a predator" (p. 201). An incentive, it is supposed, guides response selection through the excitatory or priming influence of the central motive state on somato-visceral reactions, consummatory acts, and locomotor and skilled actions. Frijda (1986), in line with Bindra, defines motivation as the elicitation of behavior systems by appropriate external stimuli or thoughts thereof. A behavior system is described as a potential action (a program) or a sequence of potential actions. With respect to sexual responses, this means that sexual motivation and the accompanying feeling of sexual desire arise when an individual interacts with appropriate sexual stimuli or thoughts thereof. Thus, in contrast to the layman's belief that sexual desire is spontaneous and arises "out of the blue," sexual desire is the outcome of the processing of sexual stimuli, although it may be felt and perceived as spontaneous (Basson, 2002; Everaerd et al., 2001).

Interaction with an incentive changes the affective state of an organism. Bindra (1974) already pointed to the similarity of motivational and emotional states. Action tendencies manifest themselves in various emotional response systems, including physiological change, emotional expression, and motivated behavior (Frijda, 1986; Lang, 1993). In addition, incentive motivation models state that motivation is the result of the interaction of the internal state of the organism and relevant stimuli in the environment. The internal state of the organism, like hormonal or other somatic factors and past experience, modulates the responsiveness to external cues. It may be expected that exposure to sexual stimuli can enhance responsiveness to subsequent sexual cues by modulating the internal state. Confrontation with a positive incentive results in activation of reward circuitry in the brain (Aharon et al., 2001; Kampe, Frith, Dolan, & Frith, 2001; Schultz, 1998, 2001). Activation of reward circuitry may result in an increase of attention for incentive stimuli and in an increase of subjective and physiological responses to these stimuli, which may result in a self-amplifying motivational process.

We hypothesized, following incentive motivation and emotion theory, that activation of the sexual system through exposure to a sexual stimulus would generate a tendency for sexual action and enhanced attention for and responsiveness to sexual stimuli. Naturally, a one-to-one relationship between sexual arousal and overt sexual activity is not to be expected. Rather, exposure to a sexual stimulus should activate sexual action tendencies, but regulation processes should affect the expression of these action tendencies. The transition of a state of genital and subjective arousal to the execution of sexual behavior should be mediated by a host of cognitive and affective processes, and the acting-out of sexual action tendencies should be influenced by rules and opportunities for sexual activity (Singer & Toates, 1987).

A number of psychophysiological studies on human sexual responses has shown that exposure to sexual stimuli in the laboratory is an adequate method to evoke genital responses and subjective sexual arousal in men and women (Geer & Jansen, 2000; Laan & Everaerd, 1995a). Sexual behavior, however, is measured in only a few experimental studies (e.g., Fisher & Byrne, 1978; Schmidt, 1975; Slob, Bax, Hop, Rowland, & van der Werff ten Bosch, 1996). Fisher and Byrne (1978) used erotic film and compared subjective and behavioral responses of erotophobic and erotophilic participants. Only erotophobic participants showed an increase in sexual behavior following exposure to erotic film. Schmidt (1975) conducted a series of studies in which male and female participants were exposed to erotic pictures, films, and stories. Sexual feelings, physiological reaction during exposure to the sexual stimuli, and sexual behavior during the 24-hour period following exposure were measured. Both men and women showed a slight increase in sexual behavior compared to the 24-hour period before the exposure. In these studies, all data were based on self-report. Although subjective estimate of physiological reaction was included, there was no (objective) physiological measurement of genital response. Therefore, there was no opportunity to look at the relationship between actual genital response, subjective sexual experience, and behavioral responses. Slob et al.'s (1996) study on changes in sexual arousability over the menstrual cycle, using a within-subjects design, did include genital measures (labium minus temperature). They assessed women's postexperimental sexual desire and activity after exposure to erotic videos. Women tested for the first time in their follicular phase showed higher labium minor temperature in response to the film and reported increased sexual desire and more frequent sexual fantasies during the 24 hours following the experimental session. These data indicate that differences in sexual arousability may be reflected in various components of sexual responding during and following a visit to the laboratory. Unfortunately, Slob et al. only reported the relationship between genital response and subjective sexual arousal, not the relationship between responses in the lab and sexual desire and activity following the lab visit.

Here we report on two experiments in which men and women were exposed to a neutral or a sexual film using a between-subjects design. In both experiments, we measured genital (penile circumference change in men and vaginal pulse amplitude in women), subjective, and behavioral sexual responses to the films. We expected the sexual film and not the neutral film to induce genital and subjective sexual arousal. Subjective action tendencies were measured with the expectation that the sexual film but not the neutral film would facilitate subjectively reported approach tendencies. We used a questionnaire to collect data on sexual desire and sexual activity during the 24 hours after film exposure. We predicted higher postexperimental sexual desire ratings and higher frequency of sexual activity in participants in the sexual film condition than in participants in the neutral film condition. In Experiment 2, in addition to postexperimental sexual behavior, we investigated the effect of film-induced sexual arousal on interest in and responsiveness to sexual stimuli.

In both experiments, both males and females participated to allow for gender comparison of sexual response patterns. There is evidence for a gender difference in sexual motivation; men seem to be more strongly motivated sexually compared to women (Baumeister, Catanese, & Vohs, 2001). Baumeister et al. concluded that, across many different studies and measures, men have been shown to have more frequent and intense sexual desire, to fantasize more frequently about sex, to masturbate more frequently, and to report fewer problems concerning low sexual desire. They concluded that the evidence points to a gender difference in frequency of sexual desire as well as in intensity of sexual desire. We reasoned that if this holds true, in the present study the stronger sexual motivation of men should be reflected in stronger sexual responses, stronger approach tendencies, higher postexperimental sexual desire ratings, and higher frequency of sexual activity in response to the sexual film in men compared to women.

EXPERIMENT 1

Method

Participants

Participants were 47 (25 female and 22 male) psychology students who received course credit or were paid for their participation. Mean age of the women was 22.6 (range = 18-37 years, SD = 4.7 years), and mean age of the men was 22.0 (range = 18-34 years, SD = 3.2 years). There was no significant difference in age between men and women, t(43) = 0.58, p > .1, or between stimulus conditions, t(43) = 0.92, p > .1.

All women had a heterosexual orientation; 16 women (64%) had a steady partner, and the duration of the relationships varied from 3 months to 4 years. All women but one had experienced sex with a partner and coitus. All women practiced masturbation. Seven women (28%) had experienced sexual coercion at least once in their lives. All female participants except one had seen erotic films prior to participation.

Of the male participants, 21 had a heterosexual orientation; one male participant reported having a mainly homo-sexual orientation. Since this participant had been randomly assigned to the neutral film condition we decided not to remove his data. Eight men (36%) had a steady partner; duration of the relationship varied from 3 to 8 years. All men except one had experienced sex with a partner and coitus. All men practiced masturbation. None of the men reported having experienced sexual coercion, and all men but one had previously seen erotic films.

Prior to participation, all participants received written information including a description of the procedure and the genital measures. Informed consent, in which confidentially, anonymity, and the opportunity to withdraw from the experiment without penalty were assured, was obtained from all participants.

Design

We used a 2 (Stimulus) X 2 (Gender) design, with stimulus and gender as between-participants variables. Men and women were randomly assigned to the neutral or sexual stimulus condition, with the restriction of equal numbers assigned to each condition.

Materials and Response Measurement

Stimulus materials. The two film excerpts consisted of 15-minute videotapes with sound. The neutral stimulus was a film about zebras in Africa. The sexual stimulus was a heterosexual erotic videotape composed of three 5-minute scenes from films, each depicting petting, cunnilingus, and intercourse. The scenes originated from films directed and produced by Candida Royalle. Films produced by Candida Royalle are aimed at women and are more female-initiated and female-centered than conventional erotic movies. Earlier studies in our laboratory have shown that female-centered erotic film compared to male-centered erotic film evokes less shame, guilt, and aversion in women (Laan, Everaerd, van Bellen, & Hanewald, 1994) and that female-centered film elicits subjective sexual arousal and genital arousal in men (Janssen, Everaerd, van Lunsen, & Oerlemans, 1994). In addition, Janssen, Carpenter, and Graham (2003) reported that clips preferred by women elicit comparable sexual arousal ratings in male and female participants.

Physiological recordings. In women, genital response was measured using a vaginal photoplethysmograph assessing vaginal pulse amplitude (VPA), the AC component of the signal, and vaginal blood volume (VBV), the DC component. A signal conditioning amplifier separated the VPA from the VBV component using a 12 dB/octave, 0.7 Hz filter. Additional filtering for VPA was 24 dB/octave, 0.4 Hz high-pass. Since former research has shown that VPA is the superior measure in terms of both convergent and divergent validity (Laan, Everaerd, & Evers, 1995), we used only VPA data. The VPA signal was sampled at 100 Hz with a Keithley KPCI3107 A/D converter, running on a Windows 2000 PC system. Depth of the probe and orientation of the light-emitting diode were controlled by a device (a 9 x 2 cm plate) attached to the photoplethysmograph. Participants were instructed to insert the photoplethysmograph such that the plate touched their labia.

Genital response in men was measured by a mechanical penile strain gauge assessing penile circumference changes (Barlow, Becker, Leitenberg, & Agras, 1970; Janssen et al., 1994). Changes in electrical output caused by expansion of the strain gauge were recorded by a continuous DC signal. The strain gauge was positioned two thirds of the way down the shaft of the penis toward the base. The experimenter checked participants for proper placement of the device. Both the vaginal photoplethysmograph and the penile strain gauge were sterilized in a solution of Cidex-activated glutaraldehyde between uses (Geer, 1980).

We recorded genital responses continuously during baseline and stimulus presentation. A computer program developed at our department timed the administration of the stimulus, employed a trigger signal to initiate sampling of the physiological measure, and marked changeover between baseline and stimulus.

Subjective measurements. Prior to stimulus presentation and after the film excerpt, we collected data on subjective sexual arousal and emotional experience. Participants were asked to assess on a 7-point scale their (a) overall sexual arousal, (b) strongest feeling of sexual arousal, and (c) strongest genital sensations. The scale extremes were not sexually aroused at all and very strongly sexually aroused for items a and b, and no sensations in my genitals and orgasm for item c. The answer categories for men and women were slightly different: Genital sensations were described for men as erection and for women as vaginal lubrication.

We measured emotional experience by a questionnaire consisting of 21 emotions (including sexual emotions). Participants were asked to indicate on a 7-point scale (with not at all and very strong as extremes) to what extent they had experienced these emotions while watching the film excerpt. In an earlier study, factor analysis indicated that the 21 emotions could be divided into four factors: 7 emotions reflecting lust (Cronbach's [alpha] = .82), 4 emotions relating to anger (Cronbach's [alpha] = .85), 8 emotions relating to threat (Cronbach's [alpha] = .71), and 2 emotions reflecting tension (Cronbach's [alpha] = .79; Laan et al., 1995).

We measured action tendencies with the Action Tendency Questionnaire (ATQ). This questionnaire, which assesses the tendency to execute overt behavior without necessarily doing so (Frijda, Kuipers, & ter Schure, 1989), was administered after the stimulus presentation. Participants were asked to assess on 5-point Likert scales (with does not apply to me and strongly applies to me as extremes) the degree to which 25 statements were applicable to them. The statements varied from those indicating approach tendencies (e.g., "I wanted to approach, to make contact") to those indicating avoidance (e.g., "I wanted to have nothing to do with something or someone, to be bothered by it as little as possible, to stay away"). Formerly, factor analysis revealed that the questionnaire could be divided into four subscales: approach (Cronbach's [alpha] = .87), avoidance (Cronbach's [alpha] = .75), protection (Cronbach's [alpha] = .81), and attention (Cronbach's [alpha] = .76; Laan & Everaerd, 1995b).

Sexual behavior. We measured sexual behavior with a questionnaire assessing the frequency of sexual activity (alone or with a partner and with or without coitus) during the 24 hours after exposure to the films. We gave participants the questionnaire at the end of the experimental session, in a sealed envelope, with the request to open it after 24 hours. The questionnaire consisted of seven items. The first three items on sexual desire asked how often the participant (a) had feelings of sexual desire, (b) had sexual fantasies or daydreams, and (c) searched for sexual incentives. The next three items on sexual activity asked how often the participant (a) masturbated, (b) had sexual intercourse, and (c) had sexual contact without intercourse. Participants were asked to answer using a 4-point scale, with never and three times or more as extremes. The last item asked whether the participant had wanted to be less or more often sexually active during the 24 hours. Participants were asked to answer using a 5-point scale, with much less often and much more often as extremes.

Procedure

To help participants make an informed decision about whether to participate in this experiment, we sent them a letter in which all experimental procedures were explained in detail. They were told that they would be exposed to a film excerpt possibly containing erotic material, and they were informed about the genital measures and the sterilizing procedures. To prevent participant awareness of the experimental hypotheses with regard to their sexual behavior, the sexual behavior questionnaire was not mentioned in the letter.

Each participant was tested by a trained experimenter of the same sex. On arrival at the laboratory, the participant read and signed an informed consent form and completed a questionnaire about sexual experience and sexual problems. The experimenter then explained all the details of the experimental procedure. After the experimenter left the room, the participant inserted the vaginal probe or attached the penile strain gauge. After the participants signaled (using a one-way intercom system) that the transducers had been placed, they rated their feelings of sexual arousal and emotional experience by answering questions presented on the TV monitor. They answered questions by pressing buttons corresponding with the seven answer categories. The answers were stored in a Windows 2000 PC system.

After this, a 3-minute baseline period followed. During this resting period participants listened to quiet music; then, the film excerpt was presented. After watching the film excerpt, participants rated their feelings of sexual arousal and emotional experience and their action tendencies by answering questions presented on the TV monitor.

At the end of the experiment an exit interview was administered. Participants were asked about their reactions to the experimental procedure and the use of the genital device. After the interview, the participants were given the questionnaire about postexperimental sexual behavior. Since the nature of the questionnaire was not disclosed beforehand, the participants did not know they would be asked about their sexual activities following the experimental session until they opened the envelope to fill out the questionnaire.

Data Reduction, Scoring, and Analysis

We sampled VPA and penile circumference across baseline and the subsequent stimulus presentation period. Data were entered into a computer program developed at our laboratory that enabled off-line graphical inspection of the AC and DC channels. Artifacts in the VPA channel and strain gauge channels are caused by movements of the lower body or by voluntary or involuntary contractions of the pelvic muscles. Since artifacts show an extreme increase in vaginal pulse amplitude and in penile response, they can be detected by visual inspection. After artifact removal, we averaged the VPA and strain gauge data over 30 seconds, which resulted in 30 data points for both VPA and penile responses. Due to problems with the software, penile response could not be scored as millimeter circumference. We therefore decided to report the genital responses in percentage of baseline. The mean response during the baseline period (X) and the stimulus presentation period (Y) were calculated. We then calculated a percentage of baseline score (percentage of baseline = Y / X x 100) for film presentation.

For emotional experience, we averaged the items belonging to each of the described factors, thus creating a lust, anger, threat, and tension score. For action tendency ratings, we used only the approach and avoidance factors for further analysis. The approach items and the avoidance items were averaged, thus creating an approach and an avoidance score.

For frequency of sexual activity during the 24 hours after participation, we calculated a sexual desire and a sexual activity score. The first score was calculated by summing the scores on the first three items about sexual desire, and the second score was calculated by summing the scores on the items about sexual activity.

We tested between-subjects effects with multivariate and univariate analysis of variance procedures using a significance level of .05. Changes in vaginal vascular responses are not comparable to changes in penile circumference because they involve two different measures on different anatomical structures (Geer & Janssen, 2000). Therefore, we analyzed genital responses for men and women separately. Genital arousal was submitted to a two-stimulus (sex stimulus versus neutral stimulus) ANOVA. Subjective sexual arousal, emotional experience, and action tendencies were submitted to 2 (Stimulus) X 2 (Gender) MANOVAs.

Inspection of the postexperimental sexual behavior data revealed that regarding sexual activity, most participants scored 0 (never sexually active) or 1 (once sexually active). Because of the extreme non-normality of these scores, we used a statistical test for two Poisson distributions (Kalbfleisch & Sprott, 1973).

Results

Responses at exit interviews indicated that participants felt comfortable during the experiment despite the genital measurement. There were no differences between stimulus groups on the pretest for the questions measuring sexual arousal and emotional experience. Likewise, there were no differences between men and women on the pretest for sexual arousal and emotional experience. Therefore, we used raw posttest scores for the analysis. For both men and women, we found no difference between stimulus groups on the baseline measurement of genital response.

Subjective Sexual Arousal, Emotional Experience, and Action Tendencies

Due to technical problems, data on subjective sexual arousal, emotional experience, and action tendencies were missing for one male and one female subject. Mean sexual arousal, emotional experience, and action tendency ratings are shown in Table 1.

Subjective sexual arousal. The stimulus presentation had the intended effect on subjective sexual arousal ratings. Ratings of participants in the sexual stimulus group differed from ratings of participants in the neutral stimulus group, multivariate F(3, 39) = 7.52, p < .001. There was no main effect of gender and no interaction of stimulus and gender. Ratings were higher in the sexual stimulus group compared to the neutral stimulus group, and all univariate tests appeared to be significant: overall sexual arousal, F(1, 41) = 21.88, p < .001; strongest feeling of sexual arousal, F(1, 41) = 15.87, p < .001; and strongest genital sensations, F(1, 41) = 13.18, p < .001.

Emotional experience. We found only a stimulus main effect on emotional experience, multivariate F(4, 38) = 6.03, p < .005. Univariate tests revealed that participants in the sexual stimulus group reported more feelings of lust, F(1, 41) = 15.75, p < .001, and less tension than participants in the neutral stimulus group, F(1, 41) = 4.17, p < .05. There was, as expected, no effect of stimulus on feelings of anger or threat.

Action tendencies. For action tendencies, the main effect of stimulus approached significance, multivariate F(2, 40) = 2.83, p = .07. We found a main effect of gender, multivariate F(2, 40) = 3.84, p < .05, and no interaction effect of gender and stimulus. Univariate tests revealed that participants in the sexual stimulus group reported, as expected, a stronger approach tendency compared to participants in the neutral stimulus group, F(1, 41) = 5.03, p < .05. The univariate test for avoidance tendency was not significant. Women reported a stronger approach tendency compared to men, F(1, 41) = 6.86, p < .05, but there were no gender differences in avoidance ratings. The interaction effect of gender and stimulus on approach ratings approached significance, F(1, 41) = 3.06, p = .09. The female participants in the sexual stimulus group reported the strongest approach tendency. There was no interaction effect of gender and stimulus on avoidance ratings.

Genital Response

Due to technical problems, genital data from one male participant were missing. Because of problems with the newly developed vaginal photoplethysmographs, genital data of 10 women were missing. Consequently, we ran the analysis with 21 male participants and 15 female participants. The stimulus presentations had the intended effect on genital responses (Table 2). In men as well as in women, genital responses were higher in the sexual film group compared to the neutral film group: men F(1, 19) = 16.41, p < .005; women F(1, 13) = 9.89, p < .01.

Sexual Behavior

Five women and three men did not return the postexperimental sexual behavior questionnaire. Consequently, we executed the analysis with 20 participants (10 men and 10 women) in the sexual stimulus group and 20 participants (9 men and 11 women) in the neutral stimulus group.

There was no effect of stimulus, gender, or stimulus by gender on the postexperimental sexual desire score (Figure la). However, the mean postexperimental sexual activity sum score of the sexual stimulus group was .95, while the mean score of the neutral film group was .40 (Figure 1b). The postexperimental activity score was significantly higher in the sexual film group, z = 1.99, p < 0.05. There was no significant difference between men's and women's postexperimental sexual activity scores.

[FIGURE 1 OMITTED]

The amount of sexual activity may have been influenced by the actual or perceived opportunity for sexual expression. Therefore, we inspected the data for a difference between conditions or genders in relationship status and the wish to have been more or less sexually active. We used chi-square tests to check equality of the frequency distributions. Only the data of the participants who completed the sexual behavior questionnaire were selected for these analyses.

In the sexual stimulus condition, 11 participants (55%) had a steady partner; for the neutral stimulus condition this percentage was exactly the same. Among the men, 47% had a steady partner; among the women, the percentage was 61%. The chi-square tests revealed no significant difference between men and women. Regarding the wish to have been less or more sexually active during the 24 hours following participation, there was no significant difference between conditions. In the sexual film condition, 63% of the participants reported that their amount of sexual activity was exactly right, 26% reported that they had wished to be somewhat more active sexually, and 11% reported that they had wished to be much more active sexually. For the neutral film condition these percentages were respectively 37%, 32%, and 32%. Similarly, there was no significant difference between men and women in the wish to be less or more sexually active.

Discussion

As expected, the sexual film and not the neutral film evoked genital responses, feelings of sexual arousal, and feelings of lust. In addition, neither the sexual film nor the neutral film evoked feelings of anger or threat. Contrary to our expectations, ratings of tension were higher in response to the neutral film. However, tension ratings were generally low. We may conclude that the films elicited a sexual versus a neutral though slightly tensed state.

We reasoned that emotions are best conceived of as action tendencies and that sexual excitement, in this respect, does not deviate from other emotions. Hence, we expected that a sexual stimulus would generate responses that prepare the organism for sexual approach behavior. Indeed, the sexual film enhanced approach tendencies relative to the neutral film. As expected, the enhanced approach tendency from the sexual stimulus resulted in a higher frequency of postexperimental sexual activity in the sexual film condition. There were no differences between conditions in the distributions of variables that indicated the actual or perceived opportunity for sexual expression. We may conclude that the difference in sexual activity between conditions can be attributed to exposure to the sexual stimulus. It is remarkable that the elicited sexual action tendency was not reflected in higher postexperimental sexual desire ratings. Participants in the sexual stimulus condition were more active sexually after film exposure than participants in the neutral condition, but they did not report higher frequencies of feelings of sexual desire, sexual fantasies, or searching for sexual incentives. Thus, the elicited tendency for sexual action was reflected at the level of postexperimental behavioral outcome, but not at the level of subjectively experienced feelings of sexual desire.

Contrary to our expectations, the male participants did not report stronger feelings of sexual arousal than the female participants. There were also no gender differences in ratings of emotional experience in response to the erotic stimulus, and the female participants reported even higher approach tendencies compared to the male participants. Also, there was no gender difference in postexperimental sexual desire and activity ratings. Although we should note that we cannot rule out the possible influence of gender bias in subjective report of sexual behavior (Geer & Janssen, 2000), we can conclude that the data of the present study indicate that exposure to the sexual stimulus elicited a tendency for sexual behavior in both men and women, and to the same degree in both genders.

EXPERIMENT 2

As noted before, exposure to a sexual stimulus may, by modulating the internal state, enhance responses to subsequent sexual stimuli. Through activation of reward circuitry in the brain, the attractiveness of sexual stimuli may increase. In this experiment, we studied the effect of a sexually excited state on preference for and responsiveness to sexual stimuli.

Emotion research has revealed that the perceptual preference for specific classes of stimuli is related to the current priority of concerns, and that a person's emotional state influences the perceptual process. For example, research shows that clinical anxiety is associated with an attentional bias for fear-arousing stimuli (e.g., Mogg, Mathews, & Eysenck, 1992). Furthermore, selective attention and anxiety are reciprocally related, although it is unclear if the perceptual changes are the cause or the result of the emotional state (for review, see Williams, Mathews, & MacLeod, 1996). To elucidate the effect of emotional state on attention for particular stimuli, it is necessary to study attention following experimentally induced emotional states.

In the same way that an anxious state may affect the perception of fear stimuli, a sexually excited state may influence the perception of sexual stimuli. Stephan, Berscheid, and Walster (1971) found that sexually aroused participants perceived attractive members of the opposite sex as even more attractive. It seems likely that people in a sexually excited state will try to continue and increase their sexual excitement by searching for further sexual stimulation. Models of sexual excitement assume that in sexually functional persons, sexual excitement results in an attentional focus on erotic cues, which leads to increased sexual arousal, which results in a further increase of attention for erotic cues (Barlow, 1986). This positive feedback loop is supposed to enhance sexual responding and sexual approach behavior. However, in experiments based on Barlow's model no direct measures were taken to assess the hypothetical changed perception (van den Hout & Barlow, 2000). In the present study, we performed a test of the prediction that a sexually excited state is associated with increased interest for sexual stimuli by assessing preference for sexual stimuli following experimentally induced sexual arousal.

Perceptual preference for particular stimuli may be reflected in the amount of time a subject deliberately views those stimuli. Viewing time has been used as a behavioral measure for interest in experimental studies on emotional responses (e.g., Drobes et al., 2001; Lang, Greenwald, Bradley, & Hamm, 1993). Lang et al. (1993) found interest ratings and viewing time to be associated with emotional arousal. Viewing time of sexual stimuli has been used as an indicator of motivational approach in different settings (e.g., Abel, Huffman, Warberg, & Holland, 1998; Martin, 1964). Several studies showed that viewing time (called visual reaction time) is longer for pictures congruent with the homo- or heterosexual orientation of the participant (e.g., Abel et al., 1998; Wright & Adams, 1994, 1999) and is an accurate predictor of sexual interest in sex offenders (Abel et al., 1998; Abel, Jordan, Hand, Holland, & Phipps, 2001; Letourneau, 2002). Using visual reaction times as opposed to directly asking participants about their preferences offers the opportunity to measure interest more implicitly. In the present study, we did not use visual reaction time as a measure for preference for a particular category of sexual stimuli, but as a behavioral measure for preference for sexual stimuli relative to neutral stimuli. We expected that sexual excitement would increase preference for sexual stimuli, which would be reflected in longer viewing times of sexual pictures.

In the present experiment we measured somatic motor preparation in response to the sexual stimuli in addition to genital responses. It has been established that the generation of sexual approach behavior will be accompanied by activity in the autonomic motor and the somatic motor system. In an earlier study we used Achilles tendon (T) reflex modulation as a measure for somatic motor preparation in response to sexual appetitive stimuli (Both, Everaerd, & Laan, 2003). Subjective approach tendencies and T reflexes were facilitated by exposure to sexual film. In the present study, we used T reflex modulation to study the effect of activation of the sexual reward system on subsequent responsiveness of this system. Since the pictures in the perceptual preference task were viewed briefly and somatomotor responses are much faster than autonomic changes, measurement of T reflexes was most appropriate to study changes in activity in the motivational system. We expected the sexual film and the sexual pictures to facilitate T reflexes more than the neutral film and the neutral pictures. Also, we expected T reflexes in response to the sexual pictures to increase more strongly in the sexual film condition than in the neutral film condition.

As in Experiment 1, participants were exposed to a neutral or a sexual film. Their physiological and subjective sexual responses to the film were measured, as were their subjective action tendencies and their sexual desire and sexual activity during the 24 hours after the film exposure. Different from Experiment 1, exposure to the neutral or sexual film was followed by a perceptual preference task. Half of the picture set used in this task had neutral content and the other half had sexual content. Participants were asked to rate how sexually arousing they judged each picture. We measured the time the participant took to rate each picture and used it as an index for perceptual preference. We expected the sexual arousal induction to result in longer rating times for the sexual pictures, while we expected rating times for the neutral pictures to be unaffected by the sexual arousal induction.

Again, both males and females participated to allow for comparisons by gender. In addition, we evaluated the relationship between physiological, subjective, and behavioral responses in men and women to provide insight into gender differences in the concordance of the various emotional response systems. Generally, in women the relationship between genital responses and subjective sexual arousal is weak or absent (e.g., Laan & Everaerd, 1995a; Palace & Gorzalka, 1990), while in men genital responses are generally highly correlated with subjective ratings (e.g., Janssen et al., 1994; Koukounas & McCabe, 2001). Only a few psychophysiological studies on sexual responses, however, included both sexes (e.g., Heiman, 1977; Steinman, Wincze, Sakheim, Barlow, & Mavissakalian, 1981; Wincze, Venditti, Barlow, & Mavissakalian, 1980). Although comparing male and female sexual responses is complicated for several reasons (Geer & Janssen, 2000), studies in which both sexes participate offer the best opportunity to investigate gender differences in sexual response patterns. For correlational analyses we pooled the data of Experiments 1 and 2 and studied the relationship between genital response, subjective sexual arousal, action tendencies, and sexual behavior in men and women. We expected a stronger relationship between genital response and subjective response in men compared to women. And, since in women genital response seems to determine the experience of a sexual situation only to a small extent (Laan & Everaerd, 1995a), we expected to find in women a relatively weak relationship between genital responding and postexperimental sexual behavior but a stronger relationship between subjective sexual arousal and postexperimental sexual behavior. For men, the experience of a sexual situation may be strongly determined by their genital response. Therefore, we expected men's postexperimental sexual behavior to be related to their genital as well as to their subjective sexual responses, and to both these variables to the same degree.

Method

Participants

Fifty-eight people (28 women and 30 men) participated. Most participants (78%) were students. All participants received course credit or were paid for their participation. Mean age of the women was 24.5 (range = 19-47 years, SD = 7.2 years) and mean age of the men was 27 (range = 19-46 years, SD = 7.1 years). There was no significant difference in age between men and women, t(56) = 1.33, p > .1, or between stimulus conditions, t(56) = 1.07, p >. 1.

Twenty-three female participants (82%) had a heterosexual orientation; 5 women (18%) considered themselves bisexual. Eighteen women (64%) had a steady partner, and duration of the relationships varied from 1 month to 7 years. All had experienced sex with a partner, had experienced coitus, and practiced masturbation. Four (14%) women reported that they had experienced sexual coercion at least once in their lives. Five women (18%) had not previously seen erotic films, and 4 women had no experience with erotic pictures.

All male participants had a heterosexual orientation. Fifteen men (50%) had a steady partner, and duration of the relationships varied from 3 months to 22 years. All men except one had experienced sex with a partner and had experienced coitus. All men except one practiced masturbation. None of the male participants reported sexual coercion experiences, and all male participants had previously seen erotic films and erotic pictures. The procedures regarding information and informed consent were similar to those in Experiment 1.

Design

We used a 2 (Film Content) X 2 (Gender) X 2 (Picture) design, with film content and gender as between-subjects variables and picture content as the within-subjects variable. Again, men and women were randomly assigned to the neutral or sexual film condition, with the restriction of equal numbers assigned to each condition. In both conditions the film was followed by the perceptual preference task, which included 20 sexual and 20 neutral pictures. The pictures were presented in random order.

Materials and Response Measurement

Stimulus materials. Similar to Experiment 1, the two film excerpts consisted of 15-minute videotapes with sound. The neutral stimulus was a documentary about Tibet. In the present experiment for the heterosexual erotic videotape two scenes of more recent Candida Royalle films were used. Each scene depicted petting, cunnilingus, and intercourse. A study in our laboratory, in which we compared responses to these female-centered film scenes to responses to male-centered film scenes, showed that both men and women reported stronger feelings of sensuality and positive affect in response to the female centered film scenes (Laan, 2004).

The picture set consisted of sexual and neutral pictures. Pictures with sexual content portrayed heterosexual couples engaged in oral or genital sexual activity. The neutral set depicted pictures of plants and bushes. We selected pictures from a set used previously in sexual response studies in men and women (Janssen, Everaerd, Spiering, & Janssen, 2000; Spiering, Everaerd, & Janssen, 2003).

Physiological recordings. Measurement of genital responses was identical to Experiment 1. We carried out the procedure for T reflex measurement in accordance with standard methods for evoking T reflexes (Both et al., 2003). T reflexes were elicited by a hammertap at the heel tendon. The hammertap at the tendon results in a reflexive electromyographic (EMG) response in the soleus muscle of the lower leg. When circumstances are held equal, taps of a constant force lead to reflex amplitudes of constant size. Changes in reflex amplitude are a peripheral manifestation of supraspinal processes influencing spinal excitability (Brunia & van Boxtel, 2000). To measure reflex activity (EMG), we placed surface electrodes (Ag/AgCl electrodes, 2 [cm.sup.2] contact area, 3 cm apart) on participants' soleus muscle, along the longitudinal axis of the calf, with the proximal electrode of the pair 2 cm distal to the insertion of the gastrocnemius muscle on the Achilles tendon. Reflexes were elicited at a constant rate of one every 7 seconds during the baseline and film presentation, which resulted in 25 reflexes during the 3-minute baseline and 128 reflexes during the film presentation period. During the picture viewing task, reflexes were elicited 1.5 seconds after picture onset. To allow for a constant rate of reflex elicitation during the picture-rating task, there was a constant timeframe of 5 seconds between the pictures. Consequently, T reflexes were elicited once every 5 seconds.

Participants were relaxed and passive throughout the tests, and they were asked to refrain from moving during the recordings, except for pushing the subjective rating button. The monitor was located in front of the subject.

Subjective measurements and sexual behavior. Measurements of subjective sexual arousal, emotional experience, subjective action tendencies, and sexual behavior in response to the film excerpts were identical to those used in Experiment 1. In the present experiment, to prevent drop-out we asked participants to return the day after the laboratory visit for administration of the questionnaire about sexual behavior. At the end of the laboratory visit the experimenter made an appointment for at least 24 hours after participation. Again, the nature of the questionnaire was not disclosed beforehand.

The picture-rating task. A Macintosh PowerPC monitor was used for picture presentation and data collection. For the registration of responses, we placed a button box in front of the participant. Images with a size of 10 cm x 10 cm were presented on a black background. The sequence of the 40 pictures was randomized afresh for each participant.

Participants were instructed to rate the arousability of the pictures by answering the question "To what degree do you find this picture sexually arousing?" The question could be answered, using the button box, on a 7-point scale that varied from not at all to extremely. The picture presentation was paced by the participants' responses. We measured rating time from onset of a picture to the pressing of a button. As noted before, for the benefit of the reflex measurement we kept a constant picture interval of 5 seconds. When a picture presentation was ended within this interval, a black background remained until the next picture was presented.

Procedure

The procedure was identical to Experiment 1, except for the picture-rating task and the measurement of T reflexes during film and picture presentation. A 3-minute return-to-baseline period followed film presentation to allow for the determination of the T reflex amplitudes in response to the pictures relative to baseline amplitudes. To facilitate return to baseline, we asked participants to count aloud backwards from 100 during the first minute of this period. The return-to-baseline period was followed by a 2-minute baseline period (Baseline 2), during which participants listened to quiet music. Then the instructions for the picture task were shown on the monitor and the picture task started.

Data Reduction, Scoring, and Analysis

Reduction and scoring of VPA and penile circumference data were similar to Experiment 1. The same holds for the reduction and scoring of emotional experience, subjective action tendencies, and postexperimental sexual behavior.

We sampled EMG across baselines and subsequent stimulus presentation periods. We calculated the mean T reflex amplitude elicited during Baseline 1 (X) and film presentation period (Y). We then calculated a percentage of baseline score (percentage of baseline = Y / X x 100) for film presentation. For the T reflexes elicited during the picture-rating task, we calculated mean reflex amplitude during Baseline 2, mean T reflex amplitude during sexual picture presentation, and mean reflex amplitude during neutral picture presentation. Then we calculated a percentage of baseline score in relation to Baseline 2 for sexual picture presentation and for neutral picture presentation. In addition, we calculated mean rating time for the picture-viewing task and mean sexual arousability rating for the neutral and sexual pictures.

We tested between-subject effects with multivariate and univariate analysis of variance procedures. Within-subjects effects were tested with repeated-measures univariate analysis of variance procedures (general linear model in SPSS). Statistical analyses of genital responses and subjective responses were similar to those in Experiment 1. We submitted T reflex magnitude during film presentation to a 2 X 2 ANOVA with stimulus and gender as between-subjects variables. Again, inspection of the postexperimental sexual activity data revealed extreme non-normality of the scores. Therefore, we used a statistical test for two Poisson distributions.

Regarding the picture-rating task, we submitted T reflex magnitude, rating times, and subjective ratings to 2 X 2 X 2 ANOVAs with stimulus and gender as between-subjects variables and picture as the within-subjects variable.

After pooling the data from Experiments 1 and 2, we calculated Pearson product-moment correlations between genital, subjective, and behavioral responses for the sex film group only. Correlations were calculated for men and women separately. Given the large number of variables that could be used in the correlational analysis, and given the degree of error rate that would be introduced if all variables were included, we decided to restrict the correlations to those central to the aims of the study and to set the level of significance at [alpha] = .01.

Results

Responses at exit interviews indicated that participants had felt comfortable during the experiment despite the genital and T reflex measurements. There were no differences between stimulus groups on the pretest for the questions measuring sexual arousal and emotional experience. Therefore, we used raw posttest scores for the multivariate analysis. For both men and women, there was also no difference between stimulus groups on the baseline measurement of genital response. Likewise, we found no difference between groups or between men and women on the baseline measurement of T reflexes.

There was no difference between men and women on the pretest for emotional experience. However, subjective sexual arousal ratings during the pretest were higher in women compared to men: for general feeling of sexual arousal, F(3, 54) = 19.61, p < .001; for strongest genital arousal, F(3, 54) = 23.13, p < .001. Therefore, for sexual arousal ratings we executed the MANOVA with mean pretest score as covariate.

Subjective Sexual Arousal, Emotional Experience, and Subjective Action Tendencies

Mean sexual arousal, emotional experience, and action tendency ratings are shown in Table 3.

Subjective sexual arousal. The main effect of stimulus was significant for sexual arousal ratings, multivariate F(3, 52) = 36.36, p < .001. There was no gender effect, but we did find a significant interaction effect of stimulus and gender, multivariate F(3, 52) = 6.45, p < .005. Univariate tests revealed that participants in the sexual stimulus group rated themselves as more sexually aroused than participants in the neutral stimulus group: overall sexual arousal, F(1, 54) = 73.39, p < .001; strongest feeling of sexual arousal, F(1, 54) = 75.77, p < .001; strongest genital sensations, F(1, 54) = 101.89, p < .001. We found an interaction effect of stimulus and gender for strongest sexual arousal, F(1, 54) = 14.34, p < .001, and for strongest genital sensations, F(1, 54) = 12.98, p = .001. Ratings were highest in the male participants in the sexual stimulus condition. A MANOVA with pretest ratings for sexual arousal as covariate revealed the same pattern of results, with virtually no differences in p values.

Emotional experience. The main effect of stimulus was significant for emotional experience ratings, multivariate F(4, 51) = 6.55, p < .001. There was no effect of gender on emotional experience, and no interaction of stimulus and gender. As expected, participants in the sexual stimulus group reported more feelings of lust than participants in the neutral stimulus group, F(1, 54) = 26.31, p < .001. There was no effect of stimulus on feelings of anger, tension, or threat.

Action tendencies. For action tendencies, the main effect of stimulus was significant, multivariate F(2, 53) = 9.66, p < .001. There was no main effect of gender and no interaction effect of gender and stimulus. Univariate tests revealed that participants in the sexual stimulus group reported a stronger approach tendency compared to participants in the neutral stimulus group, F(1, 54) = 17.84, p < .001. The univariate test for avoidance tendency was not significant.

Genital Response and T Reflex Magnitude in Response to the Film

Genital response. Due to technical problems, genital data from one male participant were missing. We found a stimulus effect on penile circumference change, F(1, 27) = 19.00, p < .001. The men in the sexual stimulus group showed a larger increase in genital response compared to the men in the neutral film group. Similarly, in women genital response was larger in the sexual film group than in the neutral film group, F(1, 26) = 25.63, p < .001 (see Table 4).

T reflexes. As expected, we found an effect of stimulus on T reflex magnitude, F(1, 54) = 12.71, p < .005. T reflex magnitude was higher in the sexual stimulus group than in the neutral stimulus group. Contrary to expectations, there was no effect of gender and no interaction of gender and stimulus.

Responses During the Picture-Rating Task

Mean rating times, arousability ratings, and T reflex magnitudes in response to the pictures are shown in Figure 2.

[FIGURE 2 OMITTED]

Picture rating times. Due to technical problems, rating times from five participants in the neutral film condition were missing. Inspection of the data revealed that participants had relatively long rating times for the first picture. We found a difference between mean rating time for the first picture and the subsequent pictures, F(1, 8) = 9.32, p < .05. Therefore, we decided to remove the rating time for the first picture.

We performed a 2 X 2 X 2 repeated measures ANOVA with stimulus condition and gender as between-subjects factors and picture (sexual vs. neutral) as the within-subjects factor. There was a main effect of picture content, F(1, 49) = 124,52, p < .001. Participants had longer rating times for the sexual pictures compared to the neutral pictures. There was also an effect of stimulus condition, F(1, 49) = 6.07, p < .05, such that participants in the sexual stimulus condition had shorter rating times than participants in the neutral stimulus condition. The effect of gender approached significance, F(1, 49) = 3.47, p = .07; women had longer rating times compared to men. We found an interaction effect of stimulus condition and gender, F(1, 49) = 4.99, p < .05; women in the neutral stimulus condition had relatively long rating times. We found no other effects.

Arousability ratings. We found only a main effect of picture, F(1, 49) = 84.39, p < .001. Participants rated the sexual pictures as more sexually arousing compared to the neutral pictures.

T reflexes. Due to technical problems, T reflex data were missing for one participant in the sexual stimulus condition and for five participants in the neutral stimulus condition. To investigate possible differences in T reflex baselines, which may impact stimuli effects, we performed a 2 X 2 X 2 repeated measures ANOVA with stimulus and gender as between-subjects variables and time as the within-subjects variable. This analysis revealed an interaction effect of time and stimulus, F(1, 48) = 5.37, p < .05. In the sexual stimulus condition, reflexes during Baseline 2 were higher than during Baseline l, indicating that participants' T reflex activity did not return to baseline levels during the return-to-baseline period preceding the picture-rating task. Therefore, we also ran the statistical analysis with mean T reflex during Baseline 2 as covariate.

Reflex magnitude was higher during sexual picture viewing compared to neutral picture viewing, F(1, 48) = 19.98, p < .001. There was also a main effect of stimulus condition, F(1, 48)= 4.12, p < .05: T reflex magnitude during picture viewing was higher in the neutral stimulus condition. There was no main effect of gender and no interaction between stimulus condition and gender. Also, interactions between picture and stimulus condition and between picture and gender were absent. The interaction between picture, stimulus condition, and gender approached significance, F(1, 48) = 3.84, p = .06. Men who had seen the neutral film prior to the picture-rating task had a relatively high T reflex magnitude in response to the sexual pictures.

The repeated measures analysis with mean T reflex amplitude during Baseline 2 as covariate revealed largely the same pattern of results. Reflex magnitude was higher during sexual picture viewing compared to neutral picture viewing, F(1, 47) = 17.01, p < .001, and the interaction between picture, stimulus condition, and gender was significant, F(1,47) = 4.84, p < .05.

Correlations Between Rating Times and Arousability Ratings of the Sexual Pictures

We expected rating times to reflect sexual interest. Therefore, we expected that the rating times of the sexual pictures and the arousability ratings would be related. The correlation between rating time and arousability rating of the sexual pictures was .23 (p < .1). Although this correlation is moderate to low, it does indicate that the time participants deliberately looked at the sexual pictures was related to how sexually arousing participants thought the pictures were. Moreover, when correlations for both stimulus groups were calculated separately, the correlation between rating time and arousability rating of the sexual pictures in the sexual film group was .41 (p < .05), and in the neutral film group .07 (ns). Thus, only in the sexual arousal condition was the time participants looked at the sexual pictures related to how sexually arousing they thought the pictures were.

Sexual Behavior

One male participant did not show up to complete the postexperimental sexual behavior questionnaire. Consequently, we ran the analysis with 30 participants (15 men and 15 women) in the sex film group and 27 participants (14 men and 13 women) in the neutral film group. Postexperimental sexual desire and activity ratings are shown in Figure 3.

[FIGURE 3 OMITTED]

Regarding the postexperimental sexual desire score, the univariate analysis revealed no effect of stimulus, F(1, 53) = .86, p = .36, and a significant effect of gender, F(1, 53) = 4.92, p < .05. The male participants had higher postexperimental sexual desire scores compared to the female participants. The male participants in the sexual stimulus group scored highest on sexual desire; however, the interaction of stimulus and gender did not reach significance, F(1, 53) = 2.22, p = .14.

For postexperimental sexual activity scores there was an effect of stimulus, z = 1.97, p < .05. Participants in the sexual stimulus condition reported more sexual activity after the experiment (M = 1.25) than did participants in the neutral stimulus condition (M = 0.75). There was no significant difference between men and women in postexperimental sexual activity.

In the sexual stimulus condition, 60% of the participants had a steady partner. In the neutral stimulus condition this percentage was 56%. Of the men, 54% had a steady partner; of the women, 61% had a steady partner. The chi-square tests revealed no significant difference between conditions or between men and women.

Regarding the wish to have been less or more sexually active during the 24 hours following participation, we found no significant difference between conditions. In the sexual film condition, 57% of the participants reported that their amount of sexual activity was just right, 30% reported that they had wished to be somewhat more active sexually, and 13% reported that they had wished to be much more active sexually. For the neutral film condition, 7% reported that they had wanted to be much less sexually active, 4% reported that they had wished to be somewhat less active sexually, for 41% it was just fight, 26% reported they had wanted to be somewhat more sexually active, and 22% had wanted to be much more active sexually.

For men and women there was a marginally significant difference in the distribution of the reported wish to be less or more sexually active, [chi square] (4) = 8.98, p = .06. For the men, 7% reported that they had wished to be much less sexually active, 3% reported they had wished to be somewhat less active sexually, for 45% it was just right, 17% reported they had wished to be somewhat more sexually active, and 28% wanted to be much more active sexually. Among the women, 54% of the participants reported that their amount of sexual activity was just right, 39% reported that they had wished to be somewhat more active sexually, and 7% reported that they had wished to be much more active sexually.

Correlations Between Genital Response, Subjective Responses, and Postexperimental Sexual Desire and Activity

Correlations between genital, subjective, and behavioral responses were calculated for the sexual stimulus group only, and for men and women separately (see Table 5).

In line with our expectations, the correlations between genital response, subjective sexual arousal ratings, and feelings of lust were low (ranging from -.01 to .15) in women, while these correlations were higher in men (ranging from .30 to .42). Although the correlations between genital and subjective responses in men were moderate, they did not reach significance.

In men and women there were, as expected, substantial correlations between subjective sexual arousal and approach ratings. However, only the correlation between strongest genital sensations and approach was significant. In women there was, as expected, a low correlation between genital response and postexperimental sexual activity, and higher correlations between lust, approach, and sexual arousal ratings and postexperimental sexual activity. Postexperimental sexual desire was also related to feelings of lust and approach ratings. Contrary to our expectations, in men we found negative correlations between subjective sexual arousal ratings and postexperimental sexual activity and between genital response and postexperimental sexual activity. These negative correlations were not very high and were nonsignificant. In contrast, postexperimental sexual desire in men was positively, although not highly, related to feelings of lust, approach tendency, and subjective sexual arousal ratings.

In both men and women there was a substantial correlation between postexperimental sexual desire rating and postexperimental sexual activity rating (respectively .57 and .67), although only in women did this correlation reach significance.

GENERAL DISCUSSION

In agreement with motivation and emotion theory, activation of the sexual system through exposure to a sexual stimulus generates a tendency for sexual action. In both experiments the participants exposed to the sexual stimulus showed genital arousal, feelings of sexual arousal, subjective approach tendencies, and higher sexual activity than the participants exposed to the neutral stimulus. The results regarding sexual behavior corroborate the findings of Schmidt et al. (1975) and Fisher and Byrne (1978) and support our view of sexual excitement as an emotional state that manifests itself in genital response, emotional experience, and behavioral action. However, the data obtained in Experiment 2 showed that, contrary to our expectations, experimentally induced sexual excitement did not enhance attention or responsiveness to sexual stimuli. In contrast, men's responsiveness to sexual stimuli, measured by means of T reflex modulation, was stronger in the neutral than in the sexual arousal condition.

The results regarding subjective sexual arousal, emotional experience, and physiological responses show that the films evoked the emotional states as intended. The sexual films in contrast to the neutral films induced genital response, subjective sexual arousal, and feelings of lust. As expected, the sexual film enhanced subjective approach tendencies, while avoidance tendencies were unaffected. Taken together we may conclude that, in both experiments, we succeeded in inducing a neutral versus a sexually excited state.

The T reflex results corroborate the enhancing effect of emotional arousal on T reflex amplitude reported by Bonnet, Bradley, Lang, and Requin (1995) and the enhancing effect of sexual arousal on T reflex strength reported by our research group (Both et al., 2003). A sexually appetitive stimulus seems to switch on a disposition to act that is reflected in increased subjective approach tendencies and increased T reflex magnitude. Moreover, our data show that the activated disposition to act resulted in actual sexual activity. Since we successfully replicated the results of Experiment 1 in Experiment 2, we may conclude that our findings regarding the effect of laboratory-induced sexual arousal on sexual activity seem to be fairly robust. Thus, exposure to a sexual stimulus seems to elicit an approach tendency that is reflected in actual sexual behavior. Another explanation for our findings may be that participants in the sexual film condition perceived the experiment as giving permission to act sexually. However, it should be noted that in Experiment 2, both conditions could be perceived as giving permission to act sexually, since in both conditions participants were exposed to sexual pictures. Nevertheless, in Experiment 2 participants in the sexual film condition were more sexually active than participants in the neutral condition. The issue of the experimental manipulation giving permission relates to the difficulty of distinguishing activating effects of emotional stimuli from disinhibiting effects. In the present study, however, it was not our purpose to make this distinction. Conspicuously, postexperimental sexual desire was not higher for participants in the sexual arousal condition. In both experiments participants exposed to the sexual film did not show higher frequency of feelings of sexual desire, sexual fantasies, or the tendency to search for sexual stimuli than participants exposed to the neutral film. This suggests that actual sexual behavior may be elicited without a person necessarily experiencing a change in the urge for this behavior or in the tendency to seek sexual stimulation. The observed disconnection of sexual desire and sexual activity is in accordance with observations in emotion research that physiological, experiential, and behavioral components of emotions are loosely integrated (Lang, 1993), and also with observations in research on pathological forms of motivation, like drug addiction, that subjective feelings of craving and actual drug intake may be relatively independent (Verheul, van den Brink, & Geerlings, 1999). Possibly, activation of the motivational system evoked by an appetitive stimulus continues for some time after termination of the stimulation. While the activity may not result in feelings of desire because attention is directed to other tasks or because the activity is not strong enough to pass the perceptual threshold, it may, via enhancement of processing of subsequent appetitive stimuli, facilitate motivated behavior.

However, the high correlation we found between postexperimental sexual desire ratings and postexperimental activity ratings shows that in most cases sexual activity coincided with sexual desire. Possibly, the items about sexual desire, sexual fantasy, and searching for sexual incentives in our postexperimental sexual activity questionnaire may have been less sensitive than the items regarding frequency of sexual activity, resulting in less chance to detect the effect of the experimental manipulation on appetitive behavior as opposed to an effect on consummative behavior. The differential findings for postexperimental sexual desire and sexual activity, however, underline the importance of the inclusion of items about appetitive behavior as well as items about consummatory behavior in questionnaires measuring (problems with) sexual motivation (Heiman, 2001).

Contrary to our expectations, interest in sexual stimuli measured by rating times in the picture-rating task was not enhanced by the experimental manipulation of sexual excitement. The experimental manipulation of sexual arousal did influence rating times in general; participants in the sexual stimulus condition had shorter rating times for sexual as well as neutral pictures than did participants in the neutral condition. This points to a general effect of emotional arousal on the picture-rating task. Emotional arousal may have resulted in a higher activation level and, therefore, faster responses instead of slower. The arousability rating of the sexual pictures was not influenced by the sexual arousal induction. Participants in the sexual film condition did not rate the sexual pictures as more sexually arousing. Thus, our data do not corroborate the results of Stephan et al. (1971), who found that sexual arousal increased the attractiveness of sexual stimuli.

As expected, and in concordance with findings from other studies on emotional responses that included viewing times, the participants had longer rating times for the (sexually) affective pictures relative to the neutral pictures. Since in the present study the participants were instructed to rate the pictures on the dimension of sexual arousability, this is not surprising. However, there was a relationship between rating times for the sexual pictures and arousability ratings. This is in agreement with Lang et al.'s (1993) results, which showed that viewing times of emotional pictures were related to emotional arousal ratings. More specifically, the correlation between rating times and arousability ratings showed that participants had the tendency to stay in contact longer with stimuli that were sexually appealing to them. This supports the validity of the picture-rating task as a measure for sexual interest and the tendency to maintain sexual stimulation. Interestingly, the relationship between rating times and arousability ratings was only present in the sexual film group. This suggests that, in agreement with our expectations, the induced sexually excited state coincided with the tendency to attend longer to sexually arousing stimuli. However, as noted before, there was an unexpected enhancing effect of sexual arousal on picture rating times in general. Unless we have more insight into this effect, the question of rating time as an appropriate index for sexual interest remains.

T reflexes in response to the pictures were, as expected, higher for the sexual pictures than for the neutral pictures. Since we were able to find increased T reflexes in response to the sexual pictures even though the arousability ratings indicated that these pictures elicited only low levels of sexual arousal, we may conclude that T reflex modulation seems to be a sensitive measure for changes in emotional arousal. However, contrary to our expectations, the sexual arousal manipulation did not enhance T reflex magnitude in response to the sexual pictures. In contrast, the male participants in the neutral stimulus condition showed relatively high T reflexes in response to the sexual pictures, and the female participants in this condition showed relatively low reflex amplitudes in response to the sexual pictures. This indicates that the experimental manipulation did modulate responsiveness to sexual stimuli, but not in the direction expected and differently for men and women. We should, however, be cautious regarding this conclusion since the baseline levels preceding the picture task were different for the two groups. However, the fact that an analysis including baseline levels as covariates resulted in an even stronger interaction effect of stimulus condition, picture, and gender indicates that the differential responses cannot be attributed to the difference in baseline levels.

The increased T reflex magnitude of the male participants in the neutral film condition may point to an enhanced drive state. Possibly, the experimental situation in the neutral film condition could be understood as the withholding of sexual stimulation. Participants were recruited for a study on sexual responses, but those in the neutral film group, probably in opposition to their expectations, were exposed to a neutral film and not to a sexual film. The increased responsiveness of men in the neutral film condition may be the result of an increase in the palatability of sexual incentives through the forced layoff period. Incentive motivation models state that the hedonic quality of particular incentives is decreased by constant use and enhanced by abstinence from that particular incentive (Singer & Toates, 1987). The differential finding for men and women may indicate a gender difference in the effect of withholding sexual stimulation.

The analysis of gender differences in sexual response patterns yielded mixed results. In Experiment 1 we found no differences in sexual arousal ratings or in emotional experience ratings in response to the erotic stimulus, and the female participants reported even higher approach tendencies. Also, we found no gender differences in reported postexperimental sexual desire and activity. In Experiment 2, however, the men reported stronger feelings of sexual arousal and stronger genital sensations in response to the sexual film compared to the women. In an earlier study, we also found slightly higher ratings of sexual arousal and genital sensations in men (Both et al., 2003). However, we should note that 18% of the women in Experiment 2 reported a bisexual orientation. The heterosexual film excerpt may have been less sexually arousing for these women, which might have influenced the mean rating of the female group. In addition, as noted before, we should be cautious in comparing men and women on subjective ratings since we have to consider possible gender bias in subjective report (Geer & Janssen, 2000).

T reflex magnitude in response to the sexual film did not differ between men and women. This is in concordance with our earlier study that included T reflex measurement. Also, we found no gender difference in rating time for the sexual pictures. Taken together, the data show that in both men and women, exposure to a sexual film evokes genital and subjective sexual arousal, elicits a tendency for sexual behavior, and instigates actual sexual activity. These findings are in line with previous studies that compared men's and women's sexual response patterns and found strong similarities between them (e.g., Both et al., 2003; Heiman, 1977; Wincze et al., 1980;).

In agreement with other studies comparing male and female sexual arousal patterns in one experiment (e.g., Heiman, 1977; Steinman et al., 1981; Wincze et al., 1980), we found higher correlations between genital responses and subjective sexual arousal in men than in women. In women the correlations between genital responses and feelings of sexual arousal were low, while in men they were moderately high. As expected, in women there was a low correlation between genital response and postexperimental sexual activity and higher correlations between lust, approach, and sexual arousal ratings and postexperimental sexual activity. Postexperimental sexual desire was also related to feelings of lust, approach, and sexual arousal ratings in the female participants. Thus, for the women, actual sexual behavior was related more to the experience of sexual feelings and less to genital responses.

We had hypothesized that since in men the experience of a sexual situation is more strongly determined by genital response, men's postexperimental sexual behavior would be related to their genital and subjective sexual responses, and to both variables to the same degree. In agreement with this expectation, men's postexperimental sexual behavior seemed to be related to both their genital and subjective sexual responses. However, the relationship between genital response and postexperimental behavior was in the opposite from the expected direction. The men showed a negative although nonsignificant correlation between genital response and postexperimental sexual activity, and between subjective sexual arousal ratings and postexperimental sexual activity. In contrast, postexperimental sexual desire in men was positively although not strongly related to feelings of lust, approach tendency, and subjective sexual arousal ratings. Thus, the weaker a man's genital and subjective response was to the sexual film, the more postexperimental sexual activity he showed. We can only speculate about this unexpected finding and note that further research is needed.

To conclude, our data show that activation of the sexual system through exposure to a sexual stimulus elicits subjective sexual and genital responses in men and women and generates an approach tendency as well as actual sexual behavior. We demonstrated that, on a group level, sexual responses exhibited in the lab relate to sexual behavior outside the lab. This finding strengthens the external validity of laboratory research on sexual responses and indicates that in laboratory research on factors influencing sexual motivation, measurement of postexperimental sexual behavior may be useful.

Table 1. Mean (SD) Subjective Ratings in Response to
Neutral and Sexual Films in Experiment 1

                                                       Film

Subjective ratings                                    Neutral

Sexual arousal
  Overall sexual arousal (a)          Men            1.4 (1.0)
                                      Women          1.6 (0.8)
                                      Total group    1.5 (0.8)
  Strongest sexual arousal (a)        Men            1.7 (1.3)
                                      Women          2.5 (1.5)
                                      Total group    2.1 (1.4)
  Strongest genital sensations (b)    Men            1.8 (1.5)
                                      Women          2.0 (0.9)
                                      Total group    1.9 (1.2)
Emotional experience (c)
  Lust                                Men            1.9 (0.4)
                                      Women          2.2 (0.7)
                                      Total group    2.0 (0.6)
  Anger                               Men            1.1 (0.2)
                                      Women          1.3 (0.6)
                                      Total group    1.2 (0.4)
  Threat                              Men            1.5 (0.4)
                                      Women          1.6 (0.5)
                                      Total group    1.6 (0.4)
  Tension                             Men            1.5 (0.4)
                                      Women          1.8 (0.9)
                                      Total group    1.7 (0.7)
Action tendencies (d)
  Approach                            Men            1.5 (0.4)
                                      Women          1.7 (1.0)
                                      Total group    1.6 (0.8)
  Avoidance/tension                   Men            2.3 (0.3)
                                      Women          2.5 (0.3)
                                      Total group    2.4 (0.3)

                                                        Film

Subjective ratings                                       Sex

Sexual arousal
  Overall sexual arousal (a)          Men            3.3 (1.7)
                                      Women          3.4 (1.7)
                                      Total group    3.4 (1.7) **
  Strongest sexual arousal (a)        Men            4.0 (2.1)
                                      Women          4.3 (2.0)
                                      Total group    4.2 (2.0) **
  Strongest genital sensations (b)    Men            3.6 (1.8)
                                      Women          3.8 (2.2)
                                      Total group    3.7 (2.0) **
Emotional experience (c)
  Lust                                Men            3.2 (1.3)
                                      Women          3.4 (1.5)
                                      Total group    3.3 (1.4) **
  Anger                               Men            1.2 (0.3)
                                      Women          1.1 (0.3)
                                      Total group    1.1 (0.3)
  Threat                              Men            1.7 (0.4)
                                      Women          1.6 (0.6)
                                      Total group    1.6 (0.5)
  Tension                             Men            1.5 (0.6)
                                      Women          1.1 (0.3)
                                      Total group    1.3 (0.5) *
Action tendencies (d)
  Approach                            Men            1.6 (0.4)
                                      Women          2.7 (1.0)
                                      Total group    2.2 (1.0) *
  Avoidance/tension                   Men            2.3 (0.3)
                                      Women          2.4 (0.5)
                                      Total group    2.3 (0.4)

Note. Statistical significance of group comparison is reported for the
total groups only.

(a) Item response format of 1 (not sexually aroused at all) to 7 (very
strongly sexually aroused). (b) Item response format of 1 (no
sensations in my genitals) to 7 (orgasm). (c) Item response format of
1 (not at all) to 7 (very strong). (d) Item response format of 1 (not
at all) to 5 (very strong).

** Neutral versus sexual film group comparison statistically
significant, p < .001. * Neutral versus sexual film group comparison
statistically significant, p < .05.

Table 2. Mean Genital Response (SD) to Neutral and
Sexual Films in Experiment 1

                                           Film

                                Neutral           Sex

Penile circumference **      103.21 (11.76)    173.69 (67.01)
Vaginal pulse amplitude *     77.18 (10.17)    173.69 (67.01)

Note. Units are percentage of baseline (response during film / baseline
x 100).

* Neutral versus sexual film group comparison statistically significant
(P < .01, df= 1,13). ** Neutral versus sexual film group comparison
statistically significant (p < .005, df= 1,19).

Table 3. Mean (SD) Subjective Ratings in Response to
Neutral and Sexual Films in Experiment 2

                                                       Film

Subjective ratings                                    Neutral

Sexual arousal
  Overall sexual arousal (a)          Men            1.3 (1.1)
                                      Women          1.8 (1.2)
                                      Total group    1.6 (1.1)
  Strongest sexual arousal (a)        Men            1.5 (1.1)
                                      Women          2.3 (1.4)
                                      Total group    1.9 (1.3)
  Strongest genital sensations (b)    Men            1.4 (1.1)
                                      Women          2.2 (1.3)
                                      Total group    1.8 (1.2)
Emotional experience (c)
  Lust                                Men            1.9 (0.8)
                                      Women          1.9 (0.8)
                                      Total group    1.9 (0.8)
  Anger                               Men            1.5 (1.2)
                                      Women          1.4 (0.5)
                                      Total group    1.4 (0.9)
  Threat                              Men            2.1 (1.3)
                                      Women          1.9 (0.6)
                                      Total group    2.0 (1.0)
  Tension                             Men            2.0 (1.8)
                                      Women          2.3 (1.1)
                                      Total group    2.1 (1.4)
Action tendencies (d)
  Approach                            Men            1.9 (1.0)
                                      Women          1.5 (0.5)
                                      Total group    1.7 (0.8)
  Avoidance/tension                   Men            2.2 (0.5)
                                      Women          2.2 (0.4)
                                      Total group    2.2 (0.4)

                                                       Film

Subjective ratings                                      Sex

Sexual arousal
  Overall sexual arousal (a)          Men            4.4 (1.4)
                                      Women          4.6 (0.9)
                                      Total group    4.5 (1.2) *
  Strongest sexual arousal (a)        Men            5.4 (0.6)
                                      Women          4.1 (1.3)
                                      Total group    4.8 (1.2) *
  Strongest genital sensations (b)    Men            5.5 (0.6)
                                      Women          4.5 (1.2)
                                      Total group    5.0 (1.1) *
Emotional experience (c)
  Lust                                Men            3.7 (1.4)
                                      Women          3.3 (1.1)
                                      Total group    3.5 (1.3) *
  Anger                               Men            1.3 (0.5)
                                      Women          1.3 (0.4)
                                      Total group    1.3 (0.4)
  Threat                              Men            2.1 (0.4)
                                      Women          1.9 (0.3)
                                      Total group    2.0 (0.4)
  Tension                             Men            2.3 (0.9)
                                      Women          2.3 (1.1)
                                      Total group    2.3 (1.0)
Action tendencies (d)
  Approach                            Men            2.9 (1.0)
                                      Women          2.6 (1.0)
                                      Total group    2.8 (1.0) *
  Avoidance/tension                   Men            2.3 (0.5)
                                      Women          2.5 (0.5)
                                      Total group    2.4 (0.5)

Note. Statistical significance of group comparison is reported for the
total groups only.

(a) Item response format of 1 (not sexually aroused at all) to 7 (very
strongly sexually aroused). (b) Item response format of 1 (no
sensations in my genitals) to 7 (orgasm). (c) Item response format of
1 (not at all) to 7 (very .strong). (d) Item response format of 1 (not
at all) to 5 (very strong).

* Neutral versus sexual film group comparison statistically
significant, p < 0.001.

Table 4. Mean Genital Response (SD) to Neutral and
Sexual Films in Experiment 2

                                           Film

                               Neutral              Sex

Penile circumference *       100.53 (4.07)     114.89 (9.36)
Vaginal pulse amplitude *     81.81 (24.45)    196.82 (68.92)

Note. Units are percentage of baseline (response during film / baseline
x 100).

* Neutral versus sexual film group comparison statistically significant
(p < .001, men df= 1,27, women df= 1,26).

Table 5. Across-Subjects Correlations for the Sexual Film Group Only,
for Men and Women Separately

                                                          Genital
                                     Approach             response

                                   Men       Women      Men       Women

Subjective sexual arousal
   Overall sexual arousal          .35        .35        .30      -.01
   Strongest sexual arousal        .49        .52        .40       .12
   Strongest genital sensations    .54 *      .47        .39       .15
Lust                               .34        .59        .42      -.01
Approach                           --         --         .01      -.11
Genital response                   --         --         --        --
Postexperimental sexual desire     --         --         --        --

                                 Postexperimental       Postexperimental
                                  sexual desire              sexual
                                                            activity

                                   Men       Women      Men     Women
Subjective sexual arousal
   Overall sexual arousal
   Strongest sexual arousal        .15        .29       -.28     .29
   Strongest genital sensations    .32        .41       -.22     .38
Lust                               .26        .18       -.22     .27
Approach                           .30        .53 *      .14     .44
Genital response                   .27        .54 *      .10     .42
Postexperimental sexual desire    -.10       -.28       -.40     .14
                                    --        --         .57 *   .67 **

Note. Ns varied from 21 to 26.
* p < .01. ** p < .001.

We thank Saskia Dijkstra, Sven Dijt, Ingrid Langedijk, Richard van Ommeren, and Elsbeth Reitzema for their assistance in the data collection and data reduction.

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Manuscript accepted November 4, 2003

Address correspondence to Stephanie Both, Department of Clinical Psychology, Faculty of Social and Behavioural Sciences, University of Amsterdam, Roetersstraat 15, 1018 WB Amsterdam, The Netherlands: e-mail: [e-mail].

Stephanie Both, Mark Spiering, Walter Everaerd, and Ellen Laan

University of Amsterdam