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Motor preparation and sexual action : a psychophysiological perspective on
sexual motivation
Both, S.
Publication date
2004
Link to publication
Citation for published version (APA):
Both, S. (2004). Motor preparation and sexual action : a psychophysiological perspective on
sexual motivation.
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2 2
Modulationn of spinal reflexes by aversive
andd sexually appetitive stimuli
Abstract t
InIn this study, modulation of spinal tendinous (T) reflexes by sexual
stimulationstimulation was investigated. T reflexes are augmented in states of appetitiveappetitive and defensive action and modified by differences in arousal intensity.intensity. Reflexes were expected to be facilitated by both pleasant (sexual)(sexual) and unpleasant (anxiety) stimuli. Subjects were exposed to a sexual,sexual, an anxiety-inducing, a sexually threatening, and a neutral film excerptexcerpt Genital arousal, emotional experience, subjective action tendencies,tendencies, and T reflexes were monitored. Self-report and genital data confirmedconfirmed the affective states as intended. T reflex amplitude significantly increasedincreased during viewing of emotionally arousing film excerpts as comparedcompared with a neutral film excerpt. T reflexes were facilitated by the sexsex stimulus to the same extent as by the anxiety and sexual threat stimuli.stimuli. The results support the view of sexual arousal as an emotional state,state, generating sex specific autonomic and general somatic motor systemsystem responses, which prepare the organism for action.
Note:Note: We thank Lars van Dalen, Janine Hooijboer, and Peter-Paul Mantjes for
Introduction n
Forr a long time it has been known that reflexes are modified by cognitive andd affective variables. Lang, Bradley and Cuthbert (1990) proposed that affectivee modification of the startle response reflects motivational priming, inn which a defensive reflex such as the eye blink is potentiated when elicitedd in the context of an ongoing aversive state, and inhibited when elicitedd in a non-primed context that involves approach behavior. Lang et al.. showed that the human startle reflex is indeed facilitated by aversive stimulii and diminished by positive stimuli. In contrast to startle reflexes, tendonn reflexes are not sensitive to the valence of the affective state. Theyy are augmented in states of action, and they are modified by differencess in arousal (Bonnet, Bradley, Lang & Requin, 1995; Brunia & Boelhouwer,, 1988). Therefore, investigation of Tendon reflex modulation offerss a window on the generation of action. In this experiment, we investigatedd modulation of spinal tendinous reflexes by emotional arousal,, specifically sexual arousal and anxiety.
Emotionn can be viewed as fundamentally an action disposition, a tendencyy to do something (Frijda, 1986; Lang, 1993). In this view, emotionss serve the satisfaction of goals and generate relevant action (fight-flightt or approach). For example, when afraid, you may feel a strong urgee to run away, and when sexually attracted you feel a strong desire to bee as close to the attractive person as you possibly can. According to Lang,, emotions are driven by two primary motive systems: the appetitive system,, prototypically expressed by behavioral approach, and the aversivee system, expressed by behavioral escape and avoidance (Lang ett al., 1990). There is, therefore, a strong resemblance between emotion andd motivation; both are fundamentally related to action. Bindra (1974) alreadyy noted that "motivational state" and "emotional state" are interchangeablee terms. Emotions move the organism towards or away fromm objects in the environment.
Sexuall excitement, in this respect, does not deviate from other emotions:: sexual excitement serves to satisfy concerns, and generates ann action tendency for sexual behavior (to continue, or search for, sexual stimulation)) (Everaerd, Laan & Spiering, 2000). Incentive motivation theoriess state that motivation is the result of the interaction of homeostaticc drives and environmental stimuli that have rewarding
propertiess (incentives). Incentives are supposed to guide response selectionn through excitatory or priming influence of the central motive statee on somatovisceral reactions, consummatory or rejectional acts, and locomotorr and skilled actions (Bindra, 1974). Following incentive motivationn models, sexual motivation is an emerging property, the outcomee of the processing of internal or external sexual stimuli. Hence, sexuall motivation can be investigated best by studying the process of actionn generation. This process can be studied through the monitoring of responsess within various response systems involved in general motivated behaviorr and specific sexual behavior.
Appetitivee behavior includes locomotor approach responses to the goall or exploratory behavior, and occurs in parallel with autonomic and endocrinee responses that prepare the animal for efficient interaction with thee goal (Robbins & Everitt, 1999). Hence, the generation of sexual appetitivee behavior will be accompanied by activity in somatic motor, autonomicc motor, and endocrine systems. Autonomic nervous system efferentt activity is the most widely used parameter to monitor the presencee and intensity of sexual arousal (Geer & Janssen, 2000). Researchh using this parameter has shown that sexual stimulation results inn changes in nonspecific autonomic arousal (Rosen & Beck, 1988) and inn sex-specific responses: relaxation of genital smooth muscles, resulting inn an increase of genital blood flow. This sex-specific response occurs withinn seconds after the onset of the stimulus, which suggests a relatively automaticc response (Laan & Everaerd, 1995a). The purpose of this study wass to investigate, in addition to the sex-specific changes in autonomic nervouss system efferent activity, changes in the somatic nervous system inn response to sexual stimuli. We expected a sexual stimulus to elicit an approachh tendency reflected in facilitated somatic motor activity.
Somaticc motor activity can be measured by monitoring of Achilles tendonn (T) reflexes resulting from a hammertap at the heel tendon. A hammertapp at the heel tendon results in a reflexive electromyographic (EMG)) response in the soleus muscle of the lower leg. The monosynaptic reflexx is a triphasic EMG response whose magnitude reflects the number off motoneurons currently activated in the pool that innervates the soleus muscle.. Because the sensitivity of the muscle spindle is controlled by fusimotoneurons,, the activity of these neurons is also reflected in the T reflex.. When circumstances are held equal, taps of a constant force lead
too reflex amplitudes of constant size. Supraspinal excitatory or inhibitory influencess on the motoneuron pool or other elements of the reflexarc are reflectedd in an increase or decrease in reflex amplitude. Thus changes in reflexx amplitude are a peripheral manifestation of supraspinal processes influencingg spinal excitability (Brunia & van Boxtel, 2000).
Thee T reflex has been used in studies of cognitive factors and motor preparationn (Brunia & Boelhouwer, 1988, Brunia, 1993). Studies investigatingg the influence of cognitive task demands showed that T reflexx amplitudes are augmented when task demands increase (Brunia & Boelhouwer,, 1988, Brunia, 1993). This facilitation of reflexes is interpretedd as the consequence of a general increase in activation. Studiess on motor preparation showed that preparing to make a leg movementt results in a diminished T reflex in the limb involved in the action,, and an augmented T reflex in the uninvolved limb (Brunia & Boelhouwer,, 1988, Requin, Bonnet, & Semjen, 1977). These results are interpretedd as reflecting two functions of preparation for action. Responsess are facilitated by a generalized increase in arousal, but activityy in the involved limb is temporary inhibited until the signal to respondd occurs. In a study on the effect of mental simulation of an action onn reflex modulation, Bonnet, Decety, Jeannerod, and Requin (1997) foundd that mental simulation of a movement resulted in an increase in spinall reflex excitability, which was only slightly weaker than the reflex facilitationn associated with the actual performance of the same movement.. Thus, both intended and imagined actions seem to belong to thee same category of neural processes as those which are involved in preparingg actually executed actions. These results support T reflex modulationn as a measure for early motor preparation of motivated action.
Bonnett et al. (1995) hypothesized that stimuli that elicit emotional arousall will facilitate T reflex magnitude, relative to neutral, low arousal stimuli.. They stated that the T reflex, which functions when the limb is activatedd for walking, standing, and other activities, is inherently nondirectionall (one can run either towards or away from stimulation). Becausee the T reflex is nondirectional, it would be involved in actions that aree appetitively motivated, as well as in defensively motivated actions. Theyy studied the modulation of T reflexes during the presentation of picturess from The International Affective Picture System designed by Lang,, Öhman, and Vaitl (1988). These pictures were designed to induce
emotionss varying in valence (positive to negative) and in intensity (low to high).. As expected, T reflexes were significantly augmented when elicited duringg processing of highly arousing emotional pictures (either negative orr positive) as compared with neutral pictures.
Similarr to Bonnet et al. (1995), we hypothesized emotional stimuli to automaticallyy generate action tendencies. These action tendencies will resultt in increased spinal excitability, reflected in facilitated T reflex magnitude.. We studied reflex modulation by appetitive (sexual) and aversivee (anxiety and sexual threat) stimuli. We hypothesized a sexual stimuluss to elicit approach responses, reflected in autonomic and somatic responsess that prepare for (sexual) action. We therefore expected a sexuall stimulus to result in vasocongestion of the genitals, and in facilitatedd T reflexes. We expected the aversive stimuli to elicit avoidance tendencies,, also reflected in facilitated T reflexes. The sexual, anxiety andd sexual threat stimuli were expected to facilitate T reflexes to the samee extent. In contrast to Bonnet et al. (1995), who exposed subjects to emotionall pictures for 6 seconds, we used film excerpts of 5 minutes lengthh to elicit emotional states. Film is found to elicit stronger emotional responsess than still photos (Laan & Everaerd, 1995a), allowing us to monitorr reflex modulation during states of relatively high emotional arousal. .
Thee film excerpts have been used in earlier studies on sexual responsee in women (Laan, Everaerd, & Evers, 1995; van der Velde & Everaerd,, 2001). These excerpts were selected for their sexual, anxiety-inducing,, sexually threatening, and neutral nature. Previous studies in our laboratoryy revealed that only the sexual excerpts evoke subjective sexual arousall and increased genital blood flow. To check for the induction of emotionss as intended, we measured subjective emotional responses and subjectivee action tendencies by self-report questionnaires. Genital responsee was measured through monitoring of Vaginal Pulse Amplitude (VPA)) in women (Laan, Everaerd & Evers, 1995), and by monitoring of penilee circumference change in men (Janssen, Everaerd, van Lunsen, & Oerlemans,, 1994).
Too summarize, the four film excerpts were expected to evoke differentiall patterns of T reflex amplitude, genital arousal, and subjectively experiencedd emotions and action (approach - avoidance) tendencies. We expectedd the sexual excerpt to result in increased T reflex amplitudes,
increasedd genital response, feelings of sexual arousal, and in subjectively experiencedd approach tendencies. Exposure to the anxiety excerpt was expectedd to result in increased T reflex amplitudes, feelings of threat, and inn subjectively experienced avoidance tendencies. The sexual threat excerptt was expected to elicit a mixed sexual and anxious state, reflected inn increased T reflex amplitudes, a smaller genital response, feelings of threatt as well as sexual arousal, and a subjectively experienced avoidancee tendency. Exposure to the neutral excerpt was expected to resultt in a neutral state, reflected in an absence of T reflex augmentation, ann absence of genital responses, and no subjective emotional responses andd subjective action tendencies.
Forr exploratory comparison of men and women's responses, both malee and female subjects participated. Evolutionary perspectives on sexuall behavior predict that men are prepared for action and women for selectivee reception (Symons, 1979, 1987). Men do seem to be stronger motivatedd sexually than women are: they masturbate more frequently (Oliverr & Hyde, 1993), they report less problems concerning low sexual desiree (Simons & Carey, 2001), and problems of hyper sexuality mostly concernn men (Kafka, 2001). We hypothesized that the more active sexual rolee of men would possibly be reflected in larger changes in reflex modulationn by the sexual stimulus in comparison to women. No sex differencess in reflex modulation by anxiety-inducing and neutral stimuli weree expected.
Method d
Participants Participants
Participantss were 10 men and 15 women. All participants were students whoo received course credit or were paid for their participation. Mean age off the men was 24.50 (range = 2 0 - 3 1 years, SD = 3.44), and mean age off the women was 21.73 (range = 19-31 years, SD = 3.37 years). There wass no significant difference in age between men and women, t (23) =
1.94,p>.05. .
Alll male participants had a heterosexual orientation. Six (60%) men hadd a steady partner. The male participants were fairly sexually experienced,, 9 (90%) men had experienced sex with a partner, and 8
(80%)) had experienced coitus. None of them had experienced sexual abuse.. In the female participants, 14 had a heterosexual orientation, and
11 subject considered herself to be bisexual. Ten (66%) women had a steadyy partner. All women had experienced coitus. Two women had experiencedd sexual violence once in their life. All participants had seen eroticc films prior to participation.
Beforee participation all participants received written information includingg a description of the procedure, the genital measures, and T reflexx elicitation and measurement. Women were not tested during menstruation.. Confidentially, anonymity and the opportunity to withdraw fromm the experiment without penalty were assured to all participants.
Design Design
AA 2 (gender) x 4 (stimulus) design was employed, with gender as between-subjectss variable. All participants were exposed to four film excerptss (neutral, anxiety, sexual threat and sex). Four order groups were createdd using a 4 x 4 Latin-square design (Kirk, 1968). In our design, eachh excerpt occupied any of the four ordinal positions only once and wass preceded or followed by each of the other film excerpts only once. Participantss were randomly assigned to one of the four order groups.
MaterialsMaterials and Response Measurement
StimulusStimulus materials. The four film excerpts consisted of 5-min
videotapess with sound. The excerpts have been used before in studies in womenn and have been shown to evoke the expected emotions (Laan, Everaerd,, & Evers, 1995; van der Velde & Everaerd, 2001). Earlier studiess in our laboratory have shown that the sexual excerpt elicits subjectivee sexual arousal and genital arousal in men as well (Janssen et al.,, 1994). The neutral film excerpt was also used with men in earlier studiess (Janssen et al., 1994), the sexual threat and anxiety excerpts weree not used with men before. The sex stimulus was an erotic videotape,, depicting petting, cunnilingus, and intercourse scenes. The neutrall stimulus was a video travelogue describing old buildings in a Dutchh village. The anxiety stimulus consisted of an excerpt of the film Cujo,, in which a woman is threatened by a wild dog. The sexual threat stimuluss was taken from the film Extremities, in which a male perpetrator forcess a woman up the stairs of her house with distinct sexual intentions.
Thee next scene shows the perpetrator lying on top of the woman, kissing andd caressing her breasts and body, and forcing her to kiss him by hitting her. .
PhysiologicalPhysiological recordings. T reflexes were elicited with a hammer. The
measurementt was carried out in accordance with standard methods and proceduress for evoking T reflexes (Desmedt, 1973). Participants sat in an individuallyy adjusted chair with their legs held in a fixed position. The kneee was maintained in a fixed, semi-flexed position , and the anglee of the ankle joint was . The feet were strapped to foot pedals to obtainn nearly isometric contractions of the soleus. The Achilles tendon of thee right leg was hit by a hammer (10-ms duration), at a right angle to the tendon,, at the level of the lateral malleolus. The hammer was connected too a Brüel and Kjaer 4809 vibration exciter. T reflexes were elicited at a constantt rate of one every 5 s during baselines and stimulus presentations,, resulting in 36 reflexes during the 3-min baseline, 24 reflexess during each 2-min baseline, and 60 reflexes during each 5-min stimuluss presentation period. Surface electrodes (Ag/AgCI electrodes, 2 cm22 contact area) were placed (3 cm apart) upon the soleus muscle, alongg the longitudinal axis of the calf; the proximal electrode of the pair wass placed 2 cm distal to the insertion of the gastrocnemius muscle on thee Achilles tendon. Reflex activity (EMG) was measured using a front-endd amplifier with a amplification factor of 1,000, a frequency response of 1Hzz - 1500Hz, an input impedance at approximately 5 MOhm, equipped withh a 50Hz (mains frequency) notch filter. The signal from the front-end amplifierr was lead to a contour follower with a time constant of 25 msec, andd a variable amplification factor of 1 - 100. Data was measured with a samplee frequency of 500 samples per second. At the start of each sine wavee impulse (at each hammer stroke), a synchronisation pulse was sent too the data-acquisition program. The output of the contour follower, was usedd to analyze the signal. For data analysis, a prestimulus baseline of 200 ms and a post trigger time window of 150 ms were used. In the post triggerr time window, the program finds the highest EMG peak, and from thatt point searches to the left and right for the point where the signal is 5 %% (of the found peak) above the baseline level. The 5 % points are consideredd start and end point of the contraction. The reported EMG valuee is the mean value of the EMG signal between these two points.
Inn women, genital response was measured using a vaginal photoplethysmographh assessing VPA (vaginal pulse amplitude, the AC componentt of the signal), and VBV (vaginal blood volume, the DC component).. A signal-conditioning amplifier separated the VPA from the VBVV component using a 12dB/octave, 0.7-Hz filter. Additional filtering for VPAA was 24 dB/octave, 0.4 Hz high-pass. Since former research has shownn that VPA is the superior measure in terms of both convergent and divergentt validity (Laan, Everaerd, & Evers, 1995), only VPA data were used.. The VPA signal was sampled at 100Hz with a Keithley KPCI3107 A/DD converter, running on a Windows2000 PC system. Depth of the probee and orientation of the light emitting diode were controlled by a devicee (a 9- x 2-cm plate) attached to the photoplethysmograph. Participantss were instructed to insert the photoplethysmograph such that thee plate touched their labia.
Genitall response in men was measured by a mechanical penile strain gaugee assessing penile circumference changes (Barlow, Becker, Leitenbergg & Agras, 1970; Janssen et al., 1994). Changes in electrical outputt caused by expansion of the strain gauge were recorded by a continuouss DC signal. Before each session, calibration was accomplishedd using a 26-step plastic cone with steps ranging from 85 to 1600 mm circumference. The strain gauge was positioned two-thirds of the wayy down the shaft of the penis toward the base. The experimenter checkedd for proper placement of the device.
Participantss were relaxed and passive throughout the tests and they weree asked to refrain from moving during the recordings. The TV monitor wass located in front of the participant.
Bothh the vaginal photoplethysmograph and the penile strain gauge weree sterilized in a solution of Cidex-activated glutaraldehyde between usess (Geer, 1980).
TT reflexes and genital responses were recorded continuously during baseliness and stimulus presentations. A computer program developed at ourr department timed the administration of the stimuli, employed a trigger signall to initiate sampling of the physiological measures, and marked changeoverr between stimuli and interstimulus intervals.
SubjectiveSubjective measurements. Prior to stimulus presentation and after
eachh film excerpt, measures of sexual arousal and emotional experience weree collected. Participants were asked to assess on a 7-point Likert
scalee (a) overall sexual arousal, (b) strongest feeling of sexual arousal, andd (c) strongest genital sensations. The extremes were nor sexually
arousedaroused at all and very strongly sexually aroused for item a and b, and no sensationssensations in my genitals and orgasm for item c. The answer categories
forr men and women were slightly different: genital sensations for men weree described as erection, and for women as vaginal lubrication.
Emotionall experience was measured by a questionnaire consisting of 211 emotions (including sexual emotions). Participants were asked to indicatee on a 7-point Likert scale (with not at all and very strong as extremes)) to what extent they had experienced these emotions while watchingg each film excerpt. In an earlier study, factor analysis indicated thatt the 21 emotions could be divided into clusters of sexual feelings, anger,, threat and tension (Laan, Everaerd, & Evers, 1995).
Actionn tendencies were measured by the Action Tendency Questionnairee (ATQ). This questionnaire assessed the tendency to executee overt behavior, without necessarily doing so (Frijda, Kuipers, ter Schure,, 1989). Participants were asked to assess on 5-point Likert scales (withh does not apply to me and strongly applies to me as extremes) the degreee to which 25 statements were applicable to them. The statements variedd from statements indicating approach tendencies (e.g., "I wanted to approach,, to make contact") to statements indicating avoidance (e.g., "I wantedd to have nothing to do with something or someone, to be bothered byy it as little as possible, to stay away"). The questionnaire was administeredd after each film excerpt.
Procedure Procedure
Too help participants make an informed decision about whether to participatee in this experiment, they received a letter in which all experimentall procedures were explained in detail. They were told that theyy would be exposed to film excerpts containing erotic and threatening materiall and they were informed about the genital measures and the sterilizingg procedures. To prevent subject awareness of the experimental hypothesess with regard to the T reflex recordings, the aim of the reflex recordingss was described using general terms ("To measure your responsee at the spinal level of the central nervous system"). Participants weree assured privacy, anonymity and confidentiality. It was stressed that theyy could withdraw from the experiment at any time, without penalty.
Eachh subject was tested individually by a trained experimenter of the samee sex. On arrival at the laboratory, the subject read and signed an informedd consent form. The subject answered questions about sexual experiencee and sexual problems. For women this questionnaire containedd also questions about length of menstrual cycle and last date of menstruation. .
Thee experimenter then explained all the details of the experimental proceduree and attached the electrodes. After adjusting the chair, the experimenterr determined the intensity of mechanical stimulation necessaryy to elicit reflexes. Then the intensity was adjusted to obtain, at rest,, a reflex EMG whose amplitude was between 25% and 50% of the estimatedd maximum T reflex. The experimenter then left the room and thee subject inserted the vaginal probe or attached the penile strain gauge whilee sitting in the adjusted chair. When the participants signaled (using a one-wayy intercom system) that the transducers had been placed, they ratedd their feelings of sexual arousal and emotional experience by answeringg questions presented on the TV monitor. These questions were answeredd by pressing buttons corresponding with the seven answer categories.. The answers were stored in a Windows2000 PC system.
Afterr this a 3-min baseline period followed. During this resting period, participantss listened to quiet music. Then the first film excerpt was presented.. After the film excerpt, participants rated their feelings of sexuall arousal and emotional experience and their action tendencies by answeringg questions presented on the TV monitor. This was followed by aa 3-min return-to-baseline period. To facilitate return-to-baseline participantss completed a concentration task (simple arithmetic problems) duringg the return-to-baseline period. The computer was programmed to indicatee when genital responses had returned within a 5% range of the firstt baseline. When responses failed to return to baseline rapidly, participantss were asked to count aloud backwards. The return-to-baseline periodd was followed by a 2-min baseline period, during which participants listenedd to music. Then the next film excerpt was presented, until all excerptss were shown. At the end of the experiment an exit interview was administered.. Participants were asked about their reactions to the experimentall procedure, the use of the genital device, and the T reflex measurement. .
DataData reduction, scoring, and analysis
VPAA was sampled across baselines and subsequent stimulus presentationn periods. The raw genital data were loaded into a Windows program,, allowing visual inspection of the signal. Artifacts in the VPA channell are caused by movements of the lower part of the body or by voluntaryy or involuntary contractions of the pelvic muscles. A two-pass algorithmm for automatic artifact removal, developed at our department, wass used to analyze the VPA data. After the artifact removal, the programm showed which data were rejected, allowing the user to overrule thee decision of the program. After artifact removal, the peak-to-trough amplitudess were averaged over 30-s intervals, resulting in 10 data points forr each stimulus presentation period.
Penilee circumference was also sampled across baselines and subsequentt stimulus presentation periods. The strain gauge data were scoredd as millimeter of circumference, based on presession calibration of thee strain gauge, and averaged over 30 s, resulting in 10 data point for eachh stimulus presentation period.
Forr genital responses, the mean overall baseline was calculated (the meann of the baselines preceding each stimulus) for each subject. Statisticall analysis was performed with deviation from overall baseline as thee dependent variable.
EMGG was sampled across baselines and subsequent stimulus presentationn periods. As with the VPA data, the raw EMG data were loadedd into a Windows program. The mean T reflex amplitude elicited duringg each baseline period (X) and each stimulus presentation period
(Y)(Y) was calculated. A percentage of baseline score was calculated
(percentagee of baseline = Y7 X * 100) for each stimulus.
Basedd on former factor analysis (Laan, Everaerd, & Evers, 1995) the 211 emotion items were divided into 7 emotions reflecting lust (Reliability Coefficientt Cronbach's a = .82), 4 emotions relating to anger (Cronbach's aa = .85), 8 emotions relating to threat (Cronbach's a = .71), and 2 emotionss reflecting tension (Cronbach's a = .79). The items belonging to eachh of the described factors were averaged, thus creating a lust, anger, threatt and tension score.
Thee Action Tendency Questionnaire was, based on earlier factor analysiss (Laan & Everaerd, 1995b), divided in 5 subscales: approach (Cronbach'ss a = .87), avoidance (Cronbach's a = .75), protection
(Cronbach'ss a = .81), attention (Cronbach's a = .76), and helplessness (Cronbach'ss a = .15). Only the approach factor and the avoidance factor weree used for further analysis. The 4 approach items and the 8 avoidancee items were averaged, thus creating an approach, and an avoidancee score.
Within-subjectt and between-subject effects were tested with repeated-measuress multivariate and univariate analysis of variance procedures (Generall Linear Model in SPSS), using Wilks' Lambda and a significance levell of .05. Because the cells in order analysis would have insufficient numberss of participants, statistical tests for order effects were not performed. .
Sincee changes in vaginal vascular responses are not comparable to changess in penile responding (Geer & Janssen, 2000) genital responses weree analysed for men and women separately. Genital arousal was submittedd to an ANOVA with stimulus as the within-subjects variable. Subjectivee sexual arousal, emotional experience and action tendencies weree submitted to 2 (gender) x 4 (stimulus) repeated measures
MANOVA'' s. T reflex magnitude was submitted to a 2 (gender) x 4 (stimulus)) repeated measures ANOVA. The Greenhouse-Geisser epsilon proceduree was applied to all repeated-measures ANOVA's to correct for thee violation of the sphericity assumption in repeated-measures designs (Vaseyy & Thayer, 1987). Following significant F ratios for each dependent measure,, univariate contrast analyses (multiple comparisons between all possiblee pairs of means) were performed to test for specific stimulus effects.. The Bonferroni procedure to set the overall level of significance at aa = .05 would result in a level of significance of a = .008 for each test. However,, because of the small number of participants we decided to performm the follow-up tests with the level of significance set at a = .01 for eachh test.
Results s
Responsess at exit interviews indicated that participants had felt comfortablee during the experiment despite the genital and T reflex measurements. .
Visuall inspection of the data revealed no differences among order groupss on the pretests for the questions measuring sexual arousal and emotionall experience, therefore raw posttest scores were used for the multivariatee analysis. Inspection of the data also indicated that there was noo effect of order on any of the dependent measures.
SubjectiveSubjective sexual arousal, emotional experience and action tendencies SubjectiveSubjective sexual arousal. The stimulus presentations had their
intendedd effects upon subjective ratings. A main effect of stimulus was found,, multivariate F (9,163) = 5.70, p < .001. There was a significant interactionn between stimulus and gender, multivariate F (9,163) = 2.25, p << .05. Tests of between subject effects revealed a main effect of gender forr strongest genital sensations, F (1,23) = 4.82, p < .05, the male participantss reported stronger genital sensations than the female participants.. Main effects of gender for overall sexual arousal and strongestt sexual arousal were not significant. Univariate tests for overall sexuall arousal, F (3,69) = 15.05, p < .001, e = 0.85, strongest feeling of sexuall arousal, F (3,69) = 21.42, p < .001, E = 0.88, and strongest genital sensations,, F (3,69) = 15.65, p < .001, e = 0.82, were significant. Univariatee tests did not reveal interactions of stimulus and gender. Comparisonn of all possible pairs of means for the three sexual arousal itemss showed that ratings for overall sexual arousal, strongest sexual arousal,, and strongest genital sensations were higher during the sexual stimuluss then during the neutral, anxiety, and sexual threat stimuli (Table 1).. Ratings for overall sexual arousal, strongest sexual arousal and strongestt genital sensations during the sexual threat stimulus were lower comparedd to the sex stimulus, and higher than during the neutral and anxietyy stimulus, but these differences did not reach significance.
EmotionalEmotional experience. The stimulus main effect was significant,
multivariatee F (12,175) = 7.48, p < .001. There was no effect of gender on emotionall experience, and no interaction of gender and stimulus. Univariatee tests for emotional responses were significant: lust, F (3,69) = 12.71,, p < .001, E = 0.79; anger, F (3,69) = 17.08, p < .001, E = 0.58; threat,threat, F (3,69) = 14.85, p < 0.001, E = 0.60; tension, F (3,69) = 13.92 p < .001,, E = 0.75. Comparison of all possible pairs of means (Table 2) revealedd that participants reported more feeling of lust during the sex stimuluss than during the other stimuli. Participants reported stronger
feelingss of threat, anger and tension during the anxiety and sexual threat stimulii than during the neutral and the sex stimulus.
Tablee 1 . Mean (SD) subjective ratings of sexual arousal in response to
thee neutral, anxiety, sexual threat, and sex stimulus.
Subjectivee ratings
Stimuli i
Neutral l Anxiety y Sexual l Threat t Sex x Males Males Overalll sexual arousal1 1 Strongestt sexual arousal1 1 Strongestt genital sensations2 2 Females Females Overalll sexual arousal1 1 Strongestt sexual arousal1 1 Strongestt genital sensations2 2 TotalTotal group Overalll sexual arousal1 1 Strongestt sexual arousal1 1 Strongestt genital sensations2 2 1.00 (1.0) 1.5 (1.3) 2.2 (1.5) 3.8 (1.8) 1.44 (0.7) 1.7 (1.5) 2.4 (1.5) 3.8 (1.6) 1.55 (0.7) 1.7 (1.5) 2.4 (1.5) 4.0 (1.8) 1.11 (0.4) 1.4 (1.1) 1.9 (1.3) 2.9 (1.3) 1.33 (0.6) 1.3 (0.5) 1.9 (1.0) 3.5 (1.5) 1.44 (0.6) 1.4 (0.5) 1.7 (0.9) 2.7 (1.4) 1.3"" (0.7) 1.4" (1.1) 2.0C (1.3) 3 . 3 ^ (1.5) 1.4'' (0.6) 1.5b (1.0) 2.1c (1.2) 3.6* (1.5) 1.4aa (0.7) 1.5b (1.0) 2.0C (1.2) 3.2abc (1.7)
Note:Note: Significance is reported for the total group only. For each dependent measure,
meanss with common character in superscripts are significantly different at p < 0.01 {df = 24). .
1
11 = not sexually aroused at all; 7 = very strongly sexually aroused.
2
Tablee 2. Mean (SD) subjective ratings of emotional experience and
actionn tendencies in response to the neutral, anxiety, sexual threat, and sexx stimulus.
Stimuli i
Neutrall Anxiety Sexual Threat Sex Subjectivee ratings Emotionall experience1 Lust t Anger r Threat t Tension n Men n W o m e n n Total2 2 Men n W o m e n n Total l Men n W o m e n n Total l Men n Women n Total l A c t i o nn t e n d e n c i e s3 Approach h Avoidance e Men n Women n Total l Men n Women n Total l 2.1 1 1.8 8 1.9a a 1.1 1 1.1 1 1 . 1 * * 1.4 4 1.7 7 1.6ab b 1.5 5 1.5 5 1.5* * 1.7 7 1.6 6 1.6a a 1.8 8 2.0 0 1.9abc c (1.0) ) (0-5) ) (0.9) ) (0.2) ) (0.3) ) (0.3) ) (0.4) ) (0.3) ) (0.4) ) (0-7) ) (0-9) ) (0.8) ) (0.9) ) (0.6) ) (0.7) ) (0.5) ) (0.5) ) (0.5) ) 1.7 7 1.5 5 1.6b b 2.0 0 2.0 0 2 0a c c 2.3 3 2.5 5 2.4ac c 2.6 6 3.4 4 3.^ 3.^ 1.5 5 1.3 3 1.4" " 2.6 6 3.0 0 2.8ad d (0-6) ) (0.9) ) (0.9) ) (1.0) ) (1.0) ) (1.0) ) (1.0) ) (0.8) ) (0.9) ) (1.3) ) (1.6) ) (1.5) ) (0.5) ) (0.5) ) (0.5) ) (0.9) ) (0.6) ) (0.7) ) 2.0 0 1.6 6 1.8C C 2.2 2 3.0 0 2 . 7M M 2.3 3 2.8 8 2 . 6M M 2.4 4 3.1 1 2 8b d d 1.7 7 1.6 6 1.6e e 2.3 3 2.9 9 2.6be e (1.0) ) (0.5) ) (0.8) ) (1.4) ) (1.6) ) (1.6) ) (1.0) ) (1.3) ) (1.2) ) (1.0) ) (1.7) ) (1.5) ) (0.7) ) (0.7) ) (0.7) ) (0.7) ) (0.9) ) (0.8) ) 2.9 9 2.5 5 oo yatoc 1.1 1 1.1 1 1.1* * 1.6 6 1.6 6 1.6* * 1.9 9 1.8 8 1.8* * 2.2 2 1.3 3 QQ <nabc 2.0 0 2.4 4 * * d-3) ) (1.2) ) (1.2) ) (0.2) ) (0.5) ) (0.4) ) (0.4) ) (0-5) ) (0.5) ) (1.1) ) (1.2) ) (1.1) ) (1.3) ) (1-0) ) (1.1) ) (0.5) ) (0.7) ) (0-6) )
Note:Note: Significance is reported for the total group only. For each dependent measure,
meanss with common character in superscripts are significantly different at p < 0.01 (df = 24).. 11 = not at all; 7 = very strong.2 Total = mean scores averaged over gender.31 = not
atat all, 5 = very strong.
ActionAction tendencies. There was a significant effect of stimulus on action
tendencies,, multivariate F (6,136) = 11.19, p < 001. There was no significantt effect of gender, and no significant interaction of gender and stimulus.. Univariate tests for approach, F (3,69) = 7.56, p < .005, e =
0.76,, and avoidance, F (3,69) = 17.19, p < .001, e = 0.92, were significant.. Follow-up comparison of means revealed that participants reportedd stronger approach tendencies in response to the sexual stimulus comparedd to the other stimuli (Table 2). Ratings of avoidance tendencies weree higher during the anxiety, sexual threat and sex stimuli compared to thee neutral stimulus, with ratings during the sex stimulus being significantlyy lower than during the sexual threat and anxiety stimuli.
GenitalGenital responses.
MaleMale participants. Genital data for one male subject were missing due
too technical problems. To determine whether carry-over effects were successfullyy minimized, a repeated-measures ANOVA was undertaken withh mean penile circumference during the baselines preceding each stimuluss as the dependent variable. There were no significant differences betweenn the baselines preceding each stimulus, F (3,24) = 1.37, p >.1, E == .57, indicating an absence of carry-over effects.
Figuree 1a shows mean penile circumference change during the four filmm excerpts. There was a significant effect of stimulus, F (3,24) = 4.88, p << .05, E = 0.45. Penile circumference change was larger during the sex stimuluss than during the neutral, and the anxiety stimuli. Contrasts betweenn all possible pairs of means (Table 3) revealed that these differencess reached significance, p < .05.
FemaleFemale participants. Also for women, mean VPA baselines preceding
eachh stimulus were examined to determine whether carry-over effects weree successfully minimized. The repeated-measures ANOVA with mean VPAA during the baselines preceding each stimulus as the dependent variablee revealed no significant differences between the baselines, F (3,42)) = 1.65, p >.1, e = .77, indicating an absence of carry-over effects.
Figuree 1b shows mean VPA change during the four film excerpts. Theree was a significant effect of stimulus, F (3,42) = 14.89, p < .001, e = 0.67,, on VPA. Contrasts between all possible pairs of means (Table 3) revealedd that VPA was significantly higher during the sex stimulus comparedd to the anxiety stimulus, and the neutral stimulus. The differencee between mean VPA change during the sex stimulus and the sexuall threat stimulus reached significance. Mean VPA change during thee sexual threat stimulus was significantly higher than during the neutral stimulus,, but not significantly higher than during the anxiety stimulus. The
differencee in mean VPA change during the neutral and the anxiety stimuluss reached significance.
a.. Genital response men
X X 1 1
Neutral l Sexx Sexual Threat Anxiety Stimuli i
b.. Genital response women
Neutral l Sexx Sexual Threat Anxiety Stimuli i
Figuree 1. Mean (and standard error of the mean) penile circumference
changee (a), and mean change in vaginal pulse amplitude (b) in response too the neutral, sex, sexual threat, and anxiety stimulus.
TT reflex magnitude
Reflexx data for one male subject were missing due to technical problems. Againn the repeated-measures ANOVA revealed that there were no significantt differences between baselines preceding each stimulus, F (3,66)) = 1.89, p >.1, e = .63, indicating an absence of carry-over effects.
Figuree 2 illustrates mean percentage of baseline of T reflex amplitude duringg the neutral, sexual, sexual threat, and anxiety film excerpts for menn and women. There was a significant effect of stimulus, F (3,66) = 12.22,, p < .001, e = 0.82, on T reflex magnitude. Contrary to expectations theree was no significant effect of gender, F (1,22) = 1.14, p - .30, and no significantt interaction of gender and stimulus, F (3,66) = 1.32, p = .28. Thee change of T reflex amplitude was significantly larger during the sexual,, anxiety, and sexual threat stimuli compared to the neutral stimulus.. There was no difference in T reflex magnitude between the sexual,, anxiety, and sexual threat stimuli. Table 3 provides contrasts betweenn all possible pairs of means.
Tablee 3. Contrasts between all possible pairs of means for the
physiologicall variables (Genital response and T Reflex Magnitude).
FF values Anxietyy . . ^ Sexual Anxietyy T L vs.. Threat vs. . ... Neutral An Neutrall Neutral vs.. vs. vss vs vs '' . ,_ Sexual - " Sexual „ ' vs.
Anxietyy T L x Sex TI_ x Sex
Threatt Threat Sex Genital l response e Men Men (AA PC) n.s. n.s. 6.25* n.s. (n=9) ) Women Women (AVPA)) 8.01* 15.31** 47.33*** n.s. (n=15) ) TT reflex magnitude11 22.66*** 27.29*** 28.30*** n.s. (n=24) )
Notes:Notes: PC = penile circumference (df = 1,8); VPA = vaginal pulse amplitude (df=(df= 1,14); n.s. = not significant; 1<ff = 1,23; * p < .05 **p < .01 *** p < .001.
5.62** n.s.
15.63*** 6.43*
TT Reflex Magnitude DMen n 1 1
-- 1
T T ; // ) : :1 1
Neutral l Sexx Sexual threat Anxiety Stimuli i
Figuree 2. Mean (and standard error of the mean) T reflex magnitude
(percentagee of baseline) in response to the neutral, sex, sexual threat, andd anxiety stimulus, for men and women.
Discussion n
Emotionallyy arousing stimuli, in contrast to neutral stimuli, significantly modulatee T reflexes. Both appetitive (sexual) and aversive (anxiety-inducing)) stimuli facilitate T reflexes, and reflexes are augmented by a sexx stimulus to the same extent as by anxiety and sexual threat stimuli. Thee results obtained in this study corroborate the enhancing effects of emotionall arousal on T reflex strength reported by Bonnet et al. (1995), andd they support our view of sexual arousal as an emotional state, resultingg in both sex specific autonomic and general somatic motor systemm responses, which prepare the organism for action.
Thee data regarding subjective sexual arousal, emotional experience, andd genital response show that the film excerpts evoked the different emotionall states as intended. That is, the neutral film evoked no genital response,, no subjective sexual arousal, and no feelings of lust, anger, threatt or tension. The sex stimulus evoked the highest genital response, highestt ratings of subjective sexual arousal and feelings of lust, and virtuallyy no anger, threat, and tension as compared with the anxiety and sexuall threat stimulus. The anxiety film evoked no genital response, and noo subjective sexual arousal, but did enhance ratings of threat, anger and
tension.. The sexual threat film excerpt resulted in a small, in women significant,, increase in genital response relative to the neutral stimulus, a weakk increase in feelings of sexual arousal, and significantly enhanced feelingss of anger, threat and tension. Taken together, we may safely concludee that we succeeded in inducing neutral versus emotional states, andd that we successfully induced a sexual state, an anxious state, and a mixedd sexual and anxious state.
WeWe reasoned that emotions are best conceived of as action tendencies,, and that sexual excitement, in this respect, does not deviate fromm other emotions. Hence, we expected that a sexual stimulus would generatee responses that prepare the organism for sexual approach behavior,, and that unpleasant stimuli would prepare the organism for avoidancee behavior. The results regarding the subjective action tendenciess show that, as expected, the sexual film enhanced approach tendenciess relatively to the neutral, anxiety and sexual threat film excerpts.. Subjective avoidance tendencies were, as expected, stronger in responsee to the anxiety and sexual threat stimuli, compared to the neutral andd the sex stimulus. Subjective avoidance tendencies during the sex stimuluss were, however, stronger compared to the neutral stimulus. This unexpectedd facilitation of avoidance ratings by the sexual stimulus may havee been mainly due to increased feelings of tension. The avoidance factorr of the action tendency questionnaire includes tension related items. Sincee the ratings for emotional experience indicate that the sexual stimuluss evoked sexual emotions and no negative emotions, it is most likelyy that the avoidance ratings were facilitated by increased sexual tension. .
Thee four stimuli were expected to result in different response patterns inn sex specific autonomic activity (increased genital blood flow), and in somaticc motor system activity (T reflex modulation). We already mentionedd that, in agreement with the expectations, the sex stimulus resultedd in the largest increase in genital response. The effects regarding TT reflex modulation obtained in this study suggest that T reflexes are augmentedd as a function of the action generating nature of the emotional stimuli.. Both the sexual appetitive stimulus that evoked a combination of subjectivee approach and avoidance tendencies, and the unpleasant stimulii that produced subjective avoidance tendencies resulted in facilitatedd T reflex modulation. The neutral stimulus evoked no subjective
actionn tendencies, nor did it facilitate T reflexes. As expected, T reflex reactivityy was modified by the parameter of emotional arousal and not by emotionall valence. Sexually arousing stimuli, like other emotionally arousingg stimuli, seem to switch on a disposition to act, and that dispositionn facilitates spinal reflexes such as the T reflex.
Onee can question whether the results regarding T reflex modulation reflectt non-specific arousal rather than emotional or motivational activity. Inn our view though, arousal is always associated with motivational activation.. Psychologically relevant somatic activity may range from completelyy undifferentiated activation to emotion specific patterns of activationn (Cacioppo et al, 1993). Cacioppo et al state that when a stimuluss is evaluated this is represented in a central state that determines thee initial motivational (e.g., approach-avoidance) tendency and generatess peripheral and central changes. Hence, general somatic arousall signifies activity in motivational systems.
Thee exploratory analysis of gender differences in sexual response yieldedd mixed results. Although there is only a small chance to find significantt gender differences with this small sample size, there was a significantt gender difference in subjective sexual arousal. The male participantss reported stronger genital sensations than the female participants.. However, regarding T reflex magnitude in response to the sexx stimulus there was no difference between men and women. Possibly, genderr differences in sexual motivation are not present at the level of automaticc processing of sexual stimuli, but mainly on the level of subjectivee experience. In our study exposure to the sexual stimulus switchedd on a disposition to act in both men and women, and in men and womenn to the same amount. This would suggest that gender differences inn sexual motivation may be mainly the result of regulation processes. However,, this suggestion should be regarded cautiously because gender differencess in motor preparation may have been absent due to a lack of power. .
Thee results of the current study show that T reflex magnitude is facilitatedd by appetitive and aversive stimuli. Most research regarding the neurall circuitry involved in motivational systems concentrates on defensivee systems (Bradley, 2000). The study of reflex modulation by appetitivee stimuli may show the usefulness of reflex modulation in researchh on appetitive motivation, and related disorders like for instance
substancee addiction, and hypo- and hyperactive sexual desire disorder. Drobess et al (2001), for example, successfully used startle reflexes modulationn in a study on emotional responses to food cues in subjects withh restrained or binge eating patterns. T reflex modulation may be a valuablee addition to genital arousal measures in research on psychologicall and pharmacological influences on sexual motivation.
Fromm animal studies there is ample evidence for the involvement of dopaminee systems in activation of responses to stimuli with incentive-motivationall properties (Berridge & Robinson, 1998; Kalivas & Nakamura, 1999;; Robbins & Everitt, 1999; Schultz, 1998). Dopamine systems seem too be involved in both reward signaling, and in the initiation of motor responsess (Kalivas & Nakamura, 1999). Regarding sexual behavior, animall studies show facilitating effects of dopamine (Melis & Argiolas, 1995),, and the very few studies in humans also show a facilitating effect off dopamine on sexual motivation and sexual arousal (Meston & Frohlich, 2000).. Reward information has to be integrated into processes mediating thee behavior leading to the reward. Schultz (2001) states that the final commonn path for reward behavior, involves the influence of the neuronal rewardd message on activity underlying the behavior directed at the rewards.. Measuring somatic motor system activity through means of T reflexx modulation may offer a sensitive measure to investigate the effects off psychomotor stimulant drugs like dopamine on sexual arousal and sexuall motivation in humans.
