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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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3 3
Modulationn of spinal reflexes by sexual
stimulii of increasing intensity
Abstract t
SexualSexual arousal can be viewed as an emotional state generating sex-specificspecific autonomic and general somatic motor system responses that prepareprepare for sexual action. In the present study modulation of spinal tendioustendious (T) reflexes by sexual stimuli of varying intensity was investigated.investigated. T reflexes were expected to increase as a function of increasedincreased stimulus intensity. Following a between subjects design participantsparticipants were exposed to 3 erotic stimuli of low, medium, and high intensity,intensity, or to 3 identical stimuli of medium intensity. In addition to T reflexes,reflexes, genital arousal, emotional experience, and subjective action tendenciestendencies were monitored. Self-report and genital data confirmed the inductioninduction of increasing versus stable levels of sexual arousal. Exposure toto the stimuli of increasing intensity resulted in increasing T reflexes. The resultsresults indicate that T reflex modulation is sensitive to varying levels of sexualsexual arousal, and may be of use in research on behavioral mechanismsmechanisms underlying appetitive motivation.
Note:Note: We thank Esther van Driel, Lot Holieman, and Edmee Nijdam for their
Introduction n
Previouslyy it was shown that the Achilles Tendon (T) reflex is modulated byy negative and positive emotional stimuli (Bonnet, Bradley, Lang, & Requin,, 1995). In line with these findings our research group showed that appetitivee sexual stimuli enhance T reflexes to the same extent as aversivee stimuli (Both, Everaerd, & Laan, 2003). In the present study it wass investigated whether appetitive sexual stimuli of increasing emotionall intensity instigate rising levels of action tendency strength reflectedd in increased somatic motor activity.
Accordingg to incentive motivation models sexual motivation is the resultt of the activation of a sensitive sexual response system by sexual stimulii in the environment, or by internal representations of these stimuli (Singerr & Toates, 1987). Once the system interacts with an attractive sexuall stimulus responses will be activated that prepare for sexual action. Thee strength of these responses is determined by the sensitivity of the system,, as well as by the attractiveness of the stimulus. Interaction with ann incentive changes the affective state of an organism; it inflames motivationn by producing affect (Singer & Toates, 1987). Bindra (1974) alreadyy pointed to the similarity of motivational and emotional states. In hiss view 'motivational state and emotional state are interchangeable terms'' (Bindra, 1974, p. 201). Currently, several emotion theorists view emotionn as fundamentally an action disposition, as a tendency to act in relationn to the emotional stimulus (Frijda, 1986; Lang, 1993; LeDoux, 2001).. In this view emotions serve to satisfy concerns, and therefore resultt in motivational states or action tendencies. The motivational state or actionn tendency is reflected in the physiological changes that accompany emotion.. We assume that sexual excitement, in this respect, does not deviatee from other emotions. Sexual excitement serves to satisfy concerns,, and generates a tendency for sexual behavior (Everaerd, Laan, Both,, & Spiering, 2001).
Thee generation of appetitive behavior will be accompanied by activity inn somatic motor, autonomic, and endocrine systems (Robbins & Everitt, 1999),, and that activity may include nonspecific as well as emotion-specificc responses (Bradley, 2000). To investigate whether sexual excitementt is accompanied by preparation for action, we previously measured,, in addition to sex-specific genital responses, somatic motor
preparationn in response to appetitive sexual and aversive stimuli by meanss of T reflex modulation (Both, Everaerd, & Laan, 2003). The T reflexx is supposed to be involved in appetitively and defensively motivated action,, and is therefore, in contrast to the startle reflex, not sensitive to the valencee of an affective state. T reflexes are augmented in states of action, andd modified by differences in arousal (Bonnet, Bradley, Lang & Requin, 1995;; Brunia & Boelhouwer, 1988; Brunia & van Boxtel, 2000). Therefore TT reflex modulation offers a window on the generation of action. In our previouss study, as expected, exposure to a sexually appetitive stimulus inducedd genital responses, and generated feelings of sexual arousal, as welll as subjective approach tendencies. Processing of both sexual and anxietyy stimuli facilitated T reflexes, and reflexes were augmented by a sexuall stimulus to the same extent as by anxiety stimuli. These data supportedd our view of sexual arousal as an emotional state, resulting in sex-specificc autonomic and somatic motor system responses, preparing thee organism for action.
Thee purpose of the present study was to investigate whether exposuree to sexual stimuli of varying intensity results in different levels of activationn in the somatic motor system. Intensity is an important componentt of emotion since the strength of action tendency may determine,, among other factors, whether emotions lead to actual behaviorr (Frijda, Ortony, Sonnemans, & Clore, 1992). Also, as is noted byy Frijda et al. (1992), it is often the intensity of emotion and the consequentiall behavior that may be considered as maladaptive. For example,, too much, but also too little fear, can be problematic for a personn or his or her social environment. Likewise, too much, and too little sexuall arousal and desire may be troubling. Studying the strength of actionn tendencies, and factors that influence it, will be useful in research onn appetitive behavior, and related disorders like for example addiction, orr hypo- or hyper-sexual desire disorder. Possibly T reflex modulation mayy provide a window on the strength of action tendencies, and on individuall or contextual factors influencing this strength. However, before studyingg individual differences in, or the effect of manipulations on the strengthh of action tendencies through T reflex modulation, the modulation off T reflexes by varying levels of emotion intensity has to be determined. Thereforee in the present study it was investigated whether exposure to
sexuall stimuli of increasing intensity results in increasing levels of sexual arousall and T reflex augmentation.
TT reflexes can be elicited by a hammertap at the heel tendon, which resultss in a reflexive electromyographic (EMG) response in the soleus musclee of the lower leg. The magnitude of the EMG response reflects the numberr of motoneurons currently activated in the pool that innervates the soleuss muscle. Since 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 reflex arc 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). It is known that TT reflexes are augmented after the presentation of a loud noise or a brightt light, or during reaction time tasks and mental arithmetic (Brunia & Boelhouwer,, 2000). These facilitations are interpreted as due to the effectss of nonspecific arousal, and indicated that T reflexes may be modulatedd by emotional arousal.
Bonnett et al. (1995) studied the modulation of T reflexes during the presentationn of pictures from The International Affective Picture System' designedd by Lang, Öhman, and Vaitl (1988). The pictures from this systemm are designed to induce emotions varying in valence (positive to negative)) and in intensity (low to high). As expected, T reflexes were significantlyy augmented when elicited during processing of emotional picturess (either negative or positive) as compared with neutral pictures. Bothh low or high arousal unpleasant stimuli augmented T reflexes, and to aa comparable extent. However, for the pleasant pictures, only the reflexess elicited during high arousal stimuli were significantly augmented. Reflexess elicited during low arousal pleasant stimuli did not differ from thosee elicited during neutral pictures. Bonnet et al. concluded that this suggestss that unpleasant stimuli are more closely associated with action engagementt than are pleasant pictures, at least when intensity is low. However,, they also noted that the affective ratings used to categorize the picturess on the basis of arousal were obtained from different subjects thann from whom the T reflexes were elicited. Therefore, although unlikely, itt cannot be ruled out that the latter sample would have rated the stimuli
differently,, which might have affected the obtained reflex magnitude pattern. .
Similarr to Bonnet et al. we hypothesized emotional stimuli, more specificallyy sexual stimuli, to automatically generate action tendencies, reflectedd in increased spinal excitability, and we expected the strength of thee action tendency to be associated with stimulus intensity. T reflexes duringg exposure to sexual stimuli of low, medium, and high intensity were monitored.. To elicit the sexual states we used film excerpts that previouslyy showed to evoke distinct, and increasing levels of genital arousall in women (Laan, Everaerd, van der Velde, & Geer, 1995). To checkk for the induction of emotional intensity levels as intended, we measuredd genital response, subjective emotional responses, and subjectivee action tendencies. To show that increased T reflex magnitudes aree a function of emotional stimulus intensity, and to rule out that responsess increase over time independent from stimulus intensity, we addedd a control condition in which participants were exposed to three identicall erotic film excerpts of medium intensity. Previously it was found thatt repeated exposure to 21 identical erotic film excerpts resulted in stablee levels of genital arousal in women (Laan, Everaerd, van der Velde, && Geer, 1995). Thus, in the experimental condition participants were exposedd to three sexual film excerpts of increasing intensity, which were expectedd to evoke increasing levels of genital arousal, subjective sexual arousal,, subjective approach tendencies, and T reflex amplitude. In the controll condition participants were exposed to three identical sexual film excerptss of medium intensity, which were expected to result in stable levelss of genital arousal, subjective sexual arousal, approach tendencies, andd T reflex amplitude.
Method d
Thee data were collected at two sites. Part of the increasing stimulus conditionn data was obtained at the Psychonomics section of the Tilburg Universityy (N=11). Additional data for the increasing stimulus condition weree collected at the department of Clinical Psychology of the University off Amsterdam (ISM 8), where also the data of the stable stimulus conditionn were collected (N=16). Stimulus materials and experimental
proceduress were identical at the two sites. Also, apart from some differencess in technical set-up, response measurement was identical at thee two sites. Subjective action tendencies, though, were measured only att the University of Amsterdam.
Participants Participants
Participantss were 45 women, mainly psychology students, who received coursee credit or were paid for their participation. Mean age of the participantss was 22.9 years (range = 1 9 - 2 8 years, SD - 2.5 years). Eighteenn (40%) participants had a heterosexual orientation, 23 (51%) participantss had a predominantly heterosexual orientation, and 4 (9%) participantss considered themselves to be bisexual. Twenty-seven participantss (60%) had a steady partner. All participants had experienced sexx with a partner, and 41 (91%) had experienced coitus. The majority of thee participants (71%) had seen erotic films once or twice prior to participation.. Two (4%) participants had never seen erotic film, 2 (4%) participantss had seen erotic films once, and 9 (20%) participants had seenn erotic film regularly prior to participation.
Precedingg participation, all participants received written information includingg a description of the procedure, and the physiological measures. Informedd consent, in which confidentially, anonymity, and the opportunity too withdraw from the experiment without penalty were assured, was obtainedd from all participants.
Design Design
AA 2 x 3 between-subjects repeated measures design was employed, with conditionn (increasing intensity versus stable intensity) as between-subjectss variable, and stimuli as within variable. At the Amsterdam site participantss were randomly assigned to the increasing and stable intensityy conditions.
MaterialsMaterials and Response Measurement
StimulusStimulus materials. The film excerpts consisted of 3-min videotapes
withh sound. Each 3-min tape consisted of three 1-min scenes. The low intensityy stimulus depicted erotic kissing, the medium stimulus showed kissingg and caressing, and the high intensity stimulus depicted intercourse.. In the increasing condition the participants saw the low
intensityy stimulus first, then the medium intensity stimulus, and then the highh intensity film clip. In the stable condition the participants saw the mediumm intensity film clip three times. As noted before, a previous study showedd that the low, medium, and high intensity film clips evoked distinct, andd increasing levels of genital arousal in women (Laan, Everaerd, van derr Velde, & Geer, 1995). All excerpts were originating from films directedd and produced by Candida Royalle. Films produced by Candida Royallee are aimed at women, and are more female initiated and female centeredd than regular erotic movies. Earlier studies in our laboratory have shownn that female-centered erotic film evokes less feeling of shame, guilt andd aversion in women compared to male centered erotic film (Laan, Everaerd,, van Bellen, & Hanewald, 1994; Laan, 2004).
PhysiologicalPhysiological recordings. T reflexes and genital responses were
recordedd continuously during baselines and stimulus presentations. T reflexess were elicited with a hammer. The measurement was carried out inn accordance with standard methods and procedures for evoking T reflexess (Desmedt, 1973). Participants sat in an individually adjusted chairr with their legs held in a fixed position. The knee wass maintained in a
fixed,, semi-flexed position , and the angle of the ankle joint was
.. The feet were strapped to foot pedals to obtain nearly isometric contractionss of the soleus. The Achilles tendon of the right leg was hit by aa hammer at a right angle to the tendon, at the level of the lateral malleolus.. The hammer was connected to a Brüel and Kjaer 4809 vibrationn exciter. T reflexes were elicited at a constant rate of one every 5ss during baselines and stimulus presentations, resulting in 24 reflexes duringg each 2-min baseline, and 36 reflexes during each 3-min stimulus
presentationn period. Surface electrodes (Ag/AgCI electrodes, 2 cm2
contactt area) were placed (3 cm apart) upon the soleus muscle, along thee longitudinal axis of the calf, the proximal electrode of the pair was placedd 2 cm distal to the insertion of the gastrocnemius muscle on the Achilless tendon.
Genitall response was measured using a vaginal photoplethys-mographh assessing VPA (vaginal pulse amplitude, the AC component of thee signal) and VBV (vaginal blood volume, the DC component). Since formerr research has shown that VPA is the superior measure in terms of bothh convergent and divergent validity (Laan, Everaerd, & Evers, 1995), onlyy VPA data were used. Depth of the probe and orientation of the light
emittingg diode were controlled by a device (a 9- x 2-cm plate) attached to thee photoplethysmograph. Participants were instructed to insert the photoplethysmographh such that the plate touched their labia. The vaginal photoplethysmographh was sterilized in a solution of Cidex-activated gg I Paraldehyde between uses (Geer, 1980).
SubjectiveSubjective measurements. Prior to stimulus presentation and after
eachh film excerpt data of subjective sexual arousal and emotional experiencee were collected. Participants were asked to assess on a 7-pointt scale: (a) overall sexual arousal; (b) strongest feeling of sexual arousal;; and (c) strongest genital sensations. The extremes were 'not sexuallyy aroused at all' and 'very strongly sexually aroused' for item a andd b, and 'no sensations in my genitals' and 'orgasm' for item c.
Emotionall experience was measured by a questionnaire consisting of 211 emotions (including sexual emotions). Participants were asked to indicatee on a 7-point scale (with not at all' and 'very strong' as extremes) too what extent they had experienced these emotions while watching the filmm excerpt. In an earlier study, factor analysis had indicated that the 21 emotionss could be divided into 7 emotions reflecting lust (Cronbach' s a = .82),, 4 emotions relating to anger (Cronbach' s a = .85), 8 emotions relatingg to threat (Cronbach' s a = .71), and 2 emotions reflecting tension (Cronbach'' s a = .79) (Laan, Everaerd, & Evers, 1995).
Subjectivee action tendencies were measured by the Action Tendency Questionnairee (ATQ). This questionnaire was administered at the Amsterdamm research site only. Therefore ATQ data were collected only forr a part of the increasing stimulus condition participants (N= 18), and for alll participants in the stable condition (N= 16). The questionnaire assessedd the tendency to execute overt behavior, without necessarily doingg so (Frijda, Kuipers, & ter Schure, 1989), and was administered afterr each stimulus presentation. Participants were asked to assess on 5-pointt 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 statements indicating approach tendenciess (e.g., 'I wanted to approach, to make contact') to statements indicatingg avoidance (e.g., 'I wanted to have nothing to do with something orr someone, to be bothered by it as little as possible, to stay away'). Formerly,, factor analysis had revealed that the questionnaire could be dividedd in 4 subscales: approach (Cronbach' s a = .87), avoidance
(Cronbach'' s a = .75), protection (Cronbach' s a = .81), attention (Cronbach'' s a = .76; Laan & Everaerd, 1995b).
Procedure Procedure
Too help participants make an informed decision about whether to participatee in this experiment, they received written information in which aill experimental procedures were explained in detail. They were informed aboutt the T reflex elicitation and the genital measure, as well as about thee sterilizing procedures.
Eachh participant was tested individually by a trained female experimenter.. On arrival at the laboratory, the participant read and signed ann informed consent form and completed a questionnaire about sexual experiencee and sexual problems. The experimenter then explained all the detailss of the experimental procedure and attached the electrodes. After adjustingg the chair, the experimenter determined the intensity of mechanicall stimulation necessary to elicit reflexes. Then the intensity wass adjusted to obtain, at rest, a reflex EMG whose amplitude was betweenn 25% and 50% of the estimated maximum T reflex. After the experimenterr had left the room, the participant inserted the vaginal probe. Afterr the participants signaled (using a one-way intercom system) that the transducerss had been placed, they rated their feelings of sexual arousal andd emotional experience.
Afterr this a 2-min baseline period followed. Then the first film excerpt wass presented. After the film excerpt, participants rated their feelings of sexuall arousal and emotional experience, and their action tendencies. Thiss was followed by a 3-min return-to-baseline period. To facilitate return-to-baselinee participants completed a concentration task (simple arithmeticc problems) during the return-to-baseline period. Then the next filmm excerpt was showed following an identical procedure, until all three filmm excerpts were shown.
AtAt the end of the experiment an exit interview was administered. Participantss were asked about their reactions to the experimental procedure,, the T reflex elicitation and the use of the genital device.
DataData reduction, scoring, and analysis
EMGG was sampled across baselines and subsequent stimulus presentationn periods. The mean T reflex amplitude elicited during each
baselinee period (X) and each stimulus presentation period (Y) was calculated.. A percentage of baseline score was calculated (percentage of baselinee = V/ X * 100) for each stimulus.
VPAA was also sampled across baselines and the subsequent stimuluss presentation periods. Data were entered into a computer program,, developed by Bert Molenkamp (Technical Support, Department off Psychology, University of Amsterdam), that enables off-line graphical inspectionn of the data. Artifacts in the VPA channel are caused by movementss of the lower part of the body or by voluntary or involuntary contractionss of the pelvic muscles. Since artifacts show an extreme increasee in vaginal pulse amplitude they can be detected by visual inspection.. After artifact removal mean VPA during each baseline period (X)) and each stimulus presentation period (V) was calculated. Then a percentagee of baseline score was calculated (percentage of baseline = Y
IIX*X* 100) for each stimulus.
Forr emotional experience the items belonging to each of the describedd factors were averaged, thus creating a lust, anger, threat and tensionn score. For action tendency ratings only the approach and avoidancee factors were used for further analysis. The approach items and thee avoidance 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 proceduress (General Linear Model in SPSS), using a significance level of .05.. Subjective sexual arousal and emotional experience were submitted too MANOVA's. Subjective approach en avoidance tendency, genital arousal,, and T reflex magnitude were submitted to ANOVAs. Following significantt F ratios for each dependent measure, univariate contrast analysess (comparisons between all possible pairs) were performed to test forr specific stimulus effects.
Results s
Responsess at exit interviews indicated that, in general, the participants hadd felt comfortable during the experiment. However, regarding the genitall measurement, 5 participants indicated that they felt somewhat
disturbedd by the measurement, 1 indicated that she felt slightly disturbed, andd 1 participant indicated that she felt strongly disturbed. Regarding the TT reflex measurement, 7 participants reported that they felt somewhat disturbedd by the measurement, 11 participants indicated that they felt slightlyy disturbed, and 1 participant reported to be strongly disturbed. The latterr participant was not the same as the participant who reported that shee felt strongly disturbed by the genital measurement.
SubjectiveSubjective Sexual Arousal, Emotional Experience, and Action Tendencies Tendencies
SubjectiveSubjective sexual arousal. The stimulus presentations had their
intendedd effect upon subjective sexual arousal ratings (Figure 1). There wass a main effect of stimuli, multivariate F(6,170) = 4.34, p < .001, and ann interaction effect of condition and stimuli, multivariate F(6,170) = 5.36, pp < .001. In the increasing intensity condition there was an effect of stimuli,, multivariate F(6,110) = 7.71, p < .001, while in the stable intensity conditionn there was not (p > .25). Comparison of all possible pairs of meanss of the three subjective sexual arousal items (Table 1) showed that inn the increasing intensity condition sexual arousal scores in response to thee medium intensity stimulus were higher than to the low intensity stimulus,, and that subjective sexual arousal scores in response to the highh intensity stimulus were higher than in response to the medium intensityy stimulus.
EmotionalEmotional experience. There was an effect of stimuli on emotional
experience,, multivariate F(8,168) = 3.90, p < .001, and an interaction of conditionn and stimuli, multivariate F(8,168) = 3.18, p < .005. Univariate analysiss showed only for feelings of lust a significant effect of stimuli, F(2,86)) = 6.01, p < .005, and a significant interaction of condition and stimuli,, F(2,86) = 10.04, p < .001. For the increasing intensity condition theree was an effect of stimuli on feelings of lust, F(2,56) = 19.45, p < .001,, feelings of lust increased over stimuli (Table 1). In the stable conditionn there was no significant change in feelings of lust. Follow-up comparisonn of means showed that in the increasing condition feelings of lustt in response to the medium intensity stimulus were higher than to the loww intensity stimulus, and lust ratings in response to the high intensity stimuluss were higher than to the medium intensity and low intensity stimulii (Table 1).
Tablee 1. Mean (SD) subjective ratings of sexual arousal, emotional
expe-riencee and action tendencies in response to the low, medium, and high intensityy sexual stimuli, for the increasing intensity and stable intensity condition. . SexualSexual arousal Overall l sexuai i arousal1 1 Strongest t sexual l arousal1 1 Strongest t genital l sensations2 2
Increasingg Intensity Condition
Low w 2.4a a (0.8) ) 2.8a a (0.9) ) 2.3a a (1.0) ) EmotionalEmotional experience3 Lust t Anger r Threat t Tension n 1.9a a (0.9) ) 1.2 2 (0.4) ) 1.4 4 (0.5) ) 1.8 8 (1.0) ) ActionAction tendencies4 Approach h Avoidance e 1.9a a (0.9) ) 2.3 3 (0.7) ) Medium m 3.5a a (0.9) ) 3.9a a (1.2) ) 3.2a a (1.4) ) 2.4a a (1.1) ) 1.2 2 (0.3) ) 1.6 6 (0.5) ) 1.8 8 (0.9) ) 2.2b b (1.0) ) 2.2 2 (0.8) ) High h 4.0a a (1.4) ) 4.6a a (1.6) ) 3.9a a (1.5) ) 2.9a a (1.4) ) 1.3 3 (0.4) ) 1.6 6 (0.6) ) 1.7 7 (1-0) ) 2.5ab b (1.2) ) 2.2 2 (0.5) )
Stablee Intensity Condition
Medium m 3.4 4 (1.4) ) 3.8 8 (1.7) ) 3.4 4 (1.8) ) 3.0 0 (1.2) ) 1.2 2 (0.4) ) 1.6 6 (0.5) ) 2.3 3 (0.9) ) 2.5 5 (0.9) ) 2.3 3 (0.8) ) Medium m 3.4 4 (1.4) ) 4.1 1 (1.6) ) 3.3 3 (1.9) ) 3.2 2 (1.5) ) 1.3 3 (0-5) ) 1.7 7 (0.6) ) 1.9 9 (0.9) ) 2.7 7 (1.1) ) 2.1 1 (0.8) ) Medium m 3.2 2 (1.8) ) 3.6 6 (1.9) ) 3.4 4 (2.0) ) 2.9 9 (1.6) ) 1.3 3 (0.4) ) 1.7 7 (0.5) ) 1.7 7 (0.9) ) 2.6 6 (1.1) ) 2.2 2 (0.6) ) Note:Note: For each dependent measure, means with common character in
super-scriptss are significantly different at p < 0.01 (sexual arousal and emotional experiencee ratings: increasing condition df = 28, stable condition df = 15) (actionn tendency ratings: increasing condition df= 16, stable condition df - 15). 1
11 = not sexually aroused at all; 7 = very strongly sexually aroused. 2
11 = no sensations in my genitals; 7 = orgasm. 31 = not at all; 7 = very strong. 4
SubjectiveSubjective approach and avoidance tendencies. For 1 participant in
thee increasing stimulus condition data on subjective action tendencies weree missing due to technical problems. There was a main effect of stimulii on subjective approach tendency, multivariate F(2,62) = 5.3, p < .01,, and an interaction of condition and stimuli, multivariate F(2,62) - 3.4, pp < .05. In the increasing intensity condition there was an effect of stimuli onn subjective approach tendency, F(2,32) = 7.5, p < .005. As expected, approachh tendency increased in the increasing intensity condition. In the stablee intensity condition there was no effect of stimuli on approach tendency.. Follow-up comparison of means showed that in the increasing conditionn subjective approach ratings in response to the medium intensity stimuluss were marginally higher than to the low intensity stimulus, and approachh ratings in response to the high intensity stimulus were higher thann to the medium intensity and low intensity stimuli (Table 1). For subjectivee avoidance tendencies there was no effect of stimuli, and no interactionn of condition and stimuli. In both conditions avoidance tendenciess showed a stable pattern (Table 1).
GenitalGenital Responses
Duee to technical problems VPA data of 5 participants in the increasing stimuluss condition, and 3 participants in the stable condition were missing.. The stimulus presentations had their intended effect on genital responsess (Figure 2). There was a main effect of stimuli on VPA, F(2,70) == 7.28, p < .001, a main effect of condition, F(1,35) = 7.67, p < .01, and ann interaction of condition and stimuli, F(2J0) - 7.45, p < .005. VPA was overalll higher in the increasing intensity condition. As expected, VPA increasedd in the increasing intensity condition, F(2,46) = 15.13, p <.001, andd did not significantly change in the stable condition, (p >.9). Comparisonn of ail possible pairs of mean VPA responses showed that, in thee increasing stimulus condition, genital responses during the medium intensityy stimulus were stronger than during the low intensity stimulus, f(25)) = -3.76, p < .005, genital responses during the high intensity stimuluss were stronger than responses during the low intensity stimulus, f(23)) = -4.7, p < .001, and genital responses during the high intensity stimuluss were stronger than responses during the medium intensity stimulus,stimulus, f(23) = -2.64, p < .05.
220 0 I JJ 190 == o o .. co EE
<a a
88 S 160 33 O) Q.. JS11 |
<?? g. 130 Genitall ResponseY^Y^
_ x - \
100 0Stimuluss 1 Stimulus 2 Stimulus 3
gg condition - - « - - s t a b l e condition
Figuree 1. Mean Vaginal Pulse Amplitude change (and SEM) in response
too stimulus 1, 2, and 3, in the increasing and stable intensity condition.
TT Reflex magnitude
Duee to technical problems, and difficulties in evoking satisfying reflexes, reflexx data of 4 participants in the increasing condition, and 4 participants inn the stable condition were missing. There was a marginally significant interactionn effect of condition and stimuli, F(2,70) = 2.29, p =.11. In the increasingg intensity condition there was an effect of stimuli, F(2,48) = 3.57,, p < .05. As expected, T reflex magnitudes increased in response to thee stimuli of increasing intensity (Figure 2). In the stable intensity conditionn there was, as expected, no effect of stimuli on T reflex magnitudee (p > .55). Comparison of all possible pairs of mean T reflex magnitudess showed that in the increasing intensity condition reflexes duringg the medium intensity stimulus were not stronger than reflexes duringg the low intensity stimulus, f(25) = -1.42, p = .17. T reflexes during thee high intensity stimulus were significantly stronger than reflexes during thee low intensity stimulus, f(24) = -2.18, p < .05, and reflexes during the highh intensity stimulus were marginally stronger than reflexes during the mediumm intensity stimulus, f(25) = -1.7, p = .1.
TT Reflex Magnitude 150 0
ï
140
| | | | || 130 XX O) f ff 120 ZZ £ 100 0Stimuluss 1 Stimulus 2 Stimulus 3
gg condition --«--stable condition
Figuree 2. T Reflex Magnitude (and SEM) in response to stimulus 1, 2,
andd 3, in the increasing and stable intensity condition.
Discussion n
Inn the present study it was shown that exposure to sexual stimuli of increasingg intensity elicits increasing levels of sexual arousal, and increasingg levels of T reflex augmentation. Thus T reflex reactivity was modifiedd by the parameter of emotional arousal, more specifically by sexuall arousal. The results obtained in this study corroborate the enhancingg effect of emotional arousal on T reflex strength reported by Bonnett et al. (1995), and the effect of sexual arousal on T reflex magnitudee reported by our research group (Both et al. 2003). Moreover, wee showed that emotion intensity influences action tendency strength reflectedd in subjective approach tendencies and somatic motor activity. Thee results show that T reflexes are modulated by varying levels of sexuall arousal, which indicates that T reflex modulation may be a workablee method to investigate manipulations of, or group differences in, somaticc motor activity strength in response to erotic stimuli.
Thee data regarding genital responses and subjective reports showed thatt the sexual stimuli evoked the intended levels of sexual arousal. Exposuree to three erotic film excerpts of respectively low, medium, and
highh intensity, resulted in increasing levels of genital arousal, increasing levelss of subjective sexual arousal, and increasing feelings of lust. In contrast,, exposure to three sexual film excerpts of medium intensity resultedd in stable levels of genital arousal, subjective sexual arousal, and feelingss of lust. In the stable intensity condition also feelings of anger slightlyy increased, and feelings of tension slightly decreased. However, ass expected, anger and tension ratings were very low, indicating that the sexuall stimuli evoked virtually no feelings of anger and tension. Therefore wee may conclude that we were successful in the induction of positive sexuallyy emotional states of increasing intensity.
Inn our view sexual emotions, as emotions in general, can be conceivedd of as action tendencies. Therefore we expected sexual stimuli too evoke subjective approach tendencies, and we expected approach tendenciess to vary as a function of stimulus intensity. The results regardingg subjective action tendencies show that, as expected, the sexuall stimuli evoked approach tendencies, and that these approach tendenciess increased in response to increasing stimulus intensity. Subjectivee avoidance tendencies, in contrast, were not affected by sexual stimuluss intensity. Thus exposure to the sexually arousing stimuli of varyingg intensity switched on approach tendencies that varied in strength. Thesee different levels of action tendency strength were accompanied by differencess in the degree of somatic motor preparation, reflected in T reflexx magnitudes. T reflex magnitudes increased in response to the low, medium,, and high intensity sexual stimuli. In contrast, in the stable intensityy condition T reflex magnitudes were enhanced by the medium intensityy stimulus, but did not significantly differ between stimuli.
Regardingg sensitivity of T reflex modulation to differences in emotionall intensity we have to note that, in the increasing intensity condition,, only the difference in T reflex magnitude during the high and loww intensity stimuli reached significance. The difference in reflex magnitudee during the high and the medium intensity stimuli was only marginallyy significant. Thus, very small differences in emotional arousal may,, possibly due to relatively high variance in reflex reactivity, be only weaklyy reflected in the strength of T reflexes.
Inn contrast to Bonnet et al. (1995), who found that for pleasant picturess only reflexes elicited during high arousal stimuli were significantly augmented,, we found that exposure to sexual stimuli of low, medium, and
highh intensity resulted in an enhancement of T reflexes of respectively 20, 29,, and 41 percent relative to baseline. Bonnet et al. concluded that, whenn intensity is low, pleasant stimuli are less associated with action engagementt then unpleasant stimuli. Although we have to note that erotic film,, even an excerpt that shows only erotic kissing, can be expected to bee more arousing than still photos that were used by Bonnet et al., our dataa indicate that pleasant stimuli, at least sexually pleasant stimuli, are associatedd with action engagement even when intensity is relatively low.
Thee current study shows that subjective sexual arousal and genital responses,, as well as subjective action tendencies and somatic motor activity,, are modulated by sexually appetitive stimuli of varying intensity. Thesee results support the view that sexual motivation is an emergent property,, the outcome of the processing of sexual stimuli, and that the strengthh of the emerging responses varies as a function of stimulus intensity.. In addition, the results show that processing of sexual stimuli resultss in activity within systems involved in general motivated behavior (reflectedd in T reflex modulation), and in systems involved in specific sexuall behavior (reflected in genital responses).
Althoughh the results regarding T reflex modulation indicate that it may bee difficult to catch subtle differences in emotional arousal in reflex magnitudes,, reflex modulation might be a useful tool in research on appetitivee motivation. According to Berridge (1996) distinct neurobiologicall processes underlie the valence and arousal dimension of motivationall responses. Robinson & Berridge (1998) suggested that sensitizedd arousal reactions to incentive stimuli may play a role in the developmentt of addiction. Recently, research on implicit and explicit alcohol-relatedd cognitions showed implicit arousal associations in heavy drinkers,, possibly reflecting a sensitized psychomotor-activating response too drug cues (Wiers, van Woerden, Smulders, & de Jong, 2002). As an indexx of psychomotor arousal T reflex modulation may be of use in researchh on the behavioral mechanisms underlying appetitive motivation inn humans, and related disorders like substance addiction and hypo- or hyperactivee sexual desire.
