Phallometric Assessment of Sexual Arousal

30 Pages·2010·0.19 MB·English

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Chapter Seven
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Phallometric Assessment of
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8 Sexual Arousal
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Hannah L. Merdian
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13 Department of Psychology, The University of Waikato
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and
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16 David T. Jones
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Te Piriti Special Treatment Unit, Auckland
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23 Introduction
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25 The penile plethysmograph is a device which measures male sexual arousal by
26 means of a transducer around the subjects’ penis while various stimuli are
27 presented. Although this seems to be a simple enough premise, half a century
28 ofresearchhasfailedtodemonstratethattheassessmentiseitherreliableorvalid.
29 It does, however, seem to be a significant predictor of risk.
30 This chapter reviews the literature around the reliability and validity of
31 phallometric assessment, the limitations to its use, its contribution to risk
32 assessment,andalternativestoitsuse,andconcludeswithremarksonthefuture
33 of the phallometry.
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36 The penile plethysmograph and its procedures
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38 Originally developed by Kurt Freund to assess sexual orientation in men, the
39 penileplethysmograph(PPG)waslateradaptedtoassessdeviantsexualarousal
40 in male offender populations by Vernon Quinsey (Marshall, 1996). The prin-
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InternationalPerspectivesontheAssessmentandTreatmentofSexualOffenders:Theory,Practice
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andResearch,EditedbyDouglasP.Boer,ReinhardEher,MichaelH.Miner,FriedemannPfa¨fflin,
44 andLeamA.Craig.(cid:1)2011JohnWiley&SonsLtd.Published2011byJohnWiley&Sons,Ltd.
142 Assessment and Treatment of Sexual Offenders
1 ciplebehindtheinstrumentcouldnotbemuchsimpler.Oneattachesadeviceto
2 the penis of a subject, and measures what happens to it when the person is
3 exposedtoavarietyofpossiblyarousingstimuli,eithervisualorauditory.Ina
4 typicalphallometricassessment,thesubjectisseatedprivatelyinacomfortable
5 chairwheretheycanattendtovisualstimuliandauditorystimuli.Assumingthat
6 penilearousalindicatessexualinterest,aperson’sarousalpatterninresponseto
7 various stimuli can be measured from the gauge around his penis. Often,
8 nonintrusive physiological measures such as galvanic skin response (GSR),
9 respiration and pulse rate are monitored in an attempt to detect suppression
10 or deliberate increases of arousal.
11 Freund’s initial device was based on a volumetric measure; an airtight glass
12 cylinderisfittedaroundthesubject’spenisandthevolumeofairdisplacedinthe
13 chamberisusedasameasureofpenilechanges(Kalmus&Beech,2005).While
14 sensitiveandaccurate,thistechniquehassomedrawbacks.Chiefamongthemis
15 thefactthatvolumetricdevicesmustbefittedbythetechnician,whichishighly
16 unpalatabletomanyassessors.Circumferentialgauges,ontheotherhand,asfirst
17 usedbyFisher,Gross,andZuch(1965),canbefittedbytheclienthimself.There
18 aretwotypesofcircumferentialgauges,bothofwhichmeasurechangestothe
19 diameterofthepenis,usuallyabouthalfwayuptheshaft.Barlowgaugesarethin
20 metalstripscurvedintoanopencircle,whilerubberstraingaugesarethinrubber
21 loops filled with mercury or indium-gallium. Both are commonly used in
22 correctionalsettings.Withthesetypes,changesinthecircumferenceofasubject’s
23 peniscanbemeasuredfromchangesintheelectricalresistanceofthegauge.
24 Overall,volumetricdevicesaresuperiortocircumferentialgauges,astheycan
25 register changes in both length and diameter (Marshall, 2006). As noted by
26 KalmusandBeech(2005),theinitialstagesofarousalinsomemenmayresultin
27 nochangeto,orevenadecreasein,circumferenceinsomemen.(Tounderstand
28 this,onemightimaginefillingthefingerofarubberglovewithwater;theend
29 mayfillfirst,contractingthemiddlebeforethepressurebalancesandthemiddle
30 expands.) Kuban, Barbaree, and Blanchard (1999) compared the two gauge
31 types and found them equivalent for high responders, but volumetric gauges
32 appeared to be superior for low responders with a maximum penile increase
33 below 10% full erection. Nonetheless, circumferential PPGs are more wide-
34 spread due to their easier application and commercial availability, and it is
35 unlikelythatanyonewouldusevolumetricdevicesinawidespreadcorrectional
36 application.
37 Therecontinuestobeagreatdealofcontroversyabouttheuseofphallometry
38 in correctional assessments. As Marshall and Fernandez (2000) point out, the
39 mainproblemisthelackofasoundempiricalbasis.AlthoughtheAssociationfor
40 the Treatment of Sexual Abusers (ATSA) recommends that the use of phallo-
41 metricassessmentshouldbeusedonlytoconfirmaclient’sselfreportofsexual
42 preferences(Howes,2003),manytreatmentprogramsusephallometricassess-
43 menttodetectdeviantsexualinterests,determinetreatmentneeds,andinform
44 riskassessments(Marshall,1996;Marshall&Fernandez,2003).Itisalsoused
Phallometric Assessment of Sexual Arousal 143
1 forbehavioraltreatment,eitherasameasureofsuccessorfordirectfeedbackto
2 the client in techniques such as covert desensitization (Adler, 1994), for
3 determining treatment progress (Blanchette, 1996) and for confronting an
4 offender’s denial of deviant arousal (Kercber, 1993).
5 Althoughearlyresearcherswereenthusiasticaboutthevalueofphallometryas
6 a fairly objective measure of male sexual arousal (see Marshall &
7 Fernandez,2003b;Zuckerman,1971),thereiscontroversyaboutwhatexactly
8 thePPGassesses.Ofcourse,fewwouldarguethefactthatsexualarousalinmen
9 leadstoswellingofthepenisasaconsequenceofincreasedbloodflowintothe
10 genitalarea.However,asSinger(1984)pointsout,sexualarousalisatrichotomy
11 ofanaestheticfeeling,anapproachreaction,andagenitalresponse.Whilethe
12 penileplethysmographseemsanobviousmeasureforthelatter,itsaysnothing
13 aboutthefirsttwoqualities.Gaither(2000)notesthatthePPGonlymeasures
14 oneformofsexualarousalwhilesexualpreferenceisamoreholisticconstruct.
15 Whereassomestudieshavedemonstratedthatmen’ssubjectivereportsoftheir
16 sexualexcitementcorrelatewellwithphysiologicalmeasures,thiswasnottrue
17 for low levels of genital response (Singer, 1984). On the other hand, high
18 correlationshavebeendemonstratedbetweenphallometricallyassessedandself-
19 reported sexual orientation in control populations (Lee-Evans, Graham, Har-
20 bison, McAllister & Quinn, 1975; Quackenbush, 1996) and more deviant
21 populations (Haywood, Grossman, & Cavanaugh, 1990), but both controls
22 andoffendersreportedsubjectivearousalthatwasnotphallometricallyindicated
23 and vice versa in this latter study.
24 ItisalsoquestionablewhetherphysicalarousalasmeasuredbythePPGisa
25 sufficientmeasuretodrawconclusionsaboutbehavior.Sexualoffencesmightbe
26 motivated by nonsexual reasons (Marshall & Fernandez, 2003) or some in-
27 dividualsmightexperiencesexualarousaltodeviantstimulibutwouldneveract
28 onit.Also,evenifphallometryisanaccuratemeasureofarousal,itisnotknown
29 whethersexualpreferencesareanenduringtraitthatshouldbedetectableina
30 laboratory setting, or whether they are influenced byenvironmental factors to
31 the extent that the assessment situation would preclude accurate assessment
32 (Marshall & Fernandez, 2003a).
33 Controversies aside, it nevertheless seems unreasonable to dispute a link
34 betweensexualarousaltodeviantstimuliandinappropriatesexualbehavior.As
35 Byrne(2001)concluded,despitethetheoreticaluncertaintiesregardingphallo-
36 metricassessment,sexualarousalisalargepartofthegenesisofsexualoffending,
37 and the PPG is a useful measure of this arousal.
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40 Psychometric properties
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42 Aside from the fundamental concerns noted earlier, there are many issues
43 concerningthepsychometricpropertiesofthepenileplethysmograph,including
44 awidevarietyofmethodologicalanddemographicvariablesconsideredbelow.
144 Assessment and Treatment of Sexual Offenders
1 Unfortunately, many studies lack detailed descriptions of these factors, which
2 further aggravates a comprehensive review (Marshall, 2006).
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5 Unstandardized assessments
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Among other variations, phallometric research has used different stimulus
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materials,differentstimulusmodalities,differentpresentationordersandtimes,
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differentgauges,anddifferenthardware.Evenrelativelyminorissuessuchasthe
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experimental instructions given can create considerable variability in the out-
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comes. However, despite many attempts, none of these factors have been
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standardized.
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Stimulus variables
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16 Obviously,ifoneisgoingtomeasurearousalthatoccursinresponsetosexual
17 stimuli,thechoiceofstimulusmaterialsislikelytohavesignificanteffectsonthe
18 results. Not surprisingly, there is significant variation among types of stimuli
19 used in the literature, roughly paralleling the development of the technology
20 usedtocreateandpresentthem.Earlierstudiestendedtouseaudiotapes,written
21 textorinstructionstofantasize,orslidesforvisualmaterials;laterstudiesmainly
22 use videotapes and current practice prefers audio and visual stimuli presented
23 from digital files on the recording computer. Visual materials may differ in
24 brightness, color, number of depicted persons, presence or absence of back-
25 ground,andineroticorneutralcontent.Theymayalsobeeitherstillvisualsor
26 livevideo,althoughthelatterisrarelyused.Audiomaterialswillvaryinthevoice
27 and dialect used, the nature of sexual activities described and the degree of
28 explicit description.As mostphallometric assessments areintended toidentify
29 subjects’ age and gender preferences, variability within the age categories
30 presented may have serious implications. For example, one metaanalysis of
31 children’s age categories demonstrated the necessity of using a developmental
32 taxonomyratherthanusingchronologicalages,sincechildrenofthesameage
33 were found to display considerable variation in their physical maturity (Fuller,
34 Barnard,Robbins,&Spears,1988).Also,noteveryexemplarofacategorywill
35 inevitablyleadtoanarousalreaction,justasaheterosexualnonoffenderwould
36 notthinkofeveryadultfemaleasequallyattractive.Individualswillvaryintheir
37 preferenceforgender,hairandskincolorandphysicalbuild,yetareexpectedto
38 respond comparably to a standard set of stimuli.
39 Giventheimportanceofthesevariables,itissurprisingthatonlyafewstudies
40 havecomparedtheeffectsofdifferentstimulussets.Onethatdidwasastudyby
41 Eccles, Marshall, and Barbaree (1994) that compared the effect of different
42 stimulussetswithvaryingdegreesofforceandhumiliationonconvictedrapists.
43 Looman (2000) and Looman and Marshall (2005) further extended this
44 approachbycomparingsetsofaudiotapeswithvaryingdegreesofbrutality.In
Phallometric Assessment of Sexual Arousal 145
1 an examination of the most effective stimulus modality, Abel, Blanchard, and
2 Barlow (1981) found that live action videotapes created the highest arousal
3 acrossalloffendertypesbarexhibitionists.However,thestrongarousalfound
4 usingvideotapesactuallyreducestheclassificationaccuracyoftheassessments,as
5 both offenders and nonoffenders often respond to live action deviant sexual
6 material (Marshall, 2006). Chaplin, Rice, and Harris (1995) suggested a
7 combinationofaudioandstillvisualstimuliasthemosteffectivediscriminator.
8 ThiswassupportedbyGolde,Strassberg,andTurner(2000),whoexaminedthe
9 differences between audio and audiovisual material in a sample of 53 nonof-
10 fenders. While both modalities created comparable results in a first session,
11 audio-onlymaterialledtolesserarousalinthefollow-upassessment,seemingly
12 moreaffectedbyhabituationeffects.However,anadvantageofthecombination
13 stimuliisthatitallowsforthemeasurementofdifferentaspectsofsexualstimuli:
14 visualstimulicanbeusedtoclearlyidentifytheageandgenderofthearousal-
15 provokingstimulus,whileaudiomaterialcandescribedifferenttypesofsexual
16 activities (Laws, Hanson, Osborn, & Greenbaum, 2000). This avoids the
17 potential problem of offenders forgetting the type of child being involved and
18 focusingonlyontheactivitydescribed.Still,thedebatecontinues,withMarshall
19 andothersrecommendingthataudiomaterialaloneproducessufficientrespond-
20 inganddiscriminantabilitywithoutvisualmaterial(Marshallpers.com.,2008).
21 Optimal presentation length is another aspect of phallometric assessments
22 thathasbeenthesubjectofdebate.Ingeneral,itappearsthatthereisaminimum
23 length of stimuli required in order to elicit arousal, but also a point at which
24 longerstimulielicitsarousalfromnonoffenders.Inaddition,somestudieshave
25 used“warm-upstimuli”inordertoprimearousaltolaterpresentations,while
26 some do not. For example, in the study by Quakenbush (1996), romantic
27 primers before sexually explicit scenes led to more rapid and higher erections.
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Technician variables
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31 Sexualarousalispeculiar,anditmakessensethatarousalpatternsareaffectedby
32 another person who is present at the time. The technician may create fear or
33 nervousness in the subjects, or might be an object of their sexual desire.
34 Adler (1994) compared the results of 65 sex offenders who had been assessed
35 by both a male and a female technician. In general, heterosexual subjects had
36 higherarousalwiththefemaleprofessionalpresent,whilehomosexualsreacted
37 moreinassessmentsconductedbyamale.Interestingly,allsubjectsexperienced
38 moresubjectiveanxietywhenassessedbythefemale.Giventhatmanytreatment
39 programsemployhighpercentagesoffemaletherapistswhomayconductthese
40 assessmentsthisisafactorwhichneedstobetakenintoaccountwhenevaluating
41 assessment results.
42 Ithasalsobeennotedthatmanyprogramsconductphallometricassessments
43 using technicians who have received little or no formal training in either the
44 assessment methodology or interpretation of results (Howes, 1995). At best,
146 Assessment and Treatment of Sexual Offenders
1 manyoftheseclinicianswillhavebeentrainedonthejobbyamoreexperienced
2 operators who themselves may or may not have been formally trained. Expe-
3 rience suggests that there are operators conducting these assessments who do
4 not understand the theory or practice of phallometric assessment and who
5 frequently draw unsupported conclusions as a result.
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7 Control group variables
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Some studies compare sexual offenders with nonoffenders (normals) or with
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nonsexual offenders while some compare within different offender types. The
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normalgroupisitselfheterogeneous,andsomedegreeofdeviantsexualinterest
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seemstobecommoninthenormalmalepopulation(Marshall,2006).Giventhe
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nature of a phallometric assessment, it is questionable whether every male
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nonoffenderisequallymotivatedtoparticipateinsuchastudy.Gaither(2000)
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mentions this self-selection effect in comparison groups, and suggests that
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volunteers for PPG trials might at least be more sexually experienced than the
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normalpopulation.Weare,afterall,basingournormalbaselineonagroupofmen
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whowillvoluntarilywatchorlistentosexuallyexplicitstimuliwithawirearound
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theirpenisconnectedtoamonitoredcomputerinanotherroom.Thismayormay
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notbeanormalthingtoagreetodo.AsPlaud,Gaither,Hegstad,Rowan,and
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Devitt (1999) demonstrated in their comprehensive study, this has serious
21
implications for the interpretationand generalizability ofthe resultingdata.
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Statistical issues
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25 As with the assessments, there is little standardization in the scoring and
26 interpretationofdata.Thereareseveralwaystodescribethedataproducedby
27 phallometricassessments.Theeasiestwayistousetherawmeasuresofcircum-
28 ferentialchangeinpenissize,buttheseareonlyusefulforcomparingresponses
29 within subjects. It may be fine to say that an offender demonstrated a 5mm
30 changeinresponsetoonestimulus,anda10mmchangetoanother,butitisnot
31 correcttosaythata5mmchangeinoneman’spenisisthesameasa5mmchange
32 in anotherone.This onlybecomes meaningfulif oneknowsthat bothpenises
33 werethesamesizetobeginwith,whichisunlikely.Also,ageisknowntoaffect
34 arousal,anda5mmchangeinamanof20yearsdoesnothavethesamemeaning
35 as a 5mm change in a man of 70 years.
36 A better way reporting results is by percentage of full erection (%FE). This
37 approach does allow comparisons between subjects, but is only accurate if the
38 size of the man’s full erection is known. There have been attempts to develop
39 normative data in order to estimate full erection from flaccid penis size
40 (Howes,2003)butthisisproblematic.Foronething,itisdifficulttoaccurately
41 measureflaccidpenissizeunlessthecliniciandoesit,whichisunpalatable,and
42 probablyimpossibleiftheclinicianisatallattractivetothesubject.Also,penis
43 size is variable, and technicians have been known to ask men to measure their
44 penisinacoldwashroom,thenplaceagaugeontheirpenisinamuchwarmer
Phallometric Assessment of Sexual Arousal 147
1 assessment room, resulting in remarkably inaccurate calibrations. It is also
2 importanttonotethatsomeassessmentsreport%FEscoresbasedonestimated
3 fullerectionsizesofperhaps30mmcircumferentialchange.Onesysteminvolves
4 theuseofdifferentestimatedmaximumfullerectionsdependingonwhethera
5 Barloworrubbergaugeisused,resultinginsubjectsbeingcomparedonthebasis
6 of %FE scores that represent completely different measurements of circumfer-
7 entialchange.Inanyevent,reporting%FEscoresbasedonstandardestimated
8 full erection sizes may be of use in explaining results to the subject but is
9 mathematicallyidenticaltoreportingrawscoresanddoesnotactuallyaccount
10 for individual differences.
11 One way of reporting results that does allow for individual differences is to
12 transform allscores to zscores, whichdescribe responses to differentstimulus
13 categories interms ofdeviation fromthe subject’s meanresponse.This allows
14 comparisons between individuals, and accounts for a greater percentage of
15 varianceaszscoresreducebetween-subjectvariability.However,zscoresmight,
16 dependingontherawscoredistribution,eitherexaggerateordiminishresponse
17 differences,andthusincreasetype1errors(Murphy&Barbaree,1994).Aswell,
18 usefulinformationontheoriginalmagnitudeofarousalislost(Adler,1994).In
19 a study by Earls, Quinsey, and Castonguay (1987), z scores were found to
20 describethesignificantlyhighestproportionofvariance(52.7%)incomparison
21 to %FE (32.5%) and raw scores (30.1%). This was supported by Harris, Rice,
22 Quinsey,Chaplin,andEarls(1992),whofoundzscorestobeslightlysuperiorto
23 percentageoffullerection.Onlyonestudydemonstratedthesuperiorityof%FE
24 tozscoretransformationsastheydidnotdistortthedataasmuch(Barbaree&
25 Mewhort, 1994). More recently, Byrne (2001) confirmed that transformation
26 intozscoreshadthehighestdiscriminativepowerofallthreescoringmethods.
27 A final way to report results is with deviance indices, the ratio of deviant to
28 appropriateresponses(Launay,1999).Thesemayeitherbederivedfrompeak
29 values or from average responses to stimulus categories. Although Harris
30 etal.(1992)andMurphyandBarbaree(1994)foundpeakresponsestoproduce
31 more reliable and sensitive indices, Launay (1999) found that both methods
32 provided acceptable outcomes. In the study by Harris et al. (1992), better
33 discrimination between offender types was obtained with indices than with
34 scoresbasedonindividualcategories.QuinseyandChaplin(1984)foundrape
35 indices to be clearly superior in the discrimination of rapists and nonrapists.
36 Indices also allow for meaningful comparisons between subjects, and remain
37 consistent within subjects after habituation effects occur (Marshall, 2006).
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Subject variables
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41 A subject’s characteristics inevitably influence the test outcome. Some differ-
42 ences are obvious; different sexual orientations, for example, will produce
43 differentarousalpatterns.Somecharacteristicssuchasageandintelligenceare
44 less obvious.
148 Assessment and Treatment of Sexual Offenders
1 Age. It is known that sexual capability declines as men age (Rowland,
2
Greenleaf, Dorfman, & Davidson, 1993). This natural process also applies to
3
sexual offenders; studies by Castonguay, Proulx, Aubut, McKibben, and
4
Campbell (1993) and Blanchard and Barbaree (2005) demonstrated the
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inverse relationship between age and sexual arousability, which affected every
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offender subtype.
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8 IQ. Murphy, Haynes, Coleman, and Flanagan (1985) found a significant
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relationshipbetweenrapeindexandintelligencequotientintheirlargesample.
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ThecorrelationbetweenIQanddeviancescorewasconfirmedbyotherstudies,
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andpreviousreviewssuggestedlowerfakingabilitiesinsubjectswithlowerIQ
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asamediatingvariable(Marshall&Fernandez,2003;Murphy&Barbaree,1994).
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WecouldonlyidentifyonestudybyWormith,Bradford,Pawlak,Borzecki,and
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Zohar (1988)where lower IQwas associated with loweroverall arousal.
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16 Ethnicity. Theethnicoriginsandsocialenvironmentofapersonwillinfluence
17 whattheyregardassexuallyattractive.NorthAmericanstimulussetsmaywell
18 notachievecomparableresponsesinoffendersfromanAsianbackground.One
19 examplewasprovidedbyMurphy,DiLillo,Haynes,andSteele(2001)whereall
20 adolescentoffendersofCaucasianoriginconsistentlydisplayedhigherresponses
21 than did their African American counterparts to stimuli of Caucasian origin.
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23 LowResponders. Manymenwillshowverylowarousalresponsestoanytype
24 ofstimuliinalaboratorysetting.Menwithresponsesbelowasetcutscoreare
25 often described as nonresponders. Kuban et al. (1999) suggest 10% of an
26 estimated full erection as a cut score, and this appears to be a widely used
27 threshold. Nonresponders are generally excluded from further statistical anal-
28 ysis, but the number excluded varies as a result of the cut score chosen. For
29 example, Byrne (2001) excluded 16% of his sample of 134 subjects using a
30 thresholdof20%FE.Looman,Abracen,Maillet,andDiFazio(1998)excluded
31 74.5% of their sample as nonresponders on an assessment of age and gender
32 preferences. It is noted that Looman and his colleagues also found high
33 correlations with social desirability in nonresponders, which might suggest
34 the voluntary suppression of arousal in some of these subjects rather than an
35 inability to become aroused.
36 Obviously, this issue has implications for the interpretability of assessment
37 data.Thereislittleutilityinanassessmentthatprovidesusefulinformationon
38 only25%ofthesubjectstested.Still,theissuecontinuestobedebated,which
39 somewriterssuchasByrne(2001)maintainingtheopinionthatnonresponder
40 data are typically not interpretable, while others such as Harris et al. (1992)
41 suggest that the data from low responders can be interpreted, provided that
42 responsestosexualorviolentstimuliarehigherthanresponsestoneutral(i.e.,
43 nonsexual, nonviolent) stimuli.
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Phallometric Assessment of Sexual Arousal 149
1 Faking. As noted, it is difficult to say whether low responding indicates a
2 genuine lack of interest, or a deliberate attempt to hide arousal. Phallometric
3 assessmentsaretransparent,andthesubjectsknowthatitisatestoftheirsexual
4 preferences. It is likely that most sexual offenders would fear negative con-
5 sequencesfromdisplayingabnormalarousalpatterns,andprobablytheywould
6 try to suppress arousal to deviant stimuli and enhance arousal to appropriate
7 material.Unfortunately,severalstudieshavedemonstratedthatbothoffenders
8 and nonoffenders can effectively manipulate their erectile response in either
9 direction(Kalmus&Beech,2005;Marshall,2006).Forinstance,Byrne(2001)
10 classifiedasmanyas68%ofhissampleofsexualoffendersassuppressors,while
11 Hall, Proctor and Nelson (1988) reported that up to 80% of their sample
12 appearedtobeabletosuppressarousal.Theabilitytodothisappearsdependant
13 tosomedegreeonthestimulusused.Perhapsnotsurprisingly,itappearseasier
14 tohidearousaltolessexplicitstimuli,andvisualmaterialappearstoevokeamore
15 genuine response than audiotapes (Card & Farrall, 1990).
16 Itisdifficulttodetectconsciousmanipulationofarousal.AccordingtoSimon
17 andSchouten(1991),twoapparentlysuccessfulstrategiesforincreasingarousal
18 are fantasizing about more desirable subjects or by voluntary muscle contrac-
19 tions in the groin. The latter can be detected through monitoring movement
20 (Kalmus & Beech, 2005), but the former will appear to be genuine arousal.
21 Suppression is also difficult to identify. Card and Farrall (1990) reportedly
22 identified suppression through examining GSR and respiration rate, and Wil-
23 son(1998)demonstratedtheutilityoffingerpulserateasameasureofconscious
24 arousal control. However, Golde et al. (2000) reported that deliberate sup-
25 pression was not identifiable through either GSR or pulse rate. In this study,
26 subjectshadmoredifficultyconsciouslyenhancingarousalthansuppressingit.
27 Unfortunately,itseemsthatinhibitionisdifficulttodetectwhenitisdoneusing
28 cognitivetechniquessuchasmentaldistraction(Marshall&Fernandez,2003),
29 which is worrying given that Golde et al. (2000) reported that these were the
30 techniques which their subjects reported using the most.
31 Therehavebeenattemptstorestrictcognitivefakingstrategies.Somestudies
32 employed semantic tracking tasks, either signal detention or stimulus-related,
33 such as a rating task if the displayed scene contains violent or sexual content
34 (Kalmus & Beech, 2005; Quinsey & Chaplin, 1988). Proulx, Cot(cid:1)e and
35 Achille(1993)successfullyusedasemantictrackingtaskinthepenileassessment
36 ofpedophiles.Whenusingthistask,theyobtainedhigherpedophileindicesand
37 results that were more consistent with the offender’s self report. Others have
38 used debriefing interviews or postassessment questionnaires to assess the sub-
39 ject’s attention level (Murphy & Barbaree, 1994). Freund (1971) suggested
40 presenting stimuli in an unpredictable, impressive, and brief manner to
41 “surprise” the subject and avoid cognitive distraction.
42 Itappearsthattheabilitytosuppressisatleastpartlyrelatedtothemagnitude
43 of response. Malcolm, Davidson, and Marshall (1985) found that arousal
44
150 Assessment and Treatment of Sexual Offenders
1 suppressionwaseasiertoexecuteatahighererectileresponse(75%fullerection
2 incomparisonto25%and50%FE).Also,CardandFarrall(1990)reportedthat
3 themoreintensethefakingeffortsare,theeasiertheyaretodetect.Accordingto
4 Adler(1994),subjectsareunawareofthefirst10–15%oftheirerectileincreases;
5 hence,theirinitialreactionappearstobemostrevealingbeforeconsciouscontrol
6 attempts can take place. A successful application of this strategy was demon-
7 stratedinastudybyFreund,Chan,andCoulthard(1979)whothensubstantially
8 improvedthediscriminativeaccuracywithintheirsampleofnonadmitters.The
9 morerecentcasestudybyMarshall(2004)isanotherproofofthebenefitsofthis
10 method of controlling for faking. However, these positive outcomes were not
11 supportedinGoldeetal.’s(2000)study:neitherpreviousexposurenornovelty
12 of stimulus had an effect on arousal or suppression ability.
13 Althoughtherearestillnogenerallyacceptedproceduresforestimatingand
14 controlling the frequencyoffaking, Marshall and Fernandez (2003a)arecon-
15 fident that control methods have increased the effectiveness of penile plethys-
16 mography.Interestingly,theinstructiontosuppressarousalmayevenenhance
17 the discriminative power of a phallometric assessment. Wormith et al. (1988)
18 askedtheirsampleofrapiststoinhibiterectileresponses.Whilethisappearedeasy
19 todowithconsentingscenes,itwasmuchharderforthemtosuppressresponding
20 on material describing rape or physical assault, suggesting that it is harder to
21 inhibitrespondingdrivenbystrongersexualpreferences.Thisisworthyoffurther
22 study,sinceitmaybethatattemptstodetectsuppressionofarousalmissthepoint,
23 anditisthoseresponseswhicharedifficulttosuppressthataremeaningful.
24
25 Denial. It appears that phallometric assessments may not be effective in
26 assessing deviant sexual preferences with subjects who deny having any such
27 interests. Sexual offenders who deny their deviant sexual preferences typically
28 displaynormalarousalpatterns(Marshall,2006),andincludingtheminresearch
29 lowersthediscriminativepowerofaphallometricassessment.Earlyresearchers
30 such as Freund suggested restricting subject population to admitters
31 (Freund, 1971). For instance, Freund et al. (1979) demonstrated that the
32 validityofPPGscoresisconsiderablysuperiorforadmittersthannonadmitters.
33 Ontheotherhand,FreundandBlanchard(1989)stillobtainedasensitivityof
34 55% for nonadmitters. In any case, this reasoning assumes that all sexual
35 offendershavedeviantpreferences,whereitmightalsobecorrecttostatethat
36 offenderswhodenydeviantpreferencesappearnormalbecausetheirpreferences
37 are normal.
38
39 Otherfactors. Sexualarousalisdependentuponhormonalreleases,andpenile
40 arousal patterns will vary with diurnal hormonal fluctuations (Rowland
41 etal.,1993).Furtherconfoundingvariablesmightincludemedicalconditions,
42 suchasheadinjuryor,unsurprisingly,impotence.Thepresenceofpsychopathic
43 traits and the number of victims may also have an effect on erectile arousal
44 patterns(Marshall,2006;MarshallandFernandez,2003a),butthisresearchisin