Intentional retrieval suppression can conceal guilty knowledge in ERP memory detection tests

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Biological

Psychology

j o u r n a l ho me p ag e :w w w . e l s e v i e r . c o m / l o c a te / b i o p s y c h o

Intentional

retrieval

suppression

can

conceal

guilty

knowledge

in

ERP

memory

detection

tests

夽

Zara

M.

Bergström

a,∗

_,

_Michael

_C.

_Anderson

b,c

_,

_Marie

_Buda

c

_,

_Jon

_S.

_Simons

c

_,

Alan

Richardson-Klavehn

d

a_{SchoolofPsychology,UniversityofKent,CanterburyCT27NP,UK}

b_{MRCCognitionandBrainSciencesUnit,15ChaucerRoad,CambridgeCB27EF,UK}

c_{BehaviouralandClinicalNeuroscienceInstituteandDepartmentofPsychology,UniversityofCambridge,DowningStreet,CambridgeCB23EB,UK} d_{DepartmentofNeurology,FacultyofMedicine,OttovonGuerickeUniversityofMagdeburg,Zenit1Building,LeipzigerStrasse44,39120Magdeburg,}

Germany

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received16March2012 Accepted23April2013 Available online xxx Keywords: Episodicretrieval Event-RelatedPotentials Memorysuppression Guiltyknowledge Cognitivecontrol

a

b

s

t

r

a

c

t

Brain-activitymarkersofguiltyknowledgehavebeenpromotedasaccurateandreliablemeasuresfor establishingcriminalculpability.Testsbasedonthesemarkersinterpretthepresenceorabsenceof memory-relatedneuralactivityasdiagnosticofwhetherornotincriminatinginformationisstoredin asuspect’sbrain.Thisconclusioncriticallyreliesontheuntestedassumptionthatremindersofacrime uncontrollablyelicitmemory-relatedbrainactivity.However,recentresearchindicatesthat,insome circumstances,humanscancontrolwhethertheyrememberapreviousexperiencebyintentionally suppressingretrieval.Weexaminedwhetherpeoplecoulduseretrievalsuppressiontoconcealneural evidenceofincriminatingmemoriesasindexedbyEvent-RelatedPotentials(ERPs).Whenpeoplewere motivatedtosuppresscrimeretrieval,theirmemory-relatedERPeffectsweresignificantlydecreased, allowingguiltyindividualstoevadedetection.Ourfindingsindicatethatbrainmeasuresofguilty knowl-edgemaybeundercriminals’intentionalcontrolandplacelimitsontheiruseinlegalsettings.

© 2013 The Authors. Published by Elsevier B.V. All rights reserved.

1. Introduction

Recent suggestions that technological advances now allow

us todecode criminal guilt from brain activitydata have

gen-erated intensive interdisciplinary debate within the scientific

community(Garland&Glimcher,2006;Greely&Illes,2007;Sip,

Roepstorff,McGregor,&Frith,2008;Wolpe,Foster,&Langleben,

2005).Severalemerging companiesare advertising commercial

implementations of brain activity guilt detection (e.g. No Lie

MRI,http://www.noliemri.com/;BrainFingerprintingLaboratories,

http://www.brainwavescience.com/), and attempts to introduce

evidencefromsuchtestsincriminaltrialsarefrequentlyreported

ininternationalmedia(Giridharadas,2008;McCall,2004;Miller,

2010). However, despite widespread interest and discussion,

empiricaldataconcerningthevalidityofthesebrainactivity-based

methodsissparse.Oneprominentconcernisthatmostresearch

todatehasbeenconductedoncompliantparticipantswithlittle

夽 Thisis anopen-accessarticledistributedunderthetermsoftheCreative CommonsAttributionLicense,whichpermitsunrestricteduse,distributionand reproductioninanymedium,providedtheoriginalauthorandsourcearecredited.

∗ Correspondingauthor.Tel.:+4401227827507;fax:+4401227827030. E-mailaddress:[email protected](Z.M.Bergström).

motivation to hide theirguilt, whereas real criminals mayuse

countermeasurestrategiestoavoiddetection.Inviewofthe

impor-tantsocietal,legalandethicalimplicationsofbrainactivitycrime

detection,itisvitaltovalidatethesemethodsbeforetheyarewidely

adopted,and, inparticular,toevaluatehowwelltheyworkfor

uncooperativesuspectsmotivatedtoconcealincriminating

knowl-edge.

Memorydetectionaimstoestablishculpabilitybydetermining

fromphysiologicalorbehaviouralcorrelatesofmemoryretrieval

whetherasuspecthasknowledgeofacrimethatonlyaguilty

per-sonwouldpossess(Meegan,2008).Scalp-recordedEvent-Related

Potentials(ERPs)areoftenusedinthesetypesoftestas

inexpen-siveandnon-invasivemeasuresofreal-timeneuralactivity(e.g.

Allen, Iacono,& Danielson,1992; Rosenfeld, Angell, Johnson, & Qian,1991;VanHooff,Brunia,&Allen,1996).ERPshavegained

popularityasanalternativetotraditionalautonomicmeasuresin

memorydetectionstudies(Lykken,1959;seeBen-Shakhar&Elaad,

2003,for review),partlybecausetherapidand process-specific

brainresponsesreflectedinERPsarebelievedtobemore

resis-tanttocountermeasuresthanotherphysiologicalandbehavioural

measures(e.g.Lykken,1998;seediscussioninBen-Shakhar,2011).

Recently however,researchershavechallengedthisassumption,

showing that ERP memory detection tests may be more

vul-nerable than previously thought (e.g. Mertens & Allen, 2008;

0301-0511/$–seefrontmatter © 2013 The Authors. Published by Elsevier B.V. All rights reserved.

Rosenfeld,2006;Rosenfeld,Soskins,Bosh,&Ryan,2004,although seeRosenfeldetal.,2008).Inthispaper,wedescribea

counter-measurethathasnotbeenexploredbeforeintheliterature,which

questionsoneof thefundamentalassumptionsofbrain-activity

memorydetection.

InanERPversionofatypicalguiltyknowledgetest(GKT,Lykken,

1959),ERPs arerecorded whileparticipantsengageina

crime-irrelevanttargetdetectiontaskthatincludesremindersofsome

incriminatinginformation(e.g.Farwell&Donchin,1991;Farwell

&Smith,2001).Participantsareaskedtodiscriminatebetweena

setoftargetitems(forexamplewordspresentedonacomputer

screen)andanothersetofirrelevantcontrolitems(otherwords)

bypressing one button for targetsand anotherfor irrelevants.

Thisprocedureproducesanenlargedpositivemid-parietal

com-ponenttermedthe“P300”(seePolich,2007,forreview)intheERP

waveformaround300–900msspecificallyaftertarget

presenta-tions,thoughttoindexprocessesrelatedtoparticipants’conscious

recognitionoftargetsasmeaningfulstimuli.BecauseP300

ampli-tudesaretypicallyinverselyrelatedtothesubjectiveprobabilityof

astimulus(Donchin,1981),asmallproportionoftargetsare

typ-icallyintermixedwithalargerproportionofirrelevantstomake

targetssubjectivelyrare, thusenhancingP300differences.

Cru-cially,toassess thepresenceorabsence ofguiltyknowledge, a

smallproportionofcrimereminders(“probes”)arealsopresented

aspartoftheirrelevantset.Totrulyinnocentsuspects,suchcrime

probesareindistinguishablefromirrelevantitemsandthuselicit

nospecialbrainresponse.Toguiltysuspects,theprobesstandout

basedontheircrime-relatedmemorystatus,andthisrecognition

elicitsanenhancedparietalP300similartotargets.Thus,guilty

suspectsshowenlargedparietalP300stobothprobesandtargets

sincebothtypeselicitrecognition,whereasinnocentsuspectsonly

showenlargedparietalP300stotargetsandnottoprobes.

Memory detection tests make the crucial assumption that

reminders of incriminating information uncontrollably elicit

recognition-relatedbrainactivity.Thisassumption gains

plausi-bilityfromthefactthat theGKTmemoryprobesdirectlyname

details from the crime, thus constituting exceedingly potent

retrievalcuesforapersonallysignificantevent,makingitappear

extremelyunlikely thatifa related memoryis present,thecue

will not automatically evoke recognition and its neural

mark-ers.Theinevitabilityofsuchretrievalisquestioned,however,by

recentevidencethatthebrainactivitycorrelatesofgeneral

mem-oryretrievalmaybeundermorevoluntarycontrolthanhasbeen

previouslyassumed(e.g.Dzulkifli&Wilding,2005;Herron&Rugg,

2003;Rissman,Greely,&Wagner,2010).Sofar,thestrongest

evi-dencethatmemoryretrievalcanbeintentionallypreventedstems

fromthe Think/No-Think (TNT) memorysuppression paradigm

(Anderson&Green, 2001).In thistask, participantsare trained

onpairsofstimuli(typicallyweaklyrelatedwords),andarelater

presented with the first item of each pair as a reminder, and

areaskedto eitherthink of theassociate item (theThink

con-dition),or tocompletely preventtheassociate fromcomingto

mindbysuppressingretrieval(theNo-Thinkcondition).Thinkand

No-Thinkremindersarerepeatedlypresented,typicallyrandomly

intermixedinequalproportions.fMRIevidencefromthisparadigm

suggeststhat peoplecanengageresponseoverridemechanisms

mediated by the lateral prefrontal cortex to suppress retrieval

bymodulating memory-related activityin thehippocampus in

responsetoreminders(Andersonetal.,2004;Benoit&Anderson,

2012;Butler&James,2010;Depue,Curran,&Banich,2007;Levy& Anderson,2012;Paz-Alonso,Ghetti,Anderson,&Bunge,2013).

Mostcriticallyformemoryguiltdetectionresearchwhichis

pre-dominantlyERP-based,askingparticipantstosuppressunwanted

memoriesinaTNTtaskcausesmemory-specificreductionsofan

ERPeffectwithsimilarpolarity,topographyandtimingtotheP300

component(Bergström,DeFockert,&Richardson-Klavehn,2009a,

2009b; Bergström,Velmans, De Fockert, &Richardson-Klavehn, 2007;Hanslmayr,Leipold,Pastötter,&Bäuml,2009;Mecklinger, Parra,&Waldhauser,2009).However,thesefindings havebeen

interpretedasvoluntarysuppressionoftheERPmarkerofepisodic

recollection,which isspecificallycorrelatedwiththeamountof

episodic detail that is consciously recollected in response toa

reminder(e.g.Vilberg,Moosavi,&Rugg,2006;seeRugg&Curran,

2007,forreview).Becauseoftheirsimilarcharacteristics,parietal

effectsrelatedtorecollectionand“classic”P300effectsrelatedto

stimulusevaluationaredifficulttoteaseapart.Thisisparticularly

thecaseintaskswhereepisodicremindersaresubjectivelyrare,

suchastheGKT,sincerecollection-relatedandclassicP300effects

maybothcontributetoparietalERPamplitudes.Theepisodic

rec-ollectioneffectishowevermorelikelytobeleft-lateralizedthan

P300effects.Furthermore,althoughtheP300ishighlysensitiveto

subjectiveprobability,theparietalrecollectioneffectmaynotbe

(Herron,Quale,&Rugg,2003;seealsoSmith&Guster,1993).These

ERPeffectsarethusthoughttoindexseparablecognitiveprocesses,

althoughthepreciserelationshipbetweenthemisstillunclear.

Theimplicationsoftheaforementionedresearchforcriminal

guiltdetectiontestsneverthelessremaintobeestablished,since

there are many features of such tests that have not yet been

exploredinthecontextofretrievalsuppression.Noresearchhas

examinedwhetherretrieval-relatedbrainactivitycan be

inten-tionallysuppressedforobjectsoreventsdirectlynamed bythe

reminderitself,inparticularwhencomparingthesepotentcuesto

novelcontrolcuesthatareunlikelytoelicitmemory-relatedbrain

activity.Moreover,it remains unclear whethermemory-related

brainactivitycanbesuppressedwhenremindersaresubjectively

rare,asintypicalGKTresearch.Ifmnemoniccontrolispossible

under conditions of exceedingly strong and subjectively

unex-pectedretrievalcueshowever,itraisesthepossibilitythatguilty

suspectsmotivatedtoconcealtheirknowledgemaybeableto

sup-pressbrainactivityelicitedbyincriminatingprobesduringmemory

testingandhenceeludedetection.

Furthermore, prior TNT research hasshown that repeatedly

suppressingretrievalinresponsetoaremindercandramatically

reduce theubiquitousbeneficial effects ofreminders on

reten-tion,andevenimpairrecallperformanceoftheavoidedmemories

comparedtoitemsinabaselineconditionthathavebeenneither

recallednorsuppressedsinceinitiallearning(e.g.Andersonetal.,

2004;Anderson&Green, 2001;Bergströmetal.,2009b; Depue etal.,2007;seeAnderson&Huddleston,2011,forareviewand

meta-analysis).Thisfindingimpliesthatretrievalsuppression

dur-ingaguiltdetectiontestmaybesuccessfultotheextentofactually

impairinglaterretentionoftheincriminatingmemories.

Todeterminewhetherpeoplecancontrolbrainresponsesto

remindersthat mightbeexpectedtoelicitincriminating

recog-nition,wecreatedanoveldesignthatcombinedelementsfrom

bothGKTandTNTparadigms,andaskedparticipantstovoluntarily

suppressmemoriesofasimulatedcrime.ERPswererecorded

dur-ingthreephasesofamemorydetectiontestthatdirectlyprobed

centraldetailsfromaprevioushomeburglarysimulation.Inone

controlphase,participantsweretrulyinnocentofthetestedcrime.

Inasecond“guiltycooperative”phase,participantswereaskedto

remembertheircrime.Finally,in athird “guiltyuncooperative”

phase,participantswereaskedtosuppresscrimerecalltoevade

detection.Followingtheguiltyknowledgetest,wecompared

mem-oryforrepeatedlysuppressedandrepeatedlyrememberedcrime

detailstomemoryforotherdetailsthatwereencounteredduring

theinitialburglarysimulationbutdidnotappearinthe

interven-ingdetectionphase(i.e.abaselinecondition),toassesswhether

retrievalsuppression of crime memorieshad lasting effectson

memoryaccessibility.

The relative probabilities of item categories were varied

experimentpresentedeachcategorywithequalprobability,which

allowed an assessment of whether retrieval-related activity to

exceedingly strong reminders of a crime can be voluntarily

suppressedintheabsenceofprobabilityeffects.Thesecond

exper-imentreducedtheprobabilityofprobesandtargetstoinvestigate

whether the neural response to crime reminders can be

sup-pressedevenwhenprobesaresubjectivelyunexpected.Ifpeople

cansuppresscrimerecallwhenmotivatedtodoso,parietalP3001

amplitudesforprobes shouldbereduced intheguilty

uncoop-erativephasecompared totheguiltycooperativephase,leading

tosignificantlypoorerguilt detectionrates.Iftheyareperfectly

successfulatsuppressingretrieval,P300amplitudesduring

sup-pressionof guilty knowledge should be indistinguishable from

thoseobservedduringtheinnocentcontrolphase.

2. Materialsandmethods 2.1. Participants

Experimentoneincludeddatafrom24right-handednativeGermanspeakers(15 females)withameanageof24(range18–35).Experimenttwoincludeddatafrom 24right-handednativeEnglishspeakers(14females)withameanageof21(range 18–35).Allparticipantshadnoknownhistoryofneurologicalorpsychiatricdisease andhadnormalorcorrected-to-normalvision,andgavewritteninformedconsent. ExperimentswereconductedinaccordancewiththeguidelinesofthelocalEthics CommitteesoftheUniversityofMagdeburg(Experimentone)andtheUniversityof Cambridge(Experimenttwo).

2.2. Design,materialsandprocedure

ExperimentonewasconductedinGermanattheOttovonGuericke Univer-sityofMagdeburg,Germany,whereasExperimenttwowasconductedinEnglishat theUniversityofCambridge,UK.Visualandverbalmaterialswerekeptassimilar aspossibleacrossexperiments.Bothexperimentsconsistedofthreemainphases: (1)aninitialburglarysimulation;(2)amemorydetectionphase,whereERPswere recorded;and(3)afinaltestphase,whereparticipants’memoryfortheburglary taskwasassessed.

Uponarrival,participantscompletedthecrimesimulationtaskonacomputer, whichwasdesignedtoleadtorich,elaborativememoryencodingof24photographs ofdistinctcommonobjects(e.g.agoldwatch,drawnatrandomforeachpersonfrom alargersetofobjectsthatwereassemanticallyunrelatedaspossible)without inten-tionallearningattempts.Participantswereaskedtovividlyimaginebeingaburglar whowasbreakingintohouseswiththeaimofstealingvaluables.Duringeachtrial,a pictureofaroominteriorwaspresentedfirst,andparticipantswereaskedtoimagine thattheyhadbrokenintotheroomandjudgewhethertheythoughtthatparticular roomwaslikelytocontainsomethingvaluable.Second,fournumbersappearedon thebackground,markingparticularlocationsintheroom(e.g.adrawer). Partic-ipantswereaskedtosearchthroughthelocationsbypressingthecorresponding numbersonthekeyboardinordertofindahiddenobject.Whentheypressedthe correctoptionanobjectappeared,superimposedontheroompicture.Next, partic-ipantscompletedthreeratingtasksontheobject-roompicture.First,theydecided whethertheobjectwasthekindofobjecttheywouldexpecttofindintheparticular room.Second,theyrateditsvalue,andthird,decidedwhethertheywantedtosteal it.Therewasnouppertimelimittorespondandthecomputeronlymovedonto thenextquestionafteraresponsehadbeenrecorded.Eachofthejudgementscould onlybegivenaftera4sdelayofviewingthepicture,meaningthateachtrialwasa minimumof16slong.

Foreachparticipant,wordsnamingonerandomlydrawnsubsetofobjectsfrom theburglarytask(e.g.“watch”)werelaterpresentedasprobesduringtheguilty cooperativeblock,andwordsnaminganothersubsetofobjects(alsorandomly drawn)werepresentedasprobesduringtheguiltyuncooperativeblock.Therest ofthestudyobjectswerenotpresentedduringtheEEGphase,butwereusedasa behaviouralbaselineforthefinalmemorytests.Otherobjectwordsforwhichthe pictureswerenotpresentedduringstudywererandomlyassignedtothetarget, irrelevantandinnocentprobeERPconditions,usingadifferentsetforeachphase. Apriorcontrolexperiment(seenextsection)withanindependentgroupthat per-formedoursimulatedburglarytaskconfirmedthattheyrecognisedthesecrime probesasreferringtothepreviouslyencounteredobjectswithceilingaccuracy, andoverwhelminglyratedtheseprobesaselicitingautomatic,involuntaryrecallof

1 _{WerefertothelateparietalERPpositivityintheseexperimentsasaP300effect,}

inlinewithtypicalGKTresearch.However,asdiscussed,thefunctionalsignificance ofparietalERPpositivitiesintheP300time-windowisunclear,sincetheseparietal positivitiesmightberelatedbothtostimulusevaluationprocessesandtoepisodic recollection.

theburglaryobjects.Thus,presentingthesecrimeprobesinourmemorydetection testwouldbeexpectedtostronglyandreflexivelyelicitretrievaloftheassociated objectsstoredinmemory.

Followingcrimesimulation,participantswerefittedwithanEEGcapand com-pletedthememorydetectionphaseonacomputer.Theyweretoldthatreminder wordsthatreferredtoobjectsfromtheburglarywouldbepresentedonthescreen, inordertotrytomakethemrememberdetailsfromthecrimesothattheirbrain activitycouldbeusedascriminalevidence.However,thesereminderwordswould beintermixedwithotherwordsthatdidnotrefertotheburglarywhiletheywere performingatargetdetectiontask,whichwouldbeconductedinthreeblocks.Before eachblockofthememorydetectiontest,participantspracticedablock-specificlist oftargetwordsandwereinstructedtodetectandpressonebuttonwheneverthey recognisedatargetword,andpressanotherbuttonforanyotherwords(buttons andresponsehandcounterbalancedacrossparticipants).

Followingtargetlearning,morespecificinstructionsfortheparticular mem-orydetectionblockweregiven(ordercounterbalancedacrossparticipants).Inthe guiltycooperativeblock,participantswereinstructedthatiftheyrecognisedan objectwordascorrespondingtoapictureseenduringthecrimesimulation,they shouldtrytorememberasmanydetailsaspossibleaboutthatobjectfromthe bur-glary(analogoustoablockedThinkconditionintheTNTparadigm).Intheinnocent controlblock,participantsweretoldthattheywouldbetestedforacrimetheyhad notcommittedsoshouldsimplyfocusonthetargetdetectiontask(withthe reason-ingthataninnocentsuspectinarealcriminalinvestigationwouldofcourseknow themselvestobeinnocent).2_{Intheguiltyuncooperativeblock,participantswere}

toldtotrytheirbesttocompletelystopanymemoriesofthecrimefromcoming tomindatall,withoutself-distraction(analogoustoablockedNo-Thinkcondition, withinstructionssimilartodirectsuppressiongroupinBergströmetal.,2009b;

Benoit&Anderson,2012).Itwasstronglyemphasisedinallphasesthattheyshould

alwaysreadandpayfullattentiontoeachwordtheentiretimeitwasonthescreen, andonlypressthe“recognition”buttonfortargetsandthe“non-recognition”button foranyotherwords.Thus,therewerenodifferencesinovertresponserequirements acrossphases.

Duringeachmemorydetectiontrial,wordswerepresentedfor2sinwhiteon ablackbackground,precededbya1swhitefixationcross,andfollowedbya0.5s greenfixationcross.Buttonpressesandblinksweretimedtothegreenfixationin ordertoavoidcontaminatingrelevantEEGwithmotor-relatedartefacts.The propor-tionofitemsintheprobe,irrelevantandtargetcategorieswasmanipulatedacross experiments.InExperimentone,eachblockcontainedanequalproportionofeight itemsineachcategory,inlinewithpreviousmemorysuppressionERPresearch thathaspresenteditemstobesuppressedatequalprobabilitytootheritems(e.g.

Bergströmetal.,2007,2009a,2009b;Hanslmayretal.,2009;Mecklingeretal.,2009).

Thislistof24wordswaspresentedtwelvetimes,randomlyintermixedeachtime. InExperimenttwo,eachblockcontainedfourprobes,sixteenirrelevantsandfour targets,i.e.withprobabilitiesofapproximately0.17,0.67and0.17respectively, whicharetypicalproportionsinguiltyknowledgetests(Allenetal.,1992;Farwell

&Donchin,1991;Mertens&Allen,2008;Rosenfeldetal.,2004),alsopresented

twelvetimeseachrandomlyintermixed.

Followingtheguiltdetectionphase,participantscompletedtwofinalteststhat aimedtodetectwhethertheearlierretrievalsuppressionmanipulationaffected laterretentionoftheavoidedmemories.Memorywascomparedforrepeatedly suppressedobjectpictures(i.e.objectpicturesforwhichcorrespondingwordswere presentedasprobesintheuncooperativephase)torepeatedlyrememberedobject pictures(i.e.objectpicturesforwhichcorrespondingwordswerepresentedas probesinthecooperativephase)andtomemoryforbaselineobjectsthatwere simplypresentedduringtheinitialburglarysimulationbutdidnotappearinthe guiltyknowledgetestphase.Becauserecognitionmemoryforobjectsthemselves waslikelytobeatceiling(asestablishedinourvalidationstudyforprobewords), thetestsfocusedonmoredifficultdetailsoftheencodingepisode.Allparticipants completedtwotestsinthesameorder:locationrecallandobjectrecall.Forthese recalltests,participantswerepresentedwithallbackgroundroompicturestogether withthefourmarkedlocationswheretheyhadsearchedforahiddenobject.First, theywereaskedtotrytorememberthelocationinwhichtheyhadfoundtheobject duringtheburglarysimulationtask.Nexttheywereaskedtorecalltheobjectthat theyfoundinthatlocation.Therewasnolimittoresponsetimesineithertest,and picturesstayedonthescreenuntilananswerwasgiven.Finally,participants com-pletedaquestionnairewheretheyratedtheirperceiveddifficultyandsuccessat suppressingcrimedetailsintheuncooperativeblockandtheirperceiveddifficulty andsuccessatrememberingcrimedetailsinthecooperativeblock.

2_{Onemightworrythattellingparticipantsthattheywereinnocentmayhave}

somehowledtodifferentERPeffectsintheinnocentphasecomparedtotheguilty phases.Importantlyhowever,topreviewtheresults,thiswasnotthecase.There werenomeasurabledifferencesbetweentargetandirrelevantERPwaveforms acrossthethreephases,demonstratingthatERPsintheinnocentphasewerenot affectedbyinstructions.

2.3. Validationrecognitiontest

Inordertovalidatethatusingobjectwordsasprobesbroughtmemoriesof thecrimesimulationtomind,anindependentgroupofparticipants(N=10) com-pletedthecrimesimulationfollowedbyanold/newrecognitiontest,wherewords referringtoobjectsfromtheburglarywereintermixedwithnewobjectwords, andparticipantsjudgedwhetherawordcorrespondedtoanobjectfromthe bur-glary.Ifparticipantsrespondedthattheyrecognisedanobjectword,theynextrated whethertheburglarymemorycametomindautomaticallyorthroughintentional effortwhenseeingtheword.

2.4. EEGrecordingandanalysis

InExperimentone,EEGwasrecordedreferencedtotheleftmastoidusinga BrainVisionBrainAmpamplifierfrom60Ag/AgClscalpelectrodesembeddedinan Easycap.InExperimenttwo,EEGwasrecordedreferencedtoCzusinga Electri-calGeodesicNetamps200systemwitha128-channelHydroCelGeodesicSensor Net.Inbothexperiments,signalswereacquiredat250Hz(bandwidth0.1–70Hz) andanalysedusingEEGLAB7(Delorme&Makeig,2004).ThecontinuousEEGdata werere-referencedtoanaveragemastoidreference,filtereddigitallywitha band-passof0.3–30Hz(two-wayleast-squaresfiniteimpulseresponsefilter),andwere thenseparatedintoepochstime-lockedtothewordstimulusonset.Concatenated epochswerecorrectedfromartefactsusingIndependentComponentAnalysis(see

Bergströmetal.,2009b,fordetails).Anytrialsthatstillcontainedvisibleartefacts

followingartefactcorrectionwereremoved.Next,ERPswereformedfortheprobe, irrelevantandtargetitemswithineachguiltycooperative,guiltyuncooperativeand innocentblock(i.e.nineERPconditionsintotal)includingonlytrialsforwhich participantsgaveacorrectresponsewithintheallocatedtime.Onlyaverysmall proportionoftrials(8%inExperimentoneand6%inExperimenttwo)weredeleted intotalaftertheseexclusioncriteria.

Basedonourstrongapriorihypotheses,wefollowedalargebodyof previ-ousP300researchbyfocusingthemainanalysesonthemid-parietalelectrodesite (Pzin10/20nomenclature),whereP300effectsareconsistentlylargestandwhere selectiveanalysesaretypicallyfocusedinGKTresearch.ParietalERPamplitudes werefirstanalysedatthegrouplevelusingparametricstatistics.Because mem-orydetectiontestsaremeanttofunctionasdiagnostictoolsfordeterminingthe guiltofanindividualperson,wealsoestimatedthereliabilityofP300differences withineachparticipant’ssingletrialdatausingnonparametricbootstrap resam-pling(Efron&Tibshirani,1986;Rosenfeldetal.,2004).Priortobootstrapanalysis, individualEEGtrialswerefurtherlowpassfilteredwithan8Hzcut-offinorderto increasesignal-to-noiseratio.Subsequently,foreachparticipant,asetof individ-ualtrialsofthesamesizeastheoriginalprobesetweredrawnatrandomwith replacement,andaveragedtocreateabootstrappedprobeERP.Thesame proce-durewasrepeatedusingirrelevanttrials,creatingabootstrappedirrelevantERP.To createabootstrapped“base-to-peak”measure(e.g.Rosenfeldetal.,2004),the max-imumamplitudeoftheirrelevantP300wasmeasuredbyfindingthe100ms-long timewindowwiththemostpositiveamplitudewithintherangeof400–900ms(this valuebeingthedifferencebetweenthebaselineandtheP300peak,sincetheepochs werebaseline-correctedpriortobootstrapping),andthisvaluewassubtractedfrom thecomparableprobeP300maximumamplitude,creatingaP300differencevalue. Using200iterationsofthisprocedure,adistributionofP300differencevalueswas created.Inordertostatewith95%confidencethatprobeP300sweremorepositive thanirrelevantP300s,thevalueat1.65standarddeviationsbelowthemeanofthis distributionofdifferencesshouldbegreaterthanzero.

Wecomparedbootstrapresultsforthebase-to-peakP300methodabovewith bootstraptestsoftwootherstatistics,meanbaseline-correctedmid-parietal ampli-tudeacrossthewholeP300time-window(400–900ms)andP300peak-to-peak difference(thedifferencebetweenthemaximumP300amplitudevaluedescribed aboveandthe100ms-longtime-windowwiththemostnegativevaluefollowingthe P300peakuptoamaximumlatencyof1600mspost-stimulus;Soskins,Rosenfeld,&

Niendam,2001).Classificationratesacrossthesestatisticswerecomparedatstrict

(95%confidence)andliberal(90%confidence)thresholds.Usingthesethresholds andmeasures,individualsforwhichprobeP300swerereliablymorepositivethan irrelevantP300swereidentifiedandassignedasguilty.

Inordertofacilitatecomparingourclassificationresultswithpreviousresearch, wealsocalculatedReceiver-OperatingCurves(ROC)andassociatedAreaUnder Curves(AUCs)fromthebootstrapdistributionsbycomparinghit-ratesinthetwo Guiltyconditions(i.e.theproportionofparticipantscorrectlyidentifiedasguiltyin theseconditions)withfalsealarmratesintheInnocentcondition(i.e.proportionof participantsincorrectlyidentifiedasguiltywheninnocent)acrossdifferent thresh-olds.TheAUCprovidesausefulsummarystatisticofclassificationperformance irrespectiveofaparticularthreshold,allowingdetectionratestobecomparedacross studiesthatusedifferentclassificationcriteria(seeBen-Shakhar&Elaad,2003).The AUCrangesfrom0to1,andwhereasanAUCvalueof1meansperfect classifica-tionacrossallthresholds(peoplewerealwaysdetectedwhenguiltybutneverfalsely identifiedassuchwheninnocent,irrespectiveoftheclassificationthreshold)anAUC valueof0.5meansclassificationisatchance(peoplewerenomorelikelytobe clas-sifiedasguiltyintheGuiltyphasethantheInnocentphase).AUCvaluessmallerthan 0.5meanthatpeopleweremorelikelytobewronglyclassifiedasguiltywhen inno-centthancorrectlydetectedwhenactuallyguilty.Apreviousmeta-analysisfounda

meanAUCvalueof0.87across42GKTstudiesthatusedskinconductancemeasures andamock-crimeproceduresimilartothecurrentparadigm(Ben-Shakhar&Elaad, 2003)whereasanewer,stillunpublishedmeta-analysisfoundameanAUCof0.93 across32GKTstudiesthatusedP300-basedmeasuresandavarietyofprotocols (Ben-Shakhar,personalcommunication).

Inthecurrentstudy,AUCswerecalculatedwiththenon-parametrictrapezoid method,andtheCooperativevs.InnocentAUCwasstatisticallycomparedagainst theUncooperativevs.InnocentAUCbyestimatingthestandarderrorsoftheAUCs usingjack-kniferesamplingandcalculatingaz-scoreforthedifference,as rec-ommendedbyHanleyandHajian-Tilaki(1997).Thez-scoreformulaincludeda correctionforcorrelationsbetweenAUCsinducedbythewithin-subjectsdesign, asestimatedbythecorrelationbetweenthejack-knifepseudo-values(seeHanley

&Hajian-Tilaki,1997,fordetails).

Finally,wealsoconductedawhole-headanalysisinordertoinvestigatethe pos-sibilitythatalthoughguiltysuspectsmaybesuccessfulatsuppressinglatepositive parietalERPs,theirguiltmayneverthelessberevealedbyotherERPeffects,such aseffectsrelatedtothecognitivecontrolprocessesthatarerecruitedtosuppress retrieval.Previousresearchhasindicatedthatthesecontrolprocessesaremanifest asearlyfronto-centralorcentro-parietalERPnegativities(Bergströmetal.,2009a,

2009b;Mecklingeretal.,2009)orfrontalslow-driftnegativities(Hanslmayretal.,

2009).Becauseoftheexploratorynatureofthisquestion,weusedadata-driven approachwithmultivariatenon-rotatedspatiotemporalPartialLeastSquares(PLS,

McIntosh&Lobaugh,2004).PLSisapowerfultechniquethatallowsexamination

ofdistributedpatternsofspatialandtemporaldependenciesintheERPdatawith minimalassumptionsregardingthetiminganddistributionofpotentialeffects. PLSanalyzesthe“cross-block”covariancebetweenamatrixofdependent meas-ures(thespatiotemporalERPdistribution)andasetofexogenousmeasures,inthis caseorthogonalcontrastvectorsrepresentingdifferencesbetweenexperimental conditions(thenumberofcontrastsequaltothedegreesoffreedom),thereby con-strainingthesolutiontocovarianceattributabletotheexperimentalmanipulation. InnonrotatedPLS(Bergströmetal.,2009a,2009b;McIntosh&Lobaugh,2004)the sumsofsquaresofthecross-blockcovariancebetweeneachcontrastmatrixand thespatiotemporaldatamatrixaredirectlytestedforsignificanceusingrandom permutationtest.

Inthecurrentanalysis,PLSwasconductedseparatelyforeachofthethree detec-tionphases,eachphasesplitintoearly(0–400ms),middle(400–800ms)andlate (800–1200ms)time-windowsinordertoincreasetemporalresolution.Two con-trasts,onetestingthedifferencebetweenprobesandirrelevantsandanothertesting thedifferencebetweenprobesandtargetswereassessedforsignificanceineach time-windowwith1000permutations.

3. Results

3.1. Validationrecognitiontestandpost-testquestionnaire

Therecognitiontestconfirmedthatparticipantscould

discrim-inatebetweencrime remindersand newwordswithveryhigh

accuracy(98%correct,SEM0.7%)andveryhighconfidence(average

rating 2.9 (SEM 0.02) on a 1–3scale where 3 is highly

confi-dentand 1isnotconfident),and thatcrimememoriescameto

mindveryautomatically(averagerating3.9(SEM0.06)ona1–4

scalewhere4isautomaticrecalland1highlyeffortfulrecall).The

validation testthus confirmedthatcrimeobjectswere strongly

encoded, and that presenting thesecrime probes in our

mem-orydetectiontestwouldbeexpectedtostronglyandreflexively

elicitretrievaloftheassociatedobjectsstoredinmemory.

Con-sistentwiththisexpectation,participantsretrospectivelyjudged

uncooperativerecallsuppressiontobemoreeffortful(t(47)=14.9,

P<0.0001;Cohen’sd=2.89,calculatedasthedifferencebetween

meansdividedbythepooledstandarddeviationtoensure

unbi-asedeffectsizeestimates;Dunlap,Cortina,Vaslow,&Burke,1996)

andlesssuccessful(t(47)=11.1,P<0.0001,d=2.28)than

cooper-ativecrimerecall,which didnotinteractwithexperiment.This

findingindicatesthat recallin responsetodirect cuestocrime

relatedobjectswashighlyautomaticandhadtobeintentionally

suppressed,andthateffortfulsuppressionwasrecruitedinboth

experiments.

3.2. FocalERPresultsatthemid-parietalsite

3.2.1. Grouplevelanalyses

Inbothexperiments,groupaverageERPsatmid-parietal

Fig.1.Groupaveragemid-parietalERPsandscalpmapscontrastingdifferentitemtypeswithinblocksinExperimentone(leftcolumn)andExperimenttwo(rightcolumn). Topographicmapsshowthemeandifferencebetweenprobesandirrelevantsbetween450and800ms.

probes depending on instructions to recall or suppress crime

memories(Fig.1),with largerprobe P300s duringcrime recall

thancrimesuppression. Thescalp mapsshowthat theaverage

differencebetweenprobesandirrelevantsbetween450and800ms

in thecooperative phase displayedthe canonical enhancement

oftenfoundinguiltyknowledgestudies,relativetotheinnocent

phase. Incontrast,when subjectswereuncooperative and

sup-pressedretrieval,thisenhancementwaswilfullyavoided.Statistics

on mean ERP amplitudesbetween 450 and 800ms (when the

P300effectwasmaximal)atthemid-parietalelectrodeconfirmed

thatatthegrouplevel,voluntarymodulationsofmemory-related

P300effectsweresuccessful,asrevealedbysignificantinteractions

betweenthecriticalitemcategories(probe/irrelevant)andguilty

phase(guilty cooperative/guilty uncooperative)in both

experi-ments(Experimentone:F(1,23)=5.57, P<0.05, Partial_2_=0.20;

Experimenttwo:F(1,23)=10.19,P<0.01,Partial2_=0.31).These

interactionsbetweenitemtypeandguiltyphasewerenot

signifi-cantlymodulatedbytheorderinwhichparticipantscompletedthe

differentphases,sinceaddingphaseorderasabetweensubjects

variabledidnotchangethesignificanceofthetwo-way

interac-tionsineitherexperiment,andthethree-wayinteractionsbetween

phaseorder×itemtype×guiltyphasewerenotsignificant(both

Fs<1,P>0.7).

Plannedt-testsrevealedthatinExperimentonewhen

partici-pantswereinthecooperativephase,probeselicitedmorepositive

parietalP300sthanirrelevants,(t(23)=3.1,P<0.01,d=0.48),

repli-catingpriorresearchwithmemorydetectiontests,althoughtarget

P300s were still slightly larger than probe P300s (t(23)=2.8,

P<0.05,d=0.31).Bystarkcontrast,whenparticipantswereasked

tobeuncooperativeandsuppresstheirknowledgeinExperiment

one,theirERPsboreremarkableresemblancetothoseobservedin

theinnocentphase:probeP300swerenotdifferentfromirrelevant

P300sineithertheuncooperativephase(t<1,n.s.,d=0.03)inwhich

crimeknowledgewaspresentinmemory,orintheinnocentphase

(t=1,n.s.,d=0.14)inwhichacrimememorywasabsent.

Signifi-cantlylargerP300stotargetsthantoprobeswereobservedinboth

innocent(t(23)=5.3,P<0.001,d=0.77)anduncooperativephases

Fig.2.Groupaveragemid-parietalERPscontrastingthesameitemtypesacrossblocksinExperimentone(leftcolumn)andExperimenttwo(rightcolumn).

In Experimenttwo,where targetsandprobecategorieswere

oflowerprobabilitythanirrelevantitems,parietalP300sto

tar-gets were indeed almost twicethe magnitude of target P300s

inExperimentone,consistentwithpreviousevidencethatP300

sizeis ofteninversely related tostimulusprobability(Donchin,

1981). P300 amplitudes to probes were also enhanced in the

low probability experiment, in particular in the cooperative

phasewhereprobe P300sweresignificantlymore positivethan

irrelevant P300s (t(23)=6.0, P<0.001, d=1.03), although target

P300s were still larger than probe P300s (t(23)=3.1, P<0.01,

d=0.48).Intheuncooperativephase,probeP300swereenhanced

comparedtoirrelevantP300s(t(23)=2.9,P<0.01,d=0.48),

indi-catingthatsuppressionofmemory-relatedactivitywassomewhat

lesspronouncedwithlowprobabilitythanwithequal

probabil-itycrime reminders.Similarly to Experimentone, targetswere

associated with significantly larger P300s than probes in both

innocent(t(23)=7.6,P<0.001,d=1.81)anduncooperativephases

(t(23)=6.7,P<0.001,d=0.99)ofExperimenttwo.

It is necessary toshowthat thereduced neural responseto

crimeprobesinExperimentsoneandtwowasnotduetosome

phase-genericprocesssuchaspayinglessattentiontoallitems

duringtheuncooperativephase,butratheragenuineandtargeted

efforttocontrolmemory.ComparingERPsacrossthecooperative,

uncooperative,andinnocentphases(Fig.2)showedthatthe

vol-untarymodulationsofP300swerememory-specificbecausethey

wererestrictedtocrimeprobes(dashedboxes),withno

modu-lationsoftargetorirrelevantP300s.T-testsrevealednoreliable

differencesinP300amplitudefortargetsorforirrelevantsineither

experiment(allts≤1,allds<0.17).Incontrast,P300responsesto

probeitemsweresignificantlyreducedintheuncooperative

com-paredtothecooperativephaseinbothExperimentone(t(23)=2.7,

P<0.05,d=0.50)andExperimenttwo(t(23)=3.0,P<0.01,d=0.52).

InExperimentone,P300responsestoprobesduringthe

uncooper-ativephasewerereducedtothepointofbeingindistinguishable

from probes during the innocent phase (t<1, n.s., d=0.07); in

Experimenttwo,uncooperativeprobeP300sweremorepositive

thaninnocentprobeP300amplitudes(t(23)=2.3,P<0.05,d=0.57),

confirmingthatsuppressionwasnotcompleteinthelow

probabil-ityexperiment,thoughclearlysuccessfultoa significantextent.

These findings converge to indicate that modulations of P300

amplitudewereentirelyselectivetocrimeprobes,reflecting

vol-untarymodulationsofmemory-specificbrainactivity.

3.2.2. Individualguiltclassification

The overall pattern of results in the individual guilt

confidencethresholds(Fig.3).Theseresultsshowthatbootstrap

testingofbase-to-peakP300andmeanP300amplitudesproduced

moreaccurateclassificationthantheP300peak-to-peakmethod,

inparticularforExperimentone.Usingastrictthresholdof95%CI

Fig.3.Percentageofparticipantsclassifiedasguiltyusingdifferentstatisticsforthe bootstraptestatdifferentguiltclassificationthresholds.

resultedinacceptablefalsepositiveratesforallstatistics,whereasa

liberalthresholdof90%CIresultedinreducedspecificity(in

partic-ularforthebase-to-peakandpeak-to-peakP300statistics),without

muchincreaseinsensitivity.Withaliberal90%confidencelevel,

anunacceptablyhighpercentageofparticipantswereerroneously

classified as guilty in the innocentphase(i.e. false alarms) for

thebase-to-peakandpeak-to-peakP300measures(approx.30%).

Allmeasuresshowedmorereasonablefalsealarmrates(12.5%or

lower)withastrict95%confidence threshold,exceptthe

peak-to-peakmeasurewhich wasstillratherhighinExperimenttwo

(17%). The peak-to-peakmeasure wasalsoparticularly

insensi-tiveatdiscriminating betweenprobesand irrelevantsacrossall

phasesinExperimentone,likelybecausethepost-P300negative

peak(Soskinsetal.,2001)wasnotverypronouncedwithequal

probabilityprobes.3

InExperimentone,forallmeasures,thepercentageof

individ-ualparticipantsclassifiedasguiltywashighlysimilaracrossthe

innocentphase,inwhichtherewasnocrimeknowledge,andthe

uncooperativephase,inwhichtheparticipanthadguilty

knowl-edge.Thissimilaritybetweeninnocentanduncooperativephases

contrastedwiththecooperativephase,in whichdetectionrates

werenotablyhigher(withtheexceptionofthepeak-to-peak

mea-sure,asdescribedabove).InExperimenttwowithinfrequentguilty

knowledgeprobes,correctdetectionratesduringtheguiltyphases

oftheexperimentwereoverallhigherthaninExperimentone.Even

under thesemore favourable conditions, however, suppressing

crimememoriessubstantiallyreduceddetectionratescompared

towhenparticipantsrecalledtheircrime.

Oncloserinspection,aroundhalfofparticipantsinExperiment

onedidnotshowreliableP300enhancementstotargetscompared

toirrelevantitemswithanyparticularmeasure.Thelowdetection

rateinthisexperimentwasthuslikelyaresultofreduced

signal-to-noise(SNR)ratiobecauseofoverallsmallerP300swhenprobes

werepresentedmorefrequently.Inordertoassessthepatternof

detectionforsubjectswithgoodSNR,wealsotestedclassification

foreachmeasureandthresholdwhenincludingonlyparticipants

thatshowedareliabletarget-irrelevantdifferenceinthat

analy-sis(sincethisdifferencecanbeconsideredabenchmarkagainst

whichtheprobe-irrelevantdifferencecanbecompared,e.g.Farwell

&Donchin,1991,seealsoIacono,2007),aspresentedinTable1.

InExperimentone,theseanalysesselectivelyenhanceddetection

ratesduringthecooperativephasesbyonaverage24%whereas

averagedetectionratesfor theuncooperative phaseswereonly

increasedby4%.InExperimenttwo,themajorityofparticipantshad

reliabletarget-irrelevantdifferencessotheconditionalisedanalysis

onlyincreasedaveragedetectionratesby4%inbothphases.Thus,

whenincludingonlyhighSNRparticipants,cooperativeguilt

clas-sificationwasmoresimilaracrossequiprobableandrareprobes.

Importantlyforourconclusions,theconditionalisedanalysis

con-firmedthatthelowuncooperativedetectionrateinExperimentone

wasnotduetolowSNR.Rather,lowSNRappearedtoobscurethe

differencebetweencooperativeanduncooperativephases,since

thisdifferencewasenhancedwhenparticipantsthatfailedtoshow

reliabletarget-irrelevantdifferenceswereexcluded.

3_{Thepeak-to-peakP300measurehasbeenproposedassuperiorfordetecting}

guiltyknowledgecomparedtootherbootstrapmeasures(Soskinsetal.,2001),and ourfindingsappearinconsistentwiththisargument.However,thepeak-to-peak measurereliesonaccuratelyestimatingthepost-P300negativepeakthatwasnot verypronouncedinourdata,particularlyinExperimentone.Sinceourexperiments (particularlyExperimentone)hadsomenotabledesigndifferencesfromprevious GKTprotocols,thesedifferencesmayhavealteredthecognitiveprocessesinvolved duringthetaskandtherebyaffectedtheERPmorphology.Thus,wedonotthink ourresultsspeakclearlytotheissueofwhichbootstrapmeasureisgenerallymost effectiveforguiltyknowledgedetectionacrossdifferentparadigms.

Table1

ConditionalisedguiltclassificationandAreaUnderCurveresultsacrossexperimentsandbootstrapmeasures.

Phase CI Experimentone Experimenttwo

Base-to-peak Mean Peak-to-peak Base-to-peak Mean Peak-to-peak

% N % N % N % N % N % N

Conditionalisedguiltclassification

Cooperative 95% 50 10 67 9 29 7 76 21 53 17 70 20 90% 58 12 63 11 33 9 73 22 76 21 82 22 Uncooperative 95% 14 7 10 10 11 9 39 23 28 18 55 22 90% 14 14 17 12 25 12 48 23 35 20 61 23 Innocent 95% 0 13 0 11 0 14 14 21 6 17 17 24 90% 13 15 25 12 20 15 32 22 5 19 33 24

Areasundercurves(standarderrorsinparentheses)

Cooperativevs.innocent 0.60(0.08) 0.66(0.07) 0.47(0.08) 0.84(0.07) 0.87(0.06) 0.83(0.06)

Uncooperativevs.innocent 0.47(0.10) 0.52(0.14) 0.45(0.08) 0.69(0.09) 0.70(0.09) 0.76(0.08) AUCdifferencepairedZ-test

Z-score 1.61 1.62 0.17 2.13 2.34 1.10

P-value 0.054 0.053 0.431 0.017 0.010 0.077

Note:CI,confidenceinterval;%,percentageofparticipantsthathadreliablylargerP300sforprobesthanirrelevantsoutofthosethatalsohadreliablelargerP300sfortargets thanirrelevantsintherelevantanalysis;N,numberofparticipantsincluded.

Table2

Significancevaluesofthecontrastsinthewhole-headPLSanalysisasestimatedby1000permutations.

Phase Comparison Experimentone Experimenttwo

0–400ms 400–800ms 800–1200ms 0–400ms 400–800ms 800–1200ms

Cooperative Probesvs.irrelevants 0.344 0.006 0.029 0.400 0.001 0.001

Probesvs.targets 0.120 0.001 0.183 0.302 0.005 0.020

Uncooperative Probesvs.irrelevants 0.619 0.345 0.390 0.216 0.158 0.450

Probesvs.targets 0.023 0.000 0.236 0.042 0.000 0.009

Innocent Probesvs.irrelevants 0.758 0.748 0.950 0.787 1.000 0.907

Probesvs.targets 0.126 0.000 0.229 0.002 0.000 0.001

The AUC summary measures of classification performance (Table 1) confirmed the general picture that, even though the

group-levelstatistics werehighlysignificant,individual

classifi-cationwasoverall poorinExperiment one.In Experimenttwo,

classificationperformance calculated onthebasis of the

Coop-erative“hits”versusInnocent“falsealarms”ROCwassimilarto

previousskin-conductance GKTresearch (Ben-Shakhar &Elaad,

2003) but still lower than previous P300-based GKT research

(Ben-Shakhar,personal communication).Importantly,

classifica-tionperformance waslower inboth experiments and usingall

measureswhencalculatedbasedon“hits”intheUncooperative

condition.ComparingtheAUCmeasureswithajack-knifebased

pairedZ-test(Hanley&Hajian-Tilaki,1997)revealedsignificantly

ormarginallysignificantlyhigherCooperativethanUncooperative

AUCvaluesforallbootstrapmeasuresinbothexperiments,withthe

exceptionofthepeak-to-peakmeasureinExperimentonesince

thismeasurefailedtodetectguiltyknowledgeinbothphasesof

Experimentone(Table1).TheAUCanalysisthusconfirmedthatthe

suppression-inducedreductioninindividualdetectionrateswas

notdependentonarbitraryclassificationcut-offpoints.

Insum,theindividualbootstrapresultsconfirmedthata

size-able proportion of participants successfully suppressed crime

recallandevadeddetection.Althoughexactsuccessratesvaried

somewhatdepending onthe specificclassification method and

threshold,theglobalpatternwasconsistent,with22%more

partic-ipantsclassifiedasguiltywhencooperatingthanwhensuppressing

theircrimememories,averagedacrossexperiments,measuresand

thresholds.

3.3. ERPwhole-headPLSanalysis

The result of the PLS analysis testing pairwise contrasts in

each of thedetection phases and time windowsare presented

inTable2.Therewerehighlysignificantwhole-headdifferences

betweentargetsandprobesinalldetectionphasesinboth

exper-iments, with the differencebeing maximally significant in the

400–800ms time-window. The whole-headdifference between

probesandirrelevantswasalsohighlysignificantduringthe

coop-erativephases,between400and800msinExperimentoneand

between400and1200msinExperimenttwo.However,therewere

nosignificantdifferencesbetweenprobesandirrelevantsinthe

innocentoruncooperativephasesineithertime-windowandin

eitherexperiment.Thesewhole-headPLSresultsthuscapturedthe

sameP300patternasthefocalparietalanalysis(withthe

excep-tionthattheP300differencebetweenprobesandirrelevantsin

Experimenttwodidnotreachsignificanceinthewhole-head

anal-ysis),withnoadditionalERPindicationsofguiltacrosstheglobal

spatiotemporal datawhen participantswereuncooperativeand

suppressingcrimerecall.

3.4. Finalrecallresults

Meanaccuracy onthefinal testsispresented inTable3.On

the four-choicelocation accuracy task, performance was above

chance in all conditions, but there were no significant main

Table3

Proportioncorrectresponsesacrossthelocationandobjectfinalrecalltests.

Test Condition Experimentone Experimenttwo

M SEM M SEM Location Recall 0.65 0.05 0.63 0.05 Suppress 0.55 0.04 0.67 0.04 Baseline 0.60 0.04 0.62 0.04 Object Recall 0.67 0.05 0.46 0.05 Suppress 0.52 0.05 0.41 0.05 Baseline 0.46 0.04 0.40 0.04

effectsor interactions. When participantswere asked to recall whichobjectsappearedineachroom,therewasamaineffectof condition(F(2,92)=11.4,P<0.001,Partial2_=0.20),butno

inter-actionwithexperiment(F(2,92)=1.2,P>0.3,Partial2_=0.03).The

conditionmaineffect wascaused bysignificantly higherobject recallaccuracy(againstaBonferronicorrected˛=0.0167forthree family-wiseposthoctests)for repeatedlyrecalled objectsthan for repeatedlysuppressed items(t(47)=2.5, P<0.0167, d=0.37) andforbaselineitems(t(47)=5.0,P<0.001,d=0.68),and trend-levelhigher objectaccuracyfor suppressedthanbaselineitems (t(47)=2.0,P=0.046,d=0.27)collapsedacrossexperiments.

4. Discussion

Thecurrentresearchisthefirstdemonstrationthat memory-related brainactivitynormallyelicited by remindersof incrim-inatingknowledgecanbeintentionallysuppressed.Inlinewith typicalguilty knowledge research,we used exceedingly strong retrievalcues as crimeprobes – object wordsas reminders of elaboratelyencodedobjectpictures–which wouldhavegreatly magnified recall prepotency compared to previously published retrievalsuppression studies(Andersonet al., 2004; Bergström etal.,2007,2009a,2009b;Depueetal.,2007;Hanslmayretal., 2009;Mecklingeretal.,2009).Moreover,ERPstothesepowerful

cueswerecomparedwithERPstopreviouslyunseencontrolitems,

unlikelytoelicitmemory-relatedbrainactivity.Despitethese

chal-lenges,suppressionofparietalERPpositivitywashighlysuccessful,

reducingdetectionratesofguiltyindividuals.

4.1. Theoreticalimplications

Importantly,voluntarymodulationsofparietalERPamplitudes

werespecifictocrimeprobes,withnosignificantmodulationsof

ERPstotargetsorcontrolitemsacrossphasesineitherexperiment.

ThisresultisnoteworthybecauseitconfirmsthattheprobeERP

effectswereunlikelyduetosomephase-genericprocess,suchas

participantspayinglessattentiontoallitemsintheuncooperative

phase.Rather,theERPdifferencesbetweenprobesacross

cooper-ativeanduncooperativephasescanbeconfidentlyinterpretedas

successfulvoluntarymodulationsofmemory-specificbrain

activ-ity.In fact, when we presentedfrequent reminders of a crime,

guiltyparticipants’effortstosuppressretrievalrenderedparietal

amplitudesindistinguishablefromthoseexhibitedwhentheywere

innocent.ThissimilarityofERPprofilesacrosstheuncooperative

andinnocentphasessuggeststhatwhenprobesand irrelevants

areequallyprobable,suspectscanvoluntarilysuppressretrieval

andmodulateneuralresponsestocrimeprobes,disguisingstored

knowledgeso thattheyappear innocent. Thisresult is thusan

importantextensiononpreviousfindingsthatthelateparietalERP

positivitythatistypicallyinterpretedasacorrelateofepisodic

rec-ollectionislargelyundervoluntarycontrol(Bergströmetal.,2007,

2009a,2009b;Dzulkifli&Wilding,2005;Hanslmayretal.,2009; Herron&Rugg,2003;Mecklingeretal.,2009).Thisabilityto

con-trolretrievalmayoriginate,inpart,fromthepreviouslyestablished

capacitytointentionallymodulatemnemonicactivityinthemedial

temporallobesandotherbrainareasinvolvedinmemory

repre-sentationandretrieval(Andersonetal.,2004;Benoit&Anderson,

2012;Butler&James,2010;Depueetal.,2007;Levy&Anderson, 2012).

Inasecondexperiment,wereducedtheprobabilityofcrime

reminderstomakethemsubjectivelyunexpected,inorderto

inves-tigate whether probability-sensitive parietal ERP effects would

be amenable to suppression. This issue is important because

the majority of GKT applications use low-probability designs.

A significant proportion of participants successfully concealed

crime memories even under these more demanding

circum-stances,althoughsuppressionwassomewhatlesspronouncedthan

withequal probabilitycrimereminders. Thisfindingsuggests a

boundaryconditionforvoluntarycontrolofmemory-relatedbrain

activity,indicatingthatsubjective expectednessisanimportant

factorforsuppressionsuccess.

The precise functional significance of this result is

how-ever unclear, because parietal ERP positivities in the P300

time-window arethought toindex additivecontributions from

multiple independent sources (Johnson, 1986). In memory

tasks, probability-sensitive cognitive processes related to

stim-ulus evaluation (e.g. Sutton, Braren, Zubin, & John, 1965) and

probability-insensitivecognitiveprocessesthattrackepisodic

rec-ollectionsuccess(e.g.Vilbergetal.,2006)maybothproduceERP

positivitiesthatoverlapatparietalscalpregions.Itistherefore

pos-siblethatvaryingtheprobeprobabilityacrossexperimentsmay

havechangedtherelativecontributionsoftheseunderlying

com-ponentprocessestoscalpamplitudes.InExperimentone,parietal

ERPpositivitiesmayhaveprimarilybeenrelatedtoepisodic

rec-ollection(ER).InExperimenttwo,theenhancedP300amplitudes

may have beenthe result of additiveepisodic recollection and

probability-related‘oddball’(O)processes(i.e.ER+O).One

specu-lativeinterpretationofourdataisthatthesedistinctprocessesare

differentiallysusceptible tovoluntarycontrolmechanisms,with

theepisodicrecollection-relatedERcomponentbeingmore

sus-ceptiblethantheprobability-sensitiveOcomponent.Thisaccount

could explain why the relative difference between cooperative

(ER+)anduncooperative(ER−)probeswassimilaracrossthetwo

experimentseventhoughERPamplitudestoprobeswereoverall

enhancedinbothconditionsinExperimenttwo(O+).Alternatively,

infrequentremindersmaysimplymakeitmoredifficulttoengage

thecognitivecontrolmechanismsrequiredtosuppressretrieval

duetoalackofpreparation(cf.Hanslmayretal.,2009)orpractice.

Inadata-drivenwhole-headanalysis,wetestedforalternative

ERPeffectsthatmighthavebeenusedtodiagnoseguiltwhenthe

P300wassuppressed,suchaseffectsrelatedtothecognitivecontrol

processesrecruitedtosuppressretrieval.Surprisingly,eventhough

thebehaviouraldataandself-reportsindicatedthatretrieval

sup-pressionrequiredagreatdealofeffort,thisanalysisfailedtoreveal

reliableevidenceofcontrol-relatedERPeffects,4_incontrastto

pre-viousliterature(Bergströmetal.,2009a,2009b;Hanslmayretal.,

2009;Mecklingeretal.,2009).Oneexplanationforthis

discrep-ancymaybethatpreviousresearchhasrequiredparticipantsto

switchonatrial-by-trialbasisbetweensuppressingand

retriev-inginformationfromthesameeventcontext,whereasthecurrent

taskrequired participantstosuppresscrimeretrievalacrossan

entirephaseoftheexperiment.Suchblockedretrievalsuppression

mayinvolvemoresustainedpatternsofbrainactivationthanthose

observedinpriorresearch.Sustainedbrainactivitycanbedifficult

tomeasurewithERPs,sinceERPsareprimarilysensitiveto

tran-sientbrainactivitypatternsthataretime-lockedtotheonsetof

externallydefinedevents.

Thefinalrecalltestconductedaftertheguiltdetectionphase

confirmed that theretrieval suppression manipulation affected

later retention of the tested memories. Compared torecall for

objectsinthecooperativephase,objectsrepeatedlycuedinthe

uncooperativephaseshowedreliablypoorermemory,indicating

4_{TherewasatrendformorenegativeERPsacrossfrontalsitesforprobesinthe}

sametime-windowastheparietalP300,particularlyinthecooperativephase(see scalpmapsinFig.1).Thesefrontalnegativitieswerethusnotspecificallyrelatedto suppression,butratherseemedinverselyrelatedtoparietalP300positivities,and thusmayreflectthenegativepoleofadipolarfieldstemmingfromthesame gener-atorastheP300.Sincethefrontalnegativitiesdidnotprovideadditionaldiagnostic informationregardingguiltorinnocenceinourdata(althoughseeFarwell&Smith, 2001)wedonotreportfurtherontheseeffects.

thatparticipantswereabletolimitcrimerecalldespiterepeated

reminders. However, suppressed items were still somewhat

strengthenedcomparedtobaselineobjectsthatwerenever

pre-sentedin theintermediate GKTtask. Thisresult contrasts with

previousfindingsthatrepeatedlysuppressingretrievalinresponse

toareminder cansignificantlyimpairrecallperformanceofthe

avoidedmemoriescomparedtobaseline(e.g.Anderson&Green,

2001;Andersonetal.,2004;Bergströmetal.,2009b;Depueetal.,

2007).The trendlevel enhancement for suppresseditems

rela-tivetobaselineitemsindependentlyconfirmsthesubjectivelyvery

highdifficultyparticipantsreportedfortherecallsuppressiontask,

confirmingthatthemnemonic controlevidentin reduced

pari-etal amplitudewas theproduct of effortful control.Such great

intrusivenesswasexpected,giventhatthecuesdirectlyreferred

totheobjectsthemselvesand thuslikelysharedmany

overlap-pingfeatureswiththeto-be-suppressedmemories(seeAnderson

&Spellman,1995).Therefore,retrievalsuppressionislikelytobe

moredifficultwiththeoverlappingcuesusedinGKTcompared

tothenon-overlappingcue-associatepairsusedinothermemory

suppressionresearch(e.g.Anderson&Green,2001).Nevertheless,

itispossiblethatunderadifferentprotocol,criminalsmaybeable

tosuppressmemoriesoftheircrime tothepoint of significant

below-baselineforgetting.

4.2. Practicalimplications

Afewpreviousstudieshaveshownthatcountermeasurescan

degradeERP-basedmemoryguiltdetection.Somehaveinvolved

trainingparticipantsoncovertresponsestoirrelevantcontrolitems

(e.g.Rosenfeld et al., 2004,2008; Meixner & Rosenfeld, 2010),

withtheaimofincreasingP300stoirrelevantsandthusmaking

probesandirrelevantsmoresimilar.Othershavetrained

partici-pantstomakeadditionalcovertresponsestotargetitemsinorder

toenhance theirrelative salience, thereby reducingthe

atten-tionalresourcesavailableforprocessingofprobesandirrelevants

(Mertens&Allen,2008).Importantly,noprevious studieshave

assessedwhethermemory-relatedbrainactivityinresponsetocrime

reminderscanbevoluntarilyandspecificallycontrolled.Ourstudy

isthusthefirsttochallengethecriticalassumptionthat

memory-relatedbrainactivityisautomaticallyelicitedwhensuspectsare

presentedwithcrimereminders.Thecurrentresultsshowthatthis

assumptionofmemorydetectiontestsisnotalwaysjustified.

Thegeneralizabilityofourfindingsissomewhatcomplicated

bythemultitudeofdifferentguiltyknowledgeprotocolsand

clas-sificationtechniquesthathavebeendevelopedbydifferentgroups

(e.g.Allenetal.,1992;Farwell&Donchin,1991;Rosenfeldetal.,

1991,2004).Althoughwekeptourdesignassimilaraspossibleto

thetypeofprotocolthathasarguablybeenthemostprevalentin

theGKTliterature,wedidintroducesomenoveldesignelements

inordertobeabletomanipulateretrievalsuppressionand

investi-gatesubsequenteffectsonmemory(Anderson&Green,2001).For

example,weemployedaveryelaborateencodingphasetoensure

thatcrimememorieswouldbehighlyintrusive,andour

manip-ulationuseddifferentinstructionsfrompracticalapplicationsof

GKTresearch.Themajority of appliedGKTprocedures uselow

probabilityprobes,soalthoughourfirstexperimentwas

theoret-icallyimportantforpriormemorysuppressionwork,thesecond

experimentwithlowprobabilityprobeswasmostrelevantto

prac-ticalapplications.Therefore,whilstourdesignemphasisedinternal

validity,aspectsofthedesignhadreducedecologicalvalidity.

Fur-thermore,newlydevelopedprotocolshavebeendemonstratedas

moreaccurateand resistantto othertypesof countermeasures

(Rosenfeldetal.,2008;Rosenfeld&Labkovsky,2010).Whetheror

notretrievalsuppressioncanbesuccessfullyappliedinthese

alter-nativeprotocolsisanempiricalquestion.Furtherresearchisalso

requiredtodeterminewhethersuppressionattemptscanreduce

guiltdetectionbasedonbehaviouralorANSmeasuresofmemory

(reviewedinBen-Shakhar&Elaad,2003).

Itisalsocrucialthatsuppressioncountermeasuresareassessed

outside thelaboratory.First,memoriesofa realcrimemay

dif-ferinintrusivenessfromthoseofacrimesimulation,whichcould

affectsuppressionsuccess.Second,realcriminalswilllikelydiffer

intheirmotivationtocontrolretrievalfromtypicalresearch

vol-unteers.Sinceouraimwastoexperimentallydemonstratepeople’s

capacitytocontrolmemory-relatedbrainactivity,wemanipulated

whetherourvolunteersshouldretrieveorsuppresscrime

memo-ries.Ofcourse,inarealcrimesetting,asuspectismorelikelyto

attempttosuppressthanintentionallyretrievecrimememories.

Incontrast,volunteersparticipatinginlab-basedstudiesonguilty

knowledge testing are likely morecooperative than real

crimi-nalsuspects.Typicalresearchvolunteerswithoutcountermeasure

instructionswillhavelittlemotivationtosuppressretrieval,and

mayeven intentionallyretrievecrimememoriesinresponse to

demandcharacteristics(e.g.Orne,1962).Suchcooperationfrom

volunteerswouldleadtoanover-estimationofthetest’sabilityto

detectmemoriesinarealcrimesetting.

Nevertheless,despitemethodologicaldifferences,thecurrent

researchhasimportantpracticalimplicationsbecauseitchallenges

theassumptionthatmemory-relatedbrainactivityisoutsideof

vol-untarycontrol,andhencemoreresistanttocountermeasuresthan

otherphysiologicalandbehaviouralmeasures(e.g.Lykken,1998;

seeBen-Shakhar,2011).Our findingsshowedanunprecedented

degreeofsuccessatintentionalcontrolovermemory-relatedbrain

activity,withlittlespecial training,andthat thiscontrolcanbe

marshalledasaneffectivecountermeasureduringmemory

detec-tiontests.Theseresultsthusdemonstratethatinprinciple,retrieval

suppressionposesachallengetoguiltdetectionteststhatrelyon

brain-activitymarkersofmemory.

The ability of uncooperative suspects motivated to disguise

theirguilttosuppressmemory-relatedneuralactivityestablished

hereraisesconcernsregardingthevalidityofERP-basedmemory

detectiontestsasameanstoestablishcriminalguiltorinnocence.

Togetherwithpreviousevidence(Mertens&Allen,2008;Rosenfeld

etal.,2004),thecurrentfindingspointtoaspecificproblemwith

enhancedfalsenegativesinmemorydetectiontests,meaningitis

particularlyriskytoconcludethatasuspectisinnocentbasedona

negativeresult.Theseconcernsareimportantbecauseithasbeen

arguedthatERPP300-basedmethodscanreliablydemonstratethat

asuspectlacksknowledgeofacrime,andthatthesetechniques

havebeeninstrumentalinwinningthereleaseofcriminalsuspects

inreallegalcases(seeMcCall,2004).Althoughnoteveryparticipant

managedtoavoiddetectionunderallcircumstances,ourresults

indicatethat,evenundersituationsmostfavourableforguilt

detec-tion,atleastanadditional20%ofguiltycriminalsuspectscould

bemisclassifiedandpotentiallysetfreeasaresultofintentional

retrievalsuppression,whichmayhavedirereallifeconsequences.

Althoughscepticismhasprevailedwhenthistypeofevidencehas

beenconsideredinUSlegalcases,boththemethodsandtheirlegal

standingarestillevolving,asrecentlynotedinScienceMagazine

(Miller,2010).

5. Conclusions

Across two experiments, we have demonstrated that the

absenceofareliablyenhancedbrainresponsetocrimereminders

isnotunequivocalevidencethatrelevantmemoriesareabsentin

thatperson’sbrain.Instead,thepresenceorabsenceof

memory-related brain activity appears to primarily track whether that

personishavingasubjectiveexperienceofremembering(cf.Allen

&Mertens,2009;Rissmanetal.,2010).Anabsenceof

notrememberinganassociatedcrimeatthatspecifictime,butdoes

notdeterminethattheyhavenosuchcrimememoriesstoredin

theirbrain.Aninnocentverdictinaguiltyknowledgetestcould

arisebecauseasuspectistrulyinnocent,becausetheyhave

for-gottentheparticulardetailsofthecrimethatarebeingtested,or

becausetheyarehighlymotivatedtodisguisetheirknowledgeand

areintentionallysuppressingcrimememories.

Acknowledgements

WethankChristinaMeierfordatacollectionhelp,andProf.

Ger-shonBen-Shakharand ananonymousreviewerforconstructive

feedbackduringthereviewprocess.Thisworkwassupportedby

DFGGrantsRI-1847/1-1,SFB779TPA7,andSFB779TPA10N

(A.R.-K.),theAlexandervonHumboldtFoundation(A.R.-K.),theFederal

State of Sachsen-Anhalt (A.R.-K.), MRC Grant MC-A060-5PR00

(M.C.A.),BBSRCGrantBB/G014795/1(J.S.S.),andbyajointaward

fromtheMRCandtheWellcomeTrust(J.S.S.).

References

Allen,J.J.,Iacono,W.G.,&Danielson,K.D.(1992).Theidentificationofconcealed

memoriesusingtheevent-relatedpotentialandimplicitbehavioralmeasures:

Amethodologyforpredictioninthefaceofindividualdifferences.

Psychophysi-ology,29,504–522.

Allen,J.J.B.,&Mertens,R.(2009). Limitationstothedetectionofdeception:True

andfalserecollectionsarepoorlydistinguishedusinganevent-relatedpotential

procedure.SocialNeuroscience,4,473–490.

Anderson,M.C.,Ochsner,K.N.,Kuhl,B.,Cooper,J.,Robertson,E.,Gabrieli,S.W.,etal. (2004). Neuralsystemsunderlyingthesuppressionofunwantedmemories.

Science,303,232–235.

Anderson,M.C.,&Green,C.(2001).Suppressingunwantedmemoriesbyexecutive

control.Nature,410,366–369.

Anderson,M.C.,&Huddleston,E.(2011).Towardsacognitiveandneurobiological

modelofmotivatedforgetting.InR.F.Belli(Ed.),Nebraskasymposiumon

moti-vation(Vol.58)Trueandfalserecoveredmemories:Towardareconciliationofthe

debate(pp.53–120).NewYork:Springer.

Anderson,M.C.,&Spellman,B.A.(1995).Onthestatusofinhibitorymechanismsin

cognition:Memoryretrievalasamodelcase.PsychologicalReview,102,68–100.

Ben-Shakhar.(2011).Countermeasures.InB.Verschuere,G.Ben-Shakhar,&E.

Mei-jer(Eds.),Memorydetection:TheoryandapplicationoftheConcealedInformation

Test(pp.200–214).Cambridge:CambridgeUniversityPress.

Ben-Shakhar,G.,&Elaad,E.(2003).Thevalidityofpsychophysiologicaldetectionof

informationwiththeGuiltyKnowledgeTest:Ameta-analyticreview.Journalof

AppliedPsychology,88,131–151.

Benoit,R.,&Anderson,M.C.(2012).Opposingmechanismssupportthevoluntary

forgettingofunwantedmemories.Neuron,76,450–460.

Bergström,Z.M.,DeFockert,J.,&Richardson-Klavehn,A.(2009a). Event-related

potentialevidencethatautomaticrecollectioncanbevoluntarilyavoided.

Jour-nalofCognitiveNeuroscience,21,1280–1301.

Bergström,Z. M.,De Fockert, J.,&Richardson-Klavehn, A.(2009b). ERP and

behaviouralevidencefordirectsuppressionofunwantedmemories.

Neuroim-age,21,1280–1301.

Bergström,Z.M.,Velmans,M.,DeFockert,J.,&Richardson-Klavehn,A.(2007).

ERPevidenceforsuccessfulvoluntaryavoidanceofconsciousrecollection.Brain

Research,1151,19–133.

Butler,A.J.,&James,K.H.(2010).Theneuralcorrelatesofattemptingtosuppress

negativeversusneutralmemories.Cognitive,Affective,&BehavioralNeuroscience,

10,182–194.

Delorme,A.,&Makeig,S.(2004).EEGLAB:Anopensourcetoolboxforanalysisof

single-trialEEGdynamicsincludingindependentcomponentanalysis.Journal

ofNeuroscienceMethods,134,9–21.

Depue,B.E.,Curran,T.,&Banich,M.T.(2007).Prefrontalregionsorchestrate

sup-pressionofemotionalmemoriesviaatwo-phaseprocess.Science,317,215–219.

Donchin,E.(1981).Surprise!...Surprise?Psychophysiology,18,493–513.

Dunlap,W.P.,Cortina,J.M.,Vaslow,J.B.,&Burke,M.J.(1996). Meta-analysisof

experimentswithmatchedgroupsorrepeatedmeasuresdesigns.Psychological

Methods,1,170–177.

Dzulkifli,M.A.,&Wilding,E.L.(2005). Electrophysiologicalindicesofstrategic

episodicretrievalprocessing.Neuropsychologia,43,1152–1162.

Efron,B.,&Tibshirani,R.(1986).Bootstrapmethodsforstandarderrors,confidence

intervals,andothermeasuresofstatisticalaccuracy.StatisticalScience,1,54–75.

Farwell,L.A.,&Donchin,E.(1991).Thetruthwillout:Interrogativepolygraphy(lie

detection)withevent-relatedbrainpotentials.Psychophysiology,28,531–547.

Farwell,L.A.,&Smith,S.S.(2001).UsingbrainMERMERtestingtodetectknowledge

despiteeffortstoconceal.JournalofForensicScience,46,135–143.

Garland,B.,&Glimcher,P.W.(2006). Cognitiveneuroscienceandthelaw.Current

OpinioninNeurobiology,16,130–134.

Greely,H.T.,&Illes,J.(2007).Neuroscience-basedliedetection:Theurgentneed

forregulation.AmericanJournalofLawandMedicine,33,377–431.

Giridharadas,A.(2008,September).India’snoveluseofbrainscansincourtsisdebated. TheNewYorkTimes.http://www.nytimes.com/

Hanley,J.A.,&Hajian-Tilaki,K.O.(1997). Samplingvariabilityofnonparametric

estimatesoftheareasunderreceiveroperatingcharacteristiccurves:Anupdate.

AcademicRadiology,4,49–58.

Hanslmayr, S., Leipold, P., Pastötter,B., & Bäuml,K.-H. (2009). Anticipatory

signatures of voluntary memory suppression. Journal of Neuroscience, 29,

2742–2747.

Herron,J.E.,Quayle,A.H.,&Rugg,M.D.(2003).Probabilityeffectsonevent-related

potentialcorrelatesofrecognitionmemory.CognitiveBrainResearch,16,66–73.

Herron,J.E.,&Rugg,M.D.(2003).Retrievalorientationandthecontrolof

recollec-tion.JournalofCognitiveNeuroscience,15,843–854.

Iacono,W.G.(2007).Detectionofdeception.InJ.T.Cacioppo,L.G.Tassinary,&G.

G.Berntson(Eds.),Handbookofpsychophysiology(3rded.,Vol.58,pp.688–703).

Cambridge,UK:CambridgeUniversityPress.

Johnson,R.(1986). AtriarchicmodelofP300amplitude.Psychophysiology,23, 367–384.

Levy,B.J.,&Anderson,M.C.(2012).Purgingofmemoriesfromconsciousawareness

trackedinthehumanbrain.JournalofNeuroscience,32,16785–16794.

Lykken,D.T.(1959).TheGSRinthedetectionofguilt.JournalofAppliedPsychology,

43,385–388.

Lykken,D.T.(1998). Atremorintheblood:Usesandabusesoftheliedetector.New

York:PlenumTrade.

McCall, B. (2004, February). Brain fingerprints under scrutiny. BBC News.

http://www.bbc.co.uk

McIntosh,A.R.,&Lobaugh,N.J.(2004).Partialleastsquaresanalysisofneuroimaging

data:Applicationsandadvances.Neuroimage,23(Suppl.1),S250–S263.

Mecklinger,A.,Parra,M.,&Waldhauser,G.T.(2009). ERPcorrelatesofintentional

forgetting.BrainResearch,1255,132–147.

Meegan,D.V.(2008). Neuroimagingtechniquesformemorydetection:Scientific,

ethical,andlegalissues.AmericanJournalofBioethics,8,9–20.

Meixner,J.B.,&Rosenfeld,J.P.(2010).CountermeasuremechanismsinP300-based

concealedinformationtest.Psychophysiology,47,57–65.

Mertens,R.,&Allen,J.J.B.(2008).Theroleofpsychophysiologyinforensic

assess-ments:Deceptiondetection,ERPs,andvirtualrealitymockcrimescenarios.

Psychophysiology,45,286–298.

Miller,G.(2010,May).fMRIliedetectionhearingends,decisionstilltocome. Scien-ceInsider.http://news.sciencemag.org/scienceinsider

Orne,M.T.(1962).Onthesocialpsychologyofthepsychologicalexperiment:With

particularreferencetodemandcharacteristicsandtheirimplications.American

Psychologist,17,776–783.

Paz-Alonso,P.M.,Bunge,S.A.,Anderson,M.C.,&Ghetti,S.(2013). Strengthof

couplingwithinamnemoniccontrolnetworkdifferentiatesthosewhocanand

cannotsuppressmemoryretrieval.JournalofNeuroscience,33,5017–5026.

Polich,J.(2007). UpdatingP300:AnintegrativetheoryofP3aandP3b.Clinical

Neurophysiology,118,2128–2148.

Rissman,J.,Greely,H.T.,&Wagner,A.D.(2010). Detectingindividual

mem-ories throughtheneuraldecodingofmemorystatesandpastexperience.

ProceedingsoftheNationalAcademiesofSciencesofUnitedStatesofAmerica,107,

9849–9854.

Rosenfeld,J.P.(2006).‘Brainfingerprinting’:Acriticalanalysis.TheScientificReview

ofMentalHealthPractice,4,20–37.

Rosenfeld,J.P.,Angell,A.,Johnson,M.,&Qian,J.-H.(1991).AnERP-based,

control-question lie detector analog:Algorithms for discriminatingeffects within

individuals’averagewaveforms.Psychophysiology,28,319–335.

Rosenfeld,J.P.,&Labkovsky,E.(2010). NewP300-basedprotocoltodetect

con-cealedinformation:Resistancetomentalcountermeasuresagainstonlyhalfthe

irrelevantstimuliandapossibleERPindicatorofcountermeasures.

Psychophys-iology,47,1002–1010.

Rosenfeld,J.P.,Labkovsky,E.,Winograd,M.,Lui,M.A.,Vandenboom,C.,&Chedid,E. (2008). TheComplexTrialProtocol(CTP):Anew,countermeasure-resistant,

accurate P300-based methodfor detection ofconcealed information.

Psy-chophysiology,45,906–919.

Rosenfeld, J. P., Soskins, M., Bosh, G., & Ryan, A. (2004). Simple, effective

countermeasurestoP300-basedtestsofdetectionofconcealedinformation.

Psychophysiology,41,205–219.

Rugg,M.D.,&Curran,T.(2007).Event-relatedpotentialsandrecognitionmemory.

TrendsinCognitiveScience,11,251–257.

Sip,K.E.,Roepstorff,A.,McGregor,W.,&Frith,C.(2008).Detectingdeception:The

scopeandlimits.TrendsinCognitiveSciences,12,48–53.

Soskins,M.,Rosenfeld,J.P.,&Niendam,T.(2001).Thecaseforpeak-to-peak

mea-surementofP300recordedat0.3Hzhighpassfiltersettingsindetectionof

deception.InternationalJournalofPsychophysiology,40,173–180.

Smith, M. E., & Guster, K. (1993). Decomposition of recognition memory

event-relatedpotentialsyieldstarget,repetition,andretrievaleffects.

Electroen-cephalographyandClinicalNeurophysiology,86,335–343.

Sutton,S.,Braren,M.,Zubin,J.,&John,E.R.(1965).Evoked-potentialcorrelatesof

stimulusuncertainty.Science,150,1187–1188.

VanHooff,J.C.,Brunia,C.H.,&Allen,J.J.(1996).Event-relatedpotentialsasindirect

measuresofrecognitionmemory.InternationalJournalofPsychophysiology,21,

15–31.

Vilberg,K.L.,Moosavi,R.F.,&Rugg,M.D.(2006). Therelationshipbetween

elec-trophysiologicalcorrelatesofrecollectionandamountofinformationretrieved.

BrainResearch,1122,161–170.

Wolpe,P.R.,Foster,K.R.,&Langleben,D.D.(2005). Emergingneurotechnologies