Reprint of "Affective picture processing as a function of preceding picture valence : an ERP analysis"

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Reprint of “Affective picture processing as a function of preceding picture valence: An ERP analysis”

Harald T. Schupp

^a,∗

, Ralf Schmälzle

^a

, Tobias Flaisch

^a

, Almut I. Weike

^b

, Alfons O. Hamm

^b

aDepartmentofPsychology,UniversityofKonstanz,Germany

bDepartmentofPsychology,UniversityofGreifswald,Germany

a r t i c l e i n f o

Keywords:

Affect Attention Pictures

Event-relatedpotentials Earlyposteriornegativity Latepositivepotential

a b s t r a c t

Event-relatedbrainpotential(ERP)studiesconsistentlyrevealedthatarelativelyearly(earlyposterior negativity;EPN)andalate(latepositivepotential;LPP)ERPcomponentdifferentiatebetweenemotional andneutralpicturestimuli.Twostudiesexaminedtheprocessingofemotionalstimuliwhenpreceded eitherbypleasant,neutral,orunpleasantcontextimages.Inbothstudies,distinctstreamsofsixpictures wereshown.InStudy1,hedoniccontextwasalternatedrandomlyacrossthe180picturestreams.InStudy 2,hedoniccontextsequenceswereblocked,resultingin60precedingsequencesofpleasant,neutral,and unpleasantcontextvalence,respectively.Themainfindingwasthatthevalenceoftheprecedingpicture sequencehadnosignificanteffectontheemotionalmodulationoftheEPNandLPPcomponents.However, previousresultswerereplicatedinthatemotionalstimulusprocessingwasassociatedwithlargerEPNand LPPcomponentsascomparedtoneutralpictures.Thesefindingssuggestthattheprioritizedprocessing ofemotionalstimuliisprimarilydrivenbythevalenceofthecurrentpicture.

1. Introduction

In a world where various stimuli compete for attentional resources,thefastandreliabledetectionofpositiveandnegative reinforcersfacilitatesadaptivebehavior(Langetal.,1997;Öhman etal.,2000).Thus,functionalandevolutionaryconsiderationssug- gestthepreferentialprocessingofemotionalcues.Overthepast decade,numerousneuroimagingstudieshaveconﬁrmedthatemo- tionalcuesguideselectivevisualattention.Functionalmagnetic resonanceimaging(fMRI)revealedincreasedBOLD(bloodoxygen level dependent)signalsin associative visualregions (extrastri- ate,occipito-parietal,andinferiortemporalcortex)andsubcortical limbic structures when viewing emotionally arousing pictures comparedtoneutralpictures(e.g.,Bradleyetal.,2003;Costafreda etal.,2008;Junghöferetal.,2006;Sabatinellietal.,2007,2011).

Furthermore,event-relatedbrainpotential(ERP)studiesrevealed thetemporaldynamicsofemotionprocessingatthelevelofdistinct processingstagesanddemonstratedthatemotionalstimulireceive enhancedprocessingearlyintheprocessingstream(Schuppetal., 2006).

TwoERPcomponents,referred toasearlyposterior negativity(EPN)andlatepositivepotential(LPP),haveconsistentlybeen

DOIoforiginalarticle:http://dx.doi.org/10.1016/j.biopsycho.2012.04.006.

∗Correspondingauthorat:InstituteofPsychology,UniversityofKonstanz,POBox D36,78457Konstanz,Germany.Tel.:+497531882504;fax:+497531882971.

E-mailaddress:Harald.Schupp@uni-konstanz.de(H.T.Schupp).

foundtobemodulatedbyemotionalpicturevalence.TheEPNcom- ponentisobservedasarelativenegativedifferenceinprocessing emotionalpictures(pleasantandunpleasant)comparedtoneutral picturesovertemporo-occipitalsitesinatimewindowbetween 150and350ms(e.g.,Junghöferetal.,2001;Schuppetal.,2003, 2006).Thelatepositivepotential,measuredovercentro-parietal regions between300and 700ms, islargerfor emotional, comparedtoneutral,stimuli(e.g.,Palombaetal.,1997;Schuppetal., 2000;Sabatinellietal.,2007).Studiesrelyingonstimulifromthe International Affective Picture System (IAPS, Lang et al., 2008) observed that EPN and LPP modulations are most accentuated for picturesdepictingevolutionarily relevantstimuluscontents, suchasreproduction-anddefense-relatedscenes(Schuppetal., 2003,2006),whichalsoprovokereliablesomatic,autonomicand humoralresponses(Bradleyetal.,2001).Recentresearchdemon- stratedtheemotionalmodulationoftheseERPcomponentsacross a broaderarray ofemotional stimuli includingemotional facial expressions(Mühlbergeretal.,2009;Satoetal.,2001;Schuppetal., 2004;Wieseretal.,2010),emotionalwords(Kissleretal.,2006), symbolicgestures(Flaischetal.,2009,2011),andclashingmoral statements(VanBerkumetal.,2009).Theseﬁndingshavebeencon- sideredfromtheperspectiveof‘naturalselectiveattention’,which holdsthatundernaturalisticconditionsstimulusperceptionand evaluationareoftendirectedbyunderlyingmotivationalsystems ofavoidanceandapproach(Bradley,2009;Langetal.,1997;Schupp etal.,2006).

Previous studies have mostly presented emotional stimuli in temporal isolation and used carefully planned presentation

Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-228490

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schemestoavoidconfoundsduetosequenceeffects(Flaischetal., 2008a,b).However,inthenaturalenvironment,stimulitypically donotoccurinisolation;instead,emotionalstimulimaycluster intimeandspace.Accordingly,peoplemayencountercongruent streamsorcontextsofpleasantorunpleasantstimuli.Thisraises thequestionofhowtherepeatedengagementofeithertheappe- titive oraversive motivational system affects theprocessing of individualemotionalcues.Onerecentstudyaddressedthisissueby presentingemotionalIAPSpictureseitherinanintermixedfashion orasstreamsof8picturesofthesamestimulustype(Pastoretal., 2008).ResultsindicatethatemotionalmodulationoftheLPPand positiveslowwavewascomparableinbothmixedandrepeated presentationconditions.Ontheotherhand,researchusingamod- iﬁedoddballparadigmsuggeststhathedoniccontextsmayindeed modulateaffectivestimulusprocessing.Forinstance,positiveand negativepersonalityadjectiveselicitlargerLPPamplitudeswhen presented in a sequence ofadjectives of opposite valence contexts than samevalence contexts(Cacioppoet al.,1993, 1994;

Critesetal.,1995).Anumberofmethodologicaldifferencesmay accountforthedivergentﬁndings obtainedinpreviousstudies.

Forinstance,studiesdifferedwithregardtothetypeofemotional stimuli(wordsvs.pictures)orthedurationofstimuluspresenta- tion(1.5vs.12s).Furtherresearchisthusneededtoelucidatethe effectsofhedoniccontextsuponemotionalstimulusprocessing.

Accordingly,thepresentstudyinvestigatedtheprocessingofemo- tionalpicturespresentedwiththeexperimentalparametersofthe modiﬁedoddballparadigm.

The mainaim of thepresent studies wasto investigatethe emotionalERPmodulation,indexedbyEPNandLPPcomponents, as a function of the valence of preceding images. To this end, stimuli were presented in streams of six pictures, in which a sequenceofpleasant,neutral,orunpleasantcontextpicturespre- cededpleasant,neutral, orunpleasanttargetpictures (i.e.,same valence context vs. opposite valence context).Studies 1 and 2 differedwithrespecttothepresentationofthehedoniccontext sequences.InStudy1,picturestreamscontainingdifferentvalence contextsalternatedrandomly(cf.Cacioppoetal.,1993).InStudy 2,60sequencesofeachvalencecontextwerepresentedinsucces- sion,counterbalancingtheirorderacrossparticipants.Asaresult, bothstudiesallowedacomparisonofemotionalpictureprocessing in the context of the same, a neutral, or the opposite valence picture sequence. Accordingly, the ﬁrst aim was to determine whetherhedoniccontextmodulatesemotionprocessingindexed bytheEPNandLPPcomponent.Ontheonehand,ithasbeensug- gestedthat thediscriminationofemotionaland neutral stimuli mayrepresentanobligatoryprocess,whichisnotmodulatedby hedoniccontext(Pastoretal.,2008).Ontheotherhand,previous researchrevealedhedoniccontexteffectsonemotionprocessing (Cacioppoetal.,1993).Furthermore,severaldistincthypotheses maybederivedfrompreviousresearchregardingtheinteraction ofhedoniccontextandcurrentpictureprocessing.Forinstance, from an affective priming perspective, congruent valence con- textsmayfacilitatetheprocessingofemotionalpictures ifthey are of thesame valence as thehedonic context (cf.Avero and Calvo, 2006).Alternatively, ifanemotional pictureis incongru- entwiththehedoniccontext,itmaybeparticularlysalientand accordinglyefﬁcientindrawingattentionalresources(Cacioppo et al., 1993).Furthermore, repeatedly presenting pictures from thesamevalencecategorymayleadtosensitizationeffects,par- ticularlyfortheprocessingofunpleasantimages, asseeninthe EMGcorrugatorresponse(Bradleyetal.,1996).Accordingly,ifthe contextwouldmodulateprocessingofcurrentemotionalstimuli, thesecondgoalofthestudywastorevealthedirectionof this modulationwithrespecttotheEPNandLPP components(gen- eralsensitizationvs.facilitationbythesameoroppositehedonic context).

2. Methods 2.1. Participants

ParticipantsinStudy1wereseventeen(11females)studentsfromtheUniver- sityofGreifswald.Participantswerebetweentheagesof19and26years.InStudy2, participantswereasecondgroupofseventeen(11females)studentsfromtheUni- versityofGreifswald,whowerebetweentheagesof19and27years.Allparticipants receivedcoursecredittowardstheirresearchrequirementsandprovidedwritten informedconsentfortheprotocol,whichwasapprovedbytheReviewBoardofthe UniversityofGreifswald.

2.2. Stimulusmaterialsanddesign

SixtytargetpicturesweretakenfromtheInternationalAffectivePictureSystem (IAPS;seeLangetal.,2008)depicting20unpleasantscenes(e.g.,spiders,mutilations),20pleasantscenes(e.g.,attractiveinfants,oppositesexnudes),and20 neutralscenes(e.g.,neutralfaces,householdobjects).¹Thethreecategoriesdif- feredsigniﬁcantlyfromeachotherintheirnormativevalenceratings(M=7.3,4.9, and2.3forpleasant,neutral,andunpleasantcontents,respectively;scalerange:

1–9).Meanarousallevelsforbothemotionalcategoriesweresigniﬁcantlyhigher thanforneutralcontents(M=5.4,2.8,and6.8forpleasant,neutral,andunpleasant contents,respectively).Thesetargetpictureswerethefocusoftheanalysisandwere presentedembeddedinasequenceofcontextpictures.

Adifferentsetof50pleasant,50neutral,and50unpleasantIAPSpictureswas selectedtocreatethehedoniccontexts.Thethreecontextcategoriesdifferedsig- niﬁcantlyfromeachotherintheirnormativevalenceratings(M=7.2,5.4,and2.5 forpleasant,neutral,andunpleasantcontents,respectively).Meanarousallevels forbothemotionalcategoriesweresigniﬁcantlyhigherthanforneutralcontents (M=5.3,3.4,and5.8forpleasant,neutral,andunpleasantcontents,respectively).

Thepictureswerepresentedinstreamsof6pictures(cf.Cacioppoetal.,1993).

Fiveofthesixpicturesweredrawnfromthecontextpictureset.Thetargetpicture wasdrawnfromthetargetpicturesetandappearedthird,fourth,orﬁfthwithinthe picturestream.Presentingpicturesfromoneofthethreevalencecategoriesrealized thepleasant,neutral,orunpleasanthedoniccontext.Furthermore,picturessubse- quenttotargetpicturesvariedinvalencetoincreasethelikelihoodthatparticipants paidattentiontothepicturestreams(Cacioppoetal.,1993,1994).Atotalof180dis- tinctpicturestreamsoccurredsinceeachstimulusofthetargetpictureset(N=60) waspresentedwithineachofthethreehedoniccontextcategories(N=20foreach oftheninecontextbytargetvalencecombinations).Theparticipantspressedabut- tontoinitiateeachofthe180picturestreams.Eachpicturewasdisplayedfor1.5s andprecededbyawarningdot(.5s)toensurethattheparticipantswereattending tothescreen.Afterpictureoffset,participantswereaskedtoratethevalenceof thepicturesusingathree-wayresponsebutton.Theinter-trialintervalwas3s.One streamof6picturesservedasapracticetrial.

Study1and Study2 differedinthearrangement ofthehedoniccontext sequences.InStudy1,picturestreamscontainingpleasant,neutral,orunpleasant contextsequenceswerepresentedinrandomorder.InStudy2,contextpicture valencewasblockedsothatthesixtystreamsofeachcontextpicturevalence werepresentedinsuccession.Thisresultedin3consecutiveexperimentalblocks, eachconsistingof60picturestreamswithpleasant,neutral,orunpleasantcon- textsequences,respectively.Theorderofpresentationwascounterbalancedacross participantsinStudy2.

2.3. ERPrecordingsandanalysis

Brainandocularscalppotentialfieldsweremeasuredwitha129leadgeodesic sensornet,on-linebandpassfilteredfrom0.1to100Hz,andsampledat250Hz usingNetstationacquisitionsoftwareandEGIamplifiers(ElectricalGeodesics,Inc., Eugene,OR).Electrodeimpedancewaskeptbelow30k,asrecommendedforthis typeofamplifierbyEGIguidelines.Datawererecordedcontinuouslywiththever- texsensorasthereferenceelectrode.A35Hzdigitallowpassfilterwasapplied off-linetothecontinuousEEGdata.Single-trialepochswerecorrectedforvertical andhorizontaleyemovements(Milleretal.,1988).Dataeditingandartifactrejec- tionwerebasedonanelaboratemethodforstatisticalcontrolofartifacts,specifically tailoredfortheanalysesofdensesensorERPrecordings(Junghöferetal.,2000).Data werebaseline-corrected(100msprestimulus)andconvertedtoanaveragerefer- ence.Finally,separateaveragewaveformswerecalculatedforthe9experimental cells(TargetValencebyContextValence)foreachsensorandparticipant.Applying strictartifactcriteria,8.7(SD=1.6)and9.8(SD=1.4)trialswereusedtocalculate averagewaveformsinStudy1andStudy2,respectively.Trialnumberswerenot

1TheIAPSslidenumberswereasfollows:pleasant–4670,4658,4660,4690,4650, 4680,4651,4652,4664,4659,2311,2341,2165,2170,2050,2080,2360,2070,2340, 2160:neutral– 2850,2570,2440,2480,2381,2230,2210,2200,2190,9070,7020, 7175,7235,7233,7010,7030,7080,7040,7002,7009:unpleasant–1201,1120, 1300,1050,1930,3530,6510,6260,6350,6540,9405,3130,3080,3110,3060, 3102,3053,3000,3071,3010.

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Fig.1. Illustrationofthestatisticalresults(p-valuesigniﬁcancemaps)ofthepoint- by-pointwaveformANOVA,averagedforillustrativepurposeacrossrelevanttime windowsfortheEPN(200–300ms;backview)andLPP(400–700ms;topview) componentforStudy1andStudy2,respectively.

differentforthetargetvalencecategoriesacrosshedoniccontexts.Acontrolanaly- siswithliberalartifactcriteria(meantrialnumber=17.3and17.6forStudy1and Study2,respectively)revealedcomparableresults.

Atwo-stepprocedurewasusedtoidentifyrelevantERPcomponents.These weresubsequentlyassessedbyconventionalERPanalysesbasedonareascores, i.e.,meanactivityinselectedsensorregionsandtimewindows.Inaﬁrststep,visual inspectionandsinglesensorwaveformanalysiswereusedinconcerttoidentifyrel- evantERPcomponents.Toreplicatepreviousemotioneffectsandexplorehedonic contexteffects,singlesensorwaveformanalyseswerecalculatedforeachsensor andtimepointseparatelyincludingthefactorsTargetValence(pleasantvs.neutral vs.unpleasant)andContextValence(pleasantvs.neutralvs.unpleasant).Tocor- rectformultipletesting,effectswereonlyconsideredmeaningful,whentheeffects wereobservedforatleasteightcontinuousdatapoints(32ms)andtwoneighbor- ingsensors(SabbaghandTaylor,2000).Previousﬁndingsregardingtheemotional modulationoftheEPNandLPPcomponentwerefullyreplicated(seeFig.1).How- ever,neithersinglesensorwaveformanalysisnorvisualinspectionindicatedeffects involvinghedoniccontextvalence.

Inasecondstep,themeanactivityacrossselectedsensorsitesandtimebins wascalculatedtoscoreERPcomponents.WithregardtotheEPN,themeanactivity overatimeintervalfrom200to300mswascalculatedinleftandrighttemporo- occipitalsensorclusters(EGIsensornumbersoftheleftcluster:57,58,59,60,63, 64,65,66,67,69,70,71,72,74,75;rightcluster:77,78,83,84,85,86,89,90, 91,92,95,96,97,100,101).Duetovolumeconductioneffects,emotioneffectsover occipito-temporalareaswereobservedwithreversedpolarityoveranteriorsites(cf.

Schuppetal.,2003).Exploringthesecentro-frontalsensorsitesmirroredtheeffects observedfortheoccipitalnegativityand,forbrevity,willnotbereportedhere.To assesstheLPPcomponent,themeanactivityinleftandrightcentro-parietalsensor clusters(leftcluster:7,13,30,31,32,37,38,43,53,54;rightcluster:80,81,88,87, 94,105,106,107,112,113)wascalculatedinatimeintervalfrom400to700ms.

EPNandLPPdatawereenteredintoafour-factorialANOVAincludingthebetween- subjectsfactorStudy(Study1:randomcontextvs.Study2:blockedcontext)and thewithin-subjectsfactorsContextValence(pleasant,neutral,unpleasant),Target Valence(pleasant,neutral,unpleasant),andLaterality(left,right).

Foreffectsinvolvingrepeatedmeasures,theGreenhouse–Geisserprocedure wasusedtocorrectforviolationsofsphericity.

3. Results

3.1. EPNcomponent

ThemainﬁndingswithregardtotheEPNcomponentareillus- tratedinFigs.1and2.Thesinglesensorwaveformanalysisrevealed

Fig.2.IllustrationoftheEPNcomponentshowingarepresentativerightoccipi- talsensor(EGI#91)andscalppotentialmapsofthedifferencewaves‘Pleasant– Neutral’,‘Unpleasant–Neutral’forthethreehedoniccontextconditions(pleasant, neutral,andunpleasant)forStudy1(upperpanel)andStudy2(lowerpanel).Aback viewofthemodelheadisshown.

highlysignificanteffectsofTargetValenceoveroccipito-temporal regionsinbothStudy1andStudy2.Asinpreviousresearch,the differentialprocessingofemotionalascomparedtoneutralpic- tureswasseenasrelativenegativityoverposteriorregions.The effectisillustratedinFig.2withregardtothetemporalinforma- tionbydisplayingarepresentativerightoccipitalsensorandwith regardtothetopographicaldistributionbydisplayingdifference maps(pleasant–neutralandunpleasant–neutral)averagedacross atimeintervalfrom200to300ms.Mostimportantly,thesingle sensorwaveformanalysisprovidednoindicationofasignificant interactionbetweenTargetValenceand ContextValence.Specifi- cally,asshownalsoinFig.2,thehedoniccontext(pleasant,neutral, andunpleasantpictures)showednoreliableeffectsonemotional stimulusprocessingasindexedbytheEPNcomponent.Statistical analysisbasedonareascoresoveroccipito-temporalregionsina timewindowfrom200to300mscorroboratedthesefindings.

Replicatingpreviousfindings,ahighlysignificantmaineffect ofTargetValencewasobserved,F(2,64)=87.5,p<.0001.However, theeffectofTargetValencewasqualifiedbyasignificantinterac- tionofTargetValencebyStudyF(2,64)=3.8,p<.05.Accordingly, separateanalyseswereconductedforStudies1and2.Bothstud- iesrevealedahighlysignificantmaineffectofTargetValence,F(2, 32)=34.2and55.2,p’s<.001,forStudy1andStudy2,respectively.

PleasantimageselicitedalargerEPNcomponentcomparedtoneu- tralimages, t(16)=7.2 and 9.4,p’s<.0001.Similarly, unpleasant pictureselicitedalargerposteriornegativityascomparedtoneu- tralpictures,t(16)=5.3and5.0,p’s<.0001.Finally,asinprevious research,pleasantpicturesalsoelicitedamorenegativepotential comparedtounpleasantpictures,t(16)=2.9and6.6,p’s<.05.

Nofurthereffectreachedsigniﬁcanceinthisanalysis.Ofparticu- larinterest,neithertheinteractionTargetValence×ContextValence,

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Fig.3.IllustrationoftheLPPcomponentshowingarepresentativecentralsensor (EGI#32)andscalppotentialmapsofthedifferencewaves‘Pleasant–Neutral’,

‘Unpleasant–Neutral’forthethreehedoniccontextconditions(pleasant,neutral, andunpleasant)forStudy1(upperpanel)andStudy2(lowerpanel).Atopviewof themodelheadisshown.

F(4,128)=1.4,northeinteractionStudy×TargetValence×Context Valence, F(4, 128)=0.4, approached signiﬁcance. Subsequent exploratory analyses were undertaken to examine the criti- calinteractionof TargetValence×ContextValenceseparately for bothstudies.TheinteractionTargetValence×ContextValence,F(4, 64)=0.3and0.7,wasnotsigniﬁcantinStudy1orStudy2.

3.2. LPPcomponent

ThemainﬁndingswithregardtotheLPPcomponentareillus- tratedinFigs.1and3.Theoutcomeofthesinglesensorwaveform revealedhighlysigniﬁcanteffects ofTargetValence overcentro- parietal regions for both studies. As in previous research, the differentialprocessingofemotional,comparedtoneutral,pictures wasseenasa positivepotentialshiftbetween400and700ms.

SimilartotheEPNcomponent,thesinglesensorwaveformanal- ysisdidnotrevealasignificantinteractionbetweenTargetValence andContextValence,neitherinStudy1,norinStudy2.Specifically, theemotionalLPPmodulationappearedsimilarlypronouncedin pleasant,neutral,andunpleasantcontextblocks.Tocorroborate thesefindings,theLPPcomponentwasscoredovercentro-parietal regionsina timewindowfrom400to700msandsubmittedto ANOVAanalysis.

AhighlysigniﬁcantmaineffectofTargetValencewasobserved, F(2,64)=98.2,p<.0001.Pleasantandunpleasantimageselicited anincreasedpositivity comparedtoneutral images, t(32)=10.9 and11.5,p’s<.0001,respectively.LPPstopleasantandunpleasant imageswerenotsigniﬁcantlydifferent,t(32)=0.7.

No further effect reached signiﬁcance in this analysis. Nei- thertheinteractionTargetValence×ContextValence,F(4,128)=1.8, northeinteraction Study×TargetValence×ContextValence,F(4,

128)=1.3, approached signiﬁcance. Furthermore, the separate analysisofStudies1and2revealednosigniﬁcantinteractionof TargetValence×ContextValence,F(4,64)=0.3and1.9,respectively.

4. Discussion

Emotionalstimuliarediscriminatedfromneutralcontentsearly intheprocessingstream.IthasbeensuggestedthattheEPNandLPP componentsreflectthemotivationalguidanceofselectivevisual attentiontowardsemotionalcues(Schuppetal.,2006).Bothstud- iesprovidedaone-to-onereplicationofpreviousfindingsregarding theselectiveprocessingofemotionalpictures.Between200and 300ms,pleasantandunpleasantpictureswereassociatedwitha relativenegativepotentialdifferenceoveroccipito-temporalsen- sorsitescomparedtoneutralpictures.Furthermore,between400 and700ms,theLPPcomponentovercentro-parietalsensorsites waslargerforemotionalcomparedtoneutralpictures.Thenovel findingofthepresentstudiesisthattheseeffectswereobserved regardlessofthevalenceoftheprecedingcontextpictures.Accord- ingly,theattentioncaptureofemotionalpicturesseemstodepend onthestimuluscharacteristicsoftheactualpictureirrespectiveof thehedoniccontextofthesequenceoftheprecedingpictures.

Thecurrentfindingsconfirmandextendpreviousfindingsthat ERPselicitedbyemotionalpicturesarenotaffectedbythehedonic context provided by preceding images. Pastor and colleagues (2008)presented emotionalpictures for 12swithalengthy ITI interval (12s) in which picturevalence varied eitherrandomly (group1)orwasrepeatedacross8presentations(group2).The mainfinding wasthattheLPP and positive slowwave compo- nentselicitedbyemotionalimagesweresimilarin randomand repeatedpresentations.Incomparison,theexperimentalparadigm usedinthepresentstudiesdifferedinseveralregards.Pictureswere presentedindistinct,self-pacedstreamsofsiximagesatfasterpre- sentationrates.Therepeatedpresentation(60streams)ofthesame hedoniccontextinStudy2shouldhavefacilitated theobserva- tionofhedoniccontexteffects.Furthermore,ratherthancomparing hedoniccontexteffectstoamixedseriesofemotionalandneutral pictures,thepresentstudypresentedemotionalpictureswithina hedoniccontextsequencewhichwaseitheraffectivelycongruent, incongruent,orneutral.Despitethesenotablemethodologicaldif- ferences,theLPPcomponentelicitedbyemotional(pleasantand unpleasant)imageswassimilarwhenpresentedinastreamincor- poratingaffectivelycongruentorincongruentcontextpictures.In addition,thesamepattern ofresultswasobservedwithregard totheEPNcomponent,whichreflectsarelativelyearlytransient processingstageatwhichemotionalstimuliaretaggedbasedon theirsignificance(Schuppetal.,2006).Whilethepatternoflarger EPNsto pleasant and unpleasant compared toneutral pictures (independentfromhedoniccontext)washighlysignificantinboth studies,theeffectappearedevenmorepronouncedinStudy2.This unexpectedfindingawaitsreplicationin futurestudies.Overall, thereis accumulatingevidencethat thediscriminationof emo- tionalandneutralstimulirepresentsanobligatoryprocessduring initialstimuluscategorization.

Hedoniccontexteffectsonemotionprocessinghavebeenexam- inedinaseparatelineofresearchusingrapidserialpresentation paradigms.Inonestudy,emotionalandneutralpictureswerepre- sentedinarapidstreamwithnointer-stimulusinterval(330ms;

Flaischetal.,2008a).Twomaineffectswereobserved.Asexpected, emotionalpictureselicitedalargerEPNcomponentcomparedto neutralimages.Ofparticularinterest,temporalinterferenceeffects wereobservedinthattheprocessingofthecurrentpicture(irre- spective of its valence) was attenuated when preceded by an emotional(pleasantorunpleasant)picture.Afurtherstudy,which presentedtheimagesfor660ms,revealedsimilareffectsforthe

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LPPcomponent(Flaischetal.,2008b).Speciﬁcally,theLPPelicited bythecurrentpicturewasattenuatedwhenprecededbyanemo- tionalratherthanbyaneutralimage.Nointerferenceeffectswere observedfortheEPNorLPPcomponentinthepresentstudy,which presentedthepictureslonger(1.5s)andatslowerrate(ITI=3s).

Thus,thepresentﬁndingsprovideboundaryinformationregarding temporalinterferenceeffects.Competitionforprocessingresources betweenthecurrentandprecedingimagemaythusbelimitedto conditionswithhighdemandsonperceptualprocessing.

Theproblemsassociatedwiththeinterpretationofnull-ﬁndings needtobeacknowledged.Itispossiblethatlargersamplesmay revealhedoniccontexteffects.However,asthecurrentstudydid notobserveanyhedoniccontexteffects,itseemssafetoconclude that potentialhedoniccontext effects are minorin comparison tothepronouncedeffect observedfor targetpicturevalence in thepresentstudies.Furthermore,hedoniccontexteffectsmaybe observedbyrelyingonotherwaystocreatehedoniccontextorby usingdifferentstimulustypes(cf.Cacioppoetal.,1993,1994;Crites etal.,1995).Inthepresentstudies,hedoniccontextwascreatedby presentingpicturestimulifromavarietyofdistinctcategoriesof humanexperience(Bradleyetal.,2001).However,hedoniccontext effectsmaybeseenwhenimagesfromasinglesemanticcategory arepresented(i.e.,erotica,babies,mutilations,oranimalthreat).

Thestudyofhedoniccontexteffectsmayfurthermorebeinforma- tivewithregardtoclinicaldisorderssuchasthespectrumofanxiety disordersordrugaddiction.Previousstudieshavealreadyrevealed theenhancedprocessingofdrug-andfear-relevantstimuliindrug addictionandsmallanimalphobia,respectively(e.g.,Frankenetal., 2008; Michalowskiet al., 2009; Miltneret al.,2005; Kopp and Altmann, 2005).Therepeatedpresentationof disorder-relevant stimulimayprovidecomplementaryinformationregardingpos- sible sensitizationeffects todisorder-relevant stimuli revealing additionalneuralsystemsnotengagedinhealthysubjects.Over- all,whilethereisyetnoevidenceforhedoniccontexteffectson IAPSpictureprocessing,futurestudiesmayrevealsucheffectsby investigatingdifferentwaystocreatehedoniccontextandselected clinicalsamples.

IncontrasttotheERPﬁndings,previousresearchexamining hedoniccontext effects onemotionprocessing revealedsigniﬁ- canteffects formotor responsemeasures.For instance,Bradley and colleagues (1996) presented continuous series of pleasant, neutral,orunpleasantpicturesandobservedsensitizationeffects for thecorrugator response duringunpleasant picture viewing.

Furthermore,Pastorandcolleagues(2008)observedthatcardiac deceleration,amotorindicatorofattentionalorienting,wasatten- uatedinblockedcomparedtomixedpicturepresentations.These studiesusedratherlongpicturepresentationtimesraisingtheissue whetherhedoniccontexteffectsformotorresponsesrelyonmore sustainedpictureprocessing.However,afurtherstudyobserved unpleasantcontexteffectsonthestartlereflexevenwhenthepic- tureswerepresentedasrapidandcontinuousstream(Smithetal., 2006).Accordingly,hedoniccontext effects maydiffer between measuresofperceptualprocessingandstimulusevaluationonthe one hand and somatic and autonomic motor responses onthe other(cf.Cacioppoetal.,1999).Abroaderperspectiveonemotion processing,includingtheconsiderationofthesocialcontextand themeasurementofcorticalandperipheral-physiologicalmeas- uresseemsinformativefortheunderstandingofpsychopathology, inparticulartheanxietyspectrum.Trackingtheflowofinforma- tionprocessingfrominitialstimulusevaluationtothemotoroutput stagewouldallowtodeterminethespecificstageofprocessingat whichstimulusprocessingoffearedobjectsissensitizedbyantic- ipatoryanxiety.

Overall,thereisincreasingevidencethattheemotionalguid- ance ofattentionis dictatedbytheinformation depictedinthe current stimulus. Studies investigating the effects of repeated

stimulus exposure and hedonic context support this hypothe- sis (Codispoti et al., 2007; Ferrari et al., 2011; Flaisch et al., 2008a,b;Pastoretal.,2008;Schuppetal.,2006).Whileimplicit andinstructedstimulussignificanceareoftenassociatedwithsim- ilar ERP modulations in terms of an occipital negativityand a latepositivepotential,arecentstudyobserveddistincteffectsfor bothmechanismsofattentionregulation(BublatzkyandSchupp, 2011).Usingtheinstructedfearparadigm,participantswerever- ballyinstructedthattheymight receiveanelectricshockwhen a specificemotional (pleasant or unpleasant) or neutral image cuewaspresented. Instructedfear signalselicited a ratherdis- tinctERPsignature(P1,P2,andLPP)whichwasindependentfrom the EPN and LPP modulations associated with emotional stimulus contents. Thus, whilestimulus detectiontasks oftenshow similar ERP modulations to emotion processing (Ferrari et al., 2008;Schuppetal.,2007),intrinsicandinstructedstimulussig- nificancecanalsobedissociatedfromeachotheratthelevelof stimulusencoding.Theobligatorynatureoftheattentioncapture byemotionalcuesmayalsohaveimplicationsforpsychotherapy research.Specifically, increasedselectiveattentiontopathology relevantcuesisoftenobserved(e.g.,increasedselectiveattention tophobia-relevantstimuli)andinterpretedasanattentionprob- lem(Mathewsand MacLeod,1994).However,theregulationof thefacilitated processingofemotionalandtask-relevantstimuli ispresumablyatleastinpartsubservedbydistinctneuralcircuits.

Emotionalstimuliengagecorticalandsubcorticallimbicstructures (LangandDavis,2006),which,inadditiontomodulatingcortical attentionsystems(PosnerandPeterson,1990),mayregulateper- ceptualprocessinginvisualcortexbydirectprojections (Emery and Amaral, 2000) or via ascending neuromodulatory systems (DerryberryandTucker,1991).Consideringsuchneuraldifferences interms ofattentionalcontrolmechanismsmayhelptounder- standwhycognitiveinterventionsattemptingtochangeselective attentiontopathologyrelevantcuesmightnotbeaseffectivethan stimulusdrivenapproaches (e.g.,exposurebased interventions) aimingtochangetheemotionalimpactofthesecuesbyextinction learning.

Acknowledgements

ThisresearchwassupportedbytheGermanResearchFounda- tion(Schu1074/10-3and1074/11-2).WewouldliketothankDr.

JessicaStockburgerforhelpindataacquisitionandanalysis.

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