The Body as a Tool for Anger Awareness—Differential Effects of Angry Facial and Bodily

13 Pages·2015·0.56 MB·English

RESEARCHARTICLE
—
The Body as a Tool for Anger Awareness
Differential Effects of Angry Facial and Bodily
Expressions on Suppression from Awareness
MinyeZhan1,RuudHortensius1,2,BeatricedeGelder1*
1 BrainandEmotionLaboratory,DepartmentofCognitiveNeuroscience,FacultyofPsychologyand
Neuroscience,MaastrichtUniversity,TheNetherlands,2 CognitiveandAffectiveNeuroscienceLaboratory,
TilburgUniversity,Tilburg,TheNetherlands
*[email protected]
Abstract
Emotionalsignalsareperceivedwhetherornotweareawareofit.Theevidencesofar
mostlycamefromstudieswithfacialexpressions.Here,weinvestigatedwhetherthepattern
OPENACCESS
ofnon-consciousfaceexpressionperceptionisfoundforwholebodyexpressions.Continu-
Citation:ZhanM,HortensiusR,deGelderB(2015)
ousflashsuppression(CFS)wasusedtomeasurethetimeforneutral,fearful,andangry
TheBodyasaToolforAngerAwareness—
DifferentialEffectsofAngryFacialandBodily facialorbodilyexpressionstobreakfromsuppression.Weobserveddifferentsuppression
ExpressionsonSuppressionfromAwareness.PLoS timepatternsforemotionsdependingonwhetherthestimuliwerefacesorbodies.Thesup-
ONE10(10):e0139768.doi:10.1371/journal.
pressiontimeforangerwasshortestforbodilyexpressions,butlongestforthefacial
pone.0139768
expressions.Thispatternindicatesdifferentprocessinganddetectionmechanismsfor
Editor:MauricePtito,UniversityofMontreal,
facesandbodiesoutsideawareness,andsuggeststhatawarenessmechanismsassoci-
CANADA
atedwithdorsalstructuresmightplayaroleinbecomingconsciousofangrybodily
Received:June26,2015
expressions.
Accepted:September17,2015
Published:October15,2015
Copyright:©2015Zhanetal.Thisisanopen
accessarticledistributedunderthetermsofthe
CreativeCommonsAttributionLicense,whichpermits Introduction
unrestricteduse,distribution,andreproductioninany
medium,providedtheoriginalauthorandsourceare Inthecourseofdailyinteraction,peoplenaturallydisplayfacialandbodilyexpressionsthatare
credited. easilyrecognizedbyothers.Manystudieshaveprovidedevidencethatfacialexpressionscan
alsobeprocessedwhentheyarenotconsciouslyperceived.Forexample,maskedfearfulfaces
DataAvailabilityStatement:Allrelevantdataare
withinthepaperanditsSupportingInformationfiles. orientspatialattention[1],influencetheperceptionofsimultaneouslypresentedunmasked
expression[2],elicitamygdalaactivation[3]andboosttheconnectivitybetweentheamygdala
Funding:Theworkwaspartlyfundedbytheproject
andthecolliculo-pulvinarpathway[4].
TANGO.TheprojectTANGOacknowledgesthe
financialsupportoftheFutureandEmerging Traditionally,studiesinvestigatingnon-consciousperceptionusedvisualmaskingtech-
Technologies(FET)programmewithintheSeventh niques,asintheaforementionedstudies.However,arecentlydevelopedparadigmcalledcon-
FrameworkProgrammeforResearchofthe tinuousflashsuppression(CFS)[5],avariantofbinocularrivalry,isincreasinglyusedto
EuropeanCommission(http://ec.europa.eu/research/
investigatetheprocessingofemotionsoutsidevisualawareness.Inthisparadigm,oneeyeis
fp7/index_en.cfm),underFET-Opengrantnumber:
presentedwiththeexperimentalstimulus,whiletheothereyeispresentedwithaflashing,col-
249858.BdGhasalsoreceivedfundingfromthe
orful“Mondrian”pattern,whichrendersthestimulusinvisiblefortheparticipant.Thisoffers
EuropeanResearchCouncilundertheEuropean
Union’sSeventhFrame-WorkProgramme(FP7/ strongersuppressionthanmasking,andcreatesamorestablenon-consciousperceptionfor
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2007–2013)/ERCgrantagreementnumber295673. participants[6].CFSexploitstherivalryofthedichopticstimuli,hypotheticallyoccurringat
Thefundershadnoroleinstudydesign,data bothmonocularneuronsinlower-levelvisualareasandbinocularpatternselectiveneuronsin
collectionandanalysis,decisiontopublish,or
highervisualareas[7].Previousstudiesusingthisparadigmhaveshownthatfacialstimuli
preparationofthemanuscript.
withcertainemotionalcontentscanbeprocessedwithoutawareness[8],andthattheseemo-
CompetingInterests:Theauthorshavedeclared tionalcontentscanaffectjudgmentsmadebyparticipantsafterwards[9].
thatnocompetinginterestsexist.
AlthoughCFScangenerallysuppressvisualstimuliforarelativelylongtime,theactual
durationofsuppressiontendstovarywiththestimuluscategoryaswellaswithcertainproper-
tiesofthestimuli.Inparticular,stimulithataresalientormeaningfultotheparticipantmay
breakfromsuppressionfaster[6].Thisdifferenceinsuppressiontimebetweenstimulicanbe
usedtoinferthedifferencesinnon-consciousprocessingbeforetheyreachawareness[10].
Thisbreaking-from-suppression(CFS-b)paradigmhasbeenutilizedtostudyprocessingdif-
ferencesofhigh-levelfeaturesincludingemotions.Forfacialexpressionsofemotion,studies
usingfearfulfacesprovidedmixedresults[11–15].Threeofthemshowedthatfearfulfaces
tendtobreakfromsuppressionfasterthanotheremotionalfacialexpressions[11–13],under-
scoringtheattention-grabbingstatusoffearfulfacialexpressionsthatwasfoundinmasking
studies[16].
Thecurrenthumanemotiontheoriesmaybeincompleteduetoanemphasisonthefacial
expressions;animportantquestioniswhethertheeffectsobtainedwithfacialexpressionsalso
generalizetobodilyexpressionsofemotions.Bodilyexpressionsarepotentemotionalsignals
whenperceivedconsciously[17],astask-irrelevantinformationunderattentionmanipulation
[18],butalsodosowhenprocessedoutsidevisualawareness.Thishasbeendemonstratedin
somepatientswithcorticalblindnessduetovisualcortexlesion,whoshowaffectiveblindsight,
theabilitytostillbeabletoprocessvisualemotionalsignals[19].Forexample,emotionalbod-
iespresentedintheblindvisualfieldelicitedactivationsinsubcorticalstructuresincluding
superiorcolliculusandpulvinar[20],andelicitedsimilarfacialmusclereactionstotheones
presentedinthesightedvisualfield[21].Studieswithneglectpatientsalsoshowedthatexpo-
suretoimageswithemotionalbodiessubstantiallyreducedtheattentionaldeficits[22,23].
Togetherwithmaskingstudiesinhealthyparticipants[24,25],thesestudiesprovideevidence
fortheprocessingofbodilyexpressionsofemotionoutsideawareness.Inviewofthefactthat
maskingmethodsarenotalwaysconclusive[26],convergentevidencefromotherapproaches
isdesirable.
TheCFSparadigmhassofarnotbeenusedtoinvestigatenon-consciousperceptionofemo-
tionsexpressedbybodypostures.Inthecurrentstudy,weusedtheCFS-bparadigmtoexamine
suppressiontimedifferencesamongstimuliwithneutral,fearful,andangryemotions,con-
veyedbyeitherthefaceorthebody.Ourstudyaimedtoanswerthreequestions.First,canCFS
alsobeusedtoinvestigatenon-consciousemotionalbodyprocessingandifso,aretherediffer-
encesinsuppressiontimesofthedifferentemotions?Second,isthepatternofsuppression
timedifferencesbetweenemotionssimilarforbodilyandfacialexpressions?Finally,inviewof
adebateonthisissueintheliterature,canweaddnewevidenceaboutthesuppressiontimes
underCFSforemotionalfacialexpressions?
Methods
Participants
ParticipantswererecruitedfromtheMaastrichtUniversitycampus(n=32,meanage=21.7,
rangingfrom18–30,withsevenmaleandthreeleft-handedparticipants).Allparticipantshad
normalstereoandcolorvision,normalorcorrected-to-normalvisualacuity,andnohistoryof
neurologicaldisorders.Theyprovidedwrittenconsentandreceivedeithercreditpointsor
monetaryrewardafterwards.TheprocedureforthestudywasapprovedbytheEthics
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CommitteeofMaastrichtUniversity,andwascarriedoutinaccordancewiththestandards
establishedbytheDeclarationofHelsinki.
Stimuli
Thestimuliwerefaceandbodyimagesingrayscale.Eachstimuluscategoryhad24identities,
andeachidentityhadaneutral,angry,andfearfulexpression.Thefacestimuliwereadapted
fromtheRadboudFacesDatabase[27].Theywerealignedattheeyelevel,andanellipse(from
belowthechintothetopofthehead,1.91°×2.67°ofvisualangle)maskedoutthevisualdetails
foreachfacialstimulusoutsidethatregion.ThebodystimuliwereadaptedfromStienenand
deGelder[24],withfacialinformationremoved,andalignedattheshoe-level.Neutralstimuli
consistedofindividualstalkingonthephone.Thebodystimulispannedwithin1.8°×4.3°visual
angles.Sinceourinterestliesmoreontheeffectsofdifferentemotionswithinthesamestimu-
luscategory(eitherfaceorbody),andtheemotionsperformedbythesameindividualwere
photographedunderthesamelightingconditionsandcamerasettings,tokeeptheecological
validity,weusedthefull-contrastimageswithoutfurtherbalancingtheluminanceandcontrast
acrossemotions,oracrossstimuluscategory.Instead,thelow-levelpropertieswerecontrolled
byperformingmixed-modelsanalyses.Fig1Ashowsexamplesofthestimuliused.
Procedure
ThestimuliwerepresentedinMATLAB(theMathWorks,Natick,MA,USA)withPsychtool-
box[28,29],onanLCDscreen(AcerVG248,3Dcapable,resolution=1920×1080,refresh
rate=60Hz),inaroomwithdimlight.Thebackgroundofthescreenwassettogray(RGB
value=128,128,128).Inthemiddleofthescreen,tworectangles(240x160pixels,6.4°x4.27°of
visualangles)wereplacedsidebysideandthecentersoftherectangleswere250pixelsapart
(visualangle=6.67°).Aframeof10pixelsdelineatedtheborderoftherectangles,andablack
Fig1.ExamplesofstimuliandtheCFS-bprocedure.(A)Examplesoffaceandbodystimuli,withneutral,fearfulandangryemotionalfacialandbodily
expressionswereused.(B)TheCFS-bprocedure.
doi:10.1371/journal.pone.0139768.g001
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fixationcrosswasplacedinthecenterofeachrectangle.Thefixationcrossesandtheframes
helpedtomaintainconvergenceofthetworectanglesforparticipants.
Achinrestwasplaced59cmawayfromthescreen.Participantsviewedthescreenthrough
apairofdiopterglasses(thediopterforeachlens=7).Thediopterswerecalculatedandchosen
accordingtothevisualanglebetweenthetworectangles[30],whichwouldshifteachrectangle
backtothecenterofscreenuponviewing.Acardboarddividerwasplacedbetweenthescreen
andthechinrest,dividingthescreenintotwoequalhalves.Participantswereinstructedtofix-
ateonthecrossandfree-fusethetworectanglesintoone.Theexperimentwouldstartonly
afterparticipantsreportedthattheycouldclearlyseeonlyonerectangle,andthattheviewwas
stable.Allparticipantsreportedsuccessfulandstablefusion.Withthissetup,eithereyeofthe
participantcouldseeonlythecontentoftheipsilateralrectangle.
Inatrial,adynamicnoise(160×240pixels,flashingat10Hz)wasprojectedintooneofthe
rectangularframes.Thenoiseimagesconsistedofoverlappingandcolorfulsmallrectangles
(withheightandwidthwithin2°).Thenoiseimagesineachtrialweredrawnrandomlyfrom
600uniquenoiseimages.Onestimulusimbeddedinthesamegraybackgroundwasprojected
intotheotherrectangularframe,asthetargetstimulus.Ineachtrial,theinitialfixationcross
changedtowhiteonesecondbeforethestartofthetrial,andremainedwhitethroughoutthe
trial.Intheinter-trialintervals(length=4s),thefixationcrosschangedbacktoblack.Each
trialhadadurationof9s.Thestimuluswasgraduallyrampedupfrom0%contrasttofullcon-
trastinthefirst8s,andremainedatfullcontrastforanother1s.Thecontrastofthenoisewas
rampeddowninthefirst8secondsto0%.Thusinthe9thsecondonlythestimuluswaspre-
sentedinoneoftherectangles.Participantswereinstructedtofixatecontinuously,toblinkas
littleaspossibleduringatrial,andtopressthespacebaronthekeyboardassoonastheyper-
ceiveanythingelseotherthanthedynamicnoise.Fig1BpresentstheCFS-bprocedure.Wedid
notprovidetheparticipantswithanypriorknowledgeaboutthenatureofthesuppressedsti-
muliinordertoexcludepossibletop-downeffects.
Thefaceandbodystimuliwerepresentedintwoseparateblocks.Theorderoftheblocks
wascounterbalancedbetweenparticipants.Eachindividualstimuluswaspresentedoncein
eacheye.Oneblockconsistedof144trials,randomizedwithintheblock,andbalancedbetween
theeyes.Inthemiddleofeachblocktherewasashortbreak.
Aftertheexperiment,participantswereaskedtofree-recalltheemotioncategoriesthatthey
recognized,andwhethertheyclearlyperceivethewholestimuliatthetimetheypressedthe
key.Iftheycouldnotlabeltheemotionofthebody,theywereaskedtodescribetheposture.
Mainanalyses
ThedatawereanalyzedinSPSSandR(RCoreTeam,Vienna,Austria).Forremovingoutliers,
thesingle-trialsuppressiontimeswerez-transformedforthedataofeachblockseparately,and
alsoacrossthetwoblocksforeachparticipant.Thedatapointsthatexceedfourstandarddevia-
tions(SD)ineitheroneofthez-transformationsperformedwereexcludedasoutliers.Trials
withoutaresponse(suppressiontime(cid:1)9s)werealsoexcluded.Intotal,1.13%ofthetrials
wereexcluded.Inthefaceblock,meannumberofexcludedtrialswas1outof144trials
(SD=1.29).Inthebodyblock,foroneparticipant28trialswereremovedduetonoresponse,
whilefortheotherparticipantsmeannumberofexcludedtrialswas1outof144trials,
SD=1.8.Therewasnodifferencebetweenthefaceandbodyblocksinthenumberofoutliers
removed,t(31)=-0.351,p=.728.
Therawsuppressiontime(inseconds)wasaggregatedbyparticipant.Atwo-wayfactorial
repeated-measureANOVAwasperformed,withcategory(face,body)andemotion(neutral,
fear,anger)aswithin-subjectsfactors.Pairedsamplesttestswereusedforpost-hoctesting.
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Mixedmodelscontrolanalyses
Wealsotooklow-levelpropertiesofthestimuliintoconsiderationbyperformingmixedmod-
elsanalyses.Sinceweexpectthatthelow-levelpropertieswillaffectthetwostimulicategories
differently,themixedmodelsanalyseswereperformedseparatelyonthedataofthefaceand
thebodyblocks.Aslow-levelproperties,wecountedthenumberofpixelsforeachbodyand
facestimulus,andobtainedtheaveragepixelvalueforeach.Wealsoobtainedtheroot-mean-
squarecontrastsofthewholebodystimuli,andoftheeye-eyebrowregionofthefacestimuli.
Thepixelcount,meanpixelvalue,andtheRMScontrastswerecentered,andresidualized
ontheemotiontypesusingSPSS,andtheresidualscorrespondedtothepartnotexplainedby
theemotiontypes.Themulticollinearitycheckswereperformedforthefaceandthebodydata
separately.Theemotiontype,withtheresidualizedpixelnumber,meanpixelvalue,andRMS
contrastwereenteredintoabackwardregressionmodelaspredictors.Thesuppressiontime
wasdefinedasthedependentvariable.Multicollinearitychecksshowedavarianceinflationfac-
torbelow1.5forallthepredictors,suggestingthattheywerefreeofmulticollinearityproblems.
Inthefollowingparagraphsthe“residualized”willbeomittedforconciseness.
ThemixedmodelsanalyseswereperformedinR(RCoreTeam,Vienna,Austria).Thelin-
earmixedmodelswereconstructedandcomparedwiththelme4toolbox[31].Forthemodels,
fixedeffectpredictorsincluded:emotiontype,pixelcount,meanpixelvalue,RMScontrast;ran-
domeffectsincluded:participant,stimulus,wherethestimuluspredictorisaby-itempredictor
forthestimuli.Thedetailsofmodelcomparisonstepsaredescribedintheresultsession.The
least-squaredmeanestimatesforthefixedeffectemotiontypewasobtainedusingthelsmeans
[32]andpbkrtest[33]toolboxes.Themodelsthatdifferedinrandomeffectpredictorswerefit-
tedbytherestrictedmaximumlikelihoodmethod(REML),andthemodelsthatdifferedin
fixedeffectpredictorswerefittedbythemaximumlikelihoodmethod(ML).Thefinalmodel
wasthenfittedwithREMLtoobtainthelinearestimates.
Results
Resultsofthemainanalyses
Therewasasignificantmaineffectsofcategory,F(1,31)=71.20,p<.000001,η 2=0.70,and
p
ofemotion,F(2,62)=8.47,p=.0006,η 2=0.21.Importantly,therewasasignificantinterac-
p
tionbetweencategoryandemotion,F(2,62)=28.64,p<.001,η 2=0.48.
p
Post-hocpaired-samplest-testsrevealedthatthesuppressiontimeforangryfaces
(M=3.45,SE=0.21)wassignificantlylongerthaneitherneutral(M=3.23,SE=0.19),t(31)=
3.93,p<.001,r=0.57,orfearfulfaces(M=3.23,SE=0.18),t(31)=3.60,p=.001,r=0.54.
Thedifferencebetweenneutralandfearfulfacialexpressionswasnotsignificant,t(31)=0.04,
p=.97,r=0.01.
Incontrast,suppressiontimeforangrybodieswassignificantlyshorter(M=4.11,
SE=0.21)comparedtofearful(M=4.58,SE=0.23),andneutral(M=4.26,SE=0.20)bodies,
witht(31)=7.67,p<.001,r=0.81andt(31)=2.63,p=.013,r=0.43,respectively.Suppres-
siontimeforfearfulbodieswaslongercomparedtoneutralbodies,t(31)=-4.29,p<.001,
r=0.61(Fig2).
Totestiftheorderoftheblocksinfluencedtheresults,weaddedorder(face!bodyversus
body!face)asabetween-subjectsfactorintherepeated-measureANOVA.Therewasnomain
effectoforder,F(1,30)=1.09,p=.31,η 2=0.04,oremotionbyorderinteraction,F(2,60)=0.98,
p
p=.38,η 2=0.03.Asignificantinteractionbetweencategoryandorderappeared,F(1,30)=
p
35.34,p=.000002,η 2=0.54.Thegroupwiththebodyblockfollowingthefaceblock(n=16,
p
M=3.87,SE=0.28)showedshortersuppressiontimesforthebodycategorycomparedtothe
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Fig2.Resultsofthefaceandbodyblocks.Suppressiontimeforneutral,fearful,andangryfacialandbodilyexpressions.Errorbarsrepresentstandard
errors.*:p<.05;***:p<.001.
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groupwiththefaceblockfollowingthebodyblock(n=16,M=4.76,SE=0.28),t(30)=-2.23,p
=.03,r=0.38.Thiswasnotthecaseforfaces,t(30)=0.24,p=.81,r=0.04(face!body:
M=3.35,SE=0.29,andbody!face,M=3.26,SE=0.25).Crucially,thethree-wayinteraction
betweenorder,emotionandcategorywasnotsignificant,F(2,60)=0.47,p=.63,η 2=0.02.
p
Orderdidnotinfluencethemainresults.
Inaddition,wecheckedwhethertheparticipantsbasedtheirdecisiononaconsistentbasis
withineachblock,andiftheydidn’twaittoolongforaclearperceptionofthestimuli.Allpar-
ticipantsreportedthattheypressedtheresponsebuttonassoonaspossible,buttheirpartial-
wholeperceptionvariedwhenpressingthebutton:20participantssawthewholestimulimost
ofthetime,7participantssawpartialfeaturesmostofthetime,and5participantshadamixed
perception.Totestifseeingthewholeorpartialofthestimuliaffectedtheobservedresults,we
addeditasabetween-subjectfactorintherepeated-measureANOVA.Therewasnomain
effectofstimulicompleteness,F(2,29)=0.27,p=.77,η 2=0.02.Nointeractionofstimulicom-
p
pletenesswaspresentwitheithercategory,F(2,29)=0.51,p=.60,η 2=0.03,oremotion,F
p
(2,29)=1.57,p=.19,η 2=0.10,orwithcategoryandemotiontogether,F(4,58)=0.94,p=.45,
p
η 2=0.06.
p
Resultsofthemixedmodelscontrolanalyses
Facestimuli.First,model1wasconstructedwithonefixedeffectpredictor(emotiontype),and
twoseparaterandomeffectpredictors(participant,stimulus).Aninterceptandrandomslope
foremotiontypewasincludedintheparticipantpredictor.Themodel1hadthemaximalran-
domeffectstructurejustifiedbythedata.Asecondmodel(model2)excludedtherandom
slopeofemotiontypeintheparticipantpredictor.Comparisonofthesetwomodelsshowed
thatmodel1,withtherandomslope,betterdescribedthedata,χ2(5)=13.86,p=.016.Theran-
domslopewaskeptinthesubsequentmodels.
Model3,4and5wereconstructedbyaddingasecondfixedeffectpredictor,respectively:
pixelcount(model3),meanpixelvalue(model4),RMScontrastfortheeye-eyebrowregion
(model5).Model5withRMScontrastdescribedthedatabetterthanmodel1,χ2(1)=24.52,p
<.001.Theestimate(β)forthepredictorRMScontrastwas-0.03,SE=0.005,t=-5.41,p=
.0001.Thepvaluewasobtainedusingthepbkrtesttoolbox,with10000simulationsamples.
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Fig3.Suppressiontimeforneutral,fearful,andangryfacialandbodilyexpressionsaftercorrectingforlow-levelfeaturesunrelatedtoemotion.
Errorbarsrepresentstandarderrors.*:p<.05;**:p<.01;***:p<.001.
doi:10.1371/journal.pone.0139768.g003
Subsequentlyaddingpixelcountandmeanpixelvaluetomodel5respectivelywasn’tjustified
bytheχ2change.Themodel5wasselectedasthefinalmodel.
Inthefinalmodel,withemotiontypeandRMScontrastasfixedeffectpredictors,theleast
squaredmeansofthecontrastsalsoshowedsimilarresultstothoseintheANOVAanalysis,
neutralversusfearfulfaces:t(38.93)=1.88,p=.159;neutralversusangryfaces:t(32.42)=
-3.73,p=.002,fearfulversusangryfaces:t(39.40)=-4.99,p<.0001.Theestimateforfearful
faceswas0.12sshorterthanneutralfaces,whichwasapatternalsoshownintheliterature,but
thisdifferencewasstillnotsignificant(Fig3andTable1).
Bodystimuli
Themodelcomparisonsforthebodystimulifollowedasimilarprocedureasthosefortheface
stimuli.Model1and2weresimilarlyconstructed,witharandomslopeforemotiontypeinthe
Table1. Estimates(βvalues,inseconds),standarderrors,andtvaluesforthefixed-effectpredictors
intheanalysesforthefaceandbodyblocks.
Predictor Estimate(s) SE t
Facestimuli
Intercept(neutralfaces) 3.275 0.184 17.845
Fearfulvs.neutralfaces -0.120 0.062 -1.923
Angryvs.neutralfaces 0.216 0.056 3.834
RMSContrastoftheeyeregion -0.031 0.006 -5.411
Bodystimuli
Intercept(neutralbodies) 4.264 0.202 21.099
Fearfulvs.neutralbodies 0.317 0.083 3.846
Angryvs.neutralbodies 0.152 0.066 -2.308
Meanpixelvalueofthestimulus 0.009 0.001 6.708
Thepvaluesintheanalyseswereobtainedbythelsmeansandpbkrtesttoolboxes,thuswerereported
separatelyinthetext.
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participantpredictor,eitherincluded(model1)oromitted(model2).Model1betterdescribed
thedata,χ2(5)=14.76,p=.01.Therandomeffectstructurewaskeptconstantinthesubse-
quentmodels.
Inmodels3,4and5,comparingtomodel1,pixelcount(model3),meanpixelvalue(model
4),RMScontrast(model5)wereaddedasthesecondfixedeffectpredictor,respectively.Com-
parisonsshowedthatinthe3models,model4withthemeanpixelvalueforthewholebody
stimulusdescribedthedatasignificantlybetterthanmodel1,χ2(0)=34.84,p<.001.Theesti-
mate(β)forthepredictormeanpixelvaluewas0.009,SE=0.001,t=6.58,p=.0001(Thep
valuewasobtainedbycomparingmodel5withmodel1,usingaparametricbootstrapping
modelcomparisontestinthepbkrtesttoolbox,with10000simulationsamples).Subsequently,
addingpixelcountandRMScontrasttomodel4respectively,wasnotjustifiedbytheχ2change.
Themodel4wasselectedasthefinalmodel.
Inthefinalmodel,withemotiontypeandmeanpixelvalueasfixedeffectpredictors,the
leastsquaredmeansofthecontrastsshowedasimilarpatternfortheemotionasinthe
ANOVAanalysis:neutralversusfearfulbodies:t(41.69)=-3.76,p=.0015;neutralversusangry
bodies:t(38.57)=2.26,p=.073,fearfulversusangrybodies:t(40.28)=6.51,p<.0001(Fig3
andTable1).
Discussion
Ourgoalwasthreefold:1)tousethesameCFS-bparadigmtoinvestigateperceptionofbodily
expressionswithoutvisualawareness,2)toinvestigatethepossibledifferencesinpatternof
suppressiontimedifferencesamongemotionsforfaceandbodystimuli,and3)toaddtothe
availableevidenceontheperceptionoffacialexpressionsusingtheCFS-bparadigm.
First,weshowedthatthesuppressiontimesdiddifferamongbodilyexpressions.Specifi-
cally,angrybodiesbrokesuppressionfaster,whilefearfulbodiesbrokesuppressionslower.
Comparedtofearfulbodies,angrybodiesrepresentamuchmoredirectthreattotheobserver,
whichtendtotriggeravoidanceandescapebehaviors[34].Consistentwiththisnotion,previ-
ousfMRIstudiesshowedincreasedactivityintheanteriortemporallobe,thepremotorcortex,
andtheventromedialprefrontalcortex,suggestingautomaticdefense-relatedactionprepara-
tion,inresponsetoangrybodies[34,35].Thisinvolvementoftheaction-preparationnetwork
mightbethemechanismthatfacilitatedthebreakingfromsuppressionforangrybodiesinour
study.Theposteriorsuperiortemporalsulcusmightalsoplayarole,asapplyingtranscranial
magneticstimulationtothisregionfacilitatedthedetectionofchangesinthemaskedangry
bodiesbutnotneutralbodies[36].
Forfacialexpressions,ourresultsshowedthatangryfacesbrokefromsuppressionslower
thanneutralandfearfulfaces.ThisisinaccordancewiththestudyofGrayetal.[12],showing
thatangryfacesbrokefromsuppressionslowerthanneutralfaces.Ourresultdidnotshowa
significantdifferencebetweenfearfulandneutralfaces.WhileseveralCFS-bstudieswithfear-
fulfacesshowedashortersuppressiontimethanneutralfaces[11–13],twootherstudies
showedanon-significantdifferenceintheirhealthycontrols[14,15].Thisdiscrepancymight
becausedbythelargenumberofidentities(24identities)inthefacialstimuliusedinthecur-
rentstudy,comparedtothenumber(4or8identities)intheaforementionedstudies.Thelarge
numberofstimulusidentitieshereintroducedecologicalvalidity,butmayalsohaveintroduced
variabilityintheresponsesoftheparticipants.Ingeneral,thepatternofsuppressiontime
amongthethreefacialexpressionsshowninourresultsdoesnotdepartfromthatinthelitera-
ture.Furtherresearchisneededtobetterunderstandtheroleofindividualdifferencesincon-
sciousandnon-consciousfearperception.Forexample,individualdifferencesinsensitivity
havebeenshownforfearful[37]andangryexpressions[25].
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Finally,ourresultsalsoprovideevidence,regardingthesuppressiontimepatternsamong
emotionsandpossibledifferencesbetweenfacialandbodilyexpressions.Ourresultsalready
showedageneralsuppressiontimedifferencebetweenfacesandbodies,withbodiesbeingsup-
pressedlonger.Thisisconsistentwiththeliterature[38],andindicatedadifferenceinnon-
consciousprocessingoffacesandbodies.Thedifferenceinthepatternobtainedforfaceand
bodilyexpressionsmaythereforeindicatethatadegreeofcategoryspecificitymaybepresent
atthelevelofnon-consciousemotionsignalprocessing.
Notwithstandingthefactthatfaceandbodilyexpressionsmayconveythesamemeaning,
theyareactuallyverydifferentvisualstimulionceonegetsawayfromaskingsubjectsfor
explicitcognitiverecognitionoftheemotion.Atthelevelofvisualfeatures,facesandbodies
clearlyconveytheemotionalinformationbyverydifferentmeans.Thefacialemotioniscon-
veyedbythefinedetailsofinternalfacialfeatures,includingthesalienteye-eyebrowregion,
whichisthoughttobedrivingthedetectionoffacesunderCFS[11,12].Thereisevidence
pointingtoeye-specificmechanismsforfaceperception,inwhichtheamygdalamayplayan
importantrole:eyecontactaloneactivatedtheamygdalaforacompletecorticalblindpatient
[39],single-cellrecordingsinmonkeyamygdalaalsofoundspecializedcellsforeyecontact
[40].Thebodilyemotionexpressionisratherconveyedbythepositionandmovementsofthe
bodypartsleadingtobetterexpressionrecognitionatafurtherdistance.
Fromthevantagepointofbasicemotiontheory,ithasbeenshownthatthesamebrain
areasarebeingactivatedbythesameemotion,whetherthestimuliarefaces,bodiesorvoices
[41].However,itisnotclearsofarwhetherthecategoricalstructureandtherepresentationof
theemotionlabelsisthesameatearlierprocessinglevels,especiallyatanon-consciouslevel
[42,43].Studiescomparingtheneuralbasisshowedthatemotionalfaceandbodyprocessing
involvedoverlappingbrainregions,includingthefusiformgyrus,superiortemporalgyrus,and
themiddleoccipitalgyrus;howeverthecalcarinesulcus,cerebellum,superiorfrontalgyrusand
anteriorcingulategyrusweremoreinvolvedinfaceprocessing,whilethesuperioroccipital
gyrus,parieto-occipitalsulcusandtheintraparietalsulcusweremoreinvolvedinbodyprocess-
ing[44].
Theseprocessingdifferencesmayindicatestimulusandemotionselectiveinteractionswith
theparietalattentionnetwork[45]forfaceandbodystimuli,thuscontributingtodifferentpat-
ternsoffacesandbodiesinreachingawareness.Forbodilyexpressions,studiesshowedthat
activationincreasesinthemotorsystem[46].Bodilyexpressionsmaytriggertheinvolvement
ofmoreaction-perceptionand-preparationprocesses[17,36,47,48].Thismaybeanimpor-
tantpartofthemechanismunderlyingtheshortersuppressiontimeforangrybodiesinour
study.
Acomplementaryexplanationmaybeprovidedbyprocessesrelatedtoproprioception.A
recentCFSstudyshowedthatwhenparticipantssawasuppressedhandimageinthesame
poseastheiractualhand,thesuppressedhandbrokesuppressionfaster[49].Thismightindi-
catethatthematchingoftheproprioceptiveinformationandtheunconsciouslyobserved
visualinformationmayhaveafacilitatoryeffectforstimulitoreachawareness[49].Another
recentstudycomparingneuralcorrelatesofseenandunseenbodilyexpressionsarguesinfavor
oftheroleoftheinsulaandsensorimotorprocessesinthetransitionfromnon-consciousper-
ceptiontoawareness[23].Theresultsindicatedthattheintegrationbetweenthemappingof
bodilychangesattheneurallevelandtheperipheralarousaliscriticalfortheconsciousvisual
experienceofemotionalsignals[23].
Apartfromthecategory-specificdifferencesbetweenthestimuli,thedepthofsuppressionwith
theCFSparadigmisrelatedtothespatialandtemporalpropertiesofboththestimuliandthe
masks,suchascontrasts[50].Ourresearchquestionsmainlyfocusedonthedifferentpatternselic-
itedbythesameemotionsinfacesandbodies,ratherthantheabsolutesuppressiontimebetween
PLOSONE|DOI:10.1371/journal.pone.0139768 October15,2015 9/13
TheBodyasaToolforAngerAwareness
thetwocategories.Thespatial-temporaleffectsofthestimuliandthemasksarecompatiblewithin
eachcategory.Still,couldthepresentresultsbeexplainedbytheselowlevelpropertiesofthesti-
muli,andcouldthisfactorthus,atleastindirectly,beresponsiblefortheobservedasymmetricpat-
ternsbetweenfacesandbodies?Forfacestimuli,threestudiesshowedthatfearfulfacesbrokefrom
suppressionfasterthanneutralfaces[11–13].Twoofthemsuggestedthatfasteraccesswascaused
mainlybylow-levelfeaturesoftheeyeandeyebrowregion(e.g.thelocalhighcontrastinthe
region),butnotbytheemotionalinformation[11,12].Hereweusedalargenumberofdifferent
identitiesinourstimuli(24identitiesforbothfaceandbodystimuli),introducingvariabilityinthe
lower-levelvisualproperties.Tofurthercontrolfortheeffectofthelow-levelfeaturesofthestimuli,
wedidananalysisthatresidualizedthelow-levelfeaturesontheemotiontypes,andseparatedthe
effectofalow-levelfeatureintotwoparts:onepartthatissystematicallyintroducedbythestereo-
typicalfeaturesrelatingtospecificemotiontypes(suchastheloweredRMScontrastintheeye-eye-
browregionforfearfulfaces,causedbythelargerareaofeyewhites,whichisrelatedtopossible
eye-specificmechanisms),andasecondpartthatispurelow-levelvariances(theresiduals,which
mightincludetheinfluenceofthefacialskintonevariationacrossindividualsthatisnotrelatedto
theemotion).Weexaminedwhetherthissecondpartwouldbeimportantinaffectingthesuppres-
siontime.Forboththebodyandfacestimuli,thesuppressiontimewasindeedinfluencedbythe
lower-levelvisualpropertiesofthestimuli,butonlytoaverysmallextent.Forthefaceandbody
datarespectively,theRMScontrastoftheeye-eyebrowregionandthemeanpixelvalueforthe
wholestimulusdescribedthedatawell,buttheestimatewasonetotwoordersofmagnitude
smallerthanthatfortheemotiontype.Theseresultsindicatedthatinthecurrentstudy,thevari-
anceofthelow-levelfeatureunrelatedtotheemotionswasnotnecessarilythedominantfactorfor
theeffectobservedinCFSexperiments.Thedifferencebetweentheemotioncontents,whichwas
processedatahigherlevel,wasstillthebiggestfactorforthedifferenceinsuppressiontimes.
Conclusion
WeexaminedthesuppressiontimeunderCFSforneutral,fearfulandangryfacialandbodily
expressions.Ourresultsshowedthatfearfulandangrybodilyexpressionsdifferinsuppression
time,withangrybodiesbreakingfromsuppressionfaster,suggestingadifferentinvolvementof
theactionperceptionnetwork.Incontrast,angryfacesbrokefromsuppressionmoreslowly
comparingtotheothertwofacialexpressions.Theseresultsindicatedifferentmechanismsand
neuralnetworksfornon-consciousperceptionofemotionalfacesandbodies.FuturefMRI
studiesareneededtofurtherexplaintheprocessingmechanismsfortheseemotionsunder
non-consciousviewingconditions.
SupportingInformation
S1Data.DataoftheCFS-bexperiment.
(XLSX)
AuthorContributions
Conceivedanddesignedtheexperiments:MZBdG.Performedtheexperiments:MZ.Analyzed
thedata:MZRH.Contributedreagents/materials/analysistools:MZRHBdG.Wrotethe
paper:MZRHBdG.
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