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首页 Human Facial Expressions as Adaptations

Human Facial Expressions as Adaptations.pdf

Human Facial Expressions as Adap…

lillianzww 2012-11-19 评分 0 浏览量 0 0 0 0 暂无简介 简介 举报

简介:本文档为《Human Facial Expressions as Adaptationspdf》,可适用于人文社科领域,主题内容包含HumanFacialExpressionsasAdaptations:EvolutionaryQuestionsinFacialExpressio符等。

HumanFacialExpressionsasAdaptations:EvolutionaryQuestionsinFacialExpressionResearchKarenLSchmidtDepartmentsofPsychologyandAnthropologyJeffreyFCohnDepartmentsofPsychologyandPsychiatryUniversityofPittsburghPittsburghPATextpages:Abbreviatedtitle:FacialExpressionsasAdaptationsCorrespondenceto:KarenLSchmidtEngineeringHallO’HaraStPittsburghPA(fax)Keywords:nonverbalcommunication,socialintelligence,signalingsystemsABSTRACTTheimportanceofthefaceinsocialinteractionandsocialintelligenceiswidelyrecognizedinanthropologyYettheadaptivefunctionsofhumanfacialexpressionremainlargelyunknownAnevolutionarymodelofhumanfacialexpressionasbehavioraladaptationcanbeconstructed,giventhecurrentknowledgeofthephenotypicvariation,ecologicalcontexts,andfitnessconsequencesoffacialbehaviorStudiesoffacialexpressionareavailable,butresultsarenottypicallyframedinanevolutionaryperspectiveThisreviewidentifiestherelevantphysicalphenomenaoffacialexpressionandintegratesthestudyofthisbehaviorwiththeanthropologicalstudyofcommunicationandsocialityingeneralAnthropologicalissueswithrelevancetotheevolutionarystudyoffacialexpressioninclude:facialexpressionsascoordinated,stereotypedbehavioralphenotypes,theuniquecontextsandfunctionsofdifferentfacialexpressions,therelationshipoffacialexpressiontospeech,thevalueoffacialexpressionsassignals,andtherelationshipoffacialexpressiontosocialintelligenceinhumansandinnonhumanprimatesHumansmilingisusedasanexampleofadaptation,andtestablehypothesesconcerningthehumansmile,aswellasotherexpressions,areproposedTABLEOFCONTENTSIINTRODUCTIONFacialExpressionsasAdaptationsIIBEHAVIORALPHENOTYPESETSAnatomicalVariationandFacialExpressionVariationinNeuralControlofFacialMusclesVariationWithinFacialExpressionPhenotypeSetsIndividualDifferencesinObservableFacialBehaviorMethodsinFacialExpressionResearchPhenotypicVariationinFacialPerceptionDiversityAmongFacialExpressionPhenotypesIIIECOLOGICALCONTEXTSANDFITNESSCONSEQUENCESFacialExpressionsasSocialSignalsSocioecologicalContextsofHumanFacialExpressionInfantCaregiverInteractionLongTermCooperativeSocialInteractionPositiveFitnessConsequencesFacialExpressionsDuringSpeechCourtshipandFacialExpressionsStrangers,Competitors,andConflictsofInterestSignalPropertiesofFacialDisplaysTheFunctionsofFacialExpressionIVPHYLOGENETICPERSPECTIVESONFACIALEXPRESSIONHomologyinFacialMusclesandExpressionsFunctionsofFacialExpressionsinNonhumanPrimatesVCONCLUSIONVILITERATURECITED(notepagenumbersfordoublespacedversion)INTRODUCTION:FacialExpressionsasAdaptationsOneofthecentralquestionsinhumanevolutionistheoriginofhumansocialityandultimately,humancultureInthesearchfortheoriginofsocialintelligenceinhumans,muchattentionisfocusedontheevolutionofthebrainandconsciousnessManyaspectsofhumancognitionandbehaviorarebestexplainedwithreferencetomillionsofyearsofevolutioninasocialcontext(Byrne,Cosmidesetal,)Humanbrainpowercanthusbeexplained,inpart,byincreasingsocialdemandsoverthecourseofhumanprehistory(Dunbar,)Socialintelligence,however,isnotreflectedonlyinthebrain,butineveryadaptationthatallowssuccessfulinteractioninsocialgroupsNewadvancesinstudyingthebiologyofsocialbehaviorhavenotfullyexploredthatmostvisiblysocialpartofthehumanbody,thefaceThefaceisavisiblesignalofothers’socialintentionsandmotivations,andfacialexpressioncontinuestobeacriticalvariableinsocialinteractionAlthoughsocialintelligenceisanincreasinglyrichsourceofhypothesesofcognitiveandbehavioraladaptations,theanthropologicalstudyoffacialexpressionremainsfocusedonessentiallynonadaptivequestionsCurrentanthropologicalviewsoffacialexpressiontendtofocusonthecontrastsbetweenuniversalandculturespecificexplanationsoffacialexpressionsFacialexpressioniseitherinterpretedasahumanuniversal,withbasicexpressionsrepresentedinallknownhumanpopulations(Brown,),oritisconceptualizedasthenaturaloutgrowthofculturaldifferences,withlittleoverlapinexpressionfrompopulationtopopulation(Birdwhistell)Physicalanthropologists,withimportantexceptions(BlurtonJones,Fessler,)(andChevalierSkolnikoff,Goodall,Hauser,PreuschoftandvanHooff,forcomparisonwithnonhumanprimates)havegenerallyavoidedthestudyofhumanfacialexpressionsandnonverbalcommunication,leavingtheinterpretationoffacialexpressionlargelytopsychologyandtootherbranchesofanthropology(Birdwhistell,LaBarre,)Thecurrentstateofresearchinfacialexpression,combinedwiththecurrentinterestinsocialintelligenceasadrivingforceinhumanevolution,callsforthereemergenceofthestudyoffacialadaptationinphysicalanthropologyEstablishinghumanfacialexpressionsasbiologicaladaptationsrequiresarigorousreviewofourcurrentknowledgeandultimatelytheformationandtestingofevolutionarilybasedhypothesesReeveandSherman’s()definitionofadaptationisaguidelinefordevelopingevolutionaryhypotheses,andallowstheexplorationofbehavioraladaptationsthathaveremainedrelativelyunknowninphysicalanthropologyTheydefineanadaptationas“aphenotypicvariantthatresultsinthehighestfitnessamongaspecifiedsetofvariantsinagivenenvironment”Thisdefinitionisparticularlysuitedtoadaptivehypothesesofhumanbehavior,becauseitsrequirementscanbemetwithobservationofcurrentphenomena,andreferencetophylogeneticfactorsisnotrequired(ReeveandSherman,)Whatisrequired,however,isevidenceofphenotypicvariation,welldefinedecologicalcontexts,andfitnessconsequencesforaparticularadaptationThepurposeofthisreviewistoprovideaframeworkforaskingevolutionary,adaptivequestionsabouthumanfacialexpressionFirst,weestablishhumanfacialexpressionasapotentialbehavioraladaptation,bydetailingthephenotypicvariation,ecologicalcontexts,andfitnessconsequencesoffacialbehaviorAparticularexpression,thehumansmile,isusedasanexampleofthepotentialoftheadaptationistapproachforunderstandinghumanfacialexpressioninanevolutionaryperspectiveFinally,facialbehavioriscomparedtothatofnonhumanprimatestoprovidesomefurtherphylogeneticperspectiveontheevolutionoffacialexpressionanditsroleintheevolutionofhumansocialintelligenceBEHAVIORALPHENOTYPESETSHumanuniversalfacialexpressionsofemotionareperhapsthemostfamiliarexamplesoffacialexpression,atleastamonganthropologistsSixbasicexpressioncategorieshavebeenshowntoberecognizableacrosscultures(seeFig),andthisfindingisgenerallyacceptedbypsychologistsworkingonfacialexpressionThesixbasicemotionalexpressions,orfacialconfigurationsassociatedwithparticularemotionalsituations,havebeenshowntobeuniversalintheirperformanceandintheirperception(EkmanandKeltner,),althoughthereissomeobjectiontotheideathattheseexpressionssignalsimilaremotionsinpeopleofdifferentcultures(Fridlund,RussellandFernandezDols,)ThecontroversysurroundingtheattributionofuniversalemotionstouniversalfacialexpressionsofemotionisimportantforunderstandingemotionscrossculturallyNevertheless,eventhosethatdisagreeontheemotionconcedethecrossculturalconsistencyofthecombinationsoffacialmovements(behavioralphenotypes)thatmakeupexpressionsof“disgust,”“fear,”“joy,”“surprise,”“sadness,”and“anger”(RussellandFernandezDols,)TheseexpressionswerefirstdiscussedbyDarwin(),asuniversals,andhavebeenrecognizedinpeoplefromwidelydivergentculturalandsocialbackgrounds,aswellasinthefacesofindividualsborndeafandblind(DarwinEiblEibesfeldt,Izard,EkmanandKeltner,)Inadditiontothesixbasicfacialexpressions,therearealsocoordinated,stereotypednonverbaldisplaysthatincludestereotypedfacialexpressioncomponentsTheseincludetheeyebrowflash,yawning,startle,thecoydisplay,andembarrassmentandshamedisplays(EiblEibesfeldt,Grammeretal,KeltnerandBuswell,KeltnerandHarker,Provine,)Thesedisplaystypicallycombinebothfacialandposturalorgesturalelementsandarefoundinwidelydistributedpopulations,suggestingspecies,ratherthanculturalspecificityTheeyebrowflashisagoodexampleofthiskindofdisplayThefrontalismuscleisconsistentlyusedtoraisebothmedialandlateralpartsoftheeyebrow(EkmanandFriesen,Grammeretal,)Acommonrepertoireofsynchronousfacialmovementsoccursincombinationwiththeeyebrowflash,includingmostfrequentlytheraisingofthelipcorners(smile),andliftingoftheupperlid(Grammeretal,)Inadditiontoconsistencyinmuscleaction,thetimingoftheeyebrowflashisalsoconsistentcrossculturallyinthethreenonwesternpopulationsanalyzedTheonsetoftheeyebrowflashtypicallyfollowsapauseinallotherfacialmovements,andtakesaboutmilliseconds,withverylittlevariationacrossculturalgroupsInaddition,coordinatedheadmovementsarefoundinassociationwitheyebrowflashes,extendingthedisplaybeyondthefaceitself(Grammeretal,seeFig)Inordertoproducetheeyebrowflashandotherrecognizable,universalexpressions,humanspresumablyusethesamefacialmusculature,andmoveitintoasimilarconfigurationundersimilarcircumstancesThuseachofthesecoordinatedfacialdisplayscanbeconsideredabehavioralphenotypeWithinthesefacialexpressionphenotypes,however,andacrossindividualhumans,thereisagreatdealofphysicalvariationinstructure,movement,andperceptionUniversaldisplays,togetherwithvariationaroundthebasiccomponentsofthesedisplays,comprisewhatcanbeconsideredphenotypesetsoffacialexpressionSourcesofthisvariationincludeanatomicalandneurobiologicaldifferences,aswellasdemographicdifferencessuchassex,age,andculturalbackgroundInaddition,theperceptionoffacialexpression,importantforunderstandingcommunicativeadaptations,isalsoasourceofindividualvariationAnatomicalVariationandFacialExpressionThestructureofhumanfacialmuscleshasbeenknownforsometime(Duchenne,Huber,)(seeFig)Theanatomicalbasisoffacialexpressionhasbeendescribedindetail,andananatomicallybasedcodingsystemisavailablefortheobjectivestudyoffacialaction(FacialActionCodingSystemEkmanandFriesen,)ThissystemoutlinesspecificactionsproducedbyparticularfacialmusclesThequalityoftheseactions,however,likelyvarieswithdifferencesinthefacialmusclesDifferentfacialmusclesproducedifferenttypesofmovements,andtheyaremostlikelyheterogeneousintheirstructureandinnervationGoodmurphyandOvalle()forexample,haveshownthatmusclefibertypes,shapesandsizesinorbicularisoculi,parspalpebralisandcorrugatorsuperciliiaresignificantlydifferent,althoughthesetwomusclessharethesameinnervationandembryonicoriginandarefoundinthesameregionoftheface(lowereyelidandlowermidforehead,respectively)Theorbicularisoculiconsistsoffasttwitchfibers,significantlymorethanthecorrugator,implyingsomedifferenceinthemovementsproducedbythetwomuscles(GoodmurphyandOvalle,)Zygomaticusmajorandminormusclesaresimilartotheorbicularisoculiintheirhighproportionsoffasttwitchfibers,relativetoothermuscles,indicatingapossiblespecializationforfastmovements(Staletal)TherearealsoindividualdifferencesinthestructureanddifferentiationoffacialmusclesForexample,adifferentiatedmusclebundle,therisorius,thoughttobeuniquetohumans,ishighlyvariableAsmanyasofspecimensinarecentstudylackedthismuscle(Pessaetal,a),andHuberbelievedthatitwasabsentcompletelyinpeopleofMelanesianancestry(Huber)Variousfurrowsandotherdeformationsofthefacialskinareproducedbyvariationsinfacialmuscles,andthesemaycontributetoindividualdifferencesinexpressionInmostindividuals,theplatysmamuscleinsertsontheskinovertheinferiormarginofthemandible,butitisoccasionallyobservedinsertinginthelateralcheek,causingaverticaldepressionorfurrowtoappearthereThezygomaticusmajormusclealsovaries,appearinginabifidversionwithtwoseparateinsertionpointsinofofspecimensinananatomicalstudy(Pessaetal,a)Thetensioncausedbythetwoheadsofthemuscleatthecornerofthemouthisbelievedtocauseadimpleorsmalldepressionduringthecontractionofthemuscleinsmiling(Pessaetal,b)Changesinfacialtexture,suchasdimplesthatappearwithasmileinsomeindividuals,couldbeofaddedvalueinmakinganexpressionnoticeable,orinprovidinginformationabouttheintensityoftheexpressionAstudyoffacialmusculatureinlivinghumansnotedasignificantsexdifferenceinthethicknessofthezygomaticusmajormuscle(McAlisteretal,)Thisstudyalsoinvestigateddifferencesinmusculature,andfoundnosignificantdifferencesineitherlevatorlabiisuperiorisorzygomaticusmajormusclethicknessbetweenAsiansandCaucasians(McAlisteretal,)Ingeneral,thereisnotagreatdealofpublishedinformationonpopulationalorsexbasedvariationinfacialmuscles,andfindingsofpopulationaldifferencesdescribedabovehavenotbeenreplicatedTheeffectsofinterindividualanatomicalvariation,includinggeneticallybasedvariationonfacialexpressionareevenlesswellknownThemusclesthemselvesarehighlyvariable,withsomemusclesappearinginsomeindividualsandnotinothers(Pessaetal,b)ThepresenceofanatomicalvariationraisesimportantquestionsaboutthelinkbetweenfacialactionsandspecificmusclesTherelationshipbetweenmuscleactivityanddisplacementoffacialfeaturesinexpressionisindividualizedtosomedegreeduringposedeyebrowraises,muscleactivityisroughlyequaltobrowdisplacementsquaredYetthereiswidevariationforindividualbrowsandleftbrowsrisehighergiventhesameamountofmuscleactivity(Pennocketal,)Ontheotherhand,iftheactionofthefaceisthesame,althoughthereisvariationintheunderlyingmuscularstructure,theresultingfacialexpressionsmaynotbemeaningfullydiscriminatedTheuniversalrecognitionofsomebasicexpressionsindicatesthatfacialexpressionsmaynotdependonaonetooneanatomicalcorrespondenceinanytwofacialsignalersBasicfacialexpressionsarealsorecognizableinabbreviatedform,withoutthecompletesetoffacialactionsdescribedfortheprototypeexpressionRegardlessofthedegreeofvariationthatcanbedetectedempirically,perceiversmaytakenonoticeoftheseslightvariations(Fridlund,Shor,),ormaycategorizethemsimilarly,withhighagreement(Campbelletal,Cashdan,)Moreimportantly,itisunknownwhethersuchphenotypicvariationinfacialexpressionmeetsthesecriteriaof“justmeaningfuldifference”(Hauser,)bycausingdifferencesinreceiverbehaviororjudgmenttoslightlyvariantdisplaysofthesametypeVariationinNeuralControlofFacialMusclesNeurobiologically,facialexpressionsareduallycontrolledbyextrapyramidalandpyramidaltracts,providingforautomaticandvoluntarycontroloffacialexpressionBasedonobservationsofindividualssufferingfromvariousneurologicalconditions,Rinn()hasdescribedbothsystemsoffacialmovement,alongwiththedifferentialvoluntarycontroloverupperandlowerface,relatedtogreaterasymmetryandvoluntarycontroloverthemouthregionthantheeyesThisdifferenceisespeciallyapparentinthefacialexpressionsofpeoplewithcorticalversusextrapyramidaldeficitsThoselackingcorticalcontrolproducelargelyasymmetricalvoluntary(posed)expressions,butsymmetricalspontaneousexpressionsExtrapyramidaldeficitsproducetheoppositeeffect(Rinn,RossandMathiesen,)Potentialasymmetryduetodifferencesininnervationofsidesofthefacemayberelatedtosexdifferencesinthebrain,andthereforeproducevariationinfacialexpressionamongindividualsThisisespeciallytrueifincreasedlateralizationofcorticalfunctioninmalesincludesmorelateralizedfacialmovementduringexpressions(Richardsonetal,)Spontaneityofexpressionalsomayplayarole,withmorespontaneousfacialexpressionsunderthecontrolofadifferentneuralpathway,andthereforemoresymmetric(GazzanigaandSmylie,Rinn,)ResearchhasnotclearlyconfirmedthepredictionsofRinn()forasymmetryinlowerfacemotion,especiallyinspontaneousexpressionsBorodetal(),inametaanalysisoffacialexpressionandasymmetry,concludedthatfacialexpressionscouldgenerallybeconsideredleftsidedHowever,theydidnotfindthatmenweremorelikelytohaveasymmetryintheirfacialexpressions,althoughindividualstudieshadpreviouslysuggestedthisOtherresearchers,usingmoreobjectivequantitativemethods(directassessmentofdigitizedimages,ratherthanobserverjudgmentsorobservercoding)foundthattheupperfacewasmuchmoreasymmetricthanexpected,particularlyduringspontaneousexpression(Richardsonetal,)Inaddition,thecomplexconnectionsthathavebeenproposedbetweentheexperienceofpositiveandnegativeemotionsandfacialexpressionandcerebrallateralityarestillinquestion(Borodetal,HagerandEkman,)Borodetal()foundsignificantleftsidednessoffacialexpressioninstudiesinvolvingmusclequantificationandtrainedobserverratings(oftotalstudiesshowedleftsidednessascomparedtoofshowingrightsidedness)Theevidenceofrightsidednessforpositiveexpressions(smile),andleftsidednessforotheremotionexpressionswasmuchweaker(Borodetal)Althoughtheroleofasymmetryinthequalityoffacialsignalsisnotclear,asymmetricfacialexpressionislikelytobeanimportantvariableinconsideringfacialdisplaysasadaptations,particularlyasitrelatestospontan

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