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Running Head: EMOTION IN THEORY OF MIND
Computational models of emotion inference in Theory of Mind:
A review and roadmap
Desmond C. Onga,b, Jamil Zakic, and Noah D. Goodmanc,d aA*STAR Artificial Intelligence Initiative, Agency for Science, Technology and Research
(A*STAR), Singapore
bInstitute of High Performance Computing, Agency for Science, Technology and Research
(A*STAR), Singapore cDepartment of Psychology, Stanford University
dDepartment of Computer Science, Stanford University
In Press at: Topics in Cognitive Science
Special Issue on: Computational Approaches to Social Cognition
Final version dated: 1 July 2017 (Minor edits to funding acknowledgements)
Address Correspondence to:
Desmond C. Ong A*STAR Artificial Intelligence Initiative Agency for Science, Technology and Research, Singapore 138632 [email protected] Author Contributions: D.C.O., J. Z., and N. D. G. wrote the paper. The authors declare no conflict of interest. Keywords: Emotion; Affective Cognition; Inference; Theory of Mind
EMOTIONINTHEORYOFMIND 2
ABSTRACT
Research on social cognition has fruitfully applied computational modeling approaches to
explain how observers understand and reason about others’ mental states. By contrast, there has
been less work on modeling observers’ understanding of emotional states. We propose an
intuitive theory framework to studying affective cognition---how humans reason about emotions-
--and derive a taxonomy of inferences within affective cognition. Using this taxonomy, we
review formal computational modeling work on such inferences, including: causal reasoning
about how others react to events, reasoning about unseen causes of emotions, reasoning with
multiple cues, as well as reasoning from emotions to other mental states. Additionally, we
provide a roadmap for future research by charting out inferences---such as hypothetical and
counterfactual reasoning about emotions---that are ripe for future computational modeling work.
This framework proposes unifying these various types of reasoning as Bayesian inference within
a common “intuitive Theory of Emotion”. Finally, we end with a discussion of important
theoretical and methodological challenges that lie ahead in modeling affective cognition.
EMOTIONINTHEORYOFMIND 3
Recentdevelopmentsincomputationalcognitivemodelinghaveallowed
researcherstospecifyandtestprecisehypothesesabouthowpeoplemakeinferences
abouttheirsocialworld.Theseincludeinferencesaboutwhatothersdesireandbelieve
abouttheworld(e.g.,Baker,Jara-Ettinger,Saxe,&Tenenbaum,2017;Goodmanetal,
2006),whatothersmeanwhentheyuselanguagetocommunicate(Goodman&Frank,
2016;Goodman&Stuhlmüller,2013;Frank&Goodman,2012),andwhatfuturedecisions
othersmightmake(Jara-Ettinger,Gweon,Schulz,&Tenenbaum,2016;Jern&Kemp,2015).
Theserecentdevelopmentscomprisethefocusofthecurrentspecialissue.However,these
modelshaveoftenneglectedhowpeoplereasonaboutoneofthemostessentialelements
ofhumanpsychology:emotions.
Emotionsplayacentralroleinoursociallives.Theysignalpeople’simmediate
reactionstoeventsintheworld(e.g.,Ellsworth&Scherer,2003),andcausemany
behaviors---bothintentionalandunintentional(Lerner,Li,Valdesolo,&Kassam,2015;
Loewenstein&Lerner,2003).Giventheimportanceofemotionsinsocialinteractions,itis
hardlysurprisingthatpeoplearenaturallyattunedtoperceivingandunderstanding
emotionsinthosearoundthem(Harris,1989;Zaki&Ochsner,2011).
Inthispaper,weconsiderthepresentandfutureofcomputationalmodelingin
understandinghowpeoplereasonaboutemotionalstates---whatwetermaffective
cognition(Ong,Zaki,&Goodman,2015).Weadoptanintuitivetheoryframeworktothe
studyofaffectivecognition,usingwhichwederiveataxonomyofaffectivecognitive
inferences(inthespiritofAdelson&Bergen,1991,andKemp&Jern,2013,who
respectivelyderivedtaxonomiesofvisualfunctionsandinductiveproblems).This
taxonomyencompassesawiderangeoflayreasoningaboutemotionalstates,suchasusing
EMOTIONINTHEORYOFMIND 4
observedbehaviororsituationcontexts(orcombinationsthereof)toinferemotionsand
othermentalstates(e.g.,DeMelo,Carnevale,Read,&Gratch,2014;Wu,Baker,Tenenbaum,
&Schulz,2018;Zaki,2013).Finally,weprovidearoadmapforfutureresearch,by
highlightinginferencesthathaveyettobestudiedcomputationally,andbydiscussing
importanttheoreticalandmethodologicalchallengesthatlieahead.
Layingoutanintuitivetheoryofemotions
Peoplehaverichintuitivetheoriesofhowothersaroundthemthinkandbehave,
allowingthemtoinferothers’motivationsandexplainothers’behavior(e.g.,Heider,1958;
Gopnik&Meltzoff,1997;Ross,1977).Anintuitivetheoryofotherpeopleconsistsoffirst,a
structuredontologyofconcepts---forexample,personality,goals,behavior---andsecond,
thecausalrelationshipsrelatingtheseconcepts(Gerstenberg&Tenenbaum,2017).These
intuitivetheoriesallowlaypeopletomakesenseofothersaroundthem,inasimilarfashion
tohowscientifictheoriesallowscientiststoexplainthephysicalworld(Carey,2009;
Wellman&Gelman,1992).
Peoplealsopossessarichintuitivetheoryofemotionsthatcomprisesconceptual
knowledgeaboutdifferentemotionalstates(e.g.,anger,happiness)andhowtheyare
relatedtotheircausesandeffects.People(“observers”)usetheirintuitivetheoryof
emotiontoreasonabouttheemotionalstatesofothers(“agents”)aroundthem,and
therebydecidehowbesttorespondinsocialsituations.Importantly,theseintuitive
theoriescomprisetheobserver’sbeliefsabouthowothers’emotionswork,whichdepend
ontheobserver’spasthistoryandtheirsubjectivebeliefs.Thoughtheobserver’sbeliefs
maynotnecessarilyreflecttherealityofhowemotions“actuallywork”,thesebeliefs
EMOTIONINTHEORYOFMIND 5
neverthelessformthebasisforhowtheobserverunderstandsandinteractswiththose
aroundthem(e.g.,Gopnik&Meltzoff,1997;Ross,1977).
Anintuitivetheoryofemotioncontainstwoimportanttypesofcausalrelationships.
Thefirstconnectsemotionstotheircauses:what,intheobserver’smind,causesanagent
tofeelanemotion?Thesecondinvolvestheeffectsofemotion:what,intheobserver’s
mind,doesanagent’semotioncausethemtodo?Thesecomponentsandtheirrelationships
arerepresentedinFigure1.
Figure1:Amodelofanintuitivetheoryofemotion,unifyingideasfromdeMeloetal(2014),Ong,Zaki,&Goodman(2015),SaxeandHoulihan(2017),andWuetal(2018).Weusestandardgraphicalmodelnotation:shadedcirclesrepresentobservablevariables,whileunshadedcirclesrepresentlatentvariables.Werendervariablesatthesubsequent“time-step”translucent.Arrowsrepresentadirectedcausalrelationship,andboldedlettersdenotetheabbreviationsusedinequations.Theobserverappliesa“third-personappraisal”processtoreasonabouthow(i)theoutcomeofaneventthatanagentexperiences,and(ii)theagent’smentalstates(beliefsanddesires),togetherresultintheagentexperiencingemotions.Theagent’semotionsinturncausetheagenttodisplayemotionalexpressions,andtakeintentionalactionsthatleadtonewoutcomesandupdatedmentalstates(andnewemotions).
Intuitivecausesofemotions
Peopleintuitivelyexpectthatothers’emotionsariseasareactiontomotivationally
salientevents.Inadditiontotheoutcomeoftheseevents,peoplealsousetheirknowledge
aboutothers’mentalstates—suchasothers’beliefsanddesires—toreasonabouthow
othersfeel.Thisintuitiveunderstandingofhoweventoutcomesandmentalstatesimpact
emotionsemergesearlyinlife(Gross&Ballif,1991;Harris,1989;Lagattuta,Wellman,&
EMOTIONINTHEORYOFMIND 6
Flavell,1997;Repacholi,Meltzoff,Hennings,&Ruba,2016;Wu,Muentener,&Schulz,
2017):toddlersandinfantsunderstandthatanagent’sdisplayofhappinessreflectsa
satisfieddesire,whileanagent’sdisplayofsadnessreflectsathwartedgoal(Repacholi&
Gopnik,1997;Skerry&Spelke,2014;Wellman,Phillips,&Rodriguez,2000).Bypreschool,
childrenassociateasurprisedemotionalexpressionwithamismatchbetweenrealityand
theagent’spriorbeliefsabouttheworld(Wellman&Banerjee,1991;Wu&Schulz,2017),
andfactoragents’expectationsintoattributionsoftheagent’semotions(Ong,Asaba,&
Gweon,2016).Adultssimilarlydrawrichinferencesfromanagent’semotionalreactionsto
theirlatentbeliefsanddesires(Scherer&Grandjean,2008;Wuetal,2018;VanKleef,De
Dreu,&Manstead,2010).Thus,theintuitivetheoryofemotionrelatesanagent’smental
states(specifically,theirbeliefsabouttheworld,andtheirdesires),andtheoutcomeof
aneventthattheagentexperiences,totheagent’semotions(Fig.1).
Howdopeopleunderstandthewayeventoutcomesandtheagent’smentalstates
giverisetoemotions?Oneideaisthatpeoplemayengageasimilarreasoningprocessto
howtheythemselvesexperienceeventsfirsthand.Accordingtoappraisaltheoriesof
emotion(Arnold,1960;Ellsworth&Scherer,2003;Moors,Ellsworth,Scherer&Frijda,
2013;Ortony,Clore,&Collins,1988;Smith&Lazarus,1993),anagent’semotionsarise
fromanevaluation(“appraisal”)ofoutcomesalongvariousself-relevantdimensions,such
aswhethertheoutcomescontributetoordetractfromtheagent’sgoals(“goal-
conduciveness”).IfSallyjudgesherjobofferasfacilitatinghercareergoals,shewould
likelyfeelhappy.
Manyresearchershaveproposedthatlaypeopleperformasimilarappraisal-like
processtoreasonaboutothers’emotions(DeMeloetal,2014;Ong,Zaki,&Goodman,
EMOTIONINTHEORYOFMIND 7
2015;Seimer&Reisenzein,2007;Skerry&Saxe,2015;Wondra&Ellsworth,2015;Wuet
al,2018;VanKleefetal,2010)---wetermthisprocess“third-personappraisal”.Thatis,
whenanobserverconsidersanagentexperiencinganoutcome,theobserverfirstreduces
theoutcometoasmallnumberoffeaturesthattheobserverthinksisrelevanttotheagent,
andthenusesthatevaluationtojudgetheagent’semotions.Forexample,observers
intuitivelyevaluate,fromtheagent’sperspective,anoutcome’sgoal-conducivenessand
whethertheoutcomewasexpected.IfBoblearnsthatSallyjustreceivedglowing
performancereviews,andknowsofhergoalsofgettingpromoted,hewouldreasonthat
sheprobablyfeelsapositively-valencedemotion.IfBobadditionallyknowsthatSallydid
notexpecttheperformancereviews,hemightpredictthatshewouldalsofeelsurprised.
Appraisalisespeciallyimportantfromacomputationalstandpoint.Thesituationsthat
agentsexperienceindailylifevarywidelyalonganinnumerablenumberofdimensions,
and(theobserver’stheoryof)anagent’sappraisalreducesthecomplexitiesofeveryday
situationstoasmallsetofrelevant“features”thatareimportantfortheagent’swell-being.
Itisalsoimportanttonotethattheobserver’sappraisalonbehalfoftheagentmaydiffer
fromtheagent’sownappraisalintwokeyways.First,theobserver’ssetofemotionally-
relevantfeatures,encapsulatedwithintheirintuitivetheory,maynotbethesameastheset
offeaturesthattheagentthemselvesconsider,suchaswhenanobserverbringstheir
culturallyheldnormsaboutemotionstoassessanoutcomeexperiencedbyanagentfroma
differentculture.Second,theobserver’sthird-personappraisalsdependontheobserver’s
inferencesoftheagent’spriorbeliefsanddesires,whichmaybedifferentfromtheagent’s
truementalstates.IfBobthoughtthatSallyhadknownaboutherperformancereviews
beforehand,hewouldnothavepredictedhersurprise.
EMOTIONINTHEORYOFMIND 8
Thesefirstfewpiecesofamodeloftheintuitivetheory(seelefthalfofFig.1),
describetheobserver’srichcausalknowledgeabouthowoutcomesandtheagent’smental
states“cause”emotion.Thisreasoningfromoutcomesandmentalstatestoemotionsrelies
onacontextualized,third-personappraisalprocess,whichwewilldescribeingreater
detaillater.WeturnnexttotherighthalfofFigure1.
Intuitiveeffectsofemotions
Peoplealsointuitivelyreasonaboutwhatbehaviorsemotionscause.Forone,
emotionalagentsproduceawidevarietyofemotionalexpressions.Decadesofscientific
researchhaveshownthatpeoplecanreliablyrecognizeemotionsfromfacialexpressions
(Ekman,Friesen,&Ellsworth,1972;Elfenbein,&Ambady,2002;Russell,Bachorowski,&
Fernández-Dols,2003),bodylanguage(Dael,Mortillaro,&Scherer,2012),aswellas
emotionalvocalizationsandotherparalinguisticchangesinspeech(Banse,&Scherer,
1996;Johnstone&Scherer,2000;Scherer,2003).Alongwithemotionaldisplays,emotions
alsoinfluencetheintentionalactionsthattheagentmaytakenext(Lerneretal,2015;
Loewenstein&Lerner,2003).Fearmayproduceatendencytoflee,angermayprompt
someonetoapproachandconfrontathreat,andhappinessmightengenderprosocial
behavior(e.g.,Frijda,Kuipers,&TerSchure,1989;Isen,1987).Peopleareintuitively
sensitivetohowemotionscaninfluenceothers’actions;forexample,peopleuseapartner’s
emotionaldisplaystoinferhowcooperativetheywouldbe(Krumhuberetal,2007;Levine,
Barasch,Rand,Berman,&Small,2018;VanCleefetal,2010).Intheintuitivetheoryin
Figure1,wehaveplacedemotionalexpressionsandintentionalactionsasdownstream
effectsofemotion,reflectingtheintuitivenotionthatemotions“cause”thesetwotypesof
EMOTIONINTHEORYOFMIND 9
behavior.Bothtypesofbehaviorarereadilyobservableindailylifeandprovidecrucial
signalsthatallowobserverstoreason“backwards”toinfertheagent’slatentemotion.
ATaxonomyofAffectiveCognitiveInferenceswithintheIntuitiveTheory
InthepreviousSection,welaidoutamodelofanintuitivetheoryofemotion(Figure
1)byconsideringhowemotionsarerelatedtotheirtwoantecedentcausesandtheirtwo
consequenteffects.Usingthisintuitivetheory,wecanderiveataxonomyofinferencesvia
exhaustiveenumeration(seeSupplementaryMaterial).TreatingthemodelinFigure1asa
Bayesiannetwork,wefirstwroteoutallthe47possibleinferencesthathaveemotionas
oneofthevariables---forexample,P(emotion|outcome),inferringemotionsfromoutcomes,
orP(expression|emotion),reasoningaboutexpressionsfromemotions.Next,weremoved
26inferencesthatreducedtosimplerinferencesbasedonconditionalindependence1.
Third,weclassifiedtheremaining21inferencesintosixcategories.Finally,weaddeda
seventhcategorytoaccountforcounterfactualinferences,suchasinferringemotionsifa
givenoutcomehadnotoccurred,P(emotion|notoutcome).ThisissummarizedinTable1.
1Forexample,underthemodel,P(outcome|emotion,expression)reducestoP(outcome|emotion)asoutcomesandexpressionsareindependentgivenemotions(d-separation,e.g.,Koller&Friedman,2009).
EMOTIONINTHEORYOFMIND 10
Categories Description Inferences ExamplesEmotionRecognition
Inferanagent’semotionsfromemotionalexpressions(facialexpressions,bodylanguage,prosody),orfromtheiractions.
P(e|x)P(e|a)
Givensmile,InferP(happy)Givenscold-others,InferP(anger)
Third-personappraisals
Reason“forward”abouthowaneventwouldcauseanagenttofeel,givenalsotheirmentalstates.
P(e|o)P(e|o,b,d)P(e|b,d)
Givenlose-wallet,InferP(sad)
Inferringcausesofemotions
Reason“backwards”abouttheeventsthatcausedanagent’semotions.
P(o|e)P(o|e,b,d)
Givensad,InferP(lose-wallet)
EmotionalCueIntegration
Givenmultiple,potentiallyconflictingcues(e.g.,multiplebehaviorsand/orcausesofemotion),combinethemandreasonaboutagent’semotions
e.g.,P(e|o,x)P(e|o,a)P(e|a,x)P(e|o,b,d,a,x)
Givensmile+lose-wallet,InferP(happy),P(sad),etc.
ReverseAppraisal
Givenaneventandanagent’semotions,reasonbackwardstomentalstateslikebeliefsanddesires
P(b,d|e,o)P(b,d|e)
Given:receive-gift+surprise+happy,InferGift-Unexpected+Gift-Desired
Predictions(HypotheticalReasoning)
Givenanagent’semotions,predictsubsequentbehavior.Or,givena(hypothetical)situation,predicttheagent’semotions.
P(a|e)P(x|e)
Ifanger,predictP(scold-others)
CounterfactualReasoning(andExplanations)
Givenastateoftheworldandanagent’semotions,reasonaboutemotionsorbehaviorincounterfactualstatesoftheworld.Thisalsoallowsexplanationsofemotionsorbehaviorintermsoftheircauses.
e.g.,P(e|noto)P(a|note)
Given:“lose-walletandsad”,reasonthat:“ifnot-lose-wallet,thennot-sad”or,reasonthat:“sadbecauselose-wallet”
Table1:AtaxonomyofinferenceswithinAffectiveCognition,derivedfromthemodelinFigure1.P(X)denotestheprobabilityofXoccurring.Thelistsofinferencespresentedforeachcategoryareexhaustive(givenourderivation),exceptfortheCueIntegrationandCounterfactualReasoningcategories.
EMOTIONINTHEORYOFMIND 11
1.EmotionRecognition
Perhapstheeasiestcategoryoflayinferenceisinferringsomeone’semotionalstate
fromtheiremotionalexpressions,oftencalledemotionrecognition(e.g.,Elfenbein&
Ambady,2002).Thedeceptiveeasebywhichlaypeople“read”emotionalexpressionshas
ledmanyresearcherstoassumeperfectemotionrecognitionintheirmodels,without
modelingthisprocessasaninferenceinitsownright(e.g.,deMeloetal,2014;Wuetal,
2018).
Inreality,laypeople’semotionrecognitionisnotperfectlyaccurate,norisit
homogenousacrossallobservers.First,suchinferencesareheavilydependentoncontext:
Bothintensepositiveandnegativeeventsmaysometimesproduceperceptually-similar
facialexpressions,makingitdifficultforlayobserverstoaccuratelyinferemotionssolely
fromexpressions(Aviezer,Trope,&Todorov,2012;Carroll&Russell,1996;Wenzleretal,
2016).Second,peoplefromdifferentculturesdiffersystematicallyinhowtheyperceive
emotionsfromfacialexpressions(Gendron,Roberson,vanderVyver,&Barrett,2014;Jack,
Blais,Scheepers,Schyns,&Caldara,2009;Russell,1994;Yuki,Maddux,&Masuda,2007).
Suchinferencesrelyonlayobservers’intuitivetheories,whichinturndependontheir
culturalbackgroundandpasthistory(Jack,Caldara,&Schyns,2012).Indeed,thesecultural
differenceshavebeenfoundtoimpactevenhowobserversattendtoanduselow-level
facialcueswhenjudgingemotions:forexample,EastAsianparticipantstendtofixate
longerontheeyeregionthanWesternparticipants(Jacketal,2009;Yukietal,2007).
Morerecently,researchershavestartedbuildingformalcomputationalmodelsof
howobserversinferemotionsfromlow-levelfeaturesoffacialexpressions(Delisetal,
2016;Jacketal,2012;Martinez&Du,2012)andbodylanguage(Schindler,VanGool,&de
EMOTIONINTHEORYOFMIND 12
Gelder,2008).Usingconditionalprobabilitynotation,modelingemotionrecognition
correspondstoestimatingtheprobabilityofalatentemotionegivenanemotional
expressionx,orP(e|x).Thegeneralrecipefollowedbythesestudiesfirstrequiressome
representationoftheemotionalexpression---forexample,apopularrepresentationfor
facialexpressionsistheFacialActionCodingSystem(Ekman&Friesen,1978).Next,one
measureshowhumanobserversclassifystimuliintopre-definedemotioncategories,i.e.,
empiricallymeasuringP(e|x)forsay,thesix“basic”emotioncategories.Finally,onethen
modelstheemotionrecognitionprocessP(e|x)bytrainingclassifiersusingsophisticated
machinelearningtechniques.Suchworkisrelativelynew,andthereisstillmuchmoreto
bedoneinmodelinghumanemotionrecognitionfromexpressionsandalsofromother
behavior:thiswillprovideacrucialfoundationformanyofthemorecomplexinferences
wediscussbelow.
2.Third-personappraisal
Computationalapproachesallowresearcherstoquantitativelymodelhowpeople
reasonaboutanagent’sresponsetoanexperiencedevent.Thisinvolves,asmentioned,a
third-personappraisalprocessthatreducestheoutcomethatanagentexperiencesintoa
smallsetoffeaturesthattheobserverthinksisimportanttotheagent’semotions(e.g.,
Skerry&Saxe,2015).Tostudythisappraisalprocessinacontrolledscenario,wedesigned
agamblingscenariowherewecouldparametricallyvarythepayoffamountsand
probabilities,andwemeasuredhowpeople’sjudgmentsofanagent’semotionsafterthe
gambledependeduponthesegamblefeatures(Ong,Zaki,&Goodman,2015).Wefound
thatparticipants’emotionjudgmentsdependednotonlyontheamountwon,buthow
EMOTIONINTHEORYOFMIND 13
muchtheagentwoncomparedtotheexpectedvalueofthegamble,oftencalleda
predictionerror(e.g.,Sutton&Barto,1998),suggestingthatparticipantsevaluatedthe
agent’searningsrelativetoareferencepoint,ratherthanjudgingtheirearningsinabsolute
terms.Wealsofoundthatlayparticipantsjudgedagentstoreactmorestronglytonegative
predictionerrorsthantopositivepredictionerrors.Thesethird-personfindingsare
strikinglyconsistentwithinfluentialscientifictheoriesoffirst-personutility,especially
notionsofreference-dependentutilityandlossaversion(Kahneman&Tversky,1979;
Kermer,Driver-Linn,Wilson,&Gilbert,2006;MellersSchwartz,Ho,&Ritov,1997).Finally,
participantsbelievedthatagentswouldfeelworseiftheycamevery“close”towinningthe
nexthigheroutcome,comparedtoifagentswerenotclosetowinningthebetteroutcome
(Ong,Goodman,&Zaki,2015).Thatis,participants’intuitivetheorieswerealsosensitiveto
the“closeness”ofalternativeoutcomes(Gleicheretal,1990;Kahneman&Tversky,1982;
Johnson,1986),whichhaveyettofeatureinfirst-personappraisaltheories.
Thesituationfeatureswestudied---predictionerrorsandthe“closeness”ofthe
outcometoalternativeoutcomes---arewell-definedwithinourexperimentalscenario,but
muchmoreworkisneededtostudythird-personappraisalsinmorecomplex,real-world
situations.Themainchallengesforfutureresearchwouldbedefiningacomprehensive
representationforthemanyappraisaldimensions---usinglistsfromfirst-personappraisal
theory(e.g.,Ellsworth&Scherer,2003;Ortonyetal,1988),orvia“data-driven”approaches
likerepresentationalsimilarityanalyses(Skerry&Saxe,2015)---andmodelinghowpeople
maptheseappraisaldimensionsontoemotions.Therealsoexistsmanytechnical
challengesinautomaticallyextractingtheseappraisaldimensionsfromnaturalisticsources
EMOTIONINTHEORYOFMIND 14
likevisualscenesorvignettedescriptions,themselvesproblemsattheforefrontofmodern
computerscience.
3.Inferringcausesofemotions
Givenanobservedemotion,peoplecanalsoreason“backwards”aboutpotential
causesofthatemotion.Uponencounteringasadfriend,mostpeoplewouldstart
generatingpotentialcausesofthefriend’ssadness,suchastheirpossiblyfailinganexam.
Intuitively,thesepossibilitiesvaryinhowlikelytheyweretohavehappened:failingan
examismorelikelywhenoneisastudent,butlesslikelyafteronehasgraduated.Theyalso
rangeinhowlikelytheyweretohavecausedtheobservedemotion:ahystericallybawling
friendprobablyexperiencedsomethingworsethanafailedexam.Peopleintuitivelyagree
thatapotentialcausewithahighprobabilityofoccurringandahighprobabilityofcausing
theobservedemotionisamorelikelycandidatethaneitheronewithalowerprobabilityof
occurringoronewithalowercausalstrength.
OnewaytomathematicallydescribethisreasoningisviaBayesianinference.First,
werepresentthethird-personappraisalprocessasP(e|o),acollectionofprobability
distributionsofemotionegivenanoutcomeo2.Then,byBayes’Rule,wecanwritethe
posteriorprobabilityP(o|e),theprobabilityofoutcomeogivenemotione,as:
. (Eqn.1)
Theposteriorprobability(e.g.,P(fail-exam|sad))isproportionaltoboththelikelihoodof
thatoutcomecausingtheemotion(e.g.,howlikelyisitthatfailinganexamwillcauseone’s
2Forthemoment,weleaveouttheagent’sbeliefsanddesiresintheappraisalprocess.Weaddthemlaterinthesectionon“reverseappraisal”.
P (o|e) / P (e|o)P (o)
EMOTIONINTHEORYOFMIND 15
friendtobesad,P(sad|fail-exam))andthepriorprobabilityofthatoutcomeoccurring(e.g.,
howlikelyisitthattheyhadjustfailedanexam,P(fail-exam)).WetestedwhetherEquation
1providesagoodmodelofparticipants’inferencesoftheposteriorinanexperimentwith
thesamegamblingcontextdescribedintheprevioussection.Participantsobservedthe
emotionsthattheagentostensiblyfeltafterplayingagamble,aswellasthepossible
outcomes,andweretaskedwithinferringhowlikelyitwasthateachoftheoutcomes
occurring.WefoundthatamodelbasedonBayes’rule(Eqn.1)accuratelypredicted
participants’judgmentsoftheposteriorprobabilitiesofunseengambleoutcomes(Ong,
Zaki,&Goodman,2015),lendingsupporttotheclaimthatlaypeople’saffectivecognition
reliesonacoherentuseofarichintuitivetheory.Indeed,recentevidencesuggeststhat
eveninfantsaresensitivetothesecausalprobabilities,activelysearchingforhiddencauses
whenfacedwithanemotionthatisimprobablegiventheobservedcause(Wuetal,2017).
Inferringcausesofemotionsreliesonfirstunderstandingthethird-personappraisal
process,andsothechallengesinherentinmodelingthethird-personappraisalprocessalso
applyhere.Inaddition,Equation1requirestheobservertoconsiderasetofpossible
outcomes.Onechallengeforfutureresearchersistodefinethesetofpossibleoutcomes
thatlaypeopleintuitivelyshortlistandconsider,aswellasthepriorprobabilitiesthat
laypeopleassignthoseoutcomes.Estimatingsuchknowledgeisalsoakeyproblemfaced
whenapplyingBayesianmodelstootherformsofcognition(e.g.,causalinduction;Griffiths,
2017).
EMOTIONINTHEORYOFMIND 16
4.EmotionalCueIntegration
Peoplehavelittledifficultyreasoningabouttheemotionsthatresultfrom
experiencingsituationoutcomes(P(e|o)),oridentifyingtheemotionsthatproduce
observedfacialexpressions(P(e|x)).Inreallife,however,peopleareoftenpresentedwith
combinationsofmultiplecuestoanagent’semotions,andhavetoreconcilethesemultiple
cues,anissueofemotionalcueintegration(Ong,Zaki,&Goodman,2015;Skerry&Saxe,
2014;Zaki,2013).PerhapsAliceknowsthatafriendhaslosthisjob(anegativeoutcome),
butseesasmileonhisface(apositiveexpression).Howdoesshemakesenseofthis?
Scientistshavelongponderedtherelativeimportanceofsituationcontextsand
emotionalexpressionstoobservers’judgmentsofemotions,especiallyincaseswhere
thesecuesconflict(e.g.,Goodenough&Tinker,1931).Ontheonehand,scholarshave
arguedthatfacialexpressionsevolvedtocommunicate,andhenceare(always)veridical
cuestoanagent’semotion(e.g.,Buck,1994).Thus,sincethejoblessfriendissmiling,they
mustbehappy,becausesmilingevolvedtocommunicatehappiness,andtheywouldnotbe
smilingotherwise.Ontheotherhand,awealthofotherstudiesshowthatlaypeople
sometimesweightthesituationalcontextandotherbehavioralcuesoverfacialexpressions
whenattributingemotions(Aviezeretal.,2008,Caroll&Russell,1996;Kayyal,Widen,&
Russell,2015;seeOng,Zaki,&Goodman,2015,foramoredetaileddiscussion).This
impasseunderscorestheneedforaprecisetheoryofhowdifferentcuesareweightedand
integrated.
Withinourframework,emotionalcueintegrationissimplya“higher-order”
inferencethatreliesonthesimplerinferencesdiscussedearlier.Giventhecausalmodelin
Figure1,wecanwriteoutapreciseandoptimalformulaforhowanobservershould
EMOTIONINTHEORYOFMIND 17
integratethesedifferentsourcesofinformation:Forexample,theprobabilityofalatent
emotionegivenanobservedoutcomeoandexpressionx,P(e|o,x),isgivenby:
. (Eqn.2)
Notethatthisinferenceintegratesboththeprobabilityoftheemotiongiventheoutcome,
P(e|o),andtheprobabilityoftheemotiongiventhefacialexpression,P(e|x),inferenceswe
discussedearlier.Unlikepriorworkinresolvingcueconflict,thismodeldoesnotassumea
priorithatanyonetypeofcue(e.g.,facialexpressions)ismore“privileged”,butweighsthe
cuesaccordingtotheirreliabilityinpredictingtheagent’slatentemotion.Toverifythis
model,weranaseriesofexperimentswherewepresentedparticipantswithcombinations
ofoutcomes(theoutcomeofagamblethattheagentexperienced)andagents’emotional
expressions(eitherafacialexpressionorverbalutterance).ABayesianmodelbasedon
Equation2accuratelypredictedlayobservers’judgmentsofagents’emotionsgiventhese
multiplecues(Ong,Zaki,&Goodman,2015).Thismodelpredictsthatobserverswillbe
sensitivetothereliabilitiesofcuesincontext,andallowsforobserverstoweighoutcomes,
faces,bodyexpressions,andothercuestodifferingamountsdependingonthecontext.
Emotionalcueintegrationisnotlimitedtosimpletwo-cuecombinations.Underthis
Bayesianframework,cueintegrationisanyhigher-orderinferencethatreliesinparton
single-cueinferenceslikethird-personappraisal(P(e|o,b,d))andemotionrecognition
(P(e|x),P(e|a)):Onceonehasmodelsofthesesimplerinferences,onecanderiveinference
fromanycombinationofcues.
P (e|o, x) / P (e|o)P (e|x)P (e)
EMOTIONINTHEORYOFMIND 18
5.ReverseAppraisal:Inferringmentalstatesfromemotions
Peoplenotonlydrawinferencesaboutanagent’semotions,butalsouseemotions
toreasonbackwardsaboutanagent’sappraisalsandmentalstates(e.g.,Hareli&
Hess,2010;Scherer&Grandjean,2008).Inparticular,emotionalreactionsprovide
informationastowhetheranagent’sgoalsweremetandwhethertheyexpectedagiven
outcome.Apositive/negativeemotionalexpressionmaysignalthattheoutcomewas
congruent/incongruentwithanagent’sdesires,andasurprisedexpressionmightsignal
thattheoutcomewasunexpectedgiventheirbeliefs.Comparingtothethird-person
appraisalprocessthatmapsoutcomesandmentalstatestoemotions,thiscurrentpieceof
reasoningworksinreverse,takinganoutcomeandobservedexpressiontoinfertheagent’s
mentalstates---whatdeMeloandcolleagues(2014)term“reverseappraisal”.
Extendingtheformalisminprevioussections,givenamodeloftheappraisalprocess
fromtheoutcomeandtheagent’sbeliefsanddesiresP(e|o,b,d),wecanwriteaninference
similartoEquation1fortheagent’sbeliefsanddesires:
.
This,however,requiresaninferenceofthelatentemotion.If,instead,whatweactually
observeisanemotionalexpressionxandtheoutcomeo,andweareonlyinterestedinthe
mentalstates,wecanmarginalizeoutthelatentemotion:
(Eqn.3)
Notethatintheprevioussections(e.g.,Eqns.1-2),theappraisalprocesswasencapsulated
inP(e|o);here,weexplicitlyrepresenttheagent’sbeliefsanddesires,sonowwewritethe
appraisalprocessasP(e|b,d,o).Asdiscussedearlier,thisprocessitselffactorsthrough
P (b, d|e, o) / P (e|b, d, o)P (b, d)
P (b, d|x, o) / P (b, d)X
e
P (x|e)P (e|b, d, o)
EMOTIONINTHEORYOFMIND 19
quantitiessuchasthepredictionerroroftheoutcome.InEquation3,thegoalofthe
inferenceistheconditionalprobabilityoftheagent’sbeliefsanddesires;theagent’s
emotionsareonlyan“intermediate”quantitythatwecanmarginalize(orsumout).From
righttoleft,theexpressioninEquation3considerstheproductof(i)theprobabilityofan
emotionebeingaresultofabelief,desire,andoutcomeP(e|b,d,o)(i.e.,theappraisal
process)and(ii)theprobabilityoftheemotioneresultingintheobservedexpression
P(x|e).Wethenconsiderallpossibleemotionsebysummingthisproductoverallpossible
emotions(“marginalizing”oute).Finally,thistermismultipliedwiththepriorprobability
ofthatcombinationofbeliefanddesire,P(b,d).
Totestiflaypeople’sinferencescanbemodeledbysuchaBayesianmodel,Wuand
colleagues(2018;Experiment3)constructedscenarioswhereagentsperformedanaction
(puttingawhitepowderintoacolleague’scoffee),witnessedtheresultantoutcome(the
agent’scolleaguelivingordying),anddisplayedanemotionalreaction(e.g.,asurprised
facialexpression).Participantsreadaboutthesesequencesofevents,andprovided
judgmentsoftheagent’sbeliefs(whattheagentthoughtthepowderwas:poisonorsugar)
anddesires(whetherornottheagentwantedtoharmhercolleague).Wuandcolleagues
(2018)presentagraphicalmodelandaninferenceequationsimilartoFigure1and
Equation3.Wenotetwokeydifferences:first,theirposteriorhasanadditionalconditional
dependenceontheagent’sactions(i.e.,P(b,d|x,o,a))---wechosenottoaddactionsinto
Equation3forsimplicity.Second,theyassumedperfectemotionrecognitionandhencedid
notexplicitlymodelthelatentemotionasanintermediatequantitybetweentheoutcome
andtheagent’sexpression.TheirBayesianmodelaccuratelytrackedparticipants’
EMOTIONINTHEORYOFMIND 20
inferencesoftheagent’sbeliefsanddesires,providingfurtherevidencethatpeoplereason
aboutothers’emotionalandmentalstatesusingacoherentintuitivetheory.
Inaddition,inferringothers’appraisalsisalsoimportantinpredictingtheirfuture
behavior.Forexample,ifsomeonechoosestocooperatewithyouonatask,andsmiles
afterdoingso,youmayinferthattheyhadintendedtocooperate,likedtheoutcome,and
willlikelydosoagain.Bycontrast,iftheyfrownedinsteadofsmiled,yourinferencesand
yoursubsequentbehaviorinresponsewouldbeverydifferent:perhapstheyregretted
cooperating,andmightnotcooperatenexttime(seealsoLevineetal,2018).DeMeloand
colleagues(2014)modeledtheseinferencesofappraisalsfromemotionalexpressionsina
stylizedsocialdilemmagamewheretwoplayerseachchosebetweenamutuallybeneficial
optionandaselfishoptionthatbenefittedoneselfattheexpenseofone’spartner.Some
participantsplayedagainstapartnerwhosmiledaftermutualcooperation,whileother
participantssawtheirpartnerfrownaftermutualcooperation.DeMeloandcolleagues
(2014)proposedandfoundsupportfora“reverseappraisal”modelwherebyparticipants
inferredeitheracooperativeorcompetitiveintentfromtheirpartner’semotional
expressions,andtheseinferencesmediatedparticipants’subsequentbehaviorinfuture
interactions.
Mentalandemotionalstatesareintimatelyrelated,andherewediscussedmodeling
inferencesofmentalstatesfromemotionalinformation.Suchworkiscrucialtointegrate
emotionsintoexistingmodelsofTheoryofMind(e.g.,Baker,Saxe,&Tenenbaum,2009;
Bakeretal,2017).Thereexistmanyopenquestionsthatarisefromsuchintegrationof
emotionsandmentalstates:Forexample,therearemanycomplexinteractionsbetween
desiresandemotions:ontheonehand,peoplehavegoalstoregulateemotions,but
EMOTIONINTHEORYOFMIND 21
conversely,emotionsthemselvesinfluencehowpeopleprioritizetheirexistinggoals.How
dolaypeoplereasonaboutthese,andhowcanresearchersfitthembothintoacausal
model?Theseareimportantpsychologicalquestionsthatshouldbeaddressedinfuture
modelsofsocialandaffectivecognition.
6.Predictions(HypotheticalReasoning)
Layreasoningaboutothers’emotionsisnotlimitedtothehereandnow;Peoplecan
reasonaboutothers’potentialbehaviorgivenafutureorhypotheticalemotion(P(x|e),
P(a|e)).Reasoninghypotheticallyinvolvesusingone’sintuitivetheorytoreasonabout
novelscenariosthatcouldbeinthepossiblefuture,ormerelyintherealmofimagination.
Planningaromanticmarriageproposalinvolvesincessantsimulationofpossibleworlds
andemotionsinthoseworlds.Indeed,experimentsthatpromptparticipantsforemotion
attributionstoafictionalcharacterinavignetteorcartoonallinvokehypothetical
reasoning,andtheeasewithwhichpeopleengageinhypotheticalreasoningiscrucialto
theirenjoymentoffilmandfiction.
Hypotheticalreasoningcanbemodeledbysimplyallowingtheinferredvariablesto
behypothetical,forexample,estimatingthebehaviorgivenahypotheticalemotionP(a|e).
WithinBayesianmodeling,thiscanbeoperationalizedassampling“posteriorpredictives”
underthemodel(i.e.,conditionalpredictionsofnewdata),andhasbeenappliedtomodel
laypredictionsinotherdomains(Griffiths&Tenenbaum,2006),butnotyetinaffective
cognition.Futureworkshouldfocusonapplyingsuchtechniquestomodellaypeople’s
predictionsof(hypothetical)emotions.Suchworkhasimportantimplicationsfordesigning
EMOTIONINTHEORYOFMIND 22
computationalagentsthathavetosimulateandforecasttheirhumanuser’semotionsand
behavior.
7.CounterfactualsReasoning(andExplanations)
Thefinalcategoryofinferencesinourtaxonomyiscounterfactualreasoning
aboutemotions.Whilethepreviousfewsectionshavetoucheduponreasoningabout
emotionsgivenastateoftheworld,peoplecanalsoreasonaboutothers’emotionsinstates
oftheworldthataredifferentfromtheexistingreality(Gleicheretal,1990;Johnson,
1986).Indeed,emotionslikeregretarecharacterizedbycounterfactualreasoning(Beck&
Crilly,2009).Counterfactualthinking,likehypotheticalreasoning,reliesonarichcausal
modelthattheobservercanmentallymanipulatetoreasonaboutotherpossibleworlds
(Byrne,2002;Roese,1997).WouldCarolnotbesadifshehadnotlostherwallet(P(sad|
notlose-wallet))?WouldCharliehavebeenlesscurtifhehadnotjustlosthisjob?
Reasoningwithcounterfactualsalsoallowsobserverstoprovideexplanations
(Lagnado,Gerstenberg,&Zultan,2013;Halpern&Pearl,2005)forothers’emotionsand
behavior(Malle,1999,2011).Explanationwithinaffectivecognitioninvolvesassigning
causalityofanemotionorabehaviortotheirpossiblecauses(Böhm&Pfister,2015;Ong,
Zaki,&Goodman,2016).WasTim’sdisappointmentafterhisspeechduetohisstuttering
orthedifficultquestionshereceivedafter(orperhaps,both)?Explanationsareimportant
inchoosinginterventionstoregulatetheagent’semotions.IfonethinksthatTimfeltthat
histalkhadnotgonewellbecauseofthedifficultquestionshereceived,onemighttry
helpingTimreappraisethedifficultquestionsasasignalofengagement,notdisdain,from
theaudience.Formingexplanationsandidentifyingthecausesofbehaviorisalso
EMOTIONINTHEORYOFMIND 23
importantinassigningresponsibility,asinmoralorlegaljudgments(e.g.,Alicke,Mandel,
Hilton,Gerstenberg,&Lagnado,2015),especiallyinlegalsystemswithlayjuries.
Althoughtherehasnotyetbeenanyworkincomputationallymodeling
counterfactualreasoninginaffectivecognition,theuseofprobabilisticcausalmodelsto
representtheintuitivetheoryofemotionsshouldallowanimmediateapplicationof
existingtechniques(e.g.,Pearl,2001,2009).Similarprobabilisticmodelshaverecently
beenusedinmodelinglaycounterfactualreasoninginotherdomains(Lucas&Kemp,
2015;Oaksford&Chater,2010).Weanticipatethatfutureresearchwillsoonapplyformal
techniquestomodelcounterfactualreasoninginaffectivecognition.
Discussion
Inthispaperwehaveoutlinedaframeworkforunderstandingaffectivecognition
asinferencewithinanintuitivetheoryofemotion.Wederivedataxonomyofinferences
(Table1),andwehavediscussedtheseinferencesbothwithrespecttorecentworkin
computationallymodelingaffectivecognition,aswellasfuturechallengesformodeling
eachoftheseinferences.Importantly,thisunifiedframeworkallowsustodescribeallthe
reasoninginTable1usingthesamegeneralprinciples(i.e.,Bayesianinference)appliedto
different“components”ofthecausalmodelinFigure1.Inotherwords,howpeoplereason
fromoutcomestoemotion,orinferemotionfromexpressions,canallbemodeledwiththe
samedomain-generalinferencemachinery,underacommonBayesian“TheoryofEmotion”
(Ong,Zaki,&Goodman,2015;Saxe&Houlihan,2017).
Throughoutthepaper,wehaveposedaffectivecognitionasa“computationallevel”
problem(Marr,1982),andhavefocusedonreviewingprobabilisticapproaches,which
EMOTIONINTHEORYOFMIND 24
offeranaturalsolutiontosuchinferentialproblems(e.g.,Griffiths,Kemp,&Tenenbaum,
2008;Oaksford&Chater,2007).TheBayesianapproachesinthestudiesdescribedhere
(deMeloetal,2014;Ong,Zaki,&Goodman,2015;Saxe&Houlihan,2017;Wuetal,2018)
sharemorecommonalitiesthandifferences,andwhatdifferencesexistliemainlyinwhich
variablesthedifferentsetsofauthorschosetoprioritizeorsimplifyout.Indeed,Figure1
resultsfromoureffortstounifythecommonideasfromthesestudies---forinstance,every
studymentionedthecrucialroleofthethird-personappraisalprocessanditscausallinkto
emotion.WethinkthatthiscomputationalBayesianframeworkoffersaprincipled
approachtounifyingtheinferencesdiscussed,butitcanalsobesupplementedby
alternative,non-Bayesianapproaches.Forexample,perhapsthecomplexexpression-to-
emotionmappingmightbebestmodeledwithneural-networkapproaches(e.g.,Schindler
etal,2008).Additionally,processmodelsandneuroscientificapproaches(e.g.,Adolphs,
2002)mayshedmorelightonthe"algorithmic"and"implementation"levelsofanalysis.
Inourview,thebiggestchallengeaheadformodelsofaffectivecognitionisfinding
suitablecomputationalrepresentations,especiallyofemotions:Whatisthespaceof
emotionsintheintuitivetheory?Clearly,binaryormultinomial(“angry”vs.not)labelingis
insufficientlycomprehensive,althoughwidelyusedinmanyclassificationtasks(like
sentimentanalysis).Shouldresearchersthenrepresentemotionsinsomehighdimensional
space,andifso,whatarethosedimensions(Barrett&Russell,1998;Mattek,Wolford,&
Whalen,2017)?Howshouldmixedemotionsberepresented?Definingtherepresentation
spaceisacrucialprerequisiteforprobabilisticmodeling,enablingsamplingfromand
marginalizingoverthespaceofemotions(asinEqn.3).
EMOTIONINTHEORYOFMIND 25
Butevenavectorinsomehigh-dimensionalspacemaystillbeinadequate.
Intuitively,thethreescenarios(a)“Johnisangry”,(b)“Johnisangryatreceivinganegative
outcome”,and(c)“Johnisangryattheunfairprocessthatledtothenegativeoutcome”,are
allqualitativelydifferentbecauseoftheappraisalthatresultedintheemotions,andthe
differentbehavioralconsequencestheyconnote.Thisinsightdemandsaricher,relational
representationofemotionthatincorporatestarget-andevent-relatedinformation
(minimally,“angry_at_X”,“sad_because_Y”),whichcurrentBayesiangraphicalmodelsdo
notsupport---althoughwethinkthatmodernincarnationslikeprobabilisticprogramming
languagesmayofferasolution(e.g.,Goodman,2013,seealsoGoodman&Frank,2016).In
ouropinion,choosingasuitablerepresentationforemotions(andappraisals)thatcaptures
therichnessoflayaffectivecognitionandthatcanbecomputedoverefficientlymayprove
tobethelargesthurdletoovercome.
Finally,wemuststressthatfutureworkmustprioritizemodelingaffectivecognition
onnaturalisticdata.Thesparsestimuli(e.g.,staticfacialexpressions)andexperimental
scenariosinthestudiesdiscussedaboveareanimportantstartingpoint,buttheypalein
comparisontotherichnessofeverydayemotionalexperiences.Itisimportantforfuture
researchtomodelhowlaypeoplereasonabouttheemotionsofothersinnaturalistic
contexts,suchaswatchingsomeoneinanunscriptedmonologue(e.g.,Zaki,Bolger,&
Ochsner,2008;Devlin,Zaki,Ong,&Gruber,2014,2016)ordialogue(e.g.,Ickes,Stinson,
Bissonnette,&Garcia,1990).Modelingnaturalisticcontextsbringsitsownsetof
challenges---forexample,extractingspontaneousemotionalexpressionsandrepresenting
thecomplexappraisalsofnaturalisticsituations---butthereisalsogreatpayoff.First,they
affordreal-worldtestsofthevalidityofcomputationalmodelsdevelopedon“clean”
EMOTIONINTHEORYOFMIND 26
laboratorystimuli.Second,theywillinformcomputationaltechnologiesthatcanreason
abouttheirusers’emotionsinahuman-likemanner(e.g.,Picard,1998).
Inconclusion,wehopethattheframeworkandtaxonomyofinferenceswepresent
hereprovidesausefulconceptualizationofworkincomputationalmodelsofaffective
cognition.Wehaveidentifiedmanyimportantchallengesthatlieaheadforthisnascent
fieldofresearch,whichweareconfidentwillbeaddressedbyfutureresearchers.Ata
broaderlevel,ourapproachintegrateswellwithstate-of-the-artcomputationalmodelsin
otherdomainsofsocialcognition(Bakeretal,2017;Goodmanetal,2006;Goodman&
Frank,2016;Jara-Ettingeretal,2016)---thisintegrationwillbecrucialforacumulative
scienceofsocialandaffectivereasoning.
EMOTIONINTHEORYOFMIND 27
Acknowledgements
WethankPatriciaChenforfeedbackonmultipleversionsofthismanuscript.Thiswork
wassupportedinpartbytheA*STARHuman-CentricArtificialIntelligenceProgramme
(SERCSSFProjectNo.A1718g0048),anA*STARNationalScienceScholarshipanda
StanfordIRiSSComputationalSocialScienceFellowshiptoDCO,NIHGrant
1R01MH112560-01toJZ,andaDARPAPPAMLAgreementnumberFA8750-14-2-0009and
SloanFoundationResearchFellowshiptoNDG.
EMOTIONINTHEORYOFMIND 28
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