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The search hypothesis of emotion

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Emotion,Evolution,andRationalityDylanEvansandPierreCruse

Printpublicationdate:2004PrintISBN-13:9780198528975PublishedtoOxfordScholarshipOnline:March2012DOI:10.1093/acprof:oso/9780198528975.001.0001

Thesearchhypothesisofemotion

DYLANEVANS

DOI:10.1093/acprof:oso/9780198528975.003.0009

AbstractandKeywords

Thischapterconsidersafurtherproposalthatpromisestorehabilitatetheroleofemotionsindeliberativerationality,whichhecallsthe‘searchhypothesisofemotion’.Rootedinamodelofdecision-makingderivedfromartificialintelligence,thesearchhypothesischaracterizesemotionsaspsychologicaldevicesthatrestrictagents'attentiontoasmallsubsetofthepossibleconsequencesofanyaction.Onthisviewemotionsareessentialcatalystsintheproductionofrationalaction,astheypreventagentsfromhavingtoconsiderthepotentiallyinfinitenumberofpossibleconsequencesthatanactionmayleadto.Thechapterarguesthatwhilethesearchhypothesisisnotviableasadefinitionofemotions,itmayprovetobeagoodaccountofwhatemotionstypicallydo.

Keywords:searchhypothesis,emotions,decision-making,artificialintelligence,rationalaction,consequences

Introduction


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Howdotheemotionsaffectreason?ThisquestionhasbeendebatedsincePlato,whoproposedwhatmaybecalled‘thenegativeviewofemotion’(Evans2001).Accordingtothenegativeview,emotionsusuallyaffectreasoningfortheworse.Totheextentthathumanscanfreethemselvesofemotion,therefore,theycanbecomemorerational.Untilrecently,mostphilosophersandpsychologistshavetendedtoagreewithPlatoonthismatter.

Inthepastcoupleofdecades,however,agrowingnumberofthinkershavechallengedthetraditionalconsensus(see,forexample,deSousa1987,Frank1988,Damasio1994,Elster1999,Evans2001).Theyargueforwhatmaybecalled‘thepositiveviewofemotion’.Accordingtothepositiveview,emotionsusuallyaffectreasoningforthebetter.Thepositiveviewsuggeststhat,otherthingsbeingequal,humanswillbelessrationaltotheextentthattheylackemotion.

Thepositiveviewofemotionismerehand-waving,ofcourse,unlesswecanspelloutexactlyhowemotionsaresupposedtoaidrationality.Thevariousproponentsofthepositiveviewhaverisentothischallengeinanumberofdifferentways.Inthispaper,Iwillexamineoneparticularwayofelucidatinghowemotionshelpreasonwhich,forwantofabettername,Iwillcall‘thesearchhypothesisofemotion’.

Inthenextsection,Iprovideabriefsketchofthesearchhypothesisofemotion.Inthefollowingsection,Idispensewithared-herringthathasmarred(p.180) previousstatementsofthesearchhypothesis.Ithensetoutthemodelofrationaldecision-makingthatisimplicitinthesearchhypothesis.Igoontodistinguishtwopossiblewaysofreadingthesearchhypothesis,andconcludethatthehypothesiscanonlybeevaluatedinthecontextofaspecifictheoryonwhatemotionsare.

ThesearchhypothesisofemotionEversinceThomasHobbesdeniedthatreasoncanfixourendsordesires,aninstrumentalconceptionofrationalityhasdominatedWesternthought.Accordingtothisview,reasonis,inHume'sfamousphrase,amere‘slaveofthepassions’.Ithasnomotivatingforce,andislimitedtofindingtherightmeanstoattaintheendswhichare‘given’bytheemotions.

Thisviewhasthemeritofprovidinganeatexplicationofthereason—emotiondistinction.Perhaps,however,itisrathertooneat.Notonlydoesitruleoutthepossibilityofaskingpeopletojustifytheirends—degustibusnondisputandumest—butitalso,conversely,rulesoutthepossibilityofanyemotionalinfluenceinrationalchoice.First,onesupposes,emotionsassignasubjectiveutilitytoeachend,withoutanyhelpfromreason;then,wheneverwehavetomakeadecisionorchoosebetweenanumberofactions,reasoncalculatestheexpectedutilityforeachactionandautomaticallyselectsthatactionwiththehighestexpectedutility.Reasonisthusreducedtocomputation,intrueHobbesianfashion.

Oneproblemwiththisviewofreasonisthatittellsusnothingabouthowwepredictthepossibleoutcomesofeachaction.Inrationalchoicetheory,therangeofpossible


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outcomes(andtheconditionalprobabilitiesrelatingoutcomestoactions)areassumedtobegiven,justlikethesubjectiveutilitiesoftheoutcomes.Thelatteraresupposedtobegivenbytheemotions;butwhatabouttheformer?Wecannotsimplyappealtotheagentsbeliefs,sincebelief-fixationissupposedtobearationalprocessitself,sothatsimplyleadstoaninfiniteregress.

Anexamplemayservetomakethisproblemabitclearer.SupposethatIwishtoarrangeanappointmentwithmydoctor,andhesuggeststwoalternativedays—say,nextMondayornextTuesday.IfIamarationalagent(accordingtotheinstrumentalviewofrationality),Iwillcalculatetheexpectedutilityofgoingtothedoctor'soneachofthesedaysandchoosethatwhichhasthehigher.BeforeIcandothis,IneedtoassignaconditionalprobabilityPr(ω|x)toeachoutcome,whereωistheoutcomeandxistheaction.BeforeIcandothat,however,Imustfirstofalllistallthepossibleoutcomes.And,toborrowaphrase,there'stherub;forwhoknows‘whatdreamsmaycome,whenwe(p.181) haveshuffledoffthismortalcoil’—orevenwhatmightensuefromarrangingtoseethedoctoronMonday?IfIhavealreadyagreedtotakemykidsouttothezooonMonday,thenarrangingtheappointmentforMondaywouldmeanhavingtoreschedulethetriptothezoo.ReschedulingthetriptothezoowouldbeoneoutcomeofarrangingtheappointmentforMonday,butwhystopthere?Whynotalsoconsiderthepossibleconsequencesofthat?.Mykidsmightgetannoyedwithme;Imighttellthemoffforbeingintransigent,thismightleadthemtobemoreflexible,whichmighthelpthemtobehappierlaterinlife…andsoon,adinfinitum.Sincetherelationbeinganoutcomeofistransitive,itfollowsthatallthesearealsooutcomesofarrangingtheappointmentforMonday.Soevenforasimpledecisionlikearranginganappointmentwiththedoctor,thesetofpossibleoutcomesforeachactionisinprincipleunbounded.Therefore,listingthepossibleoutcomesofanygivenactionisapotentiallyendlesstask.Yet,ifIamtomakeadecision,Imuststoplistingoutcomesatsomepoint.Lookingbeforeyouleapisallverywell,butthepointistoleap.Atsomepoint,youmuststopthinking,andstartacting.Letuscallthis‘Hamlet'sproblem’.1

NotethatwecannotsolveHamlet'sproblembyrecoursetorationaldecisiontheoryby,say,assigningautilityfunctiontothinking-time.Thatwouldsimplyleadtoaninfiniteregress,foritwouldmeanthat,beforemakinganydecision,wewouldhavetodecidehowmuchtimetospendonmakingit.Butbeforewecoulddecidethat,wewouldfirsthavetodecidehowmuchtimetospendonthatdecision,andsoon,adinfinitum.So,itseemsthatreasoncannotevengetoffthegroundunlesssomeprior,non-rationalprocedureisusedtodelimitthetimefordecision-making,ortherangeofconsequencestobeconsidered,orboth(orperhapstheyjustamounttothesamething).

Accordingtothesearchhypothesisofemotion,thisnon-rationalprocedurefordelimitingtherangeofconsequencestobeconsideredinarationaldecision-processisgovernedbytheemotions.Theemotions,onthisaccount,playmorethanoneroleinrationalchoice.Notonlydotheyassignasubjectiveutilitytoeachoutcome;theyalsodelimittherangeofoutcomestobeconsidered.

Thesearchhypothesisofemotionisarelativelyrecentidea.Thefirstpersontohaveput


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itforwardexplicitlyis,asfarasIcantell,thephilosopherRonalddeSousa.Inhisbook,TheRationalityofEmotion(1987,195),hearguedthatemotionslimit‘therangeofinformationthattheorganismwilltakeintoaccount,theinferencesactuallydrawnfromapotentialinfinity,andthesetofliveoptionsamongwhichitwillchoose’.Inhisarticleonemotionforthe(p.182) BlackwellCompaniontothePhilosophyofMind,deSousa(1994,276)re-iteratestheidea,statingthat‘intheprocessofrationaldeliberationitself,emotionsrendersalientonlyatinyproportionoftheavailablealternativesandoftheconceivablyrelevantfacts’.

Morerecently,similarviewshavebeenexpressedbyanumberofevolutionarypsychologists.TimothyKetelaarandPeterTodd,forexample,havesuggestedthat‘specificemotionsmighthelptosolvetheproblemofwhatinformationtoattendtoinspecificenvironmentalcircumstances’(KetelaarandTodd2000,21–2).Spellingouttheideainmoredetail,theygoontostate:

Thus,whenthefutureoutcomeofvariouscoursesofactioncannotbeobjectively‘calculated’,oftenbecausetherearesimplytoomanyplausibleconsequencestoconsider(i.e.,theframeproblem),itmaypayto‘letyouremotionsbeyourguide’inselectingwhichcourseofactiontopursue.(2000,21–2)

Sofarsogood,orsoitseems.Thesearchhypothesisofemotionseems,onthefaceofit,tobeaneatwayoffleshingouttheclaimthatemotionsplayapositiveroleinaidingrationalchoice.However,whenoneprobesitalittle,itturnsouttohavesomeseriousproblems.Inashortwhile,Iwilllookattheseproblems,butfirstIwanttodispensewithared-herring.

Ared-herring:theframeproblemInthepassagejustcited,KetelaarandToddreferto‘theframeproblem’.DeSousadoestoo.InthearticleonemotionintheBlackwellCompanion(1994,276)hemakesthefollowingclaim:

…thenumberofgoalsthatitislogicallypossibletopositatanyparticulartimeisvirtuallyinfinite,andthenumberofpossiblestrategiesthatmightbeemployedinpursuitofthemisordersofmagnitudelarger.Moreover,inconsideringpossiblestrategies,thenumberofconsequencesofanyonestrategyisagaininfinite,sothatunlesssomedrasticpreselectioncanbeeffectedamongthealternativestheirevaluationcouldneverbecompleted.Thisgivesrisetowhatisknownamongcognitivescientistsasthe‘FrameProblem’:indecidingamonganyrangeofpossibleactions,mostoftheconsequencesofeachmustbeeliminatedfromconsiderationapriori,i.e.withoutanytimebeingwastedontheirconsideration.Thatthisisnotasmuchofaproblemforpeopleasitisformachinesmaywellbeduetoourcapacityforemotions.

SoitseemsthatwhatIhavecalled‘thesearchhypothesisofemotion’couldbere-phrasedinsomethinglikethefollowingterms:emotionshelphumanstosolvetheframeproblem.Thisis,infact,moreorlesshowKetelaarandTodddescribetheirviewof


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emotion:‘asimpleemotionmechanismmighthelpussurmounttheframeproblem’(KetelaarandTodd2000,11).So,mightwenotrefertothesearchhypothesisofemotioninsteadas,say,‘theframehypothesisofemotion’?

(p.183) ThereasonwhyIhavechosennottocoinsuchaphrase,andtotalkinsteadabout‘thesearchhypothesisofemotion’,isthatthereisnoconsensusaboutwhatexactlytheframeproblemis.ThephrasewascoinedbyJohnMcCarthyin1969todenoteadifficultywithaparticularformalismthatheandPatrickHayeshaddevelopedfortemporalreasoningincomputerprograms(McCarthyandHayes1969).Astimewenton,however,thetermwasincreasinglyusedbyphilosophersinmoregeneralways.Bytheearly1980s,forexample,JerryFodorwasusingthetermtodesignatetheproblemofhowtoprogramdigitalcomputerstomakegoodabductiveinferences(Fodor1983).PatrickHayes,whoco-authoredtheoriginalpaperwithJohnMcCarthyinwhichthetermfirstappeared,hasaccusedthesebroaderdefinitionsoftheframeproblemofmuddyingthewaters.ForHayes,thesebroaderdefinitionsareunconnectedwiththeoriginalframeproblem,whichissimplyatechnicalproblemwithaparticularkindofformalism(Hayes1987).PhilosopherssuchasFodorandDennettdisagree,andthedebatehasragedthroughseveraleditedcollectionsofessays(Pylyshyn1987,FordandPylyshyn1996).Myreasonfornotwishingtospeakof‘theframehypothesisofemotion’ispragmatic;Idonotwishtogetboggeddowninendlessdisputesaboutwhattheframeproblem‘reallyis’.Itisnotnecessarytoresolvethesedisputesbeforeaddressingthesearchhypothesisofemotion.

WhendeSousa,KetelaarandToddrefertotheframeproblem,theyallhaveinmindamuchbroaderdefinitionoftheframeproblemthanthatwhichiscommoninartificialintelligence.Theproblemthattheythinkemotionssolveisthatofwhentostoplistingwhatthepossibleconsequencesofanactionwillbe.Thisisalongwayfromwhatmostresearchersinartificialintelligenceunderstandbytheframeproblem.IfwewishtolabeltheproblemidentifiedbydeSousa,KetelaarandToddwithsometechnicaltermdrawnfromthejargonofartificialintelligence,weshouldprobablycallit‘thesearchproblem’.Inthefollowingsection,Iexplainwhatthesearchproblemis.

ThesearchproblemOneoftheconceptualmainstaysofartificialintelligenceistheinsightfulidea,firstproposedbyAllenNewell,CliffShawandHerbertSimon,ofconceivingproblem-solvingasakindofsearch.Imagineastatespaceconsistingofmanypotentialsolutionstoaproblem;findingtherightsolutiontheninvolvessearchingthroughthestatespace.Now,ifwehadtogeneratethestatespaceofpotentialsolutionsinentiretyinadvanceofthesearch,wewouldoftenbestuckwithHamlet'sproblem,sincethestatespaceofmanyproblemsisinfinite.Togetroundthis,Newell,ShawandSimonproposedthatthestate(p.184) spacecanbeexpandedstepbystep,withthecurrentstatebeingtestedtoseewhetherornotitqualifiesasanacceptablesolutionbeforethenextexpansion.Ifthecurrentstatespacedoesqualifyasanacceptablesolution,thesearchisterminatedandtheproblemissolved;otherwise,thestatespaceisexpandedbygeneratinganotherstate.Thenewstateisthentested,andsoon.


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Itisthisstep-by-stepprocessofgeneratingandtestingthatmakesallthedifferencebetweentheidealizedmodelsofrationalchoicetheoryandtheboundedrationalityofartificialintelligencesystems.Insteadoftryingtofigureoutalltheconsequencesofanactionbeforeevaluatingthem,thesearchproceduregeneratesoneconsequenceatatimeandthenevaluatesitbeforegoingontogenerateanotherone.Thetestitusestoevaluatetheconsequencemustbeasimplealgorithmthatreturnsaquick‘yes’or‘no’.Iftheanswerispositive,asolutionhasbeenfoundandthesearchstops.Iftheanswerisnegative,thesearchcontinues.

ThissimpleprocesscansolveHamletsproblem—ortheproblemofarranginganappointmenttoseethedoctor.Insteadofimaginingalltheconsequencesofeachaction,andthenassigningutilitiesandconditionalprobabilitiestoeachoftheconsequencesbeforefinallycalculatingtheoverallexpectedutilityofeachaction—apotentiallyinfinitetask,aswehaveseen—Isimplyimaginetheconsequencesofeachactiononeatatime,andapplysometest.Thetestmightbesomethingsimplesuchasmeetingsomeaspirationlevel.Imight,forexample,thinkofthefirstconsequenceofarrangingtoseethedoctoronMonday—re-arrangingthetriptothezoo—andaskwhetherthatwouldbetoomuchbotherforme.Ifitisnot,IarrangemyappointmentforMonday.Otherwise,Igoontoconsiderotherconsequencesofthisactionand/ortheconsequencesofotheractions.

Now,whatmakesthiswayofdecidingrationalisthat—providingtherightkindoftestisused,andtherightsearchstrategy2—decisionsmadeonthebasisofasearchprocesslikethiscanregularlyleadtodecisionsthatcloselyapproximatethosemadebyanideallyrationalagentoperatingaccordingtoclassicaldecisiontheory.This,atleast,iswhatproponentsofboundedrationalitymaintain,followingtheworkofHerbertSimon(Simon1955).(p.185) Pickingtherighttesttouseforthegivenproblemathand,andtherightsearchstrategy,isthuscrucial.Thisisthesearchproblem.

Thesearchhypothesisofemotioncannowbere-stated;itistheclaimthatemotionsenablehumanstosolvethesearchproblem.Emotionspreventusfromgettinglostinendlessexplorationsofpotentiallyinfinitesearchspacesbyprovidinguswithboththerightkindoftestandtherightkindofsearchstrategyforeachkindofproblemwemustsolve.OnlywhenemotionsfailusdoweendupinHamletssituation,sufferingfromaseverecaseofanalysisparalysis.

TworeadingsofthesearchhypothesisTherearetwowaysinwhichthesearchhypothesiscanbeconstrued.Thefirstisthatthehypothesisisametaphysicalclaimaboutwhatemotionsreallyare;thesecondisanempiricalclaimaboutwhatemotionstypicallydo.Thereisatleastonegoodreason,however,whythefirstreadingisnottenable.Thisisthatthesearchhypothesis,whenconstruedasadefinitionofemotion,becomesvacuous.Ifitwereintendedasadefinition,ofcourse,itwouldimplyafunctionalistaccountofmentalstates,sinceitwoulddefineemotionsbywhattheytypicallydo.Andwhatemotionstypicallydo,accordingtothesearchhypothesis,ishelpusdelimittherangeofpossibleconsequencestobeconsideredinanyrationaldecisionprocess.Ifwehadanindependentideaaboutwhatsuchthingsmightlooklike,thenthehypothesiswouldbeaninterestingclaim—perhapsa


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proposaltoidentifyemotionswiththisantecedentlydiscoveredclassofmechanisms.However,thesadfactisthatwehavenoideahowsuchmechanismsmightwork.Despiteoverfortyyearsofhardwork,researchersinartificialintelligencearestillincapableofdesigningmechanismsthatcandelimit,inadvance,therangeofconsequencestobeconsideredinsuchawaythatdecisionscanbebothrapidandrational.Thereare,itistrue,anumberofinterestingproposalsaboutspecificheuristicsthatcanmakerapid,rationaldecisionsinagivendomain,butthismerelypushestheexplanatoryburdenbackonestage,tothequestionofhowagivenreal-worldproblemismappedontooneofthesystemsdomains.Andnobodyhasanyideaabouthowsuchmappingscanbeachievedinarapidandrationalway.Invoking‘heuristics’inresponsetothesearchproblemisjustpassingthebuck.But,then,soisinvoking‘emotions’.Sincewehavenoideaabouthowtosolvethesearchproblem,thentoclaimthatemotionsarewhathelpussolveitissimplytoexchangeonemysteryforanother.Whatpurportstobeanexplicationoftheconceptofemotionturnsouttobejustanobfuscation.

Inotedpreviouslythatthesearchhypothesiscanbeconstruedeitherasaclaimaboutwhatemotionsare,orasaclaimaboutwhatemotionsdo.(p.186) Theobjectionjustraisedshowsthat,asaclaimaboutwhatemotionsare,thesearchhypothesisisvacuous.Butthisobjectionisnotfataltothesearchhypothesis;afterall,itisnotthetaskofeveryhypothesisaboutemotiontotelluswhatemotionsare.Someaccountsofemotionpurporttoansweraratherdifferentquestion;namely,howdoemotionsinteractwithreason?Perhapsthesearchhypothesisisbetterconstrued,then,asaclaimaboutwhatemotionsdo.

Thisreadingseemsmuchmorepromising,thoughwithonemajorcaveat;construedasaclaimaboutwhatemotionstypicallydo,thesearchhypothesisremainsvacuousunlesswehavesomeindependentnotionofwhatemotionsare.Onlythenwouldtheclaimthatemotionshelpussolvethesearchproblemavoidsubstitutingonemysteryforanother.Inotherwords,thesearchhypothesiscanonlyproperlybeevaluatedinthecontextofaspecifictheoryofemotion.Wecanask,forexample,whetherthesearchhypothesisprovidesagoodaccountofwhatemotionsdointhecontextofAntonioDamasio'stheoryofwhatemotionsare,orofRonalddeSousa'saccount.Butwecannotaskwhetherthesearchhypothesisprovidesagoodaccountofwhatemotionsdointheabsenceofsuchatheory.Itistotheircredit,then,thatbothoftheseauthorshaveadvocatedthesearchhypothesisonlyinthecontextoftheiroriginalaccountsofwhatemotionsare.

Damasio,forexample,arguesthatemotions—oratleastthequalitative,consciousexperienceofemotionsthatsomephilosophersprefertocall‘feelings’—are‘somaticmarkers’.Thatis,theyarebodilysensations,whetherofavisceralornonvisceralkind,thataresummonedupbyparticularthoughtsormentalimages.Whenthesearchhypothesisisadvancedinthecontextofthisparticulartheoryofemotion,thefollowingaccountofhowemotionshelprationaldecision-makingemerges.Whenonestartsthinkingaboutthepossibleconsequencesofadecision,gutfeelingsmaybetriggeredbyparticularimagesassociatedwithcertainconsequences.Ifnegative,thegutfeeling‘forcesattentiononthenegativeoutcometowhichagivenactionmaylead,andfunctions


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asanautomatedalarmsignalwhichsays:Bewareofdangeraheadifyouchoosetheoptionwhichleadstothisoutcome’(Damasio1994,173).Thesignalmayleadonetorejectthisoptionstraightaway,withouttheneedforconsiderationoffurtherconsequences,andthusallowonetochoosefromamongfeweralternatives.

Damasiobacksuphisclaimswithempiricaldatadrawnfrompatientswithvariouskindsoffrontallobedamage.ThesepatientsarestrangelyHamletlike.Whenconfrontedwithadecisionofeventhemosttrivialnature,theymaylosethemselvesinendlessmusingsabouttheconsequencesofeachpossibleaction,withtheresultthatthedecisionitselfispostponedindefinitely.(p.187) Afteroneconsultation,forexample,withapatientwithfrontallobedamage,Damasioaskedhimwhenhewouldliketoarrangehisnextappointment:

Isuggestedtwoalternativedates,bothinthecomingmonthandjustafewdaysapartfromeachother.Thepatientpulledouthisappointmentbookandbeganconsultingthecalendar.Thebehaviourthatensued,whichwaswitnessedbyseveralinvestigators,wasremarkable.Forthebetterpartofahalf-hour,thepatientenumeratedreasonsforandagainsteachofthetwodates:previousengagements,proximitytootherengagements,possiblemeteorologicalconditions,virtuallyanythingthatonecouldreasonablythinkaboutconcerningasimpledate.…hewasnowwalkingusthroughatiresomecost-benefitanalysis,anendlessoutliningandfruitlesscomparisonofoptionsandpossibleconsequences.Ittookenormousdisciplinetolistentoallofthiswithoutpoundingonthetableandtellinghimtostop,butfinallywedidtellhim,quietly,thatheshouldcomeonthesecondofthealternativedates.Hisresponsewasequallycalmandprompt.Hesimplysaid:‘that'sfine’.Backtheappointmentbookwentintohispocket,andthenhewasoff.(Damasio1994,193–94)

WhentheseclinicaldataarecombinedwithDamasio'sclaimthatpatientswithfrontallobedamageareemotionallyimpaired,thislendssomeprimafaciesupporttotheclaimthatmostofusareabletoavoidanalysisparalysisonlybecauseweareemotionallyintact,andthussupportthesearchhypothesiswhenreadinconjunctionwithDamasio'stheoryofemotionsassomaticmarkers.

Damasio'saccountleavesmanyquestionsunanswered.What,forexample,isthepatientreallyfailingtodo?Suppose,forthesakeofargument,thatDamasio'spatientbeginstoconstructasearchtreeinthetypicalmanner.First,hestartsbyexpandingtheinitialnodeofthetreeintotwostates;goonMonday,andgoonTuesday.Howhethengoesaboutbuildingthetreeupfromtheredependsonhissearchstrategy.Mostofuswouldsoonstopthesearch,havingfoundsomeparticularnodethat‘tipsthebalance’towardsoneorotheroftheinitialtwonodes.Thepatientdoesnotstop;butwhynot?AccordingtoDamasio'stheory,hedoesnotstopbecausehedoesnotgenerateanappropriatesomaticmarker.Butthetheorydoesnotsayexactlywhythisfailureoccurs.

Thereareanumberofpossibleanswers.Perhapsthepatientissimplyfailingtoapplyanytesttoeachnewnodeofthesearchtreeashegeneratesit.Orperhapsheisapplyinga


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test,butnottherightone.Athirdpossibilityisthatheisapplyingtherighttest,butsomethingismalfunctioninginthetestmechanism.Thesomaticmarkertheoryofemotionisconsistentwithallofthesepossibilities.DoestheemotionaldeficitofDamasio'spatientinvolveafailuretocallupatesttobeappliedtoeachnewnodeofthesearchtreeasitisgenerated,sothatnotestisappliedatall?Ordoesthepatientsimplyapplythe(p.188)wrongtest,sothatnoappropriatesomaticmarkercanbegenerated?Or,asathirdpossibility,mightthepatientbeapplyingtherighttest,butthetestmechanismfailstotriggeranysomaticmarker?Ofcourse,thisambiguityishardlygroundsfordismissingDamasio'stheoryaltogether.ItsimplymeansthatDamasio'stheoryiscouchedatacertainlevelofgenerality,andisconsistentwithanumberofmoredetailedspecifications.Itdoes,nevertheless,provideatleastageneralwayoffleshingoutthesearchhypothesisandturningitintoatestabletheoryoftherelationbetweenreasonandemotion.

TwofinalremarksBeforeconcluding,Iwishtomaketwofinalremarks.Thefirstconcernsthefactthatthereis,atpresent,noconsensusaboutwhatemotionsare.Indeed,manyphilosophersnowdoubtthatthereisanygoodsingledefinitionofemotion.Aconsensusisemergingtotheeffectthattheverydiversityofphenomenareferredtoas‘emotions’precludesanysingledefinitionoftheterm.PaulGriffiths,forexample,arguesthat‘thegeneralcategoryofemotionsubsumesthreedifferentkindsofpsychologicalstate’,andconcludesthat‘thegeneralconceptofemotionhasnoroleinanyfuturepsychology’(1997,245,247).JonElsterconcurs.Aftersuggestingthattheemotions‘maynotbeacoherentandtheoreticallyusefulconcept’,hegoesontospeculatethat‘theunrulycategoryof“theemotions”encompassesseveral,internallyhomogeneousclassesofphenomena’(1999,241).Inasimilarvein,AaronBen-Zeʼev(2000,3)statesthat‘Nosingleessenceisnecessaryandsufficientforallemotions’,andRonalddeSousa(1994,270)makessimilargloomyremarksabout‘thesheervarietyofphenomenacoveredbytheword“emotion”’.

Theveryheterogeneityoftheemotionsmightseemtoposeafurtherproblemforthesearchhypothesis,construedasaclaimaboutwhatemotionstypicallydo.Forifitistruethattheterm‘emotion’referstoavarietyofnaturalkindsratherthanasinglekind,construingthesearchhypothesisasaclaimaboutwhatemotionsdomayappeartoreducethehypothesistothetriteclaimthataheterogeneousvarietyofmechanismshelpustosolvethesearchproblem.Onceagain,however,thisisonlyaproblemforthesearchhypothesiswhenitisconsideredinisolationfromthecontextofanyspecifictheoryofemotion,or—morepertinently,ifnosingletheoryofemotionistobefound—anyspecifictheoryofaparticularclassofemotions.Thesearchhypothesisisnotnecessarilycommittedtotheviewthereissomesingledefinitionofemotion;allthatitrequiresisthat,ifsuchadefinitioncanbefound,(p.189) thenwhateverthatdefinitionturnsouttobe,itcannotbe(onpainofcircularity)thatemotionsarethingsthathelpussolvethesearchproblem.

Mysecondfinalremarkconcernstherelationshipbetweenthesearchhypothesisandthecomputationaltheoryofmind.Fromthediscussionsofar,itmayappearasifthesearchhypothesis,howeveritisread,ispredicatedontheassumptionthathumansmake


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decisionsinawaythatcloselyresemblesthewaythatcurrentsystemsinartificialintelligencedo.Onlyifthedecision-makingprocessinhumansconsistsofgraduallyexploringasearchspace,isitpossibletoclaimthatemotionshelphumanstoavoiddoingsoindefinitely.This,inturn,seemstopresupposethecomputationaltheoryofmind.Indeed,partoftheappealofthesearchhypothesisofemotionforsomemaybethatitpromisesacoherentcomputationalaccountofemotion—somethingthatmanycognitivescientistsareincreasinglyconcernedtoprovide.

Despitetheseappearances,thesearchhypothesisisnotcommittedtothecomputationaltheoryofmind.Althoughthemetaphorof‘exploringasearchspace’by‘expandingthesearchtreeonenodeatatime’iscouchedunambiguouslyinthejargonofartificialintelligence,onecanstillthinkofitasausefulwayofdescribingcertainthoughtprocesseswithoutbeingafullypaid-up,card-carryingcomputationalist.Damasio'saccountofthesearchhypothesisisacaseinpoint.Fromhisaccountoftherolethatsomaticmarkersplayincertaindecision-makingprocesses,itisclearthatheconstruessomedecision-makingatleastasconsistingofsomethingverysimilartothesearchprocessdescribed.Itisalsoclear,however,thathetakesthisasaphenomenologicaldescription;itismeantasanaccountoftheverbalthoughtsandmentalimagesthatpassthroughthesubject'sconsciousawareness.Assuch,itisagnosticabouttheprecisenatureoftheunconsciousprocessesthatsupportthisconscioussuperstructure.Thisunconscioussubstratemaywellconsistofrule-governedtransformationsofsyntacticrepresentations,asthecomputationaltheoryofmindhasit,butthenagainitmaynot.ThefactthatDamasiocanmakeuseofthesearchhypothesiswithoutcommittinghimselftothecomputationaltheoryofmind,anddosocoherently,isenoughtorefutetheviewthatthesearchhypothesisstandsorfallswithcomputationalism.

ConclusionThesearchhypothesisofemotionistheclaimthatemotionsenablehumanstosolvethesearchproblem.Inotherwords,emotionspreventusfromgettinglostinendlessexplorationsofpotentiallyinfinitesearchspacesbyprovidinguswithboththerightkindoftestandtherightkindofsearchstrategyforeachkindofproblemwemustsolve.Thesearchhypothesisthusoffersan(p.190) accountoftherelationshipbetweenemotionsandreason,accordingtowhichemotionsplayapositiveroleinaidingreasontomakegooddecisions.However,thehypothesisisvacuousunlesswehavesomeindependentaccountofemotiontofleshitout.Itcanonlybeassessed,then,inthecontextofsomeparticulartheoryorotheraboutwhatemotionsare.

AcknowledgementsIwouldliketothankNicholasHumphreyandtwoanonymousrefereesfortheirinvaluablecommentsonanearlierversionofthispaper.

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Notes:

(1)JerryFodor(1987,140)usedthistermtodescribeasimilar,thoughmoregeneralkindofproblem.

(2)A‘searchstrategy’isdefinedbythecriterionusedtodecidewhichstatetoexpandfirst.Ifwerepresentthesearchprocessasbuildingupasearchtree,thenthesearchstrategytellsuswhichnodeofthetreetoexpandfirst.A‘breadth-first’search,forexample,expandsallthenodesatonelevelbeforeexpandinganyofthenodesatthenextlevel.A‘depth-first’search,ontheotherhand,alwaysexpandsoneofthenodesatthedeepestlevelofthetree;onlywhenthesearchhitsadeadend(anon-goalnodewithnoexpansion)doesthesearchgobackandexpandnodesatshallowerlevels.Moreinformedkindsofsearchstrategy—onesthatuseproblem-specificknowledge—arealsopossible(RussellandNorvig1995).

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