[Alexander Riegler, Markus Peschl, Astrid Von Stei(BookFi.org) (2)

UnderstandingRepresentationintheCognitiveSciencesDoesRepresentationNeedReality?

Editedby

AlexanderRieglerFreeUniversityofBrussels

Brussels,Belgium

MarkusPeschlUniversityofVienna

Vienna,Austria

and

AstridvonSteinUniversity/ETHZurichZurich,Switzerland

BasedontheproceedingsoftheconferenceNewTrendsinCognitiveScience(NTCS'97),heldMay1416,1997,inVienna,Austria

ISBN:0306462869

1999KluwerAcademic/PlenumPublishers233SpringStreet,NewYork,N.Y.10013

10987654321

AC.I.P.recordforthisbookisavailablefromtheLibraryofCongress.

Allrightsreserved

Nopartofthisbookmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans,electronic,mechanical,photocopying,microfilming,recording,orotherwise,withoutwrittenpermissionfromthePublisher

PrintedintheUnitedStatesofAmerica

Preface

Currentlyaparadigmshiftisoccurringinwhichthetraditionalviewofthebrainasrepresentingthe"thingsoftheworld"ischallengedinseveralrespects.Thepresentvolumeisplacedattheedgeofthistransition.Basedonthe1997conference"NewTrendsinCognitiveScience"inVienna,Austria,ittriestocollectandintegrateevidencefromvariousdisciplinessuchasphilosophyofscience,neuroscience,computationalapproaches,psychology,semiotics,evolutionarybiology,socialpsychologyetc.,tofosteranewunderstandingofrepresentation.

Thesubjectiveexperienceofanoutsideworldseemstosuggestamappingprocesswhereenvironmentalentitiesareprojectedintoourmindviasomekindoftransmission.Whileaprofoundcritiqueofthisideaisnearlyasoldasphilosophy,ithasgainedconsiderablesupportwiththeadvancementofempiricalscienceintothestudyofmentalprocesses.Evidencesuchasthediscoveryofsinglecellsthatrespondtoparticularenvironmentalfeatures,orspecificareasofthebrainthatlightupduringspecificmentalprocessesinimagingstudies,havesupportedthenotionofamappingprocess,andprovidedadeepfoundationformaterialismand"localism".

Buttheideaofaclearandstablereferencebetweenarepresentationalstate(e.g.,inaneuron,aHebbianensemble,anactivationstate,etc.)andtheenvironmentalstatehasbecomequestionable.Already,weknowthatlearnedexperiencesandexpectationscanhaveanimpactontheneuralactivitythatisasstrongasthestimulusitself.Sincetheseinternallystoredexperiencesareconstantlychanging,thenotionofreferentialrepresentationsischallenged.Thegoalofthisbookistodiscussthephenomenonofrepresentationonvariouslevelsofinvestigation,aswellasitsimplications.

Inordertogivemuchroomtoconceptualandepistemologicalquestions(andlesstotechnicaldetails)thebookstartswithourpositionpaper"DoesRepresentationNeedReality?"Itopensthegroundinreviewingevidencethatcreateproblemsfortheconventionalunderstandingofrepresentations.Thepaperalsosummarizestherationalefortheselectionofcontributionstothisvolume,whichwillroughlyproceedfromrelatively"realist"conceptionsofrepresentationtomore"constructivist"interpretations.Thefinalchapterofdiscussions,tapedduringandattheendoftheconference,providesthereaderwiththepossibilitytoreflectuponthedifferentapproachesandthuscontributestobetterandmoreintegrativeunderstandingoftheirthoughtsandideas.

Thisbookhasatrulyinterdisciplinarycharacter.Itispresentedinaformthatisreadilyaccessibletoprofessionalsandstudentsalikeacrossthecognitivesciencessuchasneuroscience,computerscience,philosophy,psychology,andsociology.Wehopethatitwillpavethewayforabetterunderstandingofrepresentationandinspireitsreadersintheirfieldofstudy.

Acknowledgements

WehavegreatlybenefitfromtheAustrianSocietyofCognitiveSciencewhichattractedboththeidealismofparticipantsandthemoneyoffinanciers.ItpleasesusverymuchtothanktheAustrianFederalMinistryofScience,TransportandtheArts,theformerChristianDopplerLaboratoryforExpertSystems(ViennaUniversityofTechnology),theOsterreichischeForschungsgemeinschaft,andtheCityofVienna.AlexRiegleracknowledgesthefinancialsupportoftheOesterreichischeNationalbank,projectnumber5722/4.ThetitlegraphicsisreproducedwithkindpermissionofAmandaHeitler(neePask).Last,butnotleast,wewouldliketothankthefollowingpeoplewhohavebeeninvolvedintheprocessofpreparingthisbook:LianeGabora,BrigitteRmmer,JohannesSarnthein,andVroniqueWilquet.

THEEDITORS,MARCH1999

Tableofcontents

PositionPaper

MarkusFPeschl&AlexanderRieglerDoesRepresentationNeedReality? 9

OverviewofContributions 19

DifferentFacetsofRepresentation

GeorgDorffnerTheConnectionistRoutetoEmbodimentandDynamicism 23

MatthiasScheutzTheOntologicalStatusofRepresentations 33

AnthonyChemeroEmpiricalandMetaphysicalAntiRepresentationalism 39

AlfredoPereira,Jr.RepresentationinCognitiveNeuroscience 49

DanielD.HuttoCognitionwithoutRepresentation? 57

ComputationalApproaches

GeorgSchwarzOnComputingSystemsandTheirEnvironment 75

WilliamS.RobinsonRepresentationandCognitiveExplanation 83

RobertM.French

WhenCoffeeCupsAreLikeOldElephants,orWhyRepresentationModulesDon'tMakeSense

93

L.AndrewCowardTheRecommendationArchitecture:RelatingCognitiontoPhysiology 101

CognitionasaDynamicalSystem

PimHaselagerNeurodynamicsandtheRevivalofAssociationisminCognitiveScience 115

StevenL.BresslerTheDynamicManifestationofCognitiveStructuresintheCerebralCortex 121

KenMogiResponseSelectivity,NeuronDoctrine,andMach'sPrincipleinPerception 127

MariusUsher&ErnstNieburMentalRepresentations:AComputationalNeuroscienceScheme 135

RelevanceofActionforRepresentation

ErichHarthSketchpadsinandBeyondtheBrain 143

MarkWexlerInductiveLearningwithExternalRepresentations 147

AstridVonStein

DoestheBrainRepresenttheWorld?EvidenceAgainsttheMappingAssumption

161

RalfMller

PerceptionThroughAnticipation.ABehaviourBasedApproachtoVisualPerception

169

SymbolGroundingandLanguage

TomZiemkeRethinkingGrounding 177

N.Chandler,VBalendran,L.Evett,&K.SivayoganathanReality:APrerequisitetoMeaningfulRepresentation 191

ChristianBalkenius&SimonWinterExplorationsinSyntheticPragmatics 199

CommunicationandSocialCoupling

PeterGrdenforsDoesSemanticsNeedReality? 209

J.RichardEiserEmpiricismandSocialReality:CanCognitiveScienceBeSocialized? 219

TomRoutenHabitusandAnimats 229

S.Weiss,H.M.Mller,&P.Rappelsberger

ProcessingConceptsandScenarios:ElectrophysiologicalFindingsonLanguageRepresentation

237

HannaRiskuConstructivistConsequences:TranslationandReality 247

QualitativeAspectsofRepresentationandConsciousness

WolfSingerTheObserverintheBrain 253

MichaelPauenRealityandRepresentation.Qualia,Computers,andthe"ExplanatoryGap" 257

Constructivism

AnnikaWallinCanaConstructivistDistinguishbetweenExperienceandRepresentation? 269

SverreSjolanderHowAnimalsHandleRealityTheAdaptiveAspectofRepresentation 277

ErnstVonGlasersfeldPiaget'sLegacy:CognitionasAdaptiveActivity 283

Appendix

DiscussionsofRepresentationandConstructivism 289

SubjectIndex 301

DoesRepresentationNeedReality?RethinkingEpistemologicalIssuesintheLightofRecentDevelopmentsandConceptsinCognitiveScience

MarkusF.PeschlDept.forPhilosophyofScience,Univ.ofVienna,Sensengasse8/10,A1090Wien,AustriaEmail:[email protected]

AlexanderRieglerCLEA,FreeUniversityBrussels,ruedelaStrategie33,B1160Brussels,BelgiumEmail:[email protected]

AbstractThispaperdiscussesthenotionofrepresentationandoutlinestheideasandquestionswhichledtotheorganizationofthisvolume.Weargueforadistinctionbetweentheclassicalviewofreferentialrepresentation,andthealternativeconceptofsystemrelativerepresentation.Thelatterreferstosituatedcognitiveprocesseswhosedynamicsaremerelymodulatedbytheirenvironmentratherthanbeinginstructedanddeterminedbyit.

Introduction

Howis"realityoutthere"representedinourheads?Doescognitionworkwithinformationfromthe"outside"world?Isourthinkingexclusivelydeterminedbytheworld,isitexposedtoperturbationsfromanapparentlyendlessenvironment,ordoescognitionactivelygenerateandconstructthe"world"?

Toapproachthesequestions,letusstartwithPlato'swellknownallegoryofthecave(TheRepublic.BookVII).Inthisallegory,prisonersareboundinacaveinsuchawaythattheycannotturntheirheadsormovearound.Theycanonlyseeawallinfrontofthem.Thelightofadistantfirebehindthemcastsshadowsonthecavewallofthemselvesandotherpeoplewanderingaround.Theprisonershavebeenrestrictedtothisperspectivesincebirth.Therefore,theironlyperceptionofthemselvesandtheirworldisthroughthemovingshadowsonthewall.Hence,theprisonersperceiveandtaketheseshadowstobetheactualobjectsintheworldratherthanrecognizingthemasmereshadowsofthe"real"environment.

Obviously,whenlookingattheproblemofrepresentationwefaceasimilarsituation:wearetheprisonershavingonlyamediatedaccesstothe"real"world.Howcanwedistinguishthe"true"realityfromthefake?WittgensteinapproachedthisquestioninhisTractatusPhilosophicus:"Inordertotellwhetherapictureistrueorfalsewemustcompareitwithreality."(2.223)

Thismakestheproblemofreferencetoa"realouterworld"clear.Fromsuchaperspectivewehavetodistinguishbetweentheworldasthedomainofourexperience(actuality,wirklichkeitW)andtheworldasthedomainofthingsinthemselves(realittR):

RealittfromtheLatin"res"(thing)connotestheontologicallygivenenvironmenteveryrealistmakesreferenceto.By"ontology"werefertothephilosophicaltraditionofclaimingtheexistenceandrecognizabilityofanindependentworldoutside,theexistenceofthingsinthemselves(DingeansichinthesenseofKant)likethe"real"peoplewhoseshadowsareperceivedbytheprisoners.

Wirklichkeit(actuality)ontheotherhandstemmingfromtheGermanverb"wirken",meaningtohaveaneffectoncanbeusedtodesignatethe"constructed"worldinourminds,madeupbyourexperiencesand(genetic)predispositions.

TheepistemologicallymosttrivialversionoftherelationshipbetweenWandRsuggests:W=R.Here,oneassumesthatanorganismperceivesitsenvironmentdirectlyandfreefromdistortion,andtheworldofexperienceisdirectlyrelatedtoanobjectiveworld(radicalrealism).

Thisisonlyacommonsenserelationshipandseemstobeepistemologicallynotveryplausible.Inthefollowingweintroducemoresophisticatedconceptsthathavebeendeveloped1.

ReferentialRepresentation

Fortheclassicalrepresentationaltheory,wirklichkeitisafunctionofrealitt,W=f(R).Inthisview,ourexperiencesareadistortedandnonproportionalimageofrealitt.Thistheoryisunsatisfactoryinsofarasitdoesnottellusalotaboutthenatureofthedistortionsandtheirrelationshiptotheobserver.Furthermore,itisfromaneuroscientificaswellassystemtheoreticperspectivenotveryplausiblethattherepresentationWdependsonlyontherealittR.Suchaview,i.e.,W=f(R),mightimplysomekindofdistortion.2Therepresentationalrelationship,however,remainsbasicallyreferential(whichseemstobecontradictorytoourexperiences.3

ContextDependentRepresentation

Withinadialecticmaterialisticworldviewtheconstructionofwirklichkeitisestablishedbyaninteractionbetweenanobserverandtheobserved(environment/phenomenon):W=f(R,O,C).0denotesthepropertiesoftheobserverandCtheculturalhistoricalbackground.Suchaperspectivetakesintoaccountthepropertiesoftheobserverinthesensethatheractivityofconstructionplaysanactiveroleintheformationoftherepresentation.However,itmaybedifficulttosufficientlydefinethepropertiesofCand0.

SelfReferentialRepresentation

Theconceptofcognitiveselfreferencedescribesperceptionandrepresentationasperceptionofrelations.Stimuliaremereperipheralenergeticconditions(i.e.,perturbationsP)forasemanticallyclosedandselforganizingcognitivesystem.Thestructureofthecognitivesystemdetermineswhichstructuralconfigurationsofitssurroundingsareperturbationstothesystem,andwhicharenot.Theideaisthatthecognitivesystemisinadynamicalequilibrium.Thismeansthattheperpetuallyactingcomponentsofthesystem(e.g.,neurons)respondsolelytotheactivityofothercomponents.Thereisnootherwayofinfluencingtheirstatewithoutdestroyingthem,muchasadetectorofradiowavesdisplaysactivityonlyinthepresenceofwavesofacertainlength.Fromtheperspectiveofanobserver,anorganism(withitsselfreferentialcognitiveequipment)isembeddedwithinitsenvironment.Someoftheprocesseswithintheenvironment(andexternaltotheorganism)actasperturbationstotheorganism:Throughthesensorysurfacetheyaretransducedintoneuronalactivitywhichinturnmayhaveanimpactonthedynamicalequilibriumofthecognitivesystem.Generallyspeaking,cognitiveselfreferencemeansthatwirklichkeitisafunctionofthreevariables:W=f(W,E,P).Edenotestheindividualbackgroundexperienceofaspecificorganismfromtheperspectiveofsystemstheoryorcomputationalneuroscience,Ereferstothestructureofthestatespace.Inotherwords,Edeterminesthespaceofpossiblesuccessorstatesofeveryparticularstateofthesystem.4NotethatRisnotpartoftheequation,astheneuronsreferonlytoeachother!Inaconstructivistcontext,weinterprettheabsenceofRasaconsequenceoftheoperationalclosureofthecognitiveapparatus.Thatis,thestatesofneuralactivityalwaysoriginatefromandleadtootherstatesofneuronalactivityinarecurrent,selfreferringmanner(Maturana&Varela1979Winograd&Flores1986).Fromthispointofview,todealwithanobjectmeansforanorganismtodealwithitsowninternalstates.5Laterinthispaperwewillelaboratetheideaofcognitiveselfreferenceand

1AsimilarcategorizationcanbefoundinStadlerandKruse(1990).2Thedistortioniscausedbythefunction (.)whichcanbethoughtofasadescriptionofthedistortiontakingplace,forinstance,inthesensorysystemorintheprocessesoccurringinthetransductionorprimaryprocessingoftheenvironmentalsignal.3Think,forinstanceofthephenomenonofcolorconstancymoregenerallyspeaking,thinkofallthesituationsinwhichoneparticularenvironmentalevent/phenomenonisexperiencedindifferentways(accordingtoourpresentinternalstate).4Ofcourse,thisisadescriptiveperspective.Dynamicallyspeaking,thenervoussystemdoesnotrefertopaststates,e.g.,itsstate10secondsago(cf.thenontemporalcharacterizationofthenervoussystem,Maturana&Varela1979).5Thisofcoursedoesnotrefertoasolipsisticworldview,sincethisequationdescribesamappingontowirklichkeitWratherthanrealitt!

arguethatitsupersedestheprevailingreferentialconceptofrepresentationinthecognitivesciences.

Atthispoint,aninterestingquestionappears:WhatisthenatureoftheperturbationsPinthecognitiveselfreferenceperspective?Thisquestiongiveswaytomanyinterpretations.Arathercautiousposition(e.g.,Roth1994)suggeststhatperturbationsarecertainpatternsofenergytransducedbythesensororgansthatgiverisetoamosaicofelementaryeventsthatthebraintriestomakesenseoutof.Thiswouldmeanthatobjectsinthetraditionalsense(chairs,mountains,etc.)donotexistasobjectiveentitiesbutenergy(suchaselectromagneticwaves)does(cf.Chandler'srejectionofthisconcept,thisvolume).Asomewhatmoreradicalinterpretation(suchasGlasersfeld's)acknowledgesthearbitrarinessofacceptingtheabsoluteexistenceofenergywhiledismissing"ordinary"objects.Let'sinvestigatethisalittledeeper.Aboveweemphasizedthatthisviewistheviewofanobserverwhodistinguishesbetweenanorganismanditsenvironment,bothbeingexternaltoherself.However,wearriveatacrucialpointwhenspeakingofone'sowncognitiveselfreference:Anobserverwhoobservesherselfcannevertranscendthisperspective.Thatis,wecanplacebothourselvesandourenvironmentonly"exernal"toourselveswhendescribingtheirrelationship.Thereforewecannothelpbutassumethatthereisindeedanexternalrealittwhichistheoriginatorofperturbationsthatinfluenceournervoussystemthroughmediationofoursensors.However,aswealwayshavetodothesomewhatbizarrestepofthinkingofourselvesasathirdperson,suchaperspectivecanneverrevealthe"true"natureofperturbations,evenworse,wecannotevenclaimnordenytheexistenceofrealitt.

Implications

Whataretheimplicationsforouroriginalquestionofwhetherrepresentationneedsreality?Obviously,thesolutiontotheproblemofappropriaterepresentationdependsontheperspectivefromwhichwelookattheagent.Onewellknownexamplefora,cognitivelyspeaking,"misleading"approacharemicroworldmodelsusedinartificialintelligence(Dreyfus&Dreyfus1988):i.e.,theattempttodeterminebasiccognitivemechanismsbyreducingthecomplexityoftherealworldtothesimplicityofatoyworldandstartingfromthissimplifiedand"cognitivelypreprocessedworld"tobuilduparepresentationalsystemasanetworkofpropositions.Itisobviousthatallthetaskof"understanding"wasactuallydonebytheprogrammersthemselves.Theyputalargeamountofpreprocessedinformationintothesystem,thuscreatingauniverseofinterrelatedfacts(i.e.,purelysyntacticalstructures),buttheydidnotcreateameaningfulworld.Asonecanseeinhighlycomplexexpertsystems,suchastrategyisnotlimitedtosmalltoyworlds,butcangoveryfaronthelevelofthecomplexityofknowledgeithastobeclear,however,thatthisimmenseandquantitativeincreaseincomplexity(i.e.,morerules,facts,relations,etc.)doesnotimplyanewlevel(e.g.,"semantics").Hence,itdoesnotfromanepistemologicalperspectivebringaboutanewquality.

Notonlyhassymboliccognitivesciencecometoadeadend(inthecontextoftheefforttoexplaincognitiveprocesses).Theeuphoricdaysofthenewpossibilitiesofconnectionistnetworks,includingthesimulationofcognitiveactivitiesandlearning,havepassed,too.ItseemsthatcognitivesciencehasreturnedbacktoinKuhn'ssense(1970)"normalscience"orto"puzzlesolving".Asanimplicationofthisdevelopment,connectionistcognitivesciencehasalmostlostitselfin(technical)details,suchaslearningfactors,minimaladjustments,andoptimizationsinlearningalgorithmsoractivationfunctions,andsoon.Intacklingonlythesetechnical"microproblems",itseemstohavefailedtoaddressthereallyinteresting,pressing,qualitative,and"big"questionsaboutcognition.

Nevertheless,inthecontextofrecentdevelopmentsincognitivescience(e.g.,computationalneuroscience,artificiallife,autonomousagents,situatedaction,robotics,etc.)aconsiderableamountofepistemologicalpotentialcanbefoundbasicissueshavereceivednewinputsandnewinterpretationsoverthelastyears.Thegoalofthisvolumeistoinvestigatesomeofthesetrendsandtomakethemmoreexplicitinordertoachievesomeclarityastowherecognitivesciencemightdevelopinthefuture.Amongtheseissuesare:

Thenecessityofrethinkingtheconceptofrepresentationinthelightofdynamical,topdown,andrecurrentprocessesinnaturalandartificialcognitivesystems,inparticularinneuralsystems

Theembodimentofknowledgeinitssubstratum,e.g.,inaneuralstructure

Theimportanceofsimulationasmethodologicaltoolfortheorydevelopmentincognitivescienceandforamoreprofoundconceptualunderstandingofcognition.

Amongothers,theseissueshaveimpactson

theevolutionofsemanticsandsymbolgrounding

thedesignofautonomoussystemsactinginthe"real"world,eitherasrobotsorsoftwareagents

theempiricalresearchin(cognitive)neuroscience(asfarastheirassumptions,experiments,andinterpretationofdatagoes)

thephilosophicalinterpretationofmodelsbeingproposedbycognitivescience

Inthefollowingsectionsadiscussionwillbegivenonthesepointsmentionedabove.Thisisdoneinordertounderstandthe"conceptualatmosphere"andthemotivationforthisvolume.

ReviewingtheNotionofRepresentation

Theunderstandingoftheconceptofrepresentationhasreceivednewstimulifromthedevelopmentsinconnectionism/computationalneuroscienceaswellasin(empirical)neuroscience.6Thefindingsandconceptsstemmingfromthesefieldsseemtoseriouslyquestionthetraditionalunderstandingofrepresentation.Thereareatleastthreepointswhichseemtobeofgreatimportance:

(a)givinguplinguistictransparencyinfavorofdistributedrepresentation

(b)givinguptheclassicalreferentialviewofrepresentationinfavorofagenerativeparadigmandtheconceptoffunctionalfitness

(c)theconceptsofembodimentandconstructioninknowledgerepresentation.

LinguisticTransparency

Theclassicalunderstandingofrepresentationislargelybasedontheideathatpropositions(e.g.,Fodor1981)representthe(internalandexternal)environmentinamoreorlesslinguisticallytransparentway.Withtheadventof"trulydistributed"connectionistmodels7,linguistictransparencyhadtobegivenupinfavoroftheconceptofdistributedrepresentationandsubsymbolicrepresentationinmicrofeatures(cf.Singer'scontribution,aswellasGelder1992,Hintonetal.1986,Rumelhartetal.1986,Smolensky1988,andmanyothers).

Onasuperficiallevel,givinguplinguistictransparencyseemstobeoneofthebigdisadvantagesofdistributedrepresentation(seealsoFodor&Pylyshin1988andmanyothers),asitimpliesthatwehavetogiveupthetraceabilityofthesystem'sdynamicsaswell.Takingacloserlookreveals,however,that(a)itisbynomeansclearwhyourbraindoesitsworkbymakinguseofthesamesemanticcategoriesasourlanguagedoes.(b)Whatisreferredtoasapropositionistheresultofextremelycomplexprocessesoccurringintheneuraldynamicsandleadingtotheexternalizationof"propositionalcategories"(e.g.,informofsymbols,language,etc.).Hence,itisnotatallclearwhytheprocessesresponsibleforgeneratingtheselinguisticcategoriesnecessarilyhavetobebasedonandhavetorelyonexactlythesecategories.Fromtheperspectiveofphilosophyofscienceitseemsratherquestionable,ifitisjusttouseinanexplanationofsocalledhighercognitiveabilities(suchaslanguage)thesamemechanisms/structuresbothintheexplanatorymechanism/explanans(e.g.,symbolprocessingmechanisms)andintheresultingbehavior/explanandum(e.g.,linguisticstructures).(c)Furthermore,itisknownfromempiricalneurosciencethattheactivityofmostneuronscannotbeexplicitlyrelatedtosemanticallytransparentphenomenaorevents.

Alltheseconsiderationsleadtotheconclusionthatthecriterionoflinguisticallytransparentrepresentationisperhapstheresultofourcommonsenseexperience,"autointrospection",andourcommonsenseassumptionsaboutrepresentation.Itseemsthatitarisesfromourneedtosomehowboxeverythingandeveryprocessintolinguisticcategories(and,thus,alsotheseprocesseswhichareleadingtothesecategories)inordertomakeitavailableforcognitivemanipulation.Oneoftheobjectivesofthisbookistoinvestigate,ifthereisanecessityoflinguisticcategoriesforexplainingcognitivephenomenaandtosearchforalternativeviews.

6Thetermsconnectionismandcomputationalneurosciencewillbeusedsynonymouslythroughoutthispaperforthepurposeoftheargumentstofollowthedifferencebetweenthesetwotermscanbeneglected.7"Trulydistributedrepresentation"ismainlyduetoweightconfigurationswhicharetheresultoflearningalgorithms,suchasthebackpropagationlearningrule.

ReferentialRepresentationinRecurrentArchitectures?

Thesecondandepistemologicallymoreimportantimplicationofconnectionistsystemsconcernstheveryconceptofrepresentation:duetothehighlyrecurrentarchitectureinthebrainweareconfrontedwithaphenomenonwhichquestionstheclassicalviewofreferentialrepresentation,i.e.,W=f(R):here,anystatewithinthecognitivesystemreferstoan(internalorexternal)environmentalstateinamoreorlessstablemanner(independentlywhetherithappensinalinguisticallytransparentmannerornot).Therecurrentarchitectureimplies,however,thattheneuralsystemfindsitselfinacertaininternalstateatanypointintime.8Thisinternalstatehasanindirectordirectinfluenceonthefollowinginternal/representationalstates,astheresultingtopdownprocessesarefeedingbackontheincomingstimuli.

Thisimpliesthattheenvironmentalstatedoesnotnecessarilydeterminetherepresentational(=internal)stateanymore,becausethepresentinternalstatehastobeseenassomekindofdispositionforthepossiblesuccessorstate.Moreprecisely,thepresentinternalstatedeterminesthespaceofpossiblerepresentationalsuccessorstatesandthecurrentenvironmentalstateonlychoosesoneoutofthem.Hence,adifferentpresentinternal/representationalstatedeterminesadifferentspaceofpossiblesuccessorstateswhichimpliesthatthesameenvironmentalstatemightleadintodifferentrepresentationalstates(seealsoPeschl1997).Inotherwords,asingleenvironmentalstate/eventcanberepresentedindifferentrepresentationalstates(dependingontheprecedentinternalstate).Thisimpliesthattheconceptofastablereferentialrelationshipofrepresentationcannotbefoundanymore.

Inotherwords,theclassicalideaofanenvironmentalstatedeterminingtheinternal/representationalstatehastobeforsakenduetothefeedbackinfluenceofpreviousinternal/representationalstatesintherecurrentneuralsystem.Theideaofamoreorlessstablerelationshipbetweenarepresentationalstateandan(internalorexternal)environmentalstatehastobeabandoned(forfurtherdetailsseePeschl1997).Rather,theinfluenceoftheenvironmentalinputhastobereducedtothemodulationoftheinternalrepresentationaldynamics(perturbationsPasdiscussedabove).Unfortunately,theimportanceofthisfarreachingepistemologicalissuehasnotbeenacknowledgedbyalargegroupwithinthecognitivesciencecommunity.

Representation,Construction,andGenerationofBehavior

So,iftheaimofrepresentationisnolongertomaptheenvironmentasaccuratelyaspossiblewehavetocharacterizeitasthegenerationofbehaviorintermsoffunctionalfitness(cf.contributionofvonGlasersfeldwhospeaksoftheviabilityofrepresentations).I.e.,behaviorwhich(i)facilitatestheorganism'ssurvival(inthebroadestsense)and(ii)functionallyfitsintotheparticularenvironmentalcontext.9Itisthereforenolongernecessarytosearchforneurons(orgroupsofneurons)whoseactivationscorrelatewithexternaleventsinastablereferentialmanner.

Astherepresentationalstructureistheresultofasystemrelativeconstructionprocess,itisnowonderthatweareexperiencingdifficultiesidentifying(traditional,referential)representationsinnaturalandartificialneuralsystems.Itseemsthatitissimplythewrongthingtosearchfor.Understandingrepresentationfromtheperspectiveofconstructivismandtheconceptoffunctionalfitness(e.g.,Glasersfeld1984,1995)givesusaclueastowhatwehavetolookforintherepresentationalsubstratumnamely,mechanismswhichallowthegenerationofadequatebehavior.Traditionallythesemechanismshavebeenthoughtofintermsofmanipulationsonreferentialrepresentations,however,thereisneitherneuroscientificnorepistemologicalevidenceinfavorofsuchaview.

Inthiscontextitisimportanttonotethatasimilarproblemarisesinmostapproachesinartificiallife.AsarguedinRiegler(1997),atypicaldeficiencyofmanyartificiallifemodelsisthePacMansyndrome:Simulatedorganismsinteractwithanthropomorphicallydefinedentities,suchas''food"and"enemy".Suchmodelsperformamereoptimizingtaskwhichyieldsamaximumgainofenergytogetherwithaminimumlossofhealth.Noattentionispaidto

8Thisalsoappliestofeedforwardarchitectureshowever,inthesearchitecturestheinternalstatedoesnothaveaninfluenceontheincomingactivationsbecausetheinternalstateis"shiftedout"ofthenetworkineachtimestep.9Recentdevelopmentsinagentbasedarchitecturesspeakofsituatednessofreactiveagents(cf.Clancey1997).

questionslike:Howhaveorganismsarrivedattheideathatsomethingisasourceoffood?Howdothey"know"thatanothercreatureisadangerousoponent?Predatorsdonotrunaroundwithalabelsaying"I'myourenemy".Evenifthiswouldbethecasehowwouldhavecognitivebeingslearnedtounderstandthemeaningofthoselabels?(Thinkofthedifficultiestounderstandsignsinacountrywhoselanguageandlettersyoudon'tknowatall.)However,thingsseemtobedifferentwithinmathematicalmodels.Ifwelookatmathematicalformulaewe(usually)knowwhatthemeaningofthelabels(variables)isalthoughwearenottheauthoroftheequations.E.g.,arrivingataresultofm=8.3weknowwhatmis,howmeaninggotattached(namelyaprioritothecalculation).Inlogicalcalculus,semanticsdefinesmeaningandtruthintermsofanunderlyingmodel,ontology,orlogicalinterpretation.Cognitivesciences,however,transcendthispurelysymbolicframework.Whileweasdesignerofartificiallifemodelswouldliketheupperleftpixelonthecomputerscreentobeafoodpillforthepixelinthelowerrightcornerrepresentingthecognitivecreature,thisisnotnecessarilytruefromtheperspectiveofthecreatureanditscognitiveapparatus.Thequestionregardingthephylogeneticandontogeneticemergenceofasystemrelativerepresentation,i.e.,''meanings"fortheorganisms,isnottouched.

Furthermore,itisimportanttonotethatthedynamicsofarecurrentcognitivearchitectureneednotnecessarilybeimplementedinatypicalneuralnetworkmanner.Riegler(1994,1997)describestheimplementationofarulebasedsystem:thealgorithmoperatesexclusivelyonasetof"internalstatecells"(havingnoexplicitlinguisticreference)ratherthanonanthropomorphicallypredefinedsensorandmotorstates.Asthispreservestheideaofoperationalclosure(MaturanaandVarela1979)itis,too,animplementationofcognitiveselfreferenceandhencetranscendspurelyareferentialrepresentation.Thus,weconcludethatthereisnoepistemologicaldifferencebetweenrulebasedsystemsandconnectionistapproachesaslongasweavoidforcingareferentialrepresentationscheme.

Embodiment,Construction,andDynamicsofKnowledge

Inthecontextofthesequestionsonecanobserveashiftininterestsinthefieldofknowledgerepresentationinthelastdecade:thefocushaschangedfromtryingtocaptureordepictenvironmentalstructuresstaticallyontotherepresentationalstructuretowardsstressingmorethequestionofthegenesis,development,anddynamicsofknowledge.Connectionistapproaches(i.e.,theirfocusonlearningstrategies),geneticalgorithms,andthecombinationofboth(e.g.,Elmanetal.1996,Cangelosietal.1994,andmanyothers)hadacrucialimpactonthedevelopmentofrepresentationmechanismsmodelinglearningandthedynamicalaspectofknowledge.Furthermore,resultsfromempiricalneuroscience(sometimeshavingbeentriggeredbycomputationalapproachesandconcepts)havebroughtaboutabetterunderstandingofthelearningmechanismswhichareresponsibleforthedynamicsofknowledgeinourbrains10.

Oneofthemostimportantepistemologicalimplicationsofthisdevelopmentandtheabovediscussionsistheinsightthatknowledgeistheresultofanactiveconstructionprocessratherthanofamoreorlesspassivemapping(cf.Sjlander,thisvolume).Inthisview,theorganismactivelyextractsandconstructstheseenvironmentalregularitieswhicharerelevantforitsparticularsurvival.Theenvironmentnolongerinstructsordeterminesthestructureoftherepresentationsystem,butonlyplaystheroleofconstrainingtheconstructionprocesses.Inotherwords,theknowledgecanbefreelyconstructedaslongasitdoesnot"violate"theenvironmentalconstraints.Theresultisasystemrelativerepresentationofknowledge(aboutenvironmentalregularities),whereW=f(W,E,P),aspresentedintheintroduction:representationdoesnotneedrealityasaninstructiveinstance!Hittingaflywithaflapyieldsadifferenteffectthanbeatinganelephantwiththesameflap:Representationdependsonthestructureofthecognitivesystemratherthanonoutsideentities.

Inthiscontextitseemsthatweneedtotaketheconceptofembodimentofknowledgemoreseriously.Knowledge(representation)canatleastinneurallybasedcognitivesystemsnolongerbeunderstoodassomethingabstractandcompletely

10Unfortunately,wearestandingonlyattheverybeginningtofullyunderstandtheseprocesses.However,thebasicprinciples(e.g.,longtermpotentiation/depression(LTP,LTD),Hebb'sconcepts,etc.)seemtobequitepromisingandhavebroughtaboutanewunderstandingofknowledge.

detachedfromthe(neural)substratum.Rather,wehavetomaketheeffortandtrytounderstandneuralstructures,architectures,anddynamicsintermsofcontributingtotheproductionoffunctionallyfittingbehavioronanonreferentialbasisofrepresentation.Inotherwords,thesocalledenvironmentalregularitiesarenotstoredexplicitlyinthestructureofthesynapticweights.Aparticularneuralarchitecturehastobeunderstoodastheresultofalongphyloandontogeneticadaptation/constructionprocesswhichaimsatrelatingtheorganismrelevantenvironmentalregularitieswiththeorganism'srequirementsforproductionofbehaviorensuringitssurvival.

Attheheartoftheseconstructionprocesses,neurallearning,adaptation,andplasticity,aswellasphylogeneticprocessescanbefound.Alltheseprocessesarethesubstratumforanylearningdynamicscontinuouslyoccurringinacognitivesystem.Consequently,knowledge(representation)inacognitivesystemcannotbeconsideredsomethingstatic,buthastobeseenasahighlydynamicalprocesscontinuouslyadaptingtothechanging(internalandexternal)environmentalconstraints.Oneoftheintentsofthisvolumeistostudyexactlythisrelationshipbetweentheneurophysiologicalprocesses(oflearningandadaptation)anditsepistemologicalimplications.

SimulationasMethodologicalTool

Thelastyearshaveshownasharpincreaseintheimportanceofthemethodofsimulationinthecontextoftheorydevelopmentincognitivescience.Theextensiveuseofsimulationbringsaboutawholenewmethodologicalapproachanddynamicsindisciplineswhichformerlywereworkingalmostexclusivelyempirically,suchasneuroscience,psychology,biology,andphysics.Theinterestinginsightswhichareachievedbysimulationarenotsomuchresultsaboutdetails,butconcernconceptualknowledgewhichcanbeusedasinputandstimulationforbothempiricalandepistemologicalinvestigations.

Oneofthemainpurposesofpsychology,(cognitive)neuroscience,linguistics,andmanyother"cognitivedisciplines"hasalwaysbeenabetterunderstandingofsocalledcognitiveprocesses.Mostoftheresultingapproachestocognitionwerebasedonempiricalinvestigationsand/ormoreorlessspeculativeandcommonsenseinterpretationsofcognitivephenomena.Progressinempiricalsciencesisbasedonacontinuousprocessofconstruction,negotiation,andadaptationtothe"empiricaldata".Thetargetofthisprocessistoreachastateof(epistemological)equilibriuminwhichthetheoryfitsintotheenvironmentaldynamics,meaningthatthetheoryatleastpredictstheenvironmentaldynamicscorrectlywithinsomemarginoferror.Oftenthecomplexityofcognitiveprocessesandtheirsubstratumdoesnotmatchthecomparablypoorempiricalapproachesandunderstandingofcognitivephenomena(cf.Dorffner'scontributionwhichstressestheimportanceofconnectionismasahelpfulmodelingframeworktounderstandcognition).Therefore,muchroomisopenedupforratherspeculativeconceptsinthisfield.

Fortunately,thesimulationmethodintroducesanewdimensiontocognitivescienceand,morespecifically,tocomputationalneuroscience/connectionism.Simulationmodelsareespeciallyinterestinginthecontextofcognitiveneuroscience,asitsempiricalresultsandtheoriesaresometimessorichindetail(e.g.,dataonthereleaseofneurotransmitter,theoriesonamolecularlevel,etc.)thatitisalmostimpossibletorelatethemtocognitivephenomena.Inotherwords,thereisanexplanatorygapandastrongtensionbetweentheepistemologicallyinspiredquestionsoncognition(e.g.,aboutknowledgerepresentation)andtheempiricalandhighlydetailedresultsfromneuroscience.Inthiscontexttheconnectionistapproachinthebroadestsenseplaysacrucialroleasmediator:itstandsbetweenthetwopolesoftheratherspeculativeepistemologicaltheoriesandtheempiricallygroundedneuroscientificdetailsandinmanycasesmakesthemcompatible.Thiscompatibilityisachievedbythetrickoffocusingontheconceptuallevelofneuralprocesses.Bydoingso,themostimportantcharacteristicsandstructuresofneuralsystems,suchasparallelprocessing,networkarchitectureandmassiveconnectivity,anddistributedrepresentation,arecapturedinamoreorlesssimplifiedcomputationalmodelwhosedynamicscanberelatedtoandisdirectlyrelevantforepistemologicaland"cognitive"issues.

So,whydowestresstheimportanceofsimulationmodelsofcognitioninthisbook?Itisnotsomuchthetechnicaldetailsofsimulationwhichweareinterestedin,butratherintheconceptualimplicationswhichthesemodelshaveontheproblemofknowledgerepresentation.Hence,oneoftheobjec

tivesofthisvolumeistoshow,howfocussingonexactlythisconceptuallevelcanbringaboutbothanempiricallyandepistemologicallysoundunderstandingoftheancientproblemofrepresentationincognitivesystems.Furthermore,includingsimulationtechniquesasanecessarytoolfortheoryconstructioncanguideempiricalresearchnotonlyontheleveloftechnicaldetails,butandthisseemstobeevenmoreimportantonaconceptuallevel(e.g.,concerningtheassumptions/premisesofaresearchstrategy,theepistemologicalframeworkandfoundations,etc.).

Conclusion

Wehavearguedinfavorofcompletelyrethinkingbasicissuesincognitivescienceinthecontextofrecentdevelopmentsinthisfield.Themainissueseemstobethequestionofknowledgerepresentation,whichchangesdramaticallywiththeadventoftheconceptsofconnectionismandartificiallife.Wehavesuggestedthattheconceptofareferentialunderstandingofrepresentationshouldbereplacedbyasystemrelativeformofrepresentationwhichisnotnecessarilysemanticallytransparent.

Wearguedfromanepistemologicalandneuroscientificperspectivethatthetaskofgeneratingbehaviorismoreimportantthantheaccuratemappingofenvironmentalstructurestorepresentationalstructures.Itisbynomeansclearwhatthe"pointofreference"couldbeforan"accuratemapping".Isitourownperceptionandconceptualizationoftheworld,orthatofarat,ortheworlditself,...?Oneistemptedtoassumethattheoutsideworld(inthesenserealitt)actsassomekindofconstraintforourconstruction/representationprocesses.Butassumingtheexistenceofthatrealitt(orpartsofitsuchaselectromagneticwavesseeabove)wouldputusintothecampofreferentialrealistsaswe(thoughnottrivially)mapourexperienceontotheideaofanoutsideworld.Assumingthenonexistenceoftheworld,onthecontrary,wouldstigmatizeusassolipsists.Asasolutionwehavethereforetoacceptthatclaimsabouttheexistenceofanobjectiverealittmightnotbenecessaryforthepurposeofscientificexplanations.

Wehaveseenthatsuchaviewofknowledgerepresentationiscloselyrelatedtoconstructivistconcepts.Inthisapproachtoepistemology,theonlycriterionforsuccessfulknowledge(representation)isitsfunctionalfitness.Furthermore,ithasbecomeclearthatknowledgeisnotastaticstructure,butiscontinuouslychanging.Thisdynamicscanbedescribedasaprocessofconstructionandadaptationandfindsitssubstrateintheneuraldynamics/plasticity.

Themaingoalofthisvolumeistodiscussthesefundamentalshiftsincognitivescienceandtosketchtheimplicationsonanepistemologicalandmethodologicallevelforcognitivescienceanditsrelateddisciplines.

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OverviewofContributions

Thefirstpapersaddresstheepistemologicalstatusofrepresentationandpossiblecategorizations.Theserathergeneralconsiderationsaboutrepresentationarefollowedbycontributionsthatfocusoncomputationalapproaches,especiallyonhowmeaningcanbesimulatedinartificialdevices,andhowmeaningcanbegrounded.Solutionsareofferedonvariouslevels,amongthemsymbolgroundingandsystemtheoreticalconsiderationstorepresentation.Variousdisciplinesindependentlyarriveatemphasizingtheimportanceofactionsforrepresentationsandthenecessitytoclosethesensorymotorloopexamplesfromtheperspectiveofcomputationalapproaches("embodiment"intoanenvironment),theneuroscientificperspective("topdown"processes),thepsychologicalperspectiveandothersarepresented.Severalpapersaddresstheroleofsocialinteractionsinparticularlanguageasameansofstabilizingsystems,andintheemergenceofmeaning.Thedeepepistemologicalimplicationsconnectedwiththeaboveconsiderationsarediscussedinthefinalchapterofthevolumededicatedtoconstructivistapproaches.Followingtheideaofatrueinterdisciplinaryapproach,thecontributionstothevarioussectionsareorganizedexclusivelywithrespecttothematiccontentratherthantoscientificdiscipline.Theremainderofthisoverviewpresentsthepapersandtheirmutualrelationshipinmoredetail.

Inthefirstchapter,dedicatedtotheoreticalconsiderations,GeorgDorffnerprovidesanintroductiontotheproblemofrepresentationbydefiningthreetypesofrepresentation.Heshowsthatconnectionismsolvesseveralproblemsofrepresentationandactuallyhelpstoabandononeofthesetypesofrepresentation.Similarily,AlfredoPereirainvestigatestwotypesoftherepresentationsusedintheneurosciences,perceptualandexecutiveprocesses.AnthonyChemerotriestoclassifypossiblecritiquesregardingrepresentations.Hepresentstwotypesofantirepresentationalism:eithertherepresentingstructurecanbequestioned("empiricalantirepresentationalism"),ortherepresentedstructurecanbequestioned("metaphysicalantirepresentationalism").Evidenceforthefirstcomese.g.fromconnectionismwhichhasdemonstratedthatbrainlikestructurescanfunctionwithoutexplicitrepresentations.Argumentsforthesecondareofaphilosophicnaturedenyingthepossibilityofspeakingoffixedentitiesoftheworld,and,instead,proposingthatthe"things"aredefinedonlywithrespecttotheiruserandthuscannotbe''mapped"ontothebrainofthatuser.MatthiasScheutzinvestigatestheontologicalstatusofrepresentations,andquestionswhethertheyareentitiesontheirownhearguesthatwhethersomethingcountsasrepresentationofsomethingelseisdependentonthelevelofdescription.Bytalkingaboutamentalstructurerepresentingsomethingintheworld,oneimpliesthatthesetwothingsexistontwodifferentontologicallevels.Thisisnottrue,however,sincethemindandthethingsoftheworldarebothentitieswithinourcognitiveexperience.Thus,theproblemofrepresentationarisesonlyasartifactofourdescribingthephenomenonofcognition.DanielHuttoexploresthedifferencebetweennonconceptualrepresentationsandconceptualrepresentationsandasksthequestionwhetheritmakessensetodefinerepresentationonthelowestlevelofabstractionoronthehighestlevel.

Isitpossibletosimulatemeaningorcognition?Theissueofcomputationtorepresentationispresentedinthechapter"ComputationalApproaches".ThepaperbyGeorgSchwarzdrawsconclusionsforthefunctioningofthebrainfromacomputationalperspective.Fromaphilosophicalpointofview,WilliamRobinsontriestoaddressacontroversyincomputationalapproachestocognitionbyintroducingadistinctionbetweencognitionandcognitiveabilities.RobertFrenchmakestheargumentthatcreatingrepresentationscannotbeseparatedfrommanipulatingthem.Moreover,heemphasizesthecontextdependencyoflinguisticterms(oneofthereasonsthatcomputationallinguisticsisnontrivialmatter)and,asaconsequence,thedistractivecharacterofcontextladenrepresentations.AndrewCowardproposesthatnaturalpressureshaveresultedinbiologicalbrainshaving

simplefunctionalarchitectures.Thetypeofarchitectureconstrainsthetypeofrepresentationswhicharepossible.

WhileconnectionismovercamesomeoftheproblemsderivedfromconsideringthebrainasavonNeumanComputer,seriousnewquestionscameintofocus.Withsimulatingrepresentationsinneuronalnetworksitbecameevenmoreobviousthattheproblemtobesolvedwasthatthemeaningwasputintothesystembytheengineer.Whetherthestateofthenetworkwouldstandforsomethingisdefinedbyanexternalobserverbutisnotinherenttothesystem.Thisproblemofthefoundationofmeaningisreferredtoasthegroundingproblem,whichistreatedinthechapteron"SymbolGroundingandLanguage".TomZiemkeprovidesareviewaboutthegroundingproblemandit'stwoproposedsolutions.Thefirstsolutionofgroundingisgroundingasymboltoaninput,whichwasfirstproposedbyStevanHarnad.ThepapersbyNathanChandleretal.andChristianBalkenius&SimonWinterpresentsuchmodelsongroundedlanguagesystems.AsdescribedinthepaperbyZiemke,this,however,isonlyapartialsolutiontherealbreakthroughisonlyobtainedwhenarobotisreallyembeddedintoanenvironmentandinteractingwithit.ExamplesofthiskindofgroundingaregivenbyMarkWexlerandRalfMller(seebelow).

NotonlyinclassicalAIbutalsoinconnectionism,meaningandrepresentationsaremostlyofastaticnature.Thus,althoughdistributed,representationsarestillverymuchtreatedlike"boxes".Cognition,however,isdynamicanditneedstime(seealsodiscussion,page290).Systemstheoryprovidesaframeworkthatencompassestheseissues(chapter"CognitionasaDynamicalSystem").Fromapsychologicalpointofview,PimHaselagerprovidesareviewabouttherelevanceofdynamicalsystemstheorytothetopicofrepresentationandits(philosophical)classificationinthecontextofbehaviorism.MariusUsher&ErnstNieburpresentneuroscientificevidenceandamodeldemonstratingthatneuralrepresentationsareactiveprocesseswhichcanmediatecontextualcomputationandbindrelationalproperties.KenMogidiscussestheconceptoftimeandcausalityintherelationofperceptionandneuralfiring.Hisprincipleofinteractionsimultaneityprovidesanexplanationfortheoriginofsubjectivetime.SteveBresslerpresentsacomplexsystemstheoryapproachtorepresentationandcognition.Inspiredbyempiricalfindingsoflocalandlargescalecorticalinteractions,hederivesadynamicalviewofcorticalrepresentationbasedoninterarealpatternconstraintsandlargescalerelaxation.

Inarelatedrealm,awayfromrepresentationsunderstoodasprojectionsofenvironmentalentitiesontomentalstructures,severaldisciplinesindependentlydiscoveredtheimportanceofactionsforrepresentations.Theyproposetoclosethesensorymotorloop.(Forthistopicofparallelismsinscientific/philosophicaldevelopments:seethecommentbyWolfSingerinthediscussions,page293).Inmodeling,thegroundingproblemdescribedaboveintroducedtherelevanceofinteractionforrepresentationsembodiedsystemsthatinteractwiththeirenvironmentinasensorymotorlooparecreated.Philosophically,constructivismandthetheoryofautopoieticsystemsdemonstratedthatwhatweperceiveasrepresentationsofapredefinedexternalworldisbetterdescribedasconstructionsthatservetosuccessfullygeneratebehavior.Inneuroscience,theoldconceptthatenvironmentalobjectsaremappedontoneuronsinafeedforwardmannerischallengedbyanatomicalandphysiologicalevidence.Ithasbeenshownthatinformationdoesnotexclusivelyflowfromthesensorstothehigherbrainareas,wheretherepresentationsarethenthoughttobeusedfor"thinking"andthefinalactivationofmotorprograms("bottomup").Rather,massiveactivityistransportedtheotherwayaround(''topdown").Thusmotoractivity,i.e.,plannedactions,canbeviewedassupervisingtheincomingsignalsandthusstructuringcorticalrepresentationsthemselves.Psychophysicalevidence,suchasthefigurevaseambiguity,showthatperceptionisambiguous,dependentonprimingandexpectancy.Thus,severalapproachescometotheconclusionthatperceptionisnotapassive,feedforwardprocessofmappingbutanactiveconstruction,wheretheneedforactioncreatesanhypothesisabouttheenvironmentwhichisthencomparedtotheincomingsensorysignals.Thechapter"RelevanceofActionforRepresentation"isdedicatedtotheseproblems.

Theideaof"theinversionofsensoryprocessingbyfeedbackpathways"wasintroducedbyErichHarth.Inhispaper,hedescribesneurophysiologicalevidenceforascenariowhereprocessingisnotfromtheperipherytothehigherbrainareasbutrathertheotherwayaround.Hepresentsamodelwhereacorticalhypothesis("internalsketchpad")mightbecontrolledbytheincomingsignalsina

hillclimbingalgorithm.Fromtheperspectiveofneurobiology,AstridvonSteininterpretsthecorticalarchitecturewithitsfeedforwardandfeedbackconnectionsasamediumofinterwovensensorymotorloopsinteractingondifferentlevelsofahierarchy.Representationsdonot"sit"oneitherendoftheconnections,butarestablestatesinthesesensorymotorloops.ThisisconsistentwithPiaget'sfindingthatanobjectisdefinedthroughtheperceivedchangeinsensationthatanactionperformedontheobjectinduces.Accordingtothisapproach,whatweperceiveasentitiesisneitherintheworldnorinthebrainbutintheinteractionbetweenboth.Basedontheideaof"perceptionthroughanticipation",RalfMllerperformsasimulationwithasimilarapproach:hepresentsasystemwheretherepresentationisnotabuildingblockwithinthesystem,withperceptionbeingaprojectionfromoutside,butwhereperceptionisaprocessofanticipatingthesensoryconsequencesofactions.TomWexlergivesempiricalevidencefortheimportanceofactionsinrepresentationsusingbothpsychophysicalexamplesandsimulation(representationasstrategyforactingratherthanasamappingoftheenvironment).Hedemonstratesexampleswherepreviouslyunresolvedproblems(e.g.the"nparityproblem'')canbesolvedifthelearningsystemisdirectlyinteractingwiththeenvironmentinasensorymotorrelation,i.e.,iftheenvironmentisincludedintotherepresentation.

Whenafirststepindefiningrepresentationsonanewgroundistoconsiderthesensorymotorcouplingwithanorganisms'senvironment,asecondstepistoconsiderthecouplingnotonlywithastaticenvironmentbutwithotherrepresentingsystems.Theroleofsocialinteractionsinparticularlanguageforstabilitieswithinasocioculturalnetwork,andtheemergenceofrepresentationsand"meaning"isasubjectwhichisfurthertreatedbyseveralauthorsinthechapter"CommunicationandSocialCoupling".Fromasocialpsychologicalpointofview,RichardEiserasksthequestionhowindividualsacquireknowledgeorrepresentationofsocialrealitythatadaptwithnewexperience,andalsohowgroupscancoordinatetheirbehaviorinamanneradaptivetotheirenvironment.Hepresentsatheoryabouttheself,wheretheselfisseenastheproductofthecognitivesystematwork,i.e.,asexplanatorymodelforalreadyperformedortobeperformedbehavior.TomRoutendemonstratesthattheadvantageoftheadaptivebehaviorapproachoverclassicalAIisonlyapartialone,andthatlanguagehastobeincluded.HeintroducestheideasofBourdieu,andMcDowell,whotakelanguagenotasastaticsetofwordsandgrammaticalrulesbutasa"wayoflife",aHabitus.Habitus(Bourdieu)is"asystemofdispositionswhichservestosettheindividual'sunderstandingandactionsinagreementwithitssocialandphysicalenvironment".SinceHabitusisinstalledbysocialization,itwillbethesamewithinagroup,i.e.,theexperiencingwillbesimilarandacommonworldviewwilldevelop.Thus,languageasaHabitathastobeincludedintomodelsofcognitiveagents.Aprototypicalexampleofrepresentation,languageandsemanticsisgivenbyPeterGrdenfors.Incontrasttorealisttheoriesofsemanticshesuggeststhatitisnotreasonabletospeakabouttherelationbetweensignsandthingsintheouterworld.Instead,hearguesthatitmakessensetospeakabouttherelationbetweensigns(i.e.,"linguisticexpressions")andconcepts,i.e.,meaningintheheadoftheindividuals.Thatlinguisticexpressionsmeanthesameforeverybodyisnotbecausetheymapafixedworldbutbecausetheyemergeduringinteractionfromtheconceptsintheheadsofthelanguageusers.ExamplesofneurophysiologicalcorrelatesoflanguageprocessingaregivenbySabineWeissetal.TheproblemoftransferringmeaningbetweentwolanguagestheproblemoftranslationisconsideredbyHannaRisku.

Tillnowwereferredtorepresentationasmentalenvironmentalstabilitiesthathaveevolvedtosuccessfullyguidethebehavioroforganismsobjectswouldinthissensebeconsideredasadaptiveconstructsinthisorganismenvironmentrelation.This,however,doesnotaddressthequestionofthesubjectiveexperienceofrepresentations,i.e.,theawarenessthattherearethingsintheoutsideworld,ortheawarenessofonesselfasactivepartintheinteractionwiththeworld.Thechapter"QualitativeAspectsofRepresentationandConsciousness"dealswiththisproblemofconsciousness.WolfSingeraddressestheissueofconsciousexperiencefromaneuroscientificperspective,endingwiththeconclusionthatpropertiessuchasselfawarenessandconsciousnesscannotbeexplainedintermsofneuronalcorrelatesalone,butonlybyadditionallyconsideringthe(social)interactionsamongbrains.Hispositionis,thus,bothdualisticandmaterialistic,sayingthatconsciousnessishousedbyaneuronalsubstratebutcanneverbeexplainedbyneuroscienceitselfsince

itconsidersaphenomenonwhichcannotbefoundinsinglebrains(Seealsodiscussions,page291).MichaelPauenstressestheimportanceofstructuralsimilaritiesinrepresentations:differencesintheworldhavetoscaletodifferencesintheneuronalactivities.Qualiaisproposedtoserveastheaspectorganizingthesestructures.Theproblemofqualiadissolvesifoneabandonstheartificialdistinctionbetweensubjectiveexperienceandobjectiveoutsideworld.

Finally,thechapter"Constructivism"concludeswiththedeepepistemologicalimplicationstheaboveconsiderationspresent.Ifweagreethatwhatisrepresentedinthebrainisnotjustaprojectionfromentitiesintheoutsideworldbutratherarepertoireofhypothesisaboutfutureactions,groupedandstructuredinanefficientwaytosuccessfullyactwhat,then,isthatrealityoutthere?

ErnstvonGlasersfeldhasaradicalapproachtothatquestion:hearguesthatwhatweperceiveasoutsideworldisnothingbutconstructionsofourcognitiveapparatus.Inhisarticleheproposestonotusethewordrepresentationatall,sinceitiscommonlyunderstoodasa"copy"or"reproduction"suggestingthereferencetoanoriginal.Whilethisimpliesthatwecancompareamentalexperiencetosomethingoutsideourmentalexperiencetheoutsideworldhearguesthatthisisnotpossiblesincementalcontentcannotrefertoanythingbuttofurthermentalcontent.Hesuggeststousetheword"presentation"instead,toimplythatitisaproposalthebrainofferstotheoutsideworldinadaptingtothatworldaworld,however,thatinprincipalcannotbeknown.EmpiricalevidencefortheconstructivistnatureofrepresentationispresentedbySverreSjlander.Heinvestigatesthesubjectfromanevolutionaryperspectiveanddescribeshowobjectcentered(invariant)representationsdevelopfromsimpleinputoutputprocessinginloweranimals.Heshowsthattheevolutionarypurposeofsensoryprocessingisnotamappingoftheworldbutproducingadaptivebehavior.AnnikaWallinshowsthatthefactthatwehavetwotypesofrepresentationsimmediateperceptionsandrepresentationssuchasduringimagerycreatesaseriousproblemforconstructivism:accordingtoconstructivisttheories,theconceptsconstructedtosubserveadaptivebehaviorareadjustedaccordingtotheconstraintspresentedtothesystem.

Asthisoverviewshows,ourgoalwastobringtogetherinterdisciplinarilyworkingscientistsinordertocontributetothisvolume.Webelievethatourselectionofpaperswillhelpfosterabetterunderstandingandfruitfulapplicationoftheubiquitousnatureofrepresentation.

TheConnectionistRoutetoEmbodimentandDynamicism

GeorgDorffnerAustrianResearchInstituteforArtificialIntelligence,andDept.ofMedicalCyberneticsandArtificialIntelligence,UniversityofVienna,AustriaEmail:[email protected]

AbstractInthispaperIdemonstratethatconnectionismis,orcanbe,largelyinlinewithmostrecenttrendsincognitivescience.Thecoreofmyargumentisadistinctionofseveraltypesorusesofrepresentationincognitivescience.Idemonstratehowconnectionismhelpsinabandoningoneofthesetypesthenotionthatrepresentationisamirrorofanobjectivelyexistentworldwhilemaintainingtheimportantothertwotypescausalcorrelatesofphysicalstates,andinternalmentalstatesstandinginforpastperceptions.Withthisdistinctionthequestion"Doesrepresentationneedreality?"canbeanswered.Ifurtherdepictaconnectionistroutetoembodiedandsituatedcognitivemodels,astheyareputforwardbyrecentcognitivetheories.Afterashortdiscussionofconnectionism'srolefordynamicisttheoriesofcognition,Iconcludethatmuchofcurrentconnectionistresearchishighlyrelevanttomoderncognitivescience,evenifthemodelsareapparentlyremotefromtrulyembodiedorsituatedones.

NewTrendsinCognitiveScience

Inrecentyears,anumberofnoveltrendshaveemergedincognitivescience,whichalthoughrunningbydifferentnamesandunderdifferentheadingsappeartohaveacommondenominator.Theyputthebodybackintothefocusofcognitivescience,emphasizetheinteractionbetweenacognitiveagentanditsenvironment,viewexperienceandindividualdifferencesasatleastasimportantasdetachedlogicalprinciples,andapplyamoreholisticstancetowardresearchonhumancognition.Thesetrendsarecharacterizedbykeywordssuchas

embodiment

situatedness

emergence

grounding

selforganization

nonrepresentationalism

dynamicism

andmanymore.Theyhavedecisivelyinfluencedthewaycognitivescientiststhinkaboutintelligenceandcognitivebehavior,andsomeclaimthattheywillmainlyshapecognitiveresearchyettocome.

Examplesareworkonautonomousrobots(Brooks1991Pfeifer&Verschure1992Nehmzow&Smithers1991andothers),constructivisttheoriesofcognition(e.g.Varelaetal.1991),dynamicmodelsofcognition(Port&vanGelder1995Skarda&Freeman1987andothers),workongrounding(Harnad1990),andothers.

Onequestionmightariseinthisdiscussion:Whateverhappenedtoconnectionism(Rumelhart&McClelland1986,McClelland&Rumelhart),whichinthelate1980swasseenassomethingclosetoarevolutionincognitivescience(Smolensky1988)oratleastamajorthreat(Fodor&Pylyshyn1988).Whatrolecanordoesconnectionismplayinthesechangingtimesincognitivescience?Hasitbecomeanestablishedmodelingmethodology,whichhasrunintosimilarshortfallsaspreviouscognitivistapproaches?Isitjustanewversionofclassicaltheoryviewingcognitionascomputationonstylizedrepresentationsoftheworld?Bickhard&Terveen(1995)seemtoargueforthelatter,similarlytoVarela(1990)whodistinguishesfourphasesof20thcenturycognitivescience,connectionismbeingthethird,replaced(orextended)bythelatestemergentistphase.

InthispaperIarguethatconnectionismisfarfrombeingreplacedbyanyofthelatesttrends.Tothecontrary,itcanbeamajormodelingframeworkthatencompassesmostorevenalloftheideasexpressedbytheabovekeywords.Oratleast,itcanprovidethepavementforaroutetowardrealizingthoseideas.Take,forinstance,thefollowingimag

inarydialogusedbyElmanetal.(1996)astheintroductiontotheirbook.Onepersoniswonderingaboutanotherperson'sinterestinconnectionism:

"...Ithoughtyoubelievedinconstructivism,interactionism,epigenesisandallthatmurkystuff."

"Oh,I'mstillabeliever!Buttheconnectionistframeworkallowsmetocomeupwithamuchmoreprecisenotionofwhatallthatstuffreallymeans..."

Thisisexactlythespiritofthispaper.Iwanttodemonstratethatconnectionismcancontributemuchtothelatesttrendsincognitivescience,bydiscussingtwoimportanttopics:Representation,it'suse,misuseandunderstandingincognitivescienceandhowconnectionismcancontributetoclarifyingthings.Andthedynamicistviewofcognitionandhowconnectionismrelatestoit.

ThreeMeaningsofRepresentation

Likemostepistemologicaltermsincognitivescience,'representation'hasbeenusedandabusedinmanydifferentwaysinliterature.Whilethenotionplaysacentralandunambiguousroleinclassicalcognitivistapproaches,ithasbeenmodified,analyzedandcontestedinmorerecentstreamsofcognitivescience.AuthorslikeBrooks(1991)andVarelaetal.(1991)havegoneasfarasspeakingaboutcognitionwithoutrepresentation.Thisleadstoanapparentcontradiction.If,asitiswidelybelieved,representationisseenasmediatingbetweentheimmediatelyperceptibleenvironmentandasstandinginforit(Markman&Dietrich1998),thuspermittingcomplexcognitivebehavior,howcancognitionworkwithoutit?Ontheotherhand,representationthewayitisusedinartificialintelligencebearsawiderangeofconceptuallimitations,whichwasoneofthemajormotivationsforcognitivescientiststomovetowardsuchnotionsasembodiedcognition,groundedrepresentations(yes,representationsagain),andthelike.

Now,isconnectionismnonrepresentational,orcanitbe?Ifnot,whatisdifferentaboutitandhowdoesitrelatetoembodiedmodelsofcognition?

Theanswerliesinaclarificationofthenotion'representation'.Idistinguishthreequitedifferenttypes(orbetterstill,threeuses)of'representation',anditwillbecomeclearthatnovelviewsoncognitionarestrivingtoreplaceonlyoneofthesetypes,whileitisperfectlyconsistenttomaintaintheother

Figure1:Representationsoftype1.

two.Inordernottorunintothetrapofusingoverloadedtermsandraisemoreconfusion,Isimplycallthemtype1,2and3:

RepresentationofType1

By'type1'Irefertotheclassicalnotionofrepresentationasaconceptualmirroroftheworld(seefigure1).Thisisthemainbasisofsymbolicartificialintelligence,andofmanymodelsfromcognitivepsychologyalike.Theunderlyingviewisthatthereisanobjectivelyexistentoutsideworld(reality)whichmustbemappedontoafaithful(albeitoftensimplified)imageinthecognitiveagentinorderforthelattertoactintelligently.As,forinstance,Charniak&McDermott(1985)putit,such"representationsarestylizedversionsoftheworld".Cognitionisthenseenasakindofcomputationontheserepresentations,whichcanbelargelydefinedindependentlyfromtheactualimplementation(beitasymbolicprogramorthebrain).

Theimportantthingtonoteisthatinordertouseandspeakofsuchkindsofrepresentations,onemustastheobserveridentifytwothings:therepresentationanditsmedium(e.g.symbols,oractivationpatternsinaconnectionistnet)ononehand,andtheobjectsorconceptsreferredto(thedenotata)ontheother.Forinstance,tosaythatasymbol'CHAIR'representsthecategoryofchairs,onemustnotonlyspecifythesymbol,butmustalsoassumethatacategorychairexistsintheworld,independentlyfromwhethertheobserverortheagenttobemodeledinteractswiththeworld.Theimplicitassumptionisthusthatofastructuredworldthatexistsevenwithoutintelligentagentscognizingaboutit.

Figure2:Representationsoftype2.


WhatIcallrepresentationoftype2referstointernalmentalstatesthatenableacognitiveagenttoactevenintheabsenceofimmediateperception.Whilethisisimplicitlycontainedwithintheclassicalviewoftype1,thisconceptisnotnecessarilytiedtoarepresentationoftype1.Type2representationscanexistwithoutpresupposinganobjectiveoutsidereality,sincetheycanbetheresultofacomplexindividualinteractionoftheagentwithitsenvironment,withoutthenecessityofpostulatingthatitmustdirectlycorrespondtoanythingintheworld(seefig.2).

Thisisthecrucialpoint.Ifweobserveahumanactinabsenceofimmediateperceptionofthebasicdrivingforcebehindtheiractionwecanandmustassumethatthepersonactsoninternalmentalstatesstandinginfortheirconceptsofwhatdrivestheiraction.Forinstance,ifsomebodyasksusforthenearestcoffeeshopbecausethatpersonistired,weingeneralcansafelyassumethatthepersonisactingonaninternalrepresentationoftheirconceptofcoffeeandtheeffectitcanhave.Thisiswhatdistinguisheshumansfromlowerlifeformsthatmainlyorsolelyactonperceptionsinareactiveway.

Totalkaboutandmodelsuchakindofrepresentationonedoesnothavetopresupposeanypregivenstructureintheworldandthattherepresentationreflectsthatstructure.Representationsinthisviewdonotrefertoanythinginreality,theyarerealityforthecognitiveagent.Theyaretheresultoftheagent'sinteractionswiththeworld,itsperceptionsanditsexperiencewiththem.Thisisthemajordifferencetotype1.Whenusingtheconceptofrepresentationsoftype2,onedoesnot(ornotnecessarily)assumetheexistenceofanobjectivestructuredreality,butinsteadseesrepresentationalwayswithrespecttotheindividualagent.Whateveritisthatpersonreferstoas'coffee',beitthesamethatweastheobservercall'coffee',oronlysimilar,orsomethingcompletelydifferent,itisencompassedinaspecificinternalmentalstatethatpermitsthatpersontoactonandspeakaboutcoffee.Thisstatestandsinforwhateverthepersonhadpreviouslyperceived(orconceived),andthusitisakindofrepresentation.Contrarytotype1,however,itisrepresentationwithnoidentifiabledenotata,unlessonehasaverydetailedinsightintotheperson'spastandpresentperceptionsandexperiences.


Thisistheloosestsenseofrepresentation,butthisuseisnotuncommon.Type3referstoimmediatecausalrelationshipsbetweenastimulusanditseffect.Forinstance,thefiringofaneuronintheretinarepresentstheamountoflightthathasfallenontoit.Itisthiskindofrepresentationmerelyreactivelifeformsactupon.Similarlytotype2,onedoesnothavetoassumeaprestructuredworld.Evenmoreso,theonlyassumptiononeneedstospeakabouttype3representationsistheexistenceofphysicalsignalsintheworldcapableofactingasstimulitotheagent.

Sincetype2representationsweredefinedasbeingtheresultofperceptionandactionbytheagent,type3representationsareaprerequisitefortype2statestoemerge.

TheImportanceofType2Representations

Itisworthnotingthatthedistinctionofseveraltypesofrepresentationissomewhatconsistentwitharecentsuggestionof"representationasamediatingstate"byMarkman&Dietrich(1998).Firstofall,theseauthorsalsoseetheimportanceofexamininghow"theconcept[ofrepresentation]isusedincognitivemodelsinpractice"(par.4).Theythenproposerepresentationasamediatingstatebetweenperceptualstimuliandanagent'sreactionstothem.Thisviewappliestobothmyrepresentationsoftype2and3.Markman&DietrichfurtherarguethatrepresentationsinartificialintelligencewhatIcalltype1lackthelinktoentitiesoutsidethesystemandthusarenotmediating.

Figure3:Whathappenswhendesigningrepresentationsoftype1.

Although,atfirst,Markman&Dietrichdonotdistinguishbetweentype2and3,theythenmakeanimportantobservationaboutenduringmediatingstates.Forthem,thisisanimportantfeaturedistinguishingsimplereactivefromtrulycognitivesystems.Myargumentiscastalongsimilarlines.Bysayingthatcognitiveagentsdonotneedrepresentations,oneeasilythrowsoutthebabywiththebathwater.Inordertoexplaincognition,oneneedstoexplainenduringmediatingstates(inMarkman&Dietrich'sterminology),orrepresentationsoftype2(inmyterminology).Sincemanyauthorshavefailedtorecognizethis,anapparentgapbetweenresearchonembodiedandsituatedsystemsononehand,andresearchon"higherlevel"cognition,suchaslanguageorreasoningcapabilities,hasemerged.Howconnectionismcanfillthisgap,isexplainedbelow.

ConnectionismandRepresentations

Thedistinctionofthreetypesofrepresentationhelpsclarifyingthemaindifferencebetweenconnectionistandmoreclassicalcognitivistmodels.Firstitisworthlookingatthepicturebehindrepresentationsoftype1alittlemoreclosely(fig.3).Whenassumingthattherepresentationsreflectstructureintheoutsideworld,onemakesthemistakeofincludingoneself(astheobserver)intotheloop.Inorderfor'arepresentationstandsfor(orevenrefersto)astateintheworld'tomakesense,onemustassumethestate(thedenotata)toexistinanexactlyspecifiedway.However,onsecondlook,itbecomesclearthattheonlyplacewherethatstatecanreliablybeseenasexistingisinthemindoftheobserverwhoidentifiedthereferringrelationshipoftherepresentationtobeginwith.

Amoreconsistentpicture(inlinewiththeconstructivisttheoryofcognition(Maturana&Varela1987vonGlasersfeld1988seealsovonGlasersfeld,thisvolume)isthis.Ifwepushtheobserveroutofthisloop,weneedonlyassumetheworldtoconsistofphysicalstatesandsignals,whichacognitiveagentinteractswith.Whenadesignerofacognitivemodel(oranAIprogram)insertsrepresentationsoftype1(betheysymbolicorconnectionistorotherwise)theonlythingtheyrefertoisthedesigner'sownconceptualizationsoftheworld(therealityasperceivedbythedesigner)seefig.3.However,thatindividuallyperceivedrealityneednotbeusefulforthecognitiveagenttobemodeled.Especiallyifthatagenthasnothadthesametypeofexperiences(orisnotevenabletohavethem,sinceitssensorsandmotorcapacityarequitedifferent,asinarobot),insertingrepresentationsoftype1(orassumingsuchobjective,insertablerepresentationstoplayaroleintheagent)cruciallyseverstherepresentationsfromwhattheyaresupposedtoserveinnamelyinhelpingtheagenttoactintelligently.

Connectionismisamodelingframeworkthatifusedproperlycanhelpinpushingthedesignerorobserveroutoftheloop.Onemainideabehindconnectionistmodelsistheirinherentfocusonlearningandselforganization.Withthisfocus,thedesignofmodelsforagentswhichthemselvesactontheirownperceptionsoftheworld(therepresentationsoftype3)andbuildtheirowninternalstatestoactuponappropriately(theirrepresentationsoftype2)ispossible.

Asimpleexampleofrepresentationsoftype2inconnectionsttermsisthefamousmodelbyElman(1990).HeusesarecurrentneuralnetworktolearnthetaskofpredictingsubsequentwordsinasequenceofsimpleEnglishsentences.Thewordsarerepresentedattheinputandtargetoutputaslocalactivationpatterns.Thesearerepresentations

oftype1,sinceonemustassumethatthosewordsexistassuch,andtheyaredirectlymappedtosingleunitsintheinputandoutputlayers.Wordsarepresentedoneaftertheotherandthenetworkistrainedtooutputaprobabilityofwhatthemostlikelynextwordinthesequenceis.

TheinterestingobservationcomesfromElman'sinspectionofthehiddenlayeractivationpatternsaftertraining.Foreachword,hetooktheaveragepatternthatisactivatedwhenthewordisinput,andperformedaclusteranalysisonthesepatterns.Hethenobservedthatthepatternsclusteredinawayroughlycorrespondingtoaclassificationintoverbsandnouns.Looselyspeaking,thenetworkhasdiscoveredconceptsofgrammaticalcategories,andhasarepresentationofthemintermsofhiddenlayersubspaces.Severalaspectsareimportanttonote:

Elmanasthemodeldesignerdidnothavetoassumetheexistenceofgrammaticalcategories(onlyofwords).

Onecannotsafelysaythatthoserepresentationsrefertoanyobjectivelyexistentconcept.Whatlinguistscall'nouns'or'verbs'isdecisivelydifferentfromwhatthenetworkhasdiscovered.Forinstance,nosemanticaspectsofgrammaticalcategoryisincluded,andwouldnotevenbeusefulfortheparticulartaskofthenetwork.

Nevertheless,therepresentationsstandinforsomethingusefulintreatingsentencesandgrammarandthusplayanimportantroleforthenetwork's"actions".

Forthesereasons,therepresentationsarenotoftype1,butoftype2.Theonlyexceptiontotheabovediscussionisthatthenetworkdoesnotexhibitanysignificantactionintheabsenceof"perception"(itsinputs).Thismakestherepresentationshardtodistinguishfromtype3inthiscase.Butthesteptowardtruetype2representationsisobvious.1

Thepicturebecomessomewhatclearernow.Apparentlyitisthefirstnotionrepresentationoftype1thatmanyrecentapproachestocognitivescienceseektoabandon.Whilerepresentationsoftype2and3seemtobestillconsistentwithanemergentist,constructivistviewofcognition,itisthefallacyofseeingrepresentationasmirroringorsomewhatreferringtoanobjectiveoutsideworldwhichmustbeovercome.Thus,whenauthorsspeakabout'nonrepresentationalism'theyshouldinsteadrefertonontype1representations.

TheConnectionistRoutetoEmbodiment

Thediscussionaroundrepresentationinthecontextofconnectionistmodelsmightstillappearabitfarfetched.Takeanytypicalconnectionistmodelsuchasthosebasedonmultilayerperceptronsandbackpropagation(e.g.Elman1990Seidenberg&McClelland1989,Plunkett&Marchman1991).Thosemodelsarerelativelyremotefromanyideaofasituatedembodiedcognitiveagent.Firstofall,thereisnoaction,letaloneinteractionbetweenthesystemandtheenvironment,otherthantheadaptationofthesystem'sweightstopatternsthathavebeencarefullydesignedbytheprogrammer.Thosepatternsindeedmustbeviewedasrepresentationsoftype1,sincetheycanonlybedesigned(e.g.byhandcraftingdistributedpatternsbasedonmicrofeatures)throughreferencetoworldconceptsasconceivedbytheprogrammer.Onlytheinteriorofthemodel,althoughlackinganyinterestingdynamicsinmanycases,appearstooffersomethingnewastheElmanmodelhasexemplified.

Isthiswhereconnectionismends,asVarela(1990)apparentlysuggests?Theanswerprovidedbythispaperisaclear'no'.Asarguedearlier(Dorffner1997),connectionismhasalltherequisitesofgoingallthewaytowardabasisfortrulyembodiedcognitivemodels.Fig.4highlightsthemajorstepsonsucharoutetowardembodiment.Startingfromclassicalcognitivistapproacheswhicharefirmlybasedonrepresentationsoftype1,"traditional"connectionistmodelstakeadecisivesteptowardpermittingatype1notiononlyattheirinputsandoutputs.Suchmodels,throughmechanismsoflearningandselforganization,demonstratehow"internal"representationscanbebuiltfromthetaskoflearninginputoutputbehaviorwhichmustbeseenasonlybeingoftype2,not1.

Buttheinputsandoutputstoaconnectionistmodeldonothavetoberepresentationsoftype1either.Bymovingthoseendsallthewaytosensory

lBycomparingmysuggestionsagainwithMarkman&Dietrich(1998),onenotesthefollowing.Whiletheyseeconnectionistweightmatricesastheenduringmediatingstates,Idistinctivelysuggestactivationpatternsor,inalaterstep,dynamicattractorsinactivationstatespace,asrepresentationsoftype2.

Figure4:Theconnectionistroutetoembodiment.

input(e.g.realacousticinputinsteadofphonologicalfeatures)andoutputs(e.g.articulatormovementsinsteadoffeaturesagain),intheoryamodelisconceivablethatfreesitselfofrepresentationsoftype1altogether.Thisisthecasesincesensoryinputandmotoroutputifstillcalledrepresentationsaremerelyoftype3causalcorrelatesofphysicalsignalsintheenvironment.Thisissymbolizedinfig.4byanextended"towerbridge"metaphorbyCummins&Schwarz(1987)(seealsoDorffner1991).Thelastdecisivestepalmostcomesautomatically.Inordertobuildandtrainsuchamodel,itmustitselfinteractwithitsenvironment,becausepredigestedtasks(suchasmappingawordtoitspasttenseform)becomemoreandmoredifficult,ifnotimpossible,whengoingtosuchinputsandoutputs.Inafirststep,eventhetypeoftaskwillshift,suchasawayfromlanguagetowardmorebasicautonomousbehaviorsymbolizedinfig.4throughanimageofthesimpleneuralnetworkbasedagentsbyPfeifer&Verschure(1992).Butthebasicpremisesforbeingacognitivemodel(andnotjustamodelofreactivebehavior)arestillthereandthecognitiveresearcherisnowfacedwiththeformidabletaskofdesigningtheinteriorofthemodel.Ihavepreviouslycalledthisdesign"metalevelrepresentations"aconceptIwillcomebackto.

Insummary,eventhoughconnectionismwillhavetoshiftsomeofitsfocus,andperhapsalsoitsmodelbuildingblocks,itprovidesthebasicingredientsofbecomingsomethingthatcouldbecalled"appliedconstructivism".Theconstructivistpartisthatofamodelbuildingitsownrepresentations(oftype2),basedonitsownexperience,valueschemesandperceptions,andbeingoptimalandrelevantforthemodelitself,independentofanobserverordesigner.

ImplicationsforConnectionistCognitiveResearch

Twoimportantquestionscomeupwhenviewingconnectionistresearchinthislightofrecenttrendsincognitivescience.

1.Dowehavetostoplookingatempiricaldataandforminghypothesesaboutaspectsofcognition?Oneofthemostimportantrevolutionsincognitivism(ascomparedtoitspredecessor,behaviorism)wasthenewlygainedpossibilitytospeakabouttheinnardsofthemind.Thushypothesesaboutcognitivefunctionscouldbeformedwhichcouldbetestedagainstempiricaldata.Whenresortingtorepresentationsoftype2,whichemergefromtheagent'slearningbehavior,thispossibilityseemstobelostagain.

This,however,isnotthecase.Afterall,cognitivescientistsasmentionedabovestillhavetodesignthemodelstructure(the"metalevel"representations).Itwouldbeabigmistaketoexpectafullygroundedandembodiedconnectionistmodeltolooklikeahugebackpropagationnetwork.Currentmodelsonlypresentuswithtinybitsandpiecesofalargermodel,thestructure,connectivityanddynamicsofwhichwillhavetobebuiltbasedonhypothesestestedagainstempiricaldata.

Furthermore,computationallearningtheory(Anthony&Biggs1992)showsusthatinorderforaproblemtobelearnable,thelearnerneedsbias(i.e.apregiven,orinnate,constraint).Elmanetal.(1996)haveusedconnectionismtospawnanewdis

cussionaboutinnateness.Theyargueforreplacingolder,e.g.Chmoskyan,notionsofinnatenesswithstructuralandotherconstraintsinconnectionistnetworks.Andconstraintsneedtobethere,anditisuptohypothesesandempiricaldatatoidentifywhich.

Agoodexampleishumans'conceptualizationcapability(compareLakoff1987).Ifweobservethatinhumancognitioncategorizationofenvironmentalstimuliplaysanimportantrole,theninsertingabasiccategorizationfacility(as,forinstance,inmodelsbyDorffneretal.1996Kruschke1993Murreetal.1989),intothemodelmeansrepresentingthiscapability.Thisrepresentationisonametalevel,sincenoconreteconceptisrepresentedbutonlythemetaconceptofcategory(and,perhaps,propertiesofhumancategories,suchasprototypicality,basicleveleffectsetc.cf.Dorffner1996).Withinsucharchitecturalconstraints,representationsoftype2canevolvethroughinteractiveexperiencebytheagent.

Onemustnote,however,thatthepermissionofthedesignofarchitecturalconstraintsmeansthattheprogrammerissomehowbackintheloop.Theargumentalsoputforwardpreviously(Dorffner1997)isthatthisnowhappensonadecisivelydifferentlevel.Theonlyalternativewouldbetheinclusionofamodelofevolutionarydevelopmentofarchitectureintotheapproach(asVarelaetal.1991argue).Borrowingterminologyfromlinguistics,onecansaythattheapproachfavoredhereisatypeofsynchroniccognitivescience,whichdoesnotworryabouthowandwhyacertaincognitivearchitecturehasdevelopedasopposedtoamorediachroniccognitivesciencefavoredbyVarelaetal.(1991).Byadoptingasynchronicview,onegetstheopportunityoftestinghypothesesagainstempiricaldataandtodevoteone'seffortstocomplexphenomenaobservedincognitiontoday.Thefeewehavetopayforthisisaframework,whichisnotentirelyfreeofthemodelersownperceptionoftheworld.Somerepresentationoftype1(onametalevel,though)remains.

2.Dowehavetosticktosimplereactivebehavior?Ashasbeenarguedabove,whilegoingalongtheconnectionistroutetoembodiment,thefocusseemstoshiftfrom"higherlevel"cognitionlikeaspectsoflanguagetomore"lowerlevel"behaviorofautonomousrobots.Cognitivescience,however,appearstobemoreabouttheformerthanaboutthelatter.

Thequestioncanagainbeanswerednegatively.Thereisnoreasonwhyoneshouldnotstudyphenomenalikelanguageinthecontextofanembodiedagent(whoseprimarytask,ofcourse,istoavoidobstaclesandthelike).Wejusthavetorealizethatitisnotnecessarilyhumancognitioninallitsextentwearestudying.Agoodexample,althoughnotwithinconnectionism,istheworkonlanguageinautonomousagentsbySteels(1996)andcolleagues.Whyshouldconnectionistsbepreventedfromdoingsimilarthings?

Onecantakeyetanothertwistinansweringthequestion.Ascanbeseenfromlookingattheconnectionistroutetoembodiment,connectionistresearchishighlyrelevanttomanynewtrendsincognitivescience,evenifthemodelsarenotfullyembodied,groundedorsituated.Aslongascognitivescientistskeepthebasicsettingofamodelasbeingembodiedinmind,theyaresafeinbuildingandstudyingmodelswhilelargelyleavingoutimportantfacetsofanembodiedagent(e.g.thatithasaphysicalbodyandisinteractingwithitsenvironment).Theystillarriveatimportantresultsforanewcognitivescience.TheworkbyElman(1990),Seidenberg&McClelland(1989)orPlunkett&Marchman(1991)onlanguagelearningaregoodexamples.Noneofthemapparentlysharemanyfeatureswithworkonembodiedrobotsorsimulatedautonomousagents,butneverthelesscontributemuchtoacognitivesciencethatseesrepresentationsoftype1asobsolete.Inthissense,thesetwobodiesofresearcharemuchclosertoeachotherthantheyaretoclassicalcognitivistapproaches.

WhataboutDynamicism?

Ihavestartedbylistingseveralthemesbelievedtobethemajortrendsinrecentcognitivescience.Amongthemtherewasthenotionofdynamicism.Thisreferstoworkpromotingtheconsiderationofacognitivesystemasaninherentlydynamicone,whichcanappropriatelybedescribedusingthevocabularyandformalismsofnonlineardynamicalsystemstheory(e.g.Port&vanGelder1995vanGelder1995Bickhard&Terveen1995Elmanetal.1996).

VanGelder(1995),forinstance,hasarguedthatdynamicalsystemsneitherinvolverepresentationsnorcomputations.Hepredictedthatafewyearsfromnow,thedistinctionwillnolongerbebetween

symbolicandconnectionistmodels,butonlybetweencomputationalanddynamicones.Connectionistmodelscanbeofeithersideofthisdivision.

Giventheargumentsabove,onecanmaketwoobservations.First,lookingatcognitionfromadynamicviewpointdoesnotmakerepresentationsoftype2obsolete.VanGelder'sfamousexampleofadynamicalsystemtheWattgovernorwould,incognitivescienceterms,correspondtoasimplereactivesystemwithnorealcognitiveabilities.Inotherwords,foradynamicmodelofhighercognitivefunctionsonewouldexpecttosee(dynamic)states(orstatetransitions)thatcanstandinforimmediateperceptionsandthusfulfilltheroleofarepresentationasmentionedabove(compareMarkman&Dietrich1998,par.13).SimilartoBrooks(1991)orVarelaetal.(1991),vanGelderapparentlyreferstotype1whenstatingtherearenorepresentations.

Secondly(assomeauthorsinPort&vanGelder1996exemplify),connectionsimhastheperfectprerequisitesforformingthebasisfordynamicalmodels,especiallywhencontainingrecurrentcomponents,asinElman's(1990)case(seealsoElmanetal.1996).Therefore,connectionismshouldcontinuetoplayalargeroleincognitivescienceevenunderthedynamicistparadigm.

WhereisReality?

Finallywearriveattheimportantquestionofthisvolume:Doesrepresentationneedreality?Giventhedistinctionoftype1through3,thisquestionisrelativelyeasytoanswer.

Representationsoftype3needtoassumearealityasacollectionofphysicalsignals.

Representationsoftype2needarchitecturalconstraints,whichareshapedbysomeabstractconceptofrealityasperceivedbythemodeler(e.g.thatcognitivesystemscategorizetheworld).Theactualrepresentations,however,canbeconceivedofwithoutthenecessityofassuminganobjectiverealityonthelevelofconcreteentities(suchasconcretecategories).

Representationsoftype1arehighlydependentonanobjectivereality,buttheycanbelargelyabandoned.

Thequestionariseswhetheracognitivescientistisstillpermittedtotalkaboutrepresentations,analyzethemormakehypothesesaboutthem.Ifrealityonaconcretelevelcannolongerbeassumed,thebasisforreasoningaboutrepresentationsseemstohavevanished.Orputdifferently,anythingwouldcountasavalidrepresentation,aslongasitguidesbehaviorinsomeway.

Thisadditionalquestioncanalsobeansweredpositively.Asobserversofbothrealcognitivebeingsandcomputersimulatedmodels,noharmisdoneifwetalkaboutrepresentations(oftype2),asiftheywereoftype1(i.e.asiftheycorrespondtoobjectivelyexistingitemsinreality).Thisistrueaslongasourdoingsodoesnotinfluencethemodel'sbehavior.Therefore,contrarytobehaviorism,cognitivescientistsarestillentitledtoreasonaboutmentalstates,aslongastheyrealizethatthosestatesdonotexactlycorrespondtoanyofthescientist'sownconceptsoftheworld.Forinstance,wearesafetoreasonaboutElman'smodelasiftheinternalrepresentationscorrespondtoalinguist'snotionofgrammaticalcategories,andcaninferimportantpropertiesoflanguagelearning.Wearesafeaslongasweonlydesignthegeneralprerequisitesforlearningsuchrepresentations(throughthenetworkarchitecture)insteadofhandcraftingtype1representationsofnounsandverbspriortothetasktobemodeled.

Conclusions

InthispaperIhavearguedthatconnectionistresearch,asamodelingframework,isconsistentwithmostrecenttrendsincognitivescience,fromresearchonembodiedandsituatedagentstodynamicism.Ihavecenteredmyargumentaroundaclarificationoftheconceptofrepresentationbyintroducingthreetypes.Recentapproachestocognitivemodelingabandononlythefirstofthesetypesthenotionofrepresentationasbeingamirrorofanobjectivelyexistentworld.Theothertwotypesareconsistentwithanembodied,dynamicistorconstructivistviewoncognition.Ihaveparticularlystressedtheimportanceoftype2representationasaninternalmentalstatestandinginforanagent'spastperceptionsorexperienceswhichmuchrecentresearchappearstoerronouslyabandonaswell.

StartingfromthisdistinctionIhavearguedthatconnectionismcannotonlyincorporatetheabandonmentoftype1representations,butthatitcanalsoprovideanaturalroutetoembodiedandsituatedmodels.Fromthisconnectionistroutetoembodimentitbecameclearthatcurrentconnec

tionistwork,althoughapparentlydetachedfrommostideasofembodiedandsituatedcognition,isneverthelesshighlyrelevantforthesemodernstreamsincognitivescience.Therefore,aradicaldeparturefromcurrentissuesinconnectionismisnotnecessary,aslongasthebasicsettingofacognitiveagentinteractingwiththeoutsideworldiskeptinmind.

Lastbutnotleastthequestion''Doesrepresentationneedreality"couldbeanswered.Ifweabandonrepresentationsoftype1,theonlyrealitywemustassumeistheexistenceofphysicalsignalsintheenvironment.

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TheOntologicalStatusofRepresentations

MatthiasScheutzComputerScience&EngineeringDepartment,UniversityofNotreDameNotreDame,IN46556,USAEmail:[email protected]

AbstractThegoalofthispaperistoarguethattheontologicalstatusofrepresentationscanonlybeevaluatedwithinatheory.Inotherwords,whatcountsasrepresentation,orwhetheracertainrepresentationisbetterthananotherone,dependssolelyonthe(levelof)descriptionofthephenomenonunderscrutiny.Itisshownhow"representation",beingasemanticnotion,canbedefinedintermsofthenotion"meaning".Forcognitivescience,inparticular,itfollowsthatrepresentations,functioningasmeredescriptivedevicestofacilitateone'sgoalofexplainingandmodelingbrain/thoughtprocesses,cannotinandbythemselvesgiverisetoontologicalorepistemologicalclaims.

Introduction

Representation,aswithallwidelyusedterms,isaratherambiguousnotionthatcarriesalotofsemanticoverweightwithit:inwhatsensedoesaword,forexample,representitsmeaning,alettergradestudents'abilities,theretinalimageobjects,ornuclearmissilespeace?Itisobviousthatonehastorestrictallpossibleconnotationsofrepresentationifonewantstodiscusstheapplicabilityandusefulnessofthisnotionforcognitivescience.

Mostcognitivescientistsuse"representation"todescribetherelationofcertainmind/brain1statestoeventsintheworld,i.e.,the"inner"tothe''outer"perspective,theassumptionbeingthatminds/brainshavetosomehow"represent"whatisgivenintheworldtomakesenseoutofit,orasGardnerputsit:

"[...]thecognitivescientistrestshisdisciplineontheassumptionthat,forscientificpurposes,humancognitiveactivitymustbedescribedintermsofsymbols,schemas,images,ideas,andotherformsofmentalrepresentation."2

Theterm"represent"alreadysuggeststhisusage,since"re""present",beingcomposedof"re"and"present",literallymeans"presentagain".3Itindicatesthatsomethingwhichisnotpresent,butwhichhadbeenpresentedatsomepoint,istobepresentedagain(seealsoGlasersfeld1995).Whatthisreadingmeansforcognitivescienceisthatthebrainexploitsmechanismstokeeptrackofperceivedobjectsandstorethis"impression"inawaythatitcanberetrievedandusedifnecessary.This"storedimpression"isthenlabeled"representationofthestimulu

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