CorrespondingAuthorEllenBialystokDepartmentofPsychologyYorkUniversity4700KeeleStreetTorontoOntarioM3J1P3CanadaEmailellenbyorkucaPsychologicalScienceinthePublicInterest10389 ID: 240348
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BilingualMindsEllenBialystok,FergusI.M.Craik,DavidW.Green,andTamarH.GollanDepartmentofPsychology,YorkUniversity,RotmanResearchInstitute,BaycrestCentre,DepartmentofCognitive,Perceptual,andBrainSciences,UniversityCollegeLondon,UniversityofCalifornia,SanDiegoTheregularuseoftwolanguagesbybilingualindividualshasbeenshowntohaveabroadimpactonlanguageandcognitivefunctioning.Inthismonograph,weconsiderfouraspectsofthisInthefirstsection,weexaminedifferencesbetweenmono-lingualsandbilingualsinchildrensacquisitionoflanguageandadultslinguisticprocessing,particularlyintermsoflexicalretrieval.Childrenlearningtwolanguagesfrombirthfollowthesamemilestonesforlanguageacquisitionasmono-lingualsdo(firstwords,firstuseofgrammar)butmayusedifferentstrategiesforlanguageacquisition,andtheygenerally CorrespondingAuthor:EllenBialystok,DepartmentofPsychology,YorkUniversity,4700KeeleStreet,Toronto,OntarioM3J1P3,CanadaE-mail:ellenb@yorku.caPsychologicalScienceinthePublicInterest10(3)89 129TheAuthor(s)2009Reprintsandpermission:DOI:10.1177/1529100610387084 representsabout235millionpeopleworldwideandthattwothirdsofthechildrenintheworldareraisedinbilingualRecently,evidenceindicatingthatthiscommonexperiencehasasystematicandsignificantimpactoncognitivefunctioninghasaccumulated.Inthisreview,weexaminethenatureofthatimpactacrossthelifespanandconsiderwhattheseeffectscon-tributetoourunderstandingofcognitioningeneral.Webeginbyexaminingthelinguisticdimensionsofbilingualismintermsofchildrenslanguageacquisitionandadultlanguageprocess-ing.Inthesecondsection,weinvestigatetheconsequencesofbilingualismonnonverbalcognitivefunctioning.Thethirdsec-tiondescribesresearchdocumentinghowthebrainsupportsbilingualfunctioningandhowitchangesinresponsetoit.Inthefourthsection,wereviewtheclinicalimplicationsofbilingual-ismfordiagnosisandintervention.Weconcludebyidentifyinganddiscussingsomespecificissuesforbilingualsinsociety.Byadoptingthiscognitiveperspective,thereareanumberoftopicswedonotcover,suchasreading,lexicalandsyntacticprocess-ing,andlinguisticconsequencesofbraindamage,allofwhicharebeyondthescopeofthepresentreview.Therearemanywaystobebilingual:Somepeoplearebornbilingual,someaspiretobilingualism,andothershavebilingu-alismthrustuponthemlaterinlife.Underlyingthesediffer-ences,amyriadoffactorsmakethebilingualexperiencedeeplyheterogeneousandpotentiallyalteritsconsequences.Someofthereasonsforbilingualismincludeimmigration,afamilythatspeaksaheritagelanguage,formaleducationinanotherlanguage,temporaryresidenceinanothercountry,oranationalsituationinwhichtheofficiallanguageisdifferentfromthecommunitylanguage.Eachofthesecircumstancesisassociatedwithadifferentsetofsocial,cognitive,andper-sonalfactors,andthesefactorsundoubtedlyinterveneinaswellasdetermineanypotentialeffectofbilingualism.Eachofthesituationsassociatedwithmultiplelanguageusealsocar-riesdifferentassumptionsaboutexpectationsforeducation,valuesaroundliteracy,standardsforlanguageproficiency,thepurposesforwhichoneorbothofthelanguagesareused,thelevelofcommunitysupportforthehomelanguage,andtheidentityoftheindividualasamemberofamajorityorminorityculture.Therefore,therecanbenosingleoutcomeandnodefi-nitiveconsequencethatfollowsfromincorporatingmorethanonelanguageintodailylife.Andyettheconsequencesofbilingualismaffecteducationalpolicy,socialorganization,andconceptionsofmind.1.LanguageLearningandLanguageUseinLanguageacquisitioninbilingualchildrenThemoststrikingfeatureofayoungchildsacquisitionoflanguageistheextraordinaryeasewithwhichtheprocessappearstoprogress.Perhapsmoreremarkablethanthisachievement,therefore,isthatthisfacilityforlearningacomplexsymbolicsys-temisnotdiminishedwhenthechildfacesthetaskoflearningtwoofthem.Bilinguallanguageacquisitionisaseffortless,efficient,andsuccessfulasmonolingualacquisition.Itisnowclearthatlan-guageacquisitionisnotasimplematterofbiologicalunfolding,assomehadpreviouslybelieved,butratheraprocessthatisfinelytunedtofeaturesoftheenvironmentalinput,thechildsatten-tionalandperceptualabilities,andthedevelopmentofcogni-tiveandconceptualcompetencies.Allofthesefactorsconspireaswelltoshapetheprocessofacquiringtwolanguages.More-over,aswedescribelater,themajormilestonesconcerningcompetenceinsounds,words,andsentencesthatarethefoundationofacquiringlanguagearepassedatequivalenttimesforchildrengrowingupwithonelanguageinthehomeandthosegrowingupinamultilingualhome.Theacquisitionofthephonologicalsystembyinfantshasbeenwelldocumentedforthecaseofmonolingualacquisition:Infantscandetectthecontraststhatdefinethephonologicalsystemforallhumanlanguagesalmostfrombirth(e.g.,/pa/vs./ba/;Eimas,Siqueland,Jusczyk,&Vigorito,1971),buttheirabilitytoperceivethesecontrastsinlanguagesthatarenotheardintheenvironment(e.g.,/r/vs./l/forchildrenbeingraisedinJapanesehomes)beginstodeclineatabout6monthsofage(Werker&Tees,1984;seealsoKuhletal.,2006).Thus,untilabout6monthsold,thereisnodetectabledifferenceintheperceptionofphoneticcontrastsbyinfantsinmonolingualandbilingualenvironmentsbutdivergingpatternsappearasbilin-gualbabiesmaintainanddevelopthecategoricaldistinctionsforthephoneticsysteminbothlanguagesandmonolingualinfantslosetheabilitytodetectcontraststhatarenotpartofthelanguagetheyareabouttolearn(Burns,Yoshida,Hill,&Werker,2007;Sebastian-Galles&Bosch,2005).Byabout14monthsold,infantsbeingraisedinbilingualenvironmentshaveestablishedaclearlydemarcatedphonologicalrepresenta-tionforbothlanguages.Therefore,bilingualinfantsdevelopthephonologicalbasisforbothlanguagesonroughlythesamescheduleasmonolingualchildrendofortheironlylanguage.Itmaybethatitisthisveryearlyexperiencethatleavesitslife-longtraceasaforeignaccentwhenchildhoodmonolingualsattempttolearnnewlanguageslaterinlife.Beyondthephoneticconstituents,infantsalsoneedtolearnthemoregeneralphonologicalstructureoflanguage.Recently,KovacsandMehler(2009a)presentedauditorystimulito12-month-oldinfantswhowerebeingraisedinamonolingualorbilingualenvironment.Thestimuliwerethree-syllablecombinationsthathadthesyllabicstructureofeitherABAorAAB.Thesestimuliwereartificialcreationsandwerenotwordsinanylanguage.Thecrucialmanipulationwasthateachstructurewasassociatedwithadifferentresponsenamely,lookeithertotherightortothelefttoseeaninterestingtoy.Theexperimentalresultsshowedthatthemonolingualbabiescouldlearnonlyoneoftheresponsesbutthatthebilingualbabieslearnedboth,adifferencetheresearchersinterpretedasdemonstratingmoreflexiblelearninginbilinguals.Theyoffertheirresultsaspartoftheexplanationforhowbilingualchildrencanlearntwiceasmuchaboutlanguageasmonolin-gualchildreninthesameamountoftime(althoughitisnotclearthattheydo,aswillbediscussedbelow),butthetaskwasBialystoketal. onlymarginallylinguistic.Ifanything,itismoresimilartowordlearningthantospeechperception,aprocessthatrestsondifferentperceptualandcognitiveprocessesthanphonologi-caldevelopment(Burnsetal.,2007).Infact,bilingualbabiesapplytheirdevelopingphonologicalsystemtothelearningofnewwordsthanmonolingualchildrendo(Fennell,Byers-Heinlein,&Werker,2007),althougharecentstudytesting17-month-oldinfantsraisedwithFrenchandEnglishdidnotreplicatethisfindingandattributedthedifferencebetweenstudiestodetailsofthephoneticinput(Mattock,Polka,Rvachew,&Krehm,2010).Nonetheless,theresultsreportedbyKovacsandMehlerprovidecompellingevidencefordifferentlevelsofperformanceinaphonologicaltaskinthefirstyearoflifethatcanbetracedtotheexperienceofbuildinguptwolinguisticsystems.Undoubtedlythemostsalientevidenceforchildrensprogressinlanguageacquisitioniswordlearning,particularlytheappearanceofthechildsfirstword.Aswiththedevelopingphonologicalsystem,thebasicmilestonesassociatedwiththisachievementaresimilarforchildrenlearningoneormorelanguages.Thechildsfirstwordappearsonaverageatabout1yearold,regardlessofhowmanylanguagesareintheenvironment(Pearson,Fernandez,&Oller,1993)and,moredramatically,regardlessofwhetherthelanguagesarebothspokenoroneisspokenandoneissigned(Petittoetal.,2001).However,twofactorsmaybedifferentformonolingualandbilingualchildren:thestrategiesforwordlearningandtherateandextentofvocabularyacquisition.Onestrategythatallowschildrentorapidlylearnnewwordsistoassumethatnovelwordssignifyunfamiliarobjects,presentingasimplepairingofwordandconcept.Thisstrategyofword meaningassignmentfollowsfromwhatMarkmanandWachtel(1988)positasthemutualexclusivityconstrainttheassumptionthatathingcanonlyhaveonenamealthoughthisassumptionneednotbeinnatelydetermined.Theevidenceformutualexclusivityisthatchildrenappeartocreatemappingsbetweennewwordsandnewobjectsforexample,ifachildhearsthewordbikwhilelookingatacupandanunknownobject,thechildwillassumethatthenovelitemiscalledabik.Butbilingualchildrenalreadyknowthatthingscanhavemorethanonenametheknownobjectcouldbeacuporunetasse.Dobilingualchildrenfollowthestrategyofmappingunknownwordstounknownobjects?Theevidenceismixed,withsomestudiesreportinglessrelianceonthisstrategyforbilingualchildren(Bialystok,Barac,Blaye,&Poulin-Dubois,2010;Davidson&Tell,2005)butothersreportingnodifferencebetweenmonolingualandbilingualchildren(Au&Glusman,1990;Merriman&Kutlesic,1993).Morecon-vincing,however,isevidencefromastudybyByers-HeinleinandWerker(2009)inwhichtheycomparedtheadherencetothisstrategybychildrenlearningone,two,orthreelanguages.Theirresultsshowedasystematicdeclineintherelianceonthisheuristicwiththenumberoflanguagesbeinglearned.Theseresults,inconjunctionwiththosereportedbyKovacsandMehler(2009a)suggestingthatphonologicalwordstructuresareperceiveddifferentlybymonolingualandbilingualchildren,areconsistentwithaviewinwhichtheactualmechanismsofwordlearningusedbymonolingualchildrendifferfromthoseusedbybilingualchildren.Importantly,however,theessentialcognitivelandmarkthatguidesthesemechanisms,namely,thetimeatwhichthechildisabletopro-ducethefirstmeaningfulword,iscomparableforallchildren.Theseconddifferenceinwordlearningbetweenmonolin-gualandbilingualchildrenisinthesizeoftheirdevelopingvocabularies.Asinphonologicaldiscriminationandfirstwordproduction,thetimetableforthecriticalmilestoneissimilarforchildrenwithbothtypesofexperience.Inthiscase,thecruciallandmarkistheestablishmentofavocabularyof50words,whichisachievedbybothmonolingualandbilingualchildrenatabout1½yearsold(Pearsonetal.,1993;Petitto,1987;Petittoetal.,2001),atleastfortotalvocabularyacrossthetwolanguages.Beyondthat,however,theevidenceiscompellingthat,onaverage,bilingualchildrenknowsignificantlyfewerwordsineachlanguagethancomparablemonolingualchildren.Acarefulinvestigationexamininghowmanywordschildrenbetween8and30monthsoldknewineachlanguageconfirmedthat,onaverage,thisnumberwassmallerineachlanguageforbilingualchildrenthanformonolinguallearnersofthatlanguage(Pearsonetal.,1993).Thenumberofwordsinthetotalvocabularyofabilingualchild,however,isdifficulttoestimate:Dopropernamescountforonelanguageortwo?Docognatescountonceortwice,especiallyifthepronuncia-tionisunclear?Dochildishsoundsthatarenotquitewordscountaswordsiftheyhaveaconsistentmeaning?AclearerillustrationoftherelativevocabularysizeofmonolingualsandbilingualscomesfromastudyofchildrenwhowereolderthanthoseinthePearsonetal.(1993)analysis.Bialystok,Luk,Peets,andYang(2010)measuredthereceptivevocabularyofover1,700childrenbetweentheagesof3and10yearsold.AllthebilingualchildrenspokeEnglishandanotherlanguage,withEnglishbeingthelanguageofthecom-munityandschoolforallchildren.Acrossthesampleandateveryagestudied,themeanstandardscoreontheEnglishPea-bodyPictureVocabularyTest(PPVT)ofreceptivevocabulary(Dunn&Dunn,1997)wasreliablyhigherformonolingualsthanforbilinguals.TheseresultsareshowninFigure1.Atleastinoneofthetwolanguagesand,importantly,thelanguageofschooling,monolingualchildrenhadanaveragereceptivevocabularyscorethatwasconsistentlyhigherthanthatoftheirbilingualpeers.Itisimportanttonote,however,thatthedispa-ritieswerenotequivalentforallwords.Inasubsetof6-year-oldsinthesample,allchildrenachievedcomparablescoresonwordsassociatedwithschooling(e.g.,)butbilingualsobtainedsignificantlylowerscoresforwordsassociatedwithhome(e.g.,Therefore,thenatureofthesmallervocabularyofbilingualspeakersofeachlanguagethanthatofmonolingualspeakersisinfactsomewhatcomplex(Bialystok,Luk,etal.,2010).Thehallmarkofhumanlanguage,however,isnotsoundsorwords,butthegrammaticallyconstrainedcombinationsofunitstoformutterancesorsentences.Again,thetransitionintothisstageoflanguageacquisitionoccursonthesametimetableBilingualMinds forchildrenlearningoneormorelanguages:Thefirstwordcombinationsforallchildrenappearatabout1½yearsold(Pearsonetal.,1993;Petittoetal.,2001),withutterancesbecom-ingincrementallymorecomplexonasimilartrajectory(deHouwer,1995).Thedetailsofchildrensincreasinggrammaticalsophisticationappeartobetiedtothespecificlanguage,withexamplesforthispointcomingfromchildrenlearningEnglishandSpanish(Gathercole,1997),EnglishandFrench(Paradis&Genesee,1996),andFrenchandGerman(Meisel,1990).Currenttheoriesoflanguageacquisitionarebasedontheideathatthereisadeepconnectionbetweenwordsandstructure:Grammarispartofthelinguisticsystemandemergesseamlesslywhenthelexiconhasreachedacriticalmass.Thefirstevidenceforstructureoccurswhenthechildknowsabout50words,arelationshipdemonstratedforbothmonolingual(Bates&Goodman,1997)andbilingual(Conboy&Thal,2006)children.Inthissense,discussionofchildrensearlygrammarisnotdifferentinkindfromthediscussionoftheirearlylexicon,buttheissuesintheirdevelopmentpresentthem-selvesindifferentways.Andiflanguageacquisitionisnotguidedbydedicatedmodulesequippedtodetectandrecordgrammaticalstructure,thenwhatdirectsthisprocess?Fromthecognitiveperspective,thelinguisticandcognitivesystemsareintimatelyinterconnected,eachguidingtheotherandprofitingfromthesymbioticrelationship.Whathappenswhenachildislearningtwolanguages?Acrossthemajorlinguisticfeaturessounds,words,grammartheacquisitionoflanguagebymonolingualandbilingualchildrenfollowsasimilartimetableformilestonesthatlargelyreflectcognitiveability,butthelinguisticcompetencethatisdevelopingisdifferent.Partlybecauselinguisticknowledgeforbilingualchildrenisdividedacrosstwolanguages,theorganizationandrichnessoftherepresentationalsystemineachlanguageisdifferentfromthatacquiredbyamonolingualspeakerofoneofthelanguages.Similaritiesindevelopingcognitiveabilitieskeeptheprocessoflanguageacquisitiononacommontimecourse,butvariationininputandusemakethedevelopinglinguisticsystemsquitedifferentbothqualitativelyandquantitatively.Understandingbilinguallanguageabilityandthebilingualmindmorebroadlyrequiresunderstandingtheseinterfacesbetweenthelinguisticandcognitivesystems.TwolanguagesinthemindThebilingualmindpresentsanintriguingsetofpuzzles.Arethetwolanguagesrepresentedinseparateorinoverlappingsystems?Areconceptsduplicatedorsharedacrosslanguages?Dointeractionsbetweenlanguagesfacilitateorimpedelanguageproduction?Howaretheselectionofthetargetlanguageandavoidanceofthenontargetlanguageachieved?Howdoesthebilingualswitchbetweenlanguages,bothinten-tionallyandunintentionally?Noneofthesequestionsappliestomonolinguallanguageuse,sofromtheoutset,thepresenceoftwolanguagesinmindchangesfundamentalaspectsoflan-guageprocessing.Moreover,thesequestionsareallinherentlyaboutcognitivesystemsatleastasmuchastheyareaboutlinguisticones;switchingbetweenrepresentationalsystemsandavoidinginterferenceareprocessesroutinelyhandledbythegeneralexecutivecontrolsystem.Therefore,bilinguallanguageusemustbeintimatelytiedtoacognitivesysteminawaythatislessessentialformonolingualspeech.Itisthose 801003 yearsM=91B=404 yearsM=78B=725 yearsM=155B=1436 yearsM=272B=4587 yearsM=109B=85B=37B=15Age GroupMean PPVT std. score Monolinguals Fig.1.MeanPeabodyPictureVocabularyTest(PPVT)standardscoreandstandarderrorbyageandlanguagegroup(monolinguals,M,vs.bilinguals,B).FromBialystok,Luk,Peets,andYang(2010).Bialystoketal. relationsbetweenlanguageandcognitionthatwillbeexaminedinthissection:Howislanguageprocessingdifferentwhentherearetwofullyelaboratedlinguisticsystemsavailable?Howdoesthatsituationchangethecognitiveprocesseswhoseresponsibil-ityitistomanagethoselanguagesystems?Thereisanactivebodyofresearchexaminingthesequestions,comparinghowbilingualscancarryoutthesetasksintheirtwolanguages(forexcellentreviewsofthisliterature,seeKroll&deGroot,2005).However,thepresentquestionisnottocompareprocess-ingofthetwolanguagesofbilingualspeakersbuttocomparemonolingualsandbilingualsastheyperformsimilartasks.Tounderstandhowthesimpleactofspeakingmaybedifferentformonolingualsandbilinguals,itisnecessarytoacknowledgetwocrucialdifferencesbetweenthesegroups.First,theknowledgebasefromwhichalllanguageprocessingproceedsislessrichorlessinterconnectedforabilingualineachlanguagethanitisforamonolingualspeakerofoneofthoselanguages.Themostsalientdifferenceinthelanguagecompetenceofmonolingualandbilingualchildrenisinthevocabularyscoresobtainedinagivenlanguage,asdescribedearlier(Bialystok,Luk,etal.,2010)apatternthatmaypersistintoadulthood.Althoughitismoredifficulttoattributereliabledifferencesinadultsvocabularysizetobilingualismversusmonolingualismthanitisforthatofchildrenbecauseoftheenormousvariationinadultsknowledgeofwords,thereisnone-thelessevidencethatsuchsystematicdifferencesexist(e.g.,Bia-lystok,Craik,&Luk,2008a;Portocarrero,Burright,&Donovick,2007).Gollanandcolleaguesarguethattheessentialfeatureofbilingualrepresentationsistheweakerlinksthatareestablishedwithinthenetworkbecauseoflessfrequentuseofeachlanguage(Gollan,Montoya,Cera,&Sandoval,2008);sim-plyusingeachlanguagelessoftenproducesweakerconnectionsinthenetworkthanwouldemergefromgreateruse.Inthisview,theknowledgeresourcesunderlyinglanguageperformanceformonolingualsandbilingualswhoarecomparableonmanyothercognitiveabilitiesarenotequivalent.Second,itisnowwelldocumentedthatbothlanguagesofabilingualarejointlyactivatedevenincontextsthatstronglybiastowardsonlyoneofthem.Evidenceforthisclaimcomesfrombothbehavioral(Beauvillain&Grainger,1987;Colome2001;Grainger,1993;Hernandez,Bates,&Avila,1996;Francis,1999;Kroll&deGroot,1997)andimagingstudies(Marian,Spivey,&Hirsch,2003;Martin,Dering,Thomas,&Thierry,2009;Rodriguez-Fornells,Rotte,Heinze,Nosselt,&Munte,2002).OneofthefirstpiecesofevidenceforthisconclusioncomesfromaningeniousexperimentbyGuttentag,Haith,Goodman,andHauch(1984,Experiment2).Oneachtrial,bilingualparticipantsviewedaworddrawnfromoneoffoursemanticcategories(e.g.,metals,clothing,furniture,andtrees);twocategorieswereassignedtooneresponsekeyandtheothertwocategoriestoasecondkey.Theparticipantstaskwastopressthedesignatedkeytoindicatethecategorymem-bershipofthetargetwordasrapidlyaspossible.Eachstimuluswordalsohadcopiesofafurtherwordaboveandbelowitasflankeritems.Theseflankerswerealwaysintheparticipantsotherlanguageandbelongedtooneoffourcategories:translationsofthetargetword,adifferentworddrawnfromthesamesemanticcategoryasthetarget,awordfromadifferentcategorybutrequiringthesameresponse,orawordfromacategoryrequiringadifferentresponse.Thecrucialresultisthatresponsetimesweresignificantlylongerinthesecondtwoconditions,showingthatparticipantswereunabletoignoretheflankersandthatsomeanalysisoftheflankerscategories(andpossiblyresponses)tookplacedespitethefactthattheflankerswereinthenonusedlanguage.Thisjointactivationofthetwolanguagescreatesauniqueneedforselectioninbilingualsinwhichlanguageprocessingmustresolvecompetitionnotonlyfromwithin-languagealternativesasmonolingualsdotoselectamongclosesemanticneighbors(wordsthatsharesemanticfeatures,e.g.,cupvs.mugLuce&Large,2001;Mirman&Magnuson,2008;Vitevitch,2002)butalsofrombetween-languagealternativesforthesameconcepts(e.g.,cupvs.tasse).Thepredominantviewisthatlan-guageselectiondoesnotnormallyoccurpriortospeech,makingthisselectionpartofbilingualspeechproduction(Kroll,Bobb,&Wodniecka,2006).Forthisreason,asomewhatdifferentsetofattentionandcontrolproceduresisnecessaryforspeechpro-ductioninbilingualsthanisnecessaryformonolinguals(Green,1998).However,thereislessagreementonwhatthosespecialprocessesmightbe.Somestudieshaveshownthatthenontargetlanguageisactuallyinhibitedwhileusingtheotherlanguage(e.g.,Levy,McVeigh,Marful,&Anderson,2007;Philipp&Koch,2009),butothersindicatethatcorrectselectioncanbeachievedbyincreasingtheactivationofthepreferredresponse(Costa,Santesteban,&Ivanova,2006;seeCosta,2005,foradis-cussionoftheseviews).Aswedescribelater,thesealternativesneednotbemutuallyexclusive:Selectiondependsontheactiva-tionlevelofboththetargetitemtobeselectedandthatofthecompetingitems,incorporatingaswellviewsthatrejecttheroleofcompetitionandinsteadfocusonselection(Caramazza,1997;LaHeij,1988;Mahon,Costa,Peterson,Vargas,&Caramazza,2007;Roelofs,2003).Therefore,selectionisfacilitatedbyeitherpreferentiallyenhancedactivationofthetarget,inhibitionofthecompetitor,orboth.Whateverthemechanism,selectionofappropriatelexicalitemsforbilingualsinvolveseitherdifferentoradditionalprocessesthandoesthesameactivityformonolinguals.Takentogether,thedifferencesinthelinguisticrepresentationsanddifferencesintheselectionmechanismsleadtosustaineddifferencesbetweenmonolingualsandbilingualsinfluentspeechproduction.Althoughordinaryconversationdoesnotgenerallysignalobservabledeficitsinbilinguallanguageprocessing,controlledexperimentalprocedurescanrevealmoresubtledifferencesbetweenthesetwogroups.Twosuchfeaturesarethespeedwithwhichtargetwordscanberetrievedinresponsetoacueandthenumberofwordsthatcanbegeneratedtosatisfyacriterion.Evidenceforthefirstcomesprimarilyfromstudiesofpicturenamingorsemanticclassification,andevidenceforthesecondcomesfromstudiesofverbalfluency.Lexicalretrievalinbilinguals.MuchoftheresearchinlexicalretrievalcomparestherelativeabilityofmultilingualspeakersBilingualMinds toperformsuchtasksasnamingthepicturesintheirtwo(ormore)languages(Costa&Santesteban,2004;Hernandez,Martinez,&Kohnert,2000),makingsemanticclassificationsforwordsinthetwolanguages(Dufour&Kroll,1995),ortranslatingbetweenlanguages(Kroll&Stewart,1994).Thepurposeistocomparelexicalaccesstothetwolanguagesand,insomecases,asinthestudybyDufourandKroll(1995),tocomparebilingualswhoaremoreorlessfluentinthetwolanguages.Theissuewearediscussinghereisdifferent:tocomparemonolingualandbilingualspeakersnamingpicturesinthesamelanguage.Thecomparisonisinherentlyfraughtwithdifficulty:Ifweassumethatbilingualsneverhaveidenti-calproficiencyintheirtwolanguagesand,moreover,thateventheirabilityintheirstrongerlanguagemaynotfullyresemblethelanguagecompetenceofamonolingualspeakerofthatlanguage,thenanycomparisonofmonolingualsandbilingualsseemsunfair.Andyet,proficientbilingualsmanagetofunctionperfectlywell,belyingthenotionofanunderlyinghandicap.Thusitmaybethatthetaskofrapidlyaccessingtargetlexicalitemsiscarriedoutdifferentlybymonolingualsandbilinguals,anoutcomethatwouldbeimportantinunderstandingtherelationbetweenlanguageandcognitivesystemsinthebilingualmind.Researchshowsthatbilingualparticipantstakelongerandmakemoreerrorsthanmonolingualsonnamingtasks.UsingtheBostonNamingTask(Kaplan,Goodglass,&Weintraub,1983),bilingualsproducedfewercorrectresponses(Roberts,Garcia,Desrochers,&Hernandez,2002;Gollan,Fennema-Notestine,Montoya,&Jernigan,2007)andmademoreerrorsonaspeededversionofthetask(Bialystoketal.,2008a)thandidmonolinguals.Ontimedpicturenaming,bilingualsperformedmoreslowlythandidmonolinguals(Gollan,Montoya,Fennema-Notestine,&Morris,2005).Similarresults(slowerresponsesinbilinguals)arefoundinbothcomprehend-ing(Ransdell&Fischler,1987)andproducingwords(Ivanova&Costa,2008),evenwhenbilingualsrespondintheirfirstanddominantlanguage.Thesimpleactofretrievingacommonwordseemstobemoreeffortfulforbilinguals.Healthyagingisfrequentlyaccompaniedbyareductioninproductivelanguageabilitiessearchingforwordsandnamesbecomesamoresalientpartofeveryconversation.Consistentwiththistrend,picturenamingiscarriedoutmoreslowlybyolderadultsthanbyyoungeradults,evenformonolinguals(e.g.,Albert,Heller,&Milberg,1988).Therefore,olderbilingualsshouldfindlexicalaccessparticularlydifficult,sincebothageandlanguagestatusareassociatedwithpoorerperformance.Thesituationisevenmoreproblematicforolderbilingualswhomayhavespentthemajorityoftheiradultlivesusingoneoftheirtwolanguages,usuallythesecondlanguage(L2),andhavebeenremovedfromadailycontextthatsupportsthefirstlanguage(L1).TheoutcomeofthissituationcanbeattritionoftheL1.Therefore,difficultiesinperformanceontestsoflexicalaccesssuchaspicturenamingcanbeattributa-bletonormalaging,L1attrition,orboth.ThesepossibilitieswereevaluatedinastudybyGoral,Libben,Obler,Jarema,andOhayon(2008)comparingyoungerandolderHebrew-EnglishbilingualswholivedinanEnglish-speakingorHebrew-speakingsociety.TheirconclusionwasthattheslowerretrievaltimeforolderbilingualadultsintheirL1wascausedprimarilybyattritionofthatlanguageandnotbyaging.Theseresultspointtotheimportanceofgaugingproficiencylevel,suchasvocabularyknowledge,inlinguisticprocessingandinperfor-manceonpsycholinguistictasks.Linguisticdifferencesbetweenmonolingualsandbilingualsgobeyondvocabularysize.Theconsistentresultshowinglongerpicture-namingtimesforbilingualssuggeststhatwordretrievaliscarriedoutdifferentlyforbilingualsthanformonolinguals.Toexploreapossibleexplanationforthiseffect,HernandezandMeschyan(2006)conductedafunctionalmagneticresonanceimaging(fMRI)studyinwhichSpanish-EnglishbilingualswholearnedtheL2inadolescencenamedpicturesinbothlanguages.Theresultsshowedthatnamingthepicturesintheweakersecondlanguageproducedgreateractivityintheexecutivecontrolnetwork,asystemthatwillbedescribedinmoredetailinSections2and3.Extrapolatingtomonolingualperformance,wherenamingisalwayscarriedoutinastronglanguage,itappearsthatthisexecutivecontrolnetworkisinvolvedinwordretrievalforbilingualsinawaynotrequiredbymonolinguallanguageproduction.Wewillreturntothisidealater.Studiesofverbalfluency.Thesecondexperimentalparadigminwhichreliabledifferencesbetweenmonolingualsandbilingualshavebeenreportedistheverbalfluencytask.Thebasicprocedureistoaskparticipantstogenerateasmanywordsaspossiblein60secondsthatsatisfyacriteriondeterminedeitherbythecategory(semanticfluency)ortheinitialletteroftheword(phonologicalfluency).Therearestandardizedver-sionsofthetask,suchasintheDelis-KaplanExecutiveFunctionBattery(DKEFS;Delis,Kaplan,&Kramer,2001)andtheControlledOralWordAssociationTest(COWAT;Strauss,Sherman,&Spreen,2006),thatallowperformancetobeinter-pretedintermsofnormalizedtablesandusedasaninstrumentforneuropsychologicalassessment.TheclinicalapplicationsofthistestareexplainedinSection4,butinthepresentdiscussionweconsiderthetaskasanexperimentaltool.Thesemanticandletterversionsassessdifferentaspectsofcompetenceandengagedifferentprocesses.Thedemandsofcategoryfluencyarecongruentwithnormalproceduresforwordretrievalinthatthemeaningiscuedandwordsassociatedwiththatmeaningareprimedandavailable.Thus,whenaskedtogeneratenamesoffruits,theinherentassociationsamongvariousfruitsinsemanticmemoryfacilitaterecall.Incontrast,theletterfluencyconditionimposesanarbitrarycriteriononwordgeneration:Conversationdoesnotnormallyrequirethegenerationofwordsbyvirtueoftheirinitialletter.Moreover,theletterfluencytaskadditionallyimposesasetofrestrictionsthatexcluderepetitionsofwordsindifferentformsandthereforerequiresmoreintensivemonitoringandworkingmemory.Thus,categoryfluencyisstronglyindica-tiveofvocabularysize(howmanytypesoffruitcanyouname?)andletterfluencyrequiresadditionalandeffortfulproceduresformonitoringandcontrollingattention(howwellcanyoukeepBialystoketal. trackofthewordsalreadyproducedandinitiateanewsearchtosatisfyadifferentcriterion?).Supportingthisinterpretationofdistinctprocessesinvolvedineachcondition,Grogan,Green,Ali,Crinion,andPrice(2009)relatedtheresultsofstructuralMRIscansofhigh-proficiencybilingualstotheirperformanceoncategoryandletterfluencytasks.Theyfoundthatgreymatterdensityinamedialfrontalregion(thepresupplementarymotorarea)andonesubcorticalregion(theleftcaudate;seeSection3fortheneuralbasesoflanguagecontrol)wasrelatedtoletterfluencyperformancewhereashighergreymatterdensityinleftinferiortemporalcortexwasrelatedtosemanticfluencyperformance.Thetypicaloutcomeofstudiescomparingmonolingualandbilingualadultsperformingverbalfluencytasksisforbilin-gualstogeneratefewerwordsthanmonolinguals,withgreaterdisparitybetweengroupsinthecategoryfluencytask(Bialystoketal.,2008a;Gollan,Montoya,&Werner,2002;Portocarreroetal.,2007;Rossellietal.,2000).Inadramaticdemonstration,Linck,Kroll,andSunderman(2009)reportedthatEnglish-speakingcollegestudentslivinginaSpanish-speakingenviron-mentfor1yearproducedfewerwordsonaverbalfluencytestinEnglishthandidmonolingualswhodidnottravelabroadscoresofthestudentswhohadbeenabroadwererestoredshortlyafterreturninghome.Moreover,aswithpicturenaming(Connor,Spiro,Obler,&Albert,2004),performanceinverbalfluencydeclineswithhealthyaging,sothistaskmaybeespe-ciallydifficultforolderbilingualadults(Brickmanetal.,2005).Severalpossiblereasonsforthedifferenceinverbalfluencybetweenmonolingualsandbilingualshavebeensuggested.First,bilingualsmaysimplyhaveasmalleroverallvocabularythanmonolingualsineachlanguage,adeficitthatwouldpartic-ularlyaffectthecategoryfluencytest.Indeed,itisprimarilyoncategoryfluencythatlowerscoresforbilingualshavebeenmostoftenobserved,withsomeresearchersreportingnodiffer-encebetweengroupsinletterfluency(e.g.,Rossellietal.,2000).Second,asdemonstratedintheresearchonpicturenaming,bilingualstakelongertoretrieveeachitem,sothe60-secondlimitinaverbalfluencytrialmaycurtailbilingualperformance.Onepossiblereasonforslowerwordretrievalinbilingualsistheneedtodealwiththecompetitionfromtheotherlanguage,asstatedearlier.Managingthiscompetitiontakestime,andthiscandelaywordproductionforbilingualsandresultinfewerwordsbeinggenerated.Notethatbothofthesereasonsvocabularylimitationsandcompetitionresolutionapplyprimarilytocategoryfluencywheremultipleexemplarsforthegivencategoryareactivated,includingexemplarsfromthenontargetlanguage,andmuchlesstoletterfluency.Incon-trast,letterfluencyrelieslessontherichnessofvocabularyinasemanticdomainandtheautomaticactivationofexemplarsintheotherlanguage.Therefore,thereisnoreasontoexpectmono-lingualsandbilingualstoperformdifferentlyonletterfluencytasks.Infact,theadditionalrequirementsforworkingmemoryandmonitoringintheletterfluencyconditionshouldactuallybilingualswho,aswillbeexplainedlaterinSection2,aregenerallybetterthanmonolingualsintasksrequiringworkingmemoryandmonitoring.Amoredetailedunderstandingofperformanceontheverbalfluencytaskcomesfromexaminingthefunctionshowingtheproductionofwordsinrealtimeacrossthe1minuteallottedtoeachtrial.FollowingthelogicexplainedbyRohrer,Wixted,Salmon,andButters(1995),adeficitinvocabularysizeshouldmanifestitselfinafunctionthatshowsveryfewwordsbeingproducedtowardtheendofthetimeperiodbecausethepoten-tialsetofitemshasbeenexhausted.Inthiscase,monolingualswouldcontinueproducingwordslaterintothetimecoursethanwouldbilinguals.Incontrast,slowertimetoproduceeachitem,possiblybecauseoftheneedtoresolvecompetitionfromthenontargetlanguage,wouldproduceafunctionthatcontinueslongerintothetimeperiodthanonerepresentingfasterretrie-valofthesametotalnumberofwords.Inthiscase,bilingualswouldproducewordslaterinthetimecoursethanThesepredictionsweretestedintwostudiesusingtime-courseanalysistocomparemonolingualsandbilingualsper-formingaverbalfluencytask.AstudybySandoval,Gollan,Ferreira,andSalmon(2010)comparedmonolingualsandSpanish-EnglishbilingualswhoreportedhighproficiencyinbothlanguagesfortheirperformanceonseveralcategoryandletterfluencyconditionsinEnglish,andinasecondexperimentalsocomparedthetimecourseofretrievalfrombilingualstwolanguages(Englishvs.Spanish).InanotherstudybyLuo,Luk,andBialystok(2010),astandardizedversionofthecategoryandletterfluencytasksinEnglishwasadministeredtomono-lingualsandbilingualswhowereeithermatchedonEnglishvocabularyorhadalowerEnglishreceptivevocabulary.Inbothstudies,thebilingualsproducedwordslaterintotheallottedtime,indicatingslowerandmoreeffortfulretrievalforeachwordproduced,likelyduetointerferencefromthenontar-getlanguage(Sandovaletal.,2010).Inaddition,thecompari-sonbetweenthetwoEnglishproficiencygroupsinthestudybyLuoetal.indicatedasecondeffectattributabletovocabularysize.Oncevocabularywasmatched,thebilingualswithEng-lishproficiencycomparabletothatofmonolingualsperformedaswellasthemonolingualsonthecategoryfluencytaskandthanmonolingualsonletterfluency.Havingequatedfordifferencesinvocabularyresources,thebilingualswereabletodisplaybettercontrolthanthemonolingualsintheconditionthatrequiredmonitoringandworkingmemory.Figure2adis-playstheresultsforcategoryfluencyinwhichmonolingualsandhigh-vocabularybilingualsshowidenticalretrievalpatternsbecauseperformanceisdrivenprimarilybyvocabularysize,whichinthiscaseismatched.Figure2bdisplaystheresultsforletterfluency;inthiscase,thehigh-vocabularybilingualsmain-tainahigherproductionratethroughoutthetimecoursethandotheothertwogroupsbecausethetaskadditionallyrequireshighlevelsofexecutivecontrol.Theseresultspointtotheneedtoguaranteethatparticipantswhoareperformingalanguagetaskhavelinguisticresourcesadequatetocarryoutthetask.Withoutexplicitlycontrollingforlanguageproficiency,itisimpossibletolocalizetheeffectsofbilingualismasopposedtotheeffectsofweakerproficiencyinthelanguageoftesting.Moreover,whenproficiencyintheBilingualMinds twolanguageshadbeencontrolledbyusingreceptivevocabu-laryasamatchingvariable,abilingualemergedintheletterfluencytask.Thispatternwasreplicatedinacomparisonbetweenmonolinguals,bilingualswithmatchedvocabulary,andbilingualswithlowervocabularyonasimplebehavioralcomparisonofthenumberofwordsproducedineachofthesefluencytasks(Bialystok,Craik,&Luk,2008b).Clearly,notalltasksrequiringprocessingoflinguisticmaterialareperformedmorepoorlybybilinguals.Controloverlinguisticresources.Tothispoint,thestudiesdescribedhavegenerallyfoundmoreeffortful(longerresponse Fig.2.Numberofitemsproducedasafunctionoftimein(A)categorytaskand(B)lettertaskformonolinguals,high-vocabulary(HV)bilinguals,andlow-vocabulary(LV)bilinguals.Bestfitlinesarelogarithmicfunctions.FromLuo,Luk,andBialystok(2010).Bialystoketal. time,RT)orpoorer(moreerrors)performancebybilingualsthanbymonolingualswhenrapidretrievalofspecificlexicalitemsisrequired.Whenlanguageproficiencyismatched,however,bilingualsperformaswellasmonolingualsincategoryfluency(whichdependsonvocabulary)andbetterthanmonolingualsonletterfluency(whichdependsmoreextensivelyoncognitivecontrol).Therefore,atleastsomeofthedifferencesobservedbetweenmonolingualsandbilingualsonlanguageproductiontasksreflectasimpledifferenceinlinguisticresourcesandmaymaskapotentialadvantageincontroloverthoseresourcesonceproficiencyhasbeenequated.Ifbilingualsdohavebettercontroloverlinguisticresourcesthandomonolinguals,thenitshouldbepossibletodemonstratethisprocessingdifferenceintasksthatrequiremonitoringormanipulationofverbalstimuli.Twotasksmeetthesecriteria.ThefirstisaparadigmdevelopedbyJacoby(1991),calledtheprocessdissociationprocedure(PDP),thatisdesignedtodistinguishbetweenautomatic(familiarity)andcontrolled(recollection)aspectsofmemory.Thesecondisaparadigmcalledreleasefromproactiveinhibition(PI)thatassessestheabilitytomonitoritemsfortheirsource(e.g.,Kane&Engle,2000).Bothparadigmshavebeenwidelyusedinstudiesofcog-nitiveprocessesinvolvedinmemoryperformance.Althoughsubstantiallydifferentfromeachother,theysharethefeaturethatparticipantsareaskedtorememberwordsforlaterrecallwhenaninterveningeventhasmadeitdifficulttokeeptrackofthesourceofthetargetwords.InthecaseofPDP,wordsarepresentedintwolists,ortwoformats(forexample,visuallyororally),andthecrucialrecalltestrequiresrespondingonlytothewordspresentedinoneofthem(forexample,visually)andignoringtheothers.InthecaseofPI,listsofdifferentwordsfromthesamesemanticcategoryarepresentedsuccessivelyandparticipantsareaskedtoreportthewordsonthelistjustheardwithoutreportingwordsfromthepreviouslists.ReleasefromPIisobservedwhenwordsfromadifferentcategoryarepre-sented.Bothtasks,therefore,requiremonitoringandcontroltoattendtothetargetwordsandinhibitiontoavoidmakingerrorsonthedistractorwords.Aspredicted,bilingualsobtainedlowerscoresthanmonolingualsontestsofreceptivevocabularybutperformedbetterthanmonolingualsonbothPDP(Wodniecka,Craik,Luo,&Bialystok,2010)andreleasefromPItasks(Bialystok&Feng,2009).Again,separatingverbalabilityfromcontroloververbalprocessingproducesamorecomplexpictureinwhichbilingualsdemonstratebetterprocessinginthecontextofpoorerverbalperformance.CognitivecontrolandbilinguallanguageAlltheillustrationsoflanguageacquisitionandusedescribedinthissectionhavedemonstratedtheimportanceofconsideringtheinteractionbetweenlanguageandcognitivesystemsinexplainingoutcomesforbilinguals.Bilingualchildrenacquirelanguageonthesametimetableasmonolingualchildren,largelybecausethistimetableisdeterminedbytheprocessofcognitivedevelopment.Asacquisitionproceeds,however,bilingualchildrendevelopdifferenttypesofcompetence(e.g.,smallervocabularyineachlanguage)andprobablyusedifferentstrategies(e.g.,phonemiccuesandmutualexclusivityforwordlearning).Inadulthood,theabilityofbilingualstoeffectivelyuselanguageinsuchtasksaswordretrievalandwordgenerationdependsonbothlinguisticcompetenceandcognitiveproce-duresforaccessandmonitoring.Thus,levelsofvocabularydeterminehowmanywordscanbeassociatedwithameaningfulcategorybutlevelsofcontroldeterminehowmanywordscanbeselectedtofitanarbitraryrestrictivecriterion.Whatisthesourceoftheseinteractions?Onepossibilityisthattheinteractingsystemsaresetinmotionbecausethejointactivationofthetwolanguagesforabilingualcreatesaproblemnotexperiencedbymonolingualsnamely,theneedtoselectfromthetargetsysteminthecontextofcompellingandactivealternatives.Thereissubstantialevidence,describedinSections2and3,thattheresponsetothisconflictistorecruittheexecu-tivecontrolsystemthathasevolvedtoresolveconflictacrossalldomainsofperceptualandcognitiveprocessing.Theconstantuseofthisexecutivecontrolsystemforbilinguallanguageman-agementopensthepossibilitythatthesystemitselfismodified,changingitsvalenceorefficiencyforalltasks.Thatis,theuseofasetofexecutivecontrolprocedurestomanageattentiontolan-guage,toavoidinterferencefromthenontargetlanguage,andtomonitortwosimultaneouslyactivelanguagesmayalterthenatureorefficiencyofthoseexecutivecontrolprocessesmoregenerally.Thispossibilityisexaminedinthenextsection.Toanticipate,theevidencesuggeststhatwhereasbilingualchildrenandadultshavesomewhatlowervocabularylevelsthantheirmonolingualcounterparts,thebilingualspossessanadvantageincognitivecontrolthatgeneralizesbeyondlanguageprocessingtootheraspectsofcognitivefunctioning.2.HowBilingualismAffectsCognitiveFormanyyearsitwasassumedthatwhilebilingualismmightbeanassetforadultsintermsofculture,travel,andtrade,forexampleitwasahandicapforchildrenintheeducationalsystem.Theideawasthatlearningintwolanguagesimposedanadditionalburdenonschoolchildrenwhomustlearntwovocabularies,twosetsofgrammar,andprobablytwosetsofculturalhabitsandexpectations.Thisnegativeviewofbilin-gualismwasatleastquestionedbytheresultsofastudybyPealandLambert(1962).TheygaveabatteryofintelligenceteststoFrench-speakingchildreninMontrealwhowerealsofluentEnglishspeakers.Theyexpectedtofindthatmonolin-gualandbilingualchildrenwouldbeequivalentonmeasuresofnonverbalintelligencebutthatbilingualswouldobtainlowerscoresonverbalmeasures.Totheirsurprise,however,bilingualchildrenoutperformedtheirmonolingualpeersonvirtuallyallofthetests,includingtestsofnonverbalintelli-gence.Furtheranalysisrevealedthattherewaslittlediffer-encebetweenthegroupsonspatial-perceptualtestsbutthatthebilingualchildrenshowedanadvantageontestsrequiringsymbolmanipulationandreorganization.ThislatterfindingBilingualMinds hastheinterestingimplicationthatextraeffortandmoreextensivelearningintheareaoflanguageapparentlyconfersbenefitstomentalabilities,refutingtheideathatlanguageisaseparatemoduleofmindandbrainthatreliesondedicatedprocesses(e.g.,Fodor,1983);instead,languagemustbeviewedasrecruitingprocessesfromthegeneralcogni-tivesystem.Onthebasisoftheirunexpectedfindings,PealandLambertsuggestedthatbilingualchildrenmayshowenhancedmentalflexibility,perhapsasaconsequenceofhavingtoswitchbetweentheirtwolanguages.ThestudybyPealandLambert(1962)maybecriticizedonthegroundsthatfrancophonechildreninMontrealin1960whospokeEnglishwerelikelyofhigherthanaveragesocialclass,oratleastwerethechildrenofintelligentandambitiousparents,andwerethereforelessrepresentativethantheirmono-lingualcounterparts(Bialystok,2001).Nevertheless,thestudywasimportantinshowingboththatbilingualisminchildrenmighthelpratherthanhinderthedevelopmentofotherabilitiesandalsothatlanguagelearningmayinfluencenonverbalcognitiveprocessessupportingtheviewthatlanguageisaseparateandindependentmoduleofmind.SomedecadesfollowingthePealandLambertstudy,support-ingevidenceforabilingualadvantageingeneralcognitivefunc-tioningforchildrenwasfoundinstudiesusingavarietyofexperimentalparadigms.Forexample,Bialystok(1992)reportedthatbilingualchildrenperformedbetterthantheirmonolingualcounterpartsontheEmbeddedFiguresTest.Inthistest,partici-pantsmustfindasimplevisualpatternconcealedinalargercom-plexfigure.Bialystoksuggestedthatthebetterperformanceofbilingualchildrenmightreflecttheirsuperiorabilitytofocusonwantedinformationandignoremisleadinginformation.Thatis,theadvantagemightbeoneofenhancedselectiveattention,involvingtheabilitytoinhibitirrelevantorunwantedinformationandthecomplementaryabilitytoconcentrateonrelevantaspects.Thisinterpretationwasinlinewithanotherdemonstrationinwhichchildrenwereaskedtojudgewhetherphrasesweregram-maticallycorrect,regardlessofmeaning.Bilingualchildrenwerebetterthantheirmonolingualage-matesatignoringthemislead-ingmeaninginsentencessuchasApplesgrowonnosesorWhyisthecatbarkingsoloudly?andstatingthatthegrammarwascorrect(Bialystok,1988).Moregenerally,researchdemonstratedenhancedmetalinguisticawarenessinbilingualchildrencomparedtotheirmonolingualpeers(Ben-Zeev,1977;Cummins,1978;Galambos&Hakuta,1988;Ricciardelli,1992)Whymightbilingualchildrenshowanadvantageintheabilitytoinhibitattendingtounwantedinformationandselectrelevantaspects?Theanswermayfollowfromthesurprisingfindingdescribedearlier:thatwhenbilingualspeakersuseonelanguage,theotherlanguageisstillactive.However,thisdoesnotmeanthatafullanalysisofincomingstimuliinthenonusedlanguageinevitablytakesplace,northatformulatingspeechinonelanguagefullyactivatestherelevantwordsandgrammaroftheotherlanguage.Itseemsratherthatthesecondlanguageisactive,thatsomeanalysisistypicallycarriedout,andthatmoreanalysistakesplacewhencombinationsofcontextandmeaningincreasethelikelihoodthatwordsandphrasesfromthenonusedlanguageareinfactrelevanttothespeakersorlistenersconcerns.Theideathatthenonrelevantlanguageisalwayspotentiallyactiveaccountsforanotherobservationonbilingualspeakers:thattheyoccasionallyintrudewordsfromthealternatelanguageduringspeech.Thoughsuchintrusionsarerare(Poulisse,1997;Poulisse&Bongaerts,1994;Sandovaletal.,2010),theseinstancesreflectoccasionsinwhichtheappropriatewordinthelanguagebeingusedisdifficulttolocateorthewordorphraseinthenonusedlanguageismadeparticularlylikelybecauseofthecontextoritssalience.Bialystok(2001)commen-tedthatsuchintrusionsaremorecommoninbilingualchildrenthaninadultsandarealsomorecommon(anecdotallyatleast)inolderthaninyoungeradults(Sandoval,2010).Inturn,thisage-relatedpatternsuggeststhatthebrainmechanismsresponsi-bleformaintainingattentionalset(inthiscasemaintainingatten-tionontheselectedlanguage)arelesseffectiveinchildhoodandinolderadulthood.Onecandidateforsuchmechanismsisinteg-rityoffrontallobefunctioning,sinceitiswellestablishedthatthefrontallobesdevelopslowlyinchildhoodandareamongthefirstpartsofthebraintodeclineinefficiencyinolderadulthood(Craik&Grady,2002;Diamond,2002;Raz,2000).Oursuggestionisthatbilingualspeakersmustdevelopanunusuallystrongabilitytotemporarilyinhibitaccesstothenonrelevantlanguagewhilemaintainingattentionalset(maintainingconcentration)onthelanguageincurrentuse.Thisabilitymaybemediatedbythefrontallobesandmaythereforeexhibitalifespandevelopmentaltrendthatpeaksinyoungadulthood.Thefurthersuggestionisthattheconstantnecessitytoexercisethisinhibitorycontrolleadstothedevelopmentofparticularlyeffectiveattentionalfunctionsthatarethendrawnontomediategoodperformanceonavarietyofnonverbaltasksrequiringinhibitionofunwantedormisleadingmaterialandconcurrentselectionofrelevantaspects.Inhibitionorselection?Whatwoulditmeantohaveenhancedcontroloverattentionalfunctions?WhenBialystok(2001)surveyedstudiesoftheeffectsofbilingualismonchildrenscognitiveprocesses,sheconcludedthatthemostconsistentempiricalfindingaboutthecognitionofbilingualchildrenistheiradvantageinselectiveattentionandinhibition(Bialystok,2001,p.246).Thisconclusionwasbasedonsomeofherownwork(e.g.,Bialystok,1988,1992)aswellasonagrowingnumberofstudiesfromotherlaboratories.Anexamplethatillustrateshowtheseprocessesareusedbychildrenisthedimensionalchangecardsorttask(DCCS)developedbyZelazo,Frye,andRapus(1996).Thisisagameinwhichimagesthatvaryontwodimen-sions,usuallyshapeandcolor,aresortedaccordingtooneofthem.Forexample,cardscontainingeitherredorbluecirclesorsquaresaresortedintocontainersmarkedbyanimageofeitheraredsquareorabluecircle.Childrenareaskedtofirstsortthecardsbyonedimensionbluesinthisboxandredsinthisboxandthentoswitchtotheothercirclesinthisboxandsquaresinthisbox.ThedramaticfindingisthatyoungBialystoketal. childrencaneasilystatethenewrulebutcontinuetosortbythefirstrule;theyhavegreatdifficultyoverridingthehabitsetupinthefirstphase.Whenthisexperimentwasrepeatedwithbilingualandmonolingualchildrenagedbetween4and5years,thebilingualchildrenweremarkedlybetteratswitchingtothenewrule(Bialystok,1999;Bialystok&Martin,2004).Thisresultwasobtaineddespitetherebeingnodifferenceinpre-switchperformance.Theresearchersthusconcludedthattheconstantneedtoinhibitthenonusedlanguagegeneralizedtomoreeffectiveinhibitionofnonverbalinformation.Thesedemonstrationswerefollowedbystudiesthatextendedtheinvestigationtoadultsandusedotherparadigmsinwhichaprepotentresponsetendencymustbeinhibited.OnesuchsituationisembodiedintheSimontask.Theparticipantviewsascreenonwhicheitheraredorgreensquareappears;therearetworesponsekeys,oneforredsquaresandtheotherforgreensquares.Thekeysarepositionedbelowthesidesofthescreen,andthesquarescanappeareitherimmediatelyabovetheirrelevantresponsekey(congruentcondition)orabovetheotherkey(incongruentcondition).Responselaten-ciesarelongerintheincongruentcase,andthedifferencebetweenincongruentandcongruentlatenciesistermedtheSimoneffect.Ifparticipantsareabletoresistthemisleadinginformationcarriedbyspatialpositionintheincongruentsitu-ation,theSimoneffectwillbesmaller,andwemayconcludethattheyhavewell-developedinhibitorycontrolmechanisms.Usingthislogic,Bialystok,Craik,Klein,andViswanathan(2004)testedgroupsofyoungerandolderadultswhowereeithermonolingualorbilingualonaversionoftheSimontask.Whenthecoloredsquaresarepresentedcentrally,thereisnoconflictbetweenthepositionofthestimulusandsideoftheappropriateresponse,andinthiscasetherewerenodifferencesinreactiontimebetweenmonolingualsandbilinguals,althougholderparticipantstooklongertorespond(Fig.3a).Whenthecoloredsquaresappearedlaterally,however,Simoneffectswerefound,andthesewerelargerformonolingualsespeciallyoldermonolinguals(Fig.3b).Thisevidenceforabilingualadvan-tageininhibitorycontrolinadultsextendedtheresultsofpreviousstudiesonchildren.Moreover,thebilingualadvantagewasespeciallystronginolderadults,suggestingthatbilingualismmayaffordsomeprotectionagainstatleastsomeformsofcognitiveaging.Twootherunexpectedresultsemergedfromthisstudy.Thefirstisthatthebilingualadvantageinresponsetimewasfoundforcongruentaswellasincongruentstimuli.Thisresultwasobtainedinallthreeexperimentsandhasbeenconsistentlyobservedinsubsequentstudies(e.g.,Costa,Herna´ndez,&Sebastian-Galles,2008).Whyshouldtherebeabilingualadvantageforcongruentstimuliwhenthereisnomisleadinginformationtoinhibit?Mostexperimentsofthissortarerunundermixedconditionsinthatexperimentalrunscontainbothcongruentandincongruentstimuli,soparticipantsmustkeeptheruleinmindthroughouttheexperimentalrunandmonitoreachtrialforthetypeofprocessingneeded(conflictornoconflict).Itmaybethatbilingualsarealsobetterattheseaspectsofexecutivecontrol.Thetestofthisconjectureistocheckwhathappensinexperimentscontainingpurerunsofallcongruentorallincongruentstimuli,andthefindingthereisthatthebilingualadvantagedisappears(Bialystok,Craik,&Ryan,2006).ThesecondunexpectedresultfoundbyBialystoketal.(2004)wasthatprolongedpracticeontheSimontaskreducedthedifferencebetweenmonolingualsandbilinguals.InExperiment3,participantsperformedtheSimontaskfor10consecutiveblocksof24trials;bytheendofthesessionthemonolingualdisadvantagehaddisappearedandbothgroupsshowedminimaldifferencesbetweencongruentandincongru-entstimuli.Itisinterestingtospeculatethateveryonemaybeabletoinhibittheeffectsofmisleadinginformationinspecificsituationswithsufficientpracticebutthatbilingualscanlearnthistypeofinhibitionmorerapidly.TheStroopeffectmaybeconsideredthegoldstandardoftestsofinhibition.Inthisparadigm,participantsnamecolorsasrapidlyaspossible,bothwhenthecolorsarepresentedascoloredsquaresonascreenandwhenthestimuliarecolornames(e.g.,red,green,blue)butpresentedinadiffer-entcoloredfont(e.g.,thewordredprintedingreenink).ThedifferenceinspeedbetweennamingcoloredsquaresandthecolorofwordsistheStroopeffect;again,asmallerStroopeffectindicatesastrongabilitytoinhibitthemisleadingtendencytonamethewordratherthanitscolor.Bialystoketal.(2008a)testedgroupsof24youngerandolderadultswhoweremonolingualorbilingualonthisparadigm.Infourdiffer-entconditions,participantsnamedthecolorofdisplaysofnamedacolorwordpresentedinblackfont,namedthefontcolorofwordsprintedintheirowncolor(congruentcondition),andnamedthefontcolorofwordsprintedinadifferentcolor(theincongruentStroopcondition).Forthecontrolconditions(namingwordsandcoloreds),namingtimeswerefasterforwordsandforyoungerparticipantsbuttherewerenolanguage-groupdifferences.Responsetimesforthecongruentandincongruentcolored-wordconditionsareshowninFigure4asdifferences(positiveornegative)fromthetimetakentonamecoloreds.Thefigureshowsthatcongruentstimuliareassociatedwithrelativelyfasterresponsetimes(afacilitationeffect)andareindicatedbypositiveRTdifferencesinthefigure,whereasincongruentstimulishowtheclassicStrooppatterninwhichslowerresponsetimesareindicatedbynega-tiveRTdifferences.Statisticalanalysisrevealedasignificantthree-wayinteractionofage,language,andcongruence;bothyoungerandolderbilingualssustainedsmallercoststhantheirmonolingualpeers,butonlytheolderbilingualsshowedgreaterfacilitation.Wemaythusconcludethattheolderbilingualsexhibitedgreaterdegreesofcognitivecontrolthantheirmono-lingualcounterparts,inthattheybothtookgreateradvantageofcongruentconditionsandatthesametimewerelessimpairedbyincongruentconditions.Youngerbilingualsshowedthelattereffectbutnottheformer.OtherresultsfromtheBialystoketal.(2008a)studyincludedabilingualadvantagefortheolderparticipantsinaversionoftheSimontaskusingdirectionalarrows,butnobilin-gualadvantageforeitheragegroupinaconditioninwhichBilingualMinds participantswereinstructedtorespondinthedirectionoppositetothatindicatedbyasinglearrow.TherewasalsonobilingualadvantageontheSustainedAttentiontoResponseTask(SART;Robertson,Manly,Andrade,Baddeley,&Yiend,1997),whichinvolveswithholdingaresponsetothenumber3whilerespondingrapidlytoallotherdigits.Inboththeselattertasks,theparticipantcanencodeasimplerule(e.g.,pressintheoppositedirection)andthenfollowthatrule;thereisessentiallynoneedtoselectoneaspectofthestimulusandsuppressotheraspects,aswiththeSimon,Strooporflankertasks.Thisaccountclaimingnoneedforcontrolinthesetasksisreinforcedbyotherresultsshowingnobilingualadvantageinchildrenwhowereinstructedtoresponddaywhenshownapictureofadarknight,andnightwhenshownasunnyday(Martin-Rhee&Bialystok,2008).Theseinvestigatorsalsoreplicatedthefindingofnobilingualadvantageinchildrengiventhereversearrowtask,eventhoughthesamechildrendemonstratedabilingualadvantagewhenthearrowswereplacedinsidepositionsonthedisplaythatcreatedconflict.Thispatternofpresenceandabsenceofadvantagesisinlinewiththedistinctionbetweeninterferencesuppression 30-3940-4950-5960-6970-7930-3940-4950-5960-6970-79 Monolingual Bilingual Fig.3.Meanreactiontime(RT)onSimontaskbydecadeformonolingualsandbilinguals.GraphashowsmeanRTforthecontrolcondition;GraphbshowsmeanRTcostasthedifferencebetweencongruentandincongruenttrials(Simoneffect).FromBialystok,Craik,Klein,andViswanathan(2004). FacilitationCost Young Mono Young Biling Old Mono Old Biling Fig.4.Meanreactiontime(RT)andstandarderrorforfacilitationandcostforyoungmonolingualsandbilingualsandoldermonolingualsandbilingualsintheStrooptask.Thevaluesaremeandifferencesfrombaseline(0millise-conds)calculatedastheaveragedifferenceinthetimetakentonamecolorsfromthetimetakentonameneutralstimuli(s).FromBialystok,Craik,andLuk(2008a).Bialystoketal. responseinhibitionproposedbyBunge,Hazeltine,Scanlon,Rosen,andGabrieli(2002).Interferencesuppressionreferstosituationsinwhichmisleadinginformationevokesafaultyresponseandmustthereforebeignoredorsuppressed;thisappearstobethetypeofsituationthatbilingualscandealwithparticularlywell.Responseinhibitionistheabilitytoavoidrespondinginerrortoahabitualorhighlysalientcue,andbilin-gualsshownoadvantageunderthesecircumstances.Inotherwords,thebilingualadvantageappearswhenthereisconflictbetweentwopotentialresponses,butnotwhenthereisaneedtowithholdasingleprimedresponse.Asafinalconvergingpoint,Kimberg,DEsposito,andFarah(1997)havecommentedthatpatientswithlesionsintheprefrontalcortexareimpairedontasksinwhichthemostsalientcueevokesthewrongresponseandmustthereforebesuppressedtoselectthecueassociatedwiththecorrectresponse.Ifoneeffectofbilingualismistofrontallobefunctions,itfollowsthatbilingualchildrenandadultsshouldbeadeptattasksinvolvinginterferencesuppression.Convergingevidencefromotherstudieshassupportedtheconclusionthatbilingualsshowstrongabilitiestoinhibitirre-levantorinterferinginformation.Ziedandcolleagues(2004)foundthatbalancedbilingualadultsofvariousagesrespondedmorerapidlythanunbalancedbilingualsontheStrooptask.Inaningeniousseriesofstudies,Philippandcolleagues(Philipp,Gade,&Koch,2007;Philipp&Koch,2009)askedparticipantswhowerefluentinthreelanguages(English,French,&German)toswitchamongtheirlanguagesinanumbernamingtask;thus2wasnamedeithertwo,deux,orzweidependingonaconcurrentinstruction.ThemainfindingwasthatnaminginlanguageAwassloweronthethirdtrialofasequenceABAthaninasequenceCBA.Thatis,A(e.g.,Frenchnaming)wassloweronthethirdtrialofasequenceFrench,German,FrenchthanitwasinthethirdtrialofasequenceEnglish,German,French,suggestingthatinthefirstsequenceFrenchwassubjectedtoatemporaryglobalinhibi-toryeffecttopermitaccesstoGerman.WhenFrenchwasneededimmediatelyafterthat,negativeprimingslowedaccesstothetargetname.Althoughthereisnobilingualthisstudymonolingualswerenottested,andthestudywasnotdesignedtotestforbilingualadvantagestheresultsdemonstratetheroleofageneralinhibitoryprocessappliedtothenonusedlanguageinordertoavoidinterferenceeffectsintheselectedlanguage.NegativeprimingwasalsousedinanexperimentbyTreccani,Argyri,Sorace,andDellaSala(2009).Targetscouldappearatoneoffourpositionsonascreenandparticipantsrespondedbypressingoneoffourkeys.Whenatargetwasaccompaniedbyadistractorstimulusinanotherlocation,bilingualadultswerebetterabletoignoreit(interferencesuppression)andsomadefewererrorsthandidtheirmonolingualcounterparts.However,thebilingualsweremorenegativelyaffected(makingmoreerrorsthanmonolinguals)whenatargetappearedinthepositionpreviouslyoccupiedbyadistractoritem.Inthissituation,thebetterinhibitionofthedistractorcarriedovertothenexttrial,providingmorenegativeprimingtothebilingualparticipants.Theauthorsconcludedthatwhetherbilingualsshowanadvantageoradisadvantagerelativetomonolingualsdependsontaskcharacteristics.Thestudiesreviewedsofarhaveendorsedthenotionthatthebilingualadvantagefoundinthesestudiesisduetoanadvantageininhibitionorsuppressionofinterferingmaterial,butthereremainsthepossibilitythatbilingualsshowanadvantageinthepositiveselectionofwantedinformation.Thelatterinterpreta-tionisfavoredbyanumberofinvestigators.Costa,Miozzo,andCaramazza(1999)arguethatalthoughlexicalcandidatesinbothlanguagesareactiveduringtheplanningofanutterance,theintentiontospeakinonelanguageratherthananothereffectivelyrestrictsselectiontowordsinthetargetlanguage.Colzatoandcolleagues(Colzatoetal.,2008)setouttocomparewhattheytermedactiveinhibitionwithreactiveinhibition.Byactiveinhibitiontheymeangeneralglobalsuppressionofthenonrele-vantlanguage(cf.inhibitioninthestudybyPhilipp&Koch,2009)andbyreactiveinhibitiontheymeanlackofsuppressionofspecificinterferingstimuli.Evidenceforthelatterwasfoundintheattentionalblinkparadigminwhichdetectionofatargetstimulusisimpairedifthesamestimuluswaspresentedearlierinarapidsequenceofevents.Theauthorspredictedthatifbilin-gualsshowmorereactiveinhibition,thentheywillprocessthefirstpresentationofthetargettoagreaterextentandthereforeshowlesssuppressionofinterveningitems.Withoutsuppres-sion,theseitemswouldtheninterferemorewiththesecondpresentationofthetarget,creatingalargerattentionalblinkeffect.Thisiswhattheyfound,andsotheysuggestedthatthebilingualadvantageisnotduetoconstantexerciseofinhibitionofthenonusedlanguagebutrathertoprolongedpracticeatmaintainingtherelevantattentionalset,thoughtheygrantthatsuchselectionmayinvolvestronginhibitionofcompetingitems.Thedebateoverinhibitionversusselectionmayrestonafalsedichotomy:Inhibitionmaynotbeanall-or-nonephenom-enonbutmayratherbefoundtodifferentdegreesundersomecircumstances.Onesuchfactorthatmightinfluencethedegreeofinhibitionrequiredtoperformataskistheeffectofcontext.Kroll,Bobb,Misra,andGuo(2008)describeworkshowingthatcross-languagecognateswereactivated(thatis,namingawordinonelanguageactivateditscognateinbilingualssecondlanguage)whenawordwasnamedoutofcontext,butthiscognatefacilitationwaseliminatedincontextsthatweresemanticallyconstrainedinthattherequiredwordwasmoreclearlydeterminedfromthecontext(seealsoSchwartz&Kroll,2006;vanHell&deGroot,2008).Onepossibility,then,isthatthetowhichbothlanguagesareactivemaynotbeconstantbutmayvaryprobabilisticallywiththecontextualconstraintsprovidedbylanguage,topic,andtheexternalAnotherpossibleeffectofcontextwassuggestedbyCosta,Herna´ndez,Costa-Faidella,andSebastian-Galles(2009).Theytestedmonolingualsandbilingualsonversionsofaflankertaskinwhichdifferentconditionscontainedvaryingproportionsofincongruenttrials:8,25,50,or92(thereforemixedwith,75,50,or8congruenttrials,respectively).Thebilin-gualadvantagewasstronglypresentinthe50/50version,BilingualMinds reducedinthe75/25version,andentirelyabsentinthe92version.Theauthorsconcludethatthebilingualadvantageisrelatedtotheirgreaterabilitytomonitortheenvironmentwhentheprobabilityofchangeishigh,asinthe50/50condition.Underlow-monitoringconditions,whenmostofthetrialsareofonetype,thereislittleneedtomonitorandthusnobilingualadvantageisfound.ThenotionofmonitoringissimilartotheideaofsetmaintenancedescribedpreviouslybyColzatoetal.(2008).Costaandhiscolleaguesalsomaketheinterestingpre-dictionthatbilingualswholiveinsituationsinwhichtheirtwolanguagesareusedindifferentcontexts(e.g.,Italianathome,Englishatwork)rarelyneedtomonitorlanguagechangesandsomaynotdevelopstrongmonitoringabilitiesandthusshownobilingualadvantage.Finally,thedistinctionbetweenselectionandinhibitionwasexaminedinastudybyHerna´ndez,Costa,Fuentes,Vivas,andSebastian-Galle´s(2010),inwhichparticipantsrapidlyjudgedhowmanyitems(lettersornumerals)appearedonascreen.Theitemsappearedeitherinacongruentform(1,22,333),anincon-gruentforminwhichthedisplayednumeralsdidnotmatchtherequiredresponse(e.g.3,11,222),oraneutralform(Z,GGG,MM).Relativetotheneutralbaseline,congruentstimuliwereassociatedwithfasterresponsetimes(facilitation)andincongru-entstimuliwithslowerresponsetimes(interference).Bilingualparticipantsshowedsmallerinterferenceeffectsbutlargerfacil-itationeffectsthantheirmonolingualcounterparts(cf.Bialystok,Craik,&Luk,2008a),sotheiradvantagemaybedescribedasoneofbetterexecutivecontrolofperception/actionprocessing.TheconclusionofCostaandcolleaguesisthatthebilingualadvantageisreasonablyhighlevel,involvingtop-downworkingmemoryprocesses,andismanifestedasenhancedsetmainte-nanceormonitoring.Thisdescriptionsuggeststhattheadvan-tagemaystemfromenhancedfrontallobeeffectiveness,assuggestedbyBialystok(2001).SelectiveattentionandexecutivecontrolWehaveseenintheprevioussectionthatresearchaimedatassessinginhibitoryabilitiesinbilingualsevolvedtoconsidersuchconceptsasselection,setmaintenance,andmonitoring.However,thedistinctionbetweentheseconceptsandnotionsofattentionandexecutivecontrolisdifficulttodiscern.Inmanyways,alltheseconceptsaresimplyaspectsofattentionandexecutivecontrol.Therefore,inthissectionweconsiderworkthatassessesgroupdifferencesinattentionandcontrolmoredirectly.Costaetal.,(2008)examinedtheperformanceofmonolin-gualandbilingualparticipantsontheattentionalnetworktask(ANT)developedbyFan,McCandliss,Sommer,Raz,andPosner(2002).ThebilingualswereyoungadultswhospokeCatalanandSpanish;themonolingualswereyoungadultswhospokeSpanishonly.TheANTtaskassessesabilitiesonthreedifferentattentionalnetworks:alerting,orienting,andexecu-tivecontrol.Thetestisaflankertaskinwhichtheparticipantrespondstothedirectionofacentralarrowthatisflankedbytwoarrowsoneachsidepointinginthesame(congruent)ordifferent(incongruent)directionasthecentraltargetarrow.Alertingisstudiedbypresentingacuebeforethetargetstimu-lus,andorientingisassessedbythepresenceorabsenceofacuesignalingthefuturespatialpositionofthetarget.Theresultssupportedthehypothesisofgreaterattentionalcontrolbybilingualsinthealertingandexecutivecontrolnetworks.Thebilingualparticipantsrespondedfasterthanthemonolingualsonallconditionsandshowedasmallercostfortheincongruenttrials,indicatingbetterconflictresolution.Twofinalresultsfromthisstudywerethatthisbilingualadvantagedisappearedbythethirdblockoftrials(cf.Bialystoketal.,2004,Study3)andthatbilingualshadsmallerswitchingcostsbetweencongruentandincongruenttrials,apointtowhichwewillreturn.SimilarresultswereobtainedbyCarlsonandMeltzoff(2008)withmuchyoungerparticipants.Theyadministeredabatteryofexecutivefunctionteststo50kindergartenchildrenwhowereEnglish-speakingmonolinguals,English-Spanishbilinguals,orchildrenwhowereinalanguageimmersionele-mentaryschool.Themajorfindingwasthatthenativebilingualchildrenperformedbetterontheexecutivefunctionbatterythandidbothothergroups,oncedifferencesinage,vocabulary,andparentseducationandincomelevelswerestatisticallycontrolled(recentworkextendsthisfindingthatbilingualismcanoffsetthenegativeeffectsoflowersocioeconomicstatusontaskswitchingtoyoungadults;Prior&Gollan,2010).Theeffectswerespecifictoonlysomeaspectsofcontrol:Therewerenobilingualadvantagesinsuppressingamotorresponseondelay-of-gratificationtasks(responseinhibition)butsignificantadvantagesonconditionsrequiringmemoryandinhibitionofattentiontoaprepotentresponse(interferencesuppression;cf.Martin-Rhee&Bialystok,2008).Theauthorsconcludebyendorsingthenotionthatlanguageexperiencescaninfluencefurtherdevelopmentoffrontallobefunctionssuchasinhibitionandthecontrolofattention(p.293).TaskswitchingThefeaturesofexecutivecontroldiscussedtothispointaresomewhatinvisibleinordinarycognitiveperformance.TheinterferencesuppressionthatallowsustoperformaStrooptaskorignoremisleadingflankersintheANTseemstohavelittleroleineverydaycognition.Amorenoticeableaspectofexecutivecontrolmightbetaskswitchingtheabilitytomoveeasilybetweentwotasks,keepingtwoprotocolssimultane-ouslyactive.TaskswitchingmightcomeclosesttothespecialprocessesbilingualsengageinastheyswitchbetweenInoneofthefirststudiestofindpositivethingstosayaboutbilingualism,PealandLambert(1962)suggested,aswenotedearlier,thatbilingualchildrenmayshowanadvantageinmen-talflexibilityanideapresumablystemmingfromthefactthatbilingualsmustswitcheasilyfromonelanguagetoanother.Alargebodyofresearchinvestigatestaskswitching,typicallybyaskingparticipantstoclassifyalongseriesoftwo-dimensionalstimulibyonecriterionortheotherasrapidlyaspossible.SuchsortingtimesarerelativelyshortwhensuccessivetrialsBialystoketal. continuewiththesamecriterion(e.g.,continuesortingbyshape),butswitchingcostsareincurredwheninstructionschangetosortbytheotherdimension(e.g.,switchandsortbycolor).Somerunsoftrialsinvolveonlyonedimension(e.g.,alltrialsrequiresortingbycolor),soitisalsopossibletomeasurecosts,definedasthedifferenceintimetakentoclassifyasetoftrialsundersingle-anddual-criterionconditions(Meiran&Gotler,2001;Pashler,2000).Typically,sortingtimesarelongerwhenitisnecessarytobearinmindtherequirementtoswitchwhentheinstructionchanges.Severalstudieshavenowexploredmonolingualbilingualdifferencesinsuchparadigms,withthepredictionthatbilingualsshouldshowreducedcosts,owingperhapstotheirprolongedpracticeinswitchinglanguagesandmonitoringwhichlanguagemaybespokeninwhichcontext.Thepredictionwithregardtowhichtypeofcostmightbeaffectedbybilingualismislessclear.Totakeananalogousdifferencebetweenindividualsdevelopmentandagingoverthelifespanthetypicalfindingisthatyoungeradultshavesmallermixingcoststhanchildrenorolderadultsdo,whereastheagegroupsdonotdiffermarkedlyonlocalswitchcost(Reimers&Maylor,2005;forreview,seeMayr&Liebscher,2001).Therelativelylargevalueformixingcostsinyoungchildrenandolderadultswasspeculativelyattributedtotheirgreaterdifficultyinsimultaneouslymaintainingtwotasksets.Givenbilingualsapparentadvantageinmaintainingtaskset(Colzatoetal.,2008),itshouldfollowthattheyshouldalsoshowreducedmixingcosts.ThisresultwasindeedreportedbyBialystoketal.(2006)inanexperimentinwhichpartici-pantsneededtorespondonthesameoroppositesideasatargetdependingonacue.Participantsperformedsingle-taskrunsinwhichonlyonecuewasusedandmixedrunsinwhicheithercuemightappear.Responsetimestothetargetwereslowerundermixedconditions,andmixingcostsweregreaterformonolingualparticipants.Threeothertask-switchingstudiesinvestigatingmonolin-gualandbilingualcollegestudentshaveyieldedmixedresults.First,PriorandMacWhinney(2010)askedparticipantstoclas-sifystimulibycolor(red/green)orshape(circle/triangle).Theyfoundnomixing-costadvantagetobilingualsandnospeeddifferencesbetweenthetwogroupsonnon-switchtrials,butthebilingualswerefasterthanmonolingualsonswitchtrialswheninstructionschangedtosortonthealternatedimension.Thus,theirstudyfoundalocalswitch-costadvantagetobilin-gualswithnomixing-costadvantage.Subsequentexperimentsreplicatedtheswitchingadvantageinbilingualswhoreportedthattheyfrequentlyswitchedlanguagesandnoswitchingadvan-tageinalessbalancedgroup,althoughthisless-balancedgroupexhibitedsignificantassociationsbetweenfluencyinanondomi-nantlanguageandswitchingandmixingcosts(Prior&Gollan,2010).Theseresultssuggestdissociationsofswitchingandmixingcostswithrespecttogroupdifferencesandimplythatmultipleaspectsofbilingualismmayinfluencetaskshifting.Frequentlanguageswitchingmayleadtotask-switchingadvan-tages,whereasclosemonitoringofwhichlanguagemaybespokenwhen(andavoidingswitching)mayleadtotask-mixingadvantages.Athirdstudyprovidesclueswithrespecttotheoriginofthemixingadvantage.Inthisstudy,Herna´ndez,Martin,Barcelo,andCosta(2010)alsousedacolor shapeswitchingtasktotestyoungadultSpanish-CatalanbilingualsandSpanish-speakingmonolinguals.Arulewassetatthebegin-ningofarun(e.g.,classifybyshape),thentrialscontinuedforanunpredictablenumberwithoutfurthercuesuntilasecondcuewaspresented.Thesecondcuewaseitherexplicit(e.g.,classifybycolor)orimplicit(e.g.,switchtotheotherruleorrepeatthepreviousrule).Itwasfoundthatswitchingwasslowerthanrepeatingthesamecriterionbutthatthiseffectdidnotinteractwithgroup.Implicitcueswereassociatedwithslowerresponsetimesthanwereexplicitcues,andthiseffectdidinteractwithlanguagegroup;bilingualswerefasterintheimplicitversionbutnotintheexplicitversion.TheresearchersalsomeasuredrestartcostsslowerRTsforthefirsttrialthanforthesecondtrialafterarepeatcue.Bilingualshadsmallercoststhanmonolin-gualsonthismeasuretoo,butagainonlywithimplicitcues.Theseresultssuggestthatthebilingualparticipantswerebetteratmain-tainingthecurrentset,monitoringthechangingsituation,andupdatingwhennecessary.AlthoughthetaskwassimilarinmanyrespectstothatusedbyPriorandMacWhinney,theinstructionswerepresenteddifferently,andthebilingualsuseoftwoverysimilarlanguagesmightaccountforthedifferencesinresults.Ifthatisthecase,onewouldneedtobecautiousaboutgeneraliz-ingaboutdifferencesinlocalandglobaltaskswitchingbetweenmonolingualsandbilingualswithoutconsideringfurtherdetailsoftheparticipantsandtasksituation.Therearestilltoofewstudiestoconcludemuchthatisdefinitiveontheeffectofbilingualismontaskswitching.Betterbilingualperformanceformixingcosts(Bialystoketal.,2006)anddealingwithimplicitcues(Herna´ndezetal.,2010)suggeststhattheadvantageisinmonitoringorsetmain-tenance,buttheresultsofthePriorandMacWhinney(2010)studyspeakmoretothenotionofgreatermentalflexibilityorgreaterinhibitorycontrol.Inaddition,bilinguallanguageusemayrequiredifferentunderlyingcontrolprocessesandmaythereforeleadtodifferentprocessingadvantages(Prior&Gollan,2010).Thefewcurrentstudiesinvolvemanydiffer-encesinmethodsandinparticipants,sothetraditionalcryofmoreresearchisneededisverymuchthecasebeforedecisiveconclusionscanbedrawn.BilingualismandmemorySincebeingbilingualnecessarilyentailsthemanagementandappropriatedevelopmentoftwolanguagesystems,itmakessensethatthesespecialskillsofmentalmanagementshouldalsoapplytoaspectsofattention,conflictresolution,andcognitivecontrol.Butshouldbilingualismconferbenefitsonothercognitivefunctionsonmemory,forexample?Theanswermaydependsubstantiallyonthetypeofmemorybeinginvestigated.Workingmemory(themanipulationofsmallamountsofmaterialheldbrieflyinmind)isgenerallyconsideredtobeeitherpartof,orcloselyrelatedto,executiveprocesses,sobilingualadvantagesmightbeexpectedwithsuchparadigms.BilingualMinds However,performanceonsemanticmemorytasks(tappingstoresofacquiredknowledge)islikelytoreflectexperiencewiththetypeofinformationtested.Giventhatwehaveseenthatbilingualvocabularylevelsaretypicallylowerthanthoseofcomparablemonolinguals,wemightexpectthatretrievalofverbalinforma-tionwouldbepoorerinbilingualparticipants,and,asdescribedinthefirstsection,performanceonnamingtasksandothertasksoflexicalretrievaldoinfactshowthispattern.Moreover,perfor-manceonepisodicmemorytasksmayagaindependonthemate-rialinquestion.Forbothworkingmemoryandepisodicmemory,theevidenceismixed.InoneconditionoftheSimontaskreportedbyBialystoketal.(2004),colorpatcheswerepresentedcen-trallyandsorequirednocognitivecontrol,andparticipantsrespondedtothecolorbypressingoneoftworesponsekeys.Inoneversion,twopossiblecolorsmappedtothetwokeys,andinthesecondversion,fourpossiblecolorsmappedtothetwokeys,withtwocolorsassociatedwitheachkey.Thefour-colorversionhasgreaterdemandsonworkingmemory,soworkingmemorycostsweretakenasthedifferencebetweenthetwo-colorandthefour-colorversions.Bilingualparticipantsaged30to80yearsshowedsmallercoststhandidtheirmonolin-gualcounterparts,andwerethereforedeemedtoshowabilin-gualadvantageinworkingmemory.Thisadvantagehasobvioussimilaritiestothebilingualadvantageinmixingcostsfoundinsomestudiesusingthetask-switchingparadigm.Theresultsofotherstudiesarelessclear.Bialystok,Craik,andLuk(2008a)gaveolderandyoungeradultbilingualsandmonolingualstwotestsofworkingmemory.Theself-orderedpointingtaskrequiresparticipantstorememberwhichof12abstractdrawingshavebeenselectedpreviously;nolanguage-groupdifferenceswerefound.TheCorsiBlocktaskisatestofshort-termspatialmemory,andinthiscasetherewasabilingualadvantageforyoungerbutnotolderadults.Feng(2008)alsopresentedvariousworkingmemorytaskstomono-lingualandbilingualchildrenandyoungadults.Inthelattergroup,shefoundnobilingualadvantageineithertheCorsiBlocktaskorinalphaspanaword-spantaskinwhichparti-cipantsmustmentallyrearrangeashortlistofwordsfromapresentedorderintoalphabeticorder.However,Fengdidfindabilingualadvantageforbothchildren(Feng,Diamond,&Bialystok,2007)andadults(Feng,2008)inatestofspatialworkingmemoryinwhichitemsarepresentedinarandomorderina33matrix(forchildren)orona55matrix(foradults).Thetaskistorecallthepositionsoftheitemsinmatrixorderthatis,startingatthetopleftandprogressingthroughthematrixlefttoright,linebyline.Whetherornotthereisabilingualadvantageinworkingmemorymaydependonthetypeofmaterialusedandthewayinwhichworkingmemoryistested.Workingmemorytasksmaynotbetappingonefixedcognitivemechanismbutratherreflectafamilyofrelatedfunctionsgenerallyconcernedwithholdingandmanipulatingmaterialthatisinthefocusofatten-tion(Cowan,1999)orsimplyheldinmind.Tentatively,itseemstousthatabilingualadvantageshouldbefoundinwork-ingmemory,giventhepreviouslyreviewedevidencesuggestingthatbilingualshaveanadvantageinsetmainte-nance(e.g.,Colzatoetal.,2008)andintherelatedabilitiesofmonitoring(Costaetal.,2009)andupdating(Herna´ndezetal.,2010).Theeffectsofbilingualismonepisodicmemoryarealsounclearatpresent,asonlyafewstudieshavebeenreported.Inthestudiesdescribedearlier,Fernandes,Craik,Bialystok,andKreuger(2007)foundpoorerwordrecallbybilinguals,butWodnieckaetal.(2010)reportedthatthedisadvantagewasovercomewhenmonitoringthelistwasrequired,asintheassessmentofrecollection.Atpresent,therefore,thereislittleclearevidenceforabilingualadvantageinepisodicmemory,sometentativesuggestionsofanadvantageinworkingmem-ory,andaclearforbilingualsintheretrievalofitemsfromsemanticmemory.ThebilingualadvantageacrossthelifespanDoesthebilingualadvantageincognitivecontrolchangethroughthelifespan?Itiswellestablishedthatexecutivecon-trolfunctionsfirstincreaseineffectivenessfromchildhoodtoyoungadulthoodandthendeclineinthecourseofaging(Craik&Bialystok,2006;Dempster,1992;Diamond,2002),soitseemspossiblethatbilingualismmightmodifysuchfunctionsandthatthebilingualadvantagemightalsoshowthesamelifespantrajectory.Ifthebilingualadvantageincognitiveperformancewehaveseeninthissectionisrelatedtotheenhancementoftheexecutivecontrolfunction,howearlymightweexpectthesedifferencestoemergegiventhattheexecutivefunctionsystemislatetodevelop?Similarly,ifthecognitiveadvantagedependsonprotractedexperiencewithtwolanguagesinwhichattentiontosystemsandswitchingbetweenthembecomespracticed,couldsuchadvantagesbefoundinchildrenbeforetheyuselanguageproductively?ArecentstudybyKovacsandMehler(2009b)providesdramaticevidencefortheveryearlyappearanceofabilingualadvantagein7-month-oldinfants.Theinfantswhoparticipatedintheexperimentswerepreverbalbutwereclassifiedasbilingualiftheyhadbeenexposedtotwolanguagesfrombirthbecauseoneparentconsistentlyspoketotheminonelanguageandtheotherparentusedadifferentlanguage.Theresearchersreportedthreeexperimentsinwhichtheinfantslearnedtolookforavisuallyrewardingpuppetatoneoftwosquaresonascreeninresponsetoeitheraspeechstimulus(atrisyllabicnonsenseword)oravisualpattern.Afterthelearningphase,whichwasperformedequallywellbymonolingualandbilingualinfants,anewcuesignaledtheappearanceofthevisualrewardinthealternatesquare.Thus,infantshadtoinhibittheirfirstlearnedresponseandswitchtoanewresponse.Thefindinginallthreeexperimentswasthatthebilingualinfantslearnedtoswitchtotheothersquarebutthemonolingualinfantsdidnot.Theauthorssuggestthatsim-plyperceivingandprocessingutterancesfromthetwolan-guagesduringthefirstfewmonthsoflifeservestoacceleratethedevelopmentofgeneralexecutivefunctionsthatcanthenbeappliedinavarietyofcognitivesituations.ThisinterestingBialystoketal. resultdoesnotnegatethenotionthatsomeformsofthebilingualadvantagearecausedbyinhibitionofthenonusedlanguagebutratherraisestheinterestingpossibilitythattheadvantagemayhavemorethanonecausativemechanism.Whathappensthroughoutlifeoncebilingualismhasmodifiedtheseexecutivecontrolsystems?Doesthebilingualadvantagesimplyincreaseasthepersonaccumulatesexperiencedealingwithtwoormorelanguages?Andifbilingualismofferssomeprotectionagainstage-relatedcogni-tivedecline(Bialystok,Craik,&Freedman,2007;Kave´,Eyal,Shorek,&Cohen-Mansfield,2008),doesanincreaseinthebilingualadvantageoccursimplyasaresultofmonolingualsshowingasteeperdeclineincognitivefunctioningthanbilingualsdo?Oneproblemwithassessingthesepossibilitiesisthatmoststudiesdealwithjustoneagegroup,sotheopportunitytomakelifespandevelopmentalcomparisonsislimited.OneexceptionisanarticlebyBialystok,Martin,andViswanathan(2005)reportingstudieson5-year-oldsandyoung,middle-aged,andolderadultsperformingthesametask,theSimontask.Thisseriesofstudiesshowedabilingualadvantage(fasterRTs)thatwassubstantialinthe5-year-oldchildren,virtuallyabsentin20-year-oldundergraduateparticipants,butpresentagainingroupsofmiddle-aged(30 59)andolder(60 80)adults.Theauthorssuggestedthattheabsenceofanadvantageinyoungadultsmayreflectthefactthatcognitivecontrolismostefficientatthattime,sobilingualismprovidesnofurtherboost.Thetwostudiesinvolvingmiddle-agedandolderadultswereconsistentinshowingalargerbilingualadvantagefortheoldest(60 80)group,becausethedropinefficiencyfromthemiddle-agedtoolderparticipantswasgreaterformonolingualsthanforbilinguals.ThispatternofanespeciallystrongadvantagefortheoldestbilingualparticipantswasalsofoundinthreeotherstudiesbyBialystokandcollaborators(Bialystoketal.,2004,2006,2008a;seeFig.3b).Inthefirsttwosectionsofthisreport,wereviewedbehavioralstudiesoflanguageandcognition,presentingthegeneralfindingthatbilingualchildrenandadultshavesmallervocabulariesandslowerlexicalaccesstimesthandotheirmonolingualpeersbutthattheyalsoshowenhancedcognitivecontrolonavarietyoftasks.Whataretheneuralcorrelatesoftheseeffects?Isitpossibletodetectthesesubtledifferencesthroughneuroimagingtechniques?Inthenextsection,wesurveythecurrentevidenceforstructuralandfunctionalchangesinthebrainthatresultfrombilingualexperience.3.NeuralBasesofLanguageControlinWhetheronespeaksjustonelanguageormorethanonelanguage,everydayuseoflanguageinvolvescognitivecontrol.Bilingualspeakersdonotdevelopaseparatecontrolsystem;rather,aswehavearguedabove,theuseoftwolanguagesimposesonasinglecontrolsystemadditionaldemandsbeyondthoseexperiencedbyspeakersofjustonelanguage.Ourcentralclaimisthatthiscontrolsystemornetworkisusedbybothmonolingualsandbilingualsbutthattheadditionalroleinbilinguallanguageprocessingmodifiesit,changingitsperfor-manceforalltasks.InSection2weexaminedthecognitiveconsequencesofsuchenhancedcontrol.Herewemakeexplicitthecomponentsofthenetworkinvolvedinlanguagecontrol,demonstratehowtheyalsomediatethecognitiveadvantagesshownbybilinguals,andexploretheneuralbasesofcontrolusingmanyofthesametasksdiscussedinSection2.Figure5identifiesthebasiccomponentsofthecontrolnetwork,distinguishingitfromthebilinguallanguagesystemthatitcontrols.Wecanthinkofthebilingualspeakerasperform-ingmultiplelanguagetaskssuchasspeakingonelanguageratherthananother.Abilingualmustalsomonitorthelanguageinuseandeithermaintainitifthecircumstancedemands(e.g.,whenspeakingtoamonolingualspeakerofthatlanguage)andsoavoidinadvertentlyswitchingintotheotherlanguageor,onoccasion,deliberatelyswitchtotheotherlanguageifthecircum-stancechangesforexample,whenamonolingualspeakeroftheotherlanguageenterstheconversation.Thetask-switchingparadigmdescribedinSection2canbeadaptedtotestlanguageswitchinginbilinguals,andweuseitheretoillustratetheworkingsofthenetworkforlanguagecon-trol.Thetaskistonameapresentednumeral,forinstance4,inL1(e.g.,French)orinL2(e.g.,English).Theparticipantsselectionofonetaskratherthananothergovernstheoutputfromthebilinguallanguagesystem;ifthetaskistonameinFrench,thepersonsaysquatre.Tobesuccessful,theactivationoftheselectedtask(i.e.,thementalrepresentationCognitive Control NetworkExecutive process Monitoringprocess Competing taskschemas Bilingual system Fig.5.Basiccomponentsofthecognitivecontrolnetworkforbilinguals,distinguishingitfromthebilinguallanguagesys-temthatitcontrols.Thebilinguallanguagesystemreferstoapersonsmentalrepresentationoftheirlanguages;forpresentpurposes,weleavethisundifferentiatedandfocusonthecomponentsofthecontrolsystem.Abilingualcanperformdifferentlanguagetasks:Heorshecanchoosetospeakonelanguageratherthananother,canswitchbetweenlanguages,orcantranslatebetweenthem.Taskschemasconfigurethebilinguallanguagesystemsoastoachievetheintendedtask,buttheseschemasareincompetitiontocon-trolthebilinguallanguagesystem.Theiractivationmustbemonitoredand,ifnecessary,adjustedbyahigher-orderexecutiveprocess.Forexample,abilingualmusteithermaintainthecurrentlanguageinuseifthecircumstancedemands(e.g.,whenspeakingtoamonolingualspeakerofthatlanguage)andsoavoidinadvertentlyswitchingintotheotherlanguageor,onoccasion,deliberatelyswitchtotheotherlanguageifthecircumstancechangesforexample,whenamonolingualspeakeroftheotherlanguageenterstheconversation.BilingualMinds ofthetaskset,itstaskschema)mustexceedandcontinuetoexceedthatofthecompetingtask.Therefore,thespeakermustmonitorthespeechoutput,andwheremarkedslowingisdetectedoranerrorisnoticed(i.e.,sayingfourratherthanquatre)thespeakermustmakesomeadjustments.Thespeakermightincreasetheactivationoftherequiredtask(nameinFrench)orsuppresstheactivationofthealternativetask(nameinEnglish)asdiscussedSection2whenweexaminedselectionversusinhibition.Executiveandmonitor-ingprocessesareneededtoestablishnewschemas(e.g.,inthecaseofanexperimentaltask)andinvokeonesthatarealreadypartofapersonsrepertoire.Inthisrole,theseprocessesworkproactively;inresponsetoperformancedifficulties,theyworkreactively(Green,1998).Apersonmaybeconsciousoftheneedtomakesuchadjustmentswhenanoverterrorismade,butonotheroccasionscontroladjustmentmayoccurautomati-cally,asinthewayathermostatadjustspoweroutputinresponsetoadeviationfromthedesiredtemperature(Green,1998;Paradis,2009;seeFernandez-Duque&Knight,2008,forworksuggestingthatonlyconsciouscontrolleadstoperfor-mancebenefitsacrosstasks).Whatproducesslowerresponsesorovertnamingerrors?MarkedslowinginnaminginFrench,forexample,mayreflectsuccessfulinhibitionofastronglycompetingnameintheotherlanguage(i.e.,English),whereasnaminginthewronglanguageindicatesafailureofcontrol.ActivationoftheEnglishnamemayalsoincreasetheactivationofthetaskschemaforEnglishandleadtoincreasedcompetitionwiththetaskschemaforFrench.ResolvingsuchcompetitionrequiressuppressionoftheEnglishtaskschema.Inotherwords,whenabilingualspeakstwolanguagesregularly,speakinginjustoneoftheselanguagesrequiresuseofthecontrolnetworktolimitinterfer-encefromtheotherlanguageandtoensurethecontinueddominanceoftheintendedlanguage.WouldtherebeadifferenceintheswitchcostifthebilingualweremorefluentinFrench(L1)thaninEnglish(L2)?Inthatcase,FrenchwouldbetheeasiertaskandEnglishthemoredifficulttask,andtheinterestingfindingisthatittakeslongertoswitchintotheeasiertask(143milliseconds,ms)thanitdoestoswitchintothemoredifficulttask(85ms;Meuter&Allport,1999).AplausibleexplanationforthisseeminglyparadoxicalasymmetryofswitchcostsisthatinordertonameinEnglish(themoredifficulttask),theeasiertask(naminginFrench)mustbestronglyinhibited,andittakesmoretimetoreinstatetheeasiertask,producinganasymmetryintheswitchingcost.SimilarresultswereobtainedinastudybyMisra,Guo,Bobb,andKroll(2007).ParticipantswereaskedtonamepicturesinL1orL2undereithermixedconditions,wheneitherL1orL2couldberequired,orinblockedconditions,whenonlyonelanguagewasused.TheirresultsshowedthatnaminginL1wasslowerundermixedconditionsthanitwasunderblockedconditionsandthatL1namingwasslowerthanL2naminginthemixedconditions(aneffectofreversedlanguagedominance),supportingtheinterpretationthatL1wasinhibitedtopermitthepossibilityofL2naming.Noasymmetryofswitchcostsisfoundwhenbilingualsswitchlanguagesvoluntarily,yetacompletereversaloflanguagedominanceisfoundagainsuggestingsomeformofinhibitionoftheL1(Gollan&Ferriera,2009).Notalltheresearchisconsistentonthispoint.Finkbeiner,Almeida,Janssen,andCaramazza(2006)hadbilingualparticipantsnamedigitsineitherL1orL2andthenperformapicture-namingtaskintheirdominantlanguage.Followingtheargumentforgreaterinhibitionofthedominantlanguage,thehypothesisisthatitshouldtakelongertonamepicturesinL1ifthedigitnaminghadbeenperformedinL2.However,Finkbeineretal.foundnodifferenceinpicture-naminglatencyandsoconcludedthatnoinhibitionofthenonusedlanguagetookplace.Theirconclusion,though,isdifficulttoreconcilewithevidenceofgloballanguageinhibitionidentifiedinthelaterstudybyPhilippandKoch(2009).AmorecompletereviewoftheseissuesispresentedbyKrolletal.(2006).Theexperimentalresearchonbilingualtaskswitchinggenerallyusesexplicitcuestosignalthelanguagerequiredonthecurrenttrial.Deliberatelanguageswitchinginreallifealsorequiresaspeakertomonitorthecontextforcuesastowhichlanguagetospeak(e.g.,thispersonspeaksL1butnotL2)andensurecorrectlanguageselectionandsuppressionofanycompetingresponses.Ourpremise,then,isthattheaddi-tionaldemandsonbilingualspeakersrelativetomonolingualspeakersentailgreateruseofthiscontrolnetwork.Thepartic-ulartasksthataresubjecttocontrolarevaried(e.g.,namingpicturesinonelanguage,describingasceneinasecondlanguage,translatingfromonelanguagetoanother).However,thecomponentsinvolvedinmonitoringperformanceandensuringcorrectselectionoftheintendedlanguagetaskareapplicabletoothernonlanguagetasks,and,aswesawintheprevioussection,theyappeartogeneralizetononverbaltasks.NeuralbasesofcognitivecontrolFigure6identifiesthecorticalandsubcorticalstructuresthatarecomponentsofthecognitivecontrolnetworkinFigure5.Wefollowothersinseparatingtheneuralstructuresmediatingcontrolfromthosethatprocesslinguisticorotherkindsofsen-soryormotordata(Posner&Petersen,1990).Theideaisthatthesecorticalandsubcorticalstructuresworktogethertolimittheeffectsofinterferenceandtoswitchbetweentasks.Forexample,theymayfunctionasacontrolloopthatcontinu-allymonitorsattentiontotherequiredtask(e.g.,Botvinick,Braver,Barch,Carter,&Cohen,2001;Kernsetal.,2004).Initsmonitoringrole,theanteriorcingulatecortexmaydetectandhelpresolveinterference(Lau,Rogers,&Passingham,2006)andsignaltheprefrontalcortex,withitswidespreadconnectionstootherregions(Dehaene&Changeux,1991;Desimone&Duncan,1995;Miller&Cohen,2001),toaltertheactivationofthetaskschemas.Anotherregioninthemedialfrontalcortexsuperiortotheanteriorcingulatecortex,thepre-supplementarymotorarea(pre-SMA),isalsoimplicatedinthecontrolofactionbutseemslinkedmorecloselytospontaneouslychosenactionsthantoresponseconflict(Lauetal.,2006).Theparietalcortexisinvolvedinrepresentingthetask,throughitsconnectiontotheprefrontalcortex,andinselectingBialystoketal. amongcompetingresponses,throughitsconnectiontothebasalganglia(Bungeetal.,2002).Thebasalgangliaarepar-ticularlyimportantintaskswitching.Whereastraditionalviews(Alexander&Crutcher,1990;Mink,1996)emphasizetheroleofthebasalgangliainthecontrolofmovement,recentworkemphasizestheirkeyroleincognitivecontroltoo(e.g.,Graybiel,2000;Kotz,Schwartze&Schmidt-Kassow,2009).Bothcorticalandsubcorticalstructuresarethereforeimportantinunderstandinghowinterferenceiscontrolledandtaskswitchingachieved,soitisnecessarytounderstandtheirroleinlanguagecontrol.Weshallexaminetheinvolvementoftheseregionsintwobroadcategoriesoftasks:thoserequiringthecontrolofinterferenceandthosebasedonswitchingbetweentasksandlanguages.ThecontrolofinterferenceUsingneuroimagingstudies,wenowconsidertheneuralbasesforcontrollinginterference.Thesestudiesmostlyrelyonfunc-tionalmagneticresonanceimaging(fMRI)toassesstheresponseofdifferentneuralstructureswhenthereisanincreaseddemandtocontrolinterference.ThebasicdataaretherelativeactivationofdifferentneuralregionsasdetectedbyfMRI.Acommonassumptionisthatanincreaseinactivationreflectsanincreaseindifficulty.Thereismoreextensiveresearchonthecontrolofinterferenceinmonolingualspeakers,soourreviewmakesuseofmeta-analysesofdatafromanumberofstudies.Interferencecontrolinmonolinguals.TheargumentbeingdevelopedhereisthatbilingualsusethecognitivecontrolnetworkshowninFigure6tocontrolinterferencefromthecompetinglanguage.Therefore,itisnecessarytoestablishthattheseregionsarerecruitedwhenmonolingualsperformtasksinvolvingresponseconflict.Weconsiderworkthathaslookedattheneuralregionsinvolvedincontrollinginterferenceinthreedifferenttasksthat,asdescribedinSection2,showabilingualadvantage:anonverbalflankertask,aSimontask,andaStrooptask.Althoughstudieshaveexaminedthesetasksseparately,thestrongestevidenceforacommonsetofregionsinvolvedincognitivecontrolcomesfromstudiestestingtwoormoreoftheminthesameindividuals(Fan,Flombaum,McCandliss,Thomas,&Posner,2003;Liu,Banich,Jacobson&Tanabe,2004;Petersonetal.,2002).Fanetal.(2003)contrastedperfor-manceonaflankertask,aSimontask,andamanualversionoftheStrooptaskinwhichindividualspressedoneoffourbuttonscorrespondingtothefontcolorofapresentedword.Inallthetasks,individualsrespondedfasterincongruenttrialsthaninincongruenttrials.Fanetal.identifiedtworegionsthatshowedacommoneffectofconflict:oneintheanteriorcingulatecor-texandoneintheleftprefrontalcortex(seeRoberts&Hall,2008,forareview).Nee,Wager,andJonides(2007)examineddatafrom47papersusingdifferentinterferencetasks.Theirreviewcon-firmedtheimportanceoftheleftprefrontalcortex(dorsolateral Anterior Cingulate Cortex Attention Conflict monitoring Error detection Inferior Parietal Lobule Maintenance of Representations Basal Ganglia, CaudateLanguage selection Set switching Lexical selection Executive functions Decision-making Response selection Working memoryPrefrontal Cortex Fig.6.Principalbrainstructuresinvolvedincognitivecontrol,andtheirputativefunctions.FromAbutalebiandGreen(2007).BilingualMinds region)andtheanteriorcingulatecortex,alongwitharegionintheleftposteriorparietalcortex,inovercomingStroopconflict.Neuropsychologicaldataalsosupporttheimportanceofafrontalregioninverbalcontrol.HamiltonandMartin(2005)foundthatapatientwithdamagetoaleftinferiorfrontalregionshowedalargeinterferenceeffectintheStrooptaskbutinterferencewithinthenormalrangeforaspatial-conflicttask.TheanalysesofNeeetal.alsoshowedthatdifferentkindsofconflictinduceslightlydifferentpatternsofneuralresponse.Inresolvingconflictbasedonresistingrespondingtoaninfrequentstimulus,frontalandparietalregionsintherighthemisphere,inadditiontotheleftdorsolateralprefrontalcortexandtheanteriorcingulatecortex,wereactivated.Muchresearchonthecontrolofinterferencehasexaminedtheroleofcorticalstructuresbutignoredtheroleofsubcorticalstructures,suchasthecaudate,that,asindicatedinFigure6,shouldbeinvolvedinselectingamongcompetingresponses.However,thereissomerelevantresearchonthesesubcorticalstructures.Theleftheadofthecaudateactivateswhenaprevi-ouslylearnedmovementhastobeinhibited(Shadmeher&Holcomb,1999;Parsons,Harrington,&Rao,2005)andwhenaprepotentresponsehastobeblocked(Li,Yan,Sinha,&Lee,2008).ThecaudateisalsoactiveincontrollinginterferenceintheStrooptask(Ali,Green,Kherif,Devlin,&Price,2010).Areasonablesupposition,then,isthatthecaudateisinvolvedintheinhibitionofplansofactionandthereforecontrolsbothver-balandnonverbaltypesofinterference.Tosummarize,neuroimagingresearchwithmonolingualsconfirmsthatanetworkinvolvingtheprefrontalcortex,anteriorcingulatecortex,andcaudateisrecruitedintasksthatrequireresolutionofconflictfromcompetingresponses.Interferencecontrolinbilinguals.Wearguethatbilingualsusethissamenetworktocontrolconflictfromtwolanguages.Therefore,ifretrievingthenameofapictureiseffortfulforbilingualsbecauseoftheneedtoovercomeinterferencefromtheotherlanguage,thenwewouldexpecttofindevidencefortheinvolvementofthiscontrolnetworkinapicturenamingtask.DeBleseretal.(2003)examinedcovertpicturenaminginanL1andalater-acquiredL2.(Fortechnicalreasons,neuroimagingstudiessometimesadopttheexpedientofaskingparticipantstomouthpicturenamesortonamepicturesonlycovertly,sotheywillnotmove.)ParticipantswerenativespeakersofFlemish/DutchwhohadlearnedFrenchfromtheageof10.Inoneconditionthepicturenameswerecognates(i.e.,thetranslationequivalentswerephonologicalandorthographicallysimilar),andinanotherconditiontheywerenoncognates.Forpictureswithnoncognatenames,namingintheL2showedmoreactivationinregionsresponsibleforlink-ingconceptualinformationandwordformthandidnamingintheL1.Themoreimportantresultisthatactivationincreasedintwoinferiorfrontalregionsassociatedwithmoreeffortfullex-icalandsemanticretrieval.Therefore,datafromthisstudy,alongwithothers(e.g.,Abutalebi,Cappa,&Perani,2001;Rodriguez-Fornellsetal.,2005),suggestthatnamingintheL2isassociatedwithmoreeffortfulprocessing,anideaconsistentwiththeinvolvementofcognitivecontrolprocesses.Moreover,asproficiencyintheL2increases,therelativedifferenceinactivationbetweenL1andL2decreases,againconsistentwiththeideathatthereisadecreaseineffort(Abutalebi&Green,2007).EvenearlyandhighlyproficientbilingualspeakersshowevidenceofmoreeffortfulprocessingintheirL2andrecruit-mentofcontrolregions,despitedemonstratingaprocessingprofilethatissimilartothatofnativespeakers.Kovelman,Baker,andPetitto(2008)askedSpanish-EnglishbilingualsandEnglishmonolingualspeakerstojudgewhethervisuallypre-sentedsentenceswereplausibleornot.Forthebilinguals,thesentenceswerepresentedinseparateexperimentalblocksforeachlanguage.TheEnglishsentences(andtheirSpanishtranslations)variedintheirsyntacticcomplexity,beingeithersubject objectrelatives(e.g.,Thechildspilledthejuicethatstainedthecarpet)orarguablymorecomplexobject subjectrelatives(e.g.,Thejuicethatthechildspilledstainedthecar-pet).Asexpected,bilingualspeakersshowedadifferentialresponsetocomplexityasafunctionofthepresentedlan-guage.Spanishreliesmoreonmorphologicalmarkingthanwordordertosignalgrammaticalrelations.LiketheEnglishmonolinguals,bilingualspeakersshowedincreasedleftinfer-iorfrontalactivationforthemorecomplexEnglishsentences.Incontrast,theyshowednodifferentiationasafunctionofcomplexitywhenprocessingtheSpanishsentences.However,thestudyalsoshowedthatbilingualspeakersprocessingEnglishshowedmoreactivationintheleftfrontalregionthanmonolingualEnglishspeakersdid.Inotherwords,processingeveninalanguageinwhichtheyarehighlyfluentismoreeffortfulforbilingualspeakersandengagesregionsassoci-atedwithcognitivecontrol.IncreasedproficiencyintheL2mayalsoalterprocessingintheL1preciselybecauseofincreasedcompetition.Inreading,themappingsbetweenlettersandsoundsdifferbetweenlan-guages,sothesamestringofletterscangiverisetoconflictingpronunciations.Forexample,whathappenswhennativeread-ersofItalian(whichhasaregularrelationshipbetweenlettersandsounds)readintheirL1afterlearningEnglish,inwhichtherelationshipisirregular?AsvocabularyknowledgeinEnglishincreases,nativeItalianreadersreadingItalianshowalinearincreaseinactivationinaleftfrontalregionassociatedwithmappingletterstosounds(Nosarti,Mechelli,Green,&Price,2010).Suchanoutcomeindicatesincreasedcompetition.Moretothepoint,thereisalinearincreaseinactivationinaleftfrontalregionusedtoresolveirregularpronunciationsinmonolingualnativeEnglishreaders.Interestingly,thisregionisalsoonethathelpsresolvelexicalcompetition(e.g.,deZubicaray,McMahon,Eastburn,&Pringle,2006).Thesedataagainsuggestthatbilingualspeakersandreaders,atleastincontextswherebothlanguagesareactive,experienceincreasedverbalconflictandrecruitaleftfrontalregiontoresolveit.Otherresearchallowsustoseebothcorticalandsubcorticalregionsinvolvedincontrollinginterference.VanHeuven,Schriefers,Dijkstra,andHagoort(2008)madeuseofaspecialrelationshipthatexistsbetweenwordsintwolanguagessuchasBialystoketal. EnglishandDutch.TheirparticipantswerehighlyproficientDutch-EnglishuniversitystudentswhohadlearnedEnglishattheageof10to12years.VanHeuvenetal.askedparticipantstodecidewhetherapresentedwordwasarealEnglishwordornotanEnglishlexicaldecisiontask.SomeEnglishwords,termedinterlingualhomographs,arealsorealwordsinDutch;forexample,meanscreaminDutch.InanEnglishlex-icaldecisiontask,roomelicitsacompetingNoresponsebecauseitisawordinDutch,andinanEnglishlexicaldecisiontaskDutchwordsshouldreceiveaNoresponse.Relativetocontrolwords,therefore,correctlydecidingthataninterlingualhomographwasarealEnglishwordelicitedincreasedactivationinthreeregionsdisplayedinFigure6:theleftinfer-iorprefrontalregions,theanteriorcingulatecortex(togetherwithanotherregionwehavenotedpreviouslyinthemedialfrontalcortex,thepre-SMA)andtheleftcaudate.Asexpected,vanHeuvenetal.observednodifferentialactivationforinterlingualhomographsinagroupofmonolingualEnglishspeakers.Thisexperimentleftunresolvedwhethertheactivatedregionsweresignalingconflictarisingfromthestimulusitself(i.e.,roomelicitstwomeaningsinDutch-Englishbilinguals)orconflictarisingfromambiguitiesasso-ciatedwiththeresponse(i.e.,isroomawordin?).Todeterminewhichregionsrespondedtostimulus-basedratherthanresponse-basedconflict,theresearchersper-formedanotherexperimentonaseparategroupofbilingualsfromthesamepopulation.Inthiscase,participantsknewthatsomeofthewordsmightbeDutchwordsandrespondedYestoeachrealEnglishwordregardlessofwhetheritwasalsoaDutchword.Inthiscase,interlingualhomographselicitedincreasedactivationonlyinleftprefrontalregions,suggestingthattheleftprefrontalregionsaresensitivetostimulus-basedconflict.Incontrast,theresponseprofileoftheanteriorcingulatecortex(andthepre-SMA)andleftcau-daterevealsregionsthatareeithersensitiveto,orhelpresolve,response-basedconflict.Thepreciseimpactoftheotherlanguagemightdependonhowactiveitis.ItisreasonabletoexpectthatitwillbemostactivewhenitisbeingusedatthesametimewhenbilingualsareinwhatGrosjean(1998)termedabilingualmodeandtheyareswitchingbetweenlanguages.Weconsidertheresponseofthecontrolregionsinthesectiononlanguageswitching.TaskswitchingThesecondparadigmwithinwhichtoexaminetheneuralbasesofcognitivecontrolistaskswitching.Differenttypesofdatacanhelpidentifythestructuresrecruitedinswitchingbetweenlanguagesorbetweenothertypesoftasks.Strokedamagetoaspecificstructurecanleadtodifficultiesintaskperformanceandsoprovideevidenceofitscausalroleincog-nitivecontrolthatcomplementsthedatafromneuroimagingstudies.Again,webeginbyestablishingtheneuralbasisoftaskswitchinginmonolingualsandthencomparethosepat-ternstodatafrombilingualsperformingtaskswitchingandlanguageswitching.Taskswitchinginmonolingualspeakers.TheoccurrenceofastrokeisatragicanddramaticeventthathelpstoexplicatetheroleofregionsinFigure6fortaskswitching.Greaterdamagetotheleftfrontalcortexleadstoincreasesinswitchcostsandsoreflectsdifficultyinholdingthecurrenttaskinmindorinselectingthecorrectresponse,althoughinhibitionofinap-propriatetasksorassociatedresponsesmightbemorecloselylinkedtotherightfrontalcortex(Aron,Monsell,Sahakian,&Robbins,2004).Theanteriorcingulatecortexislesssuscepti-bletostroke,butitissometimesnecessarytoablatepartofitsurgically.Postoperatively,suchpatientshavedifficultyrespondingtoacuethatrequiresthemtoswitchthedirectioninwhichtheymoveajoystick(Williams,Bush,Rauch,Cosgrove,&Eskandar,2004).Damagetothebasalgangliaalsoseverelyimpairsapersonsabilitytoswitchbetweentasksandtoovercometheinterferencefromthepriortask.Weillus-tratewithanonverbaltask(Yehene,Meiran,&Soroker,2008).Yeheneetal.askedtheirpatientstopressoneoftwokeysinresponsetothepositionofatargetschematicfaceina2matrixonthebasisofoneoftworules.Inthetop-downtasktheyhadtopressKey1ifthetargetwasinthetophalfofthegridandKey2ifitwasinthebottomhalf.Intheleft righttasktheypressedKey1ifitwasontheleftsideofthegridandKey2ifitwasontheright.Therulewascuedoneachtrial.Oncrit-icaltrials,thecorrectresponsedependedontheapplicationofthecorrectrule,becauseKey1designatedatargetthatwasuporleftandKey2designatedatargetonthebottomorright.Therefore,ifatargetwasintheupperrightcellofthegrid,pressingKey1wascorrectforthetop-downtaskbutKey2wascorrectfortheleft-righttask.Basalgangliapatientswereseverelyimpairedwhentheruleswitchedinthistask,signalingtheimportanceofthatstructureinsuchtasks.Inameta-analysisofdatafromneuroimagingstudiesinvolv-ingdifferenttypesoftaskswitches(e.g.,ruleswitching,changesintargetlocations,anddifferentresponsesets),Wager,Jonides,andReading(2004)confirmedthattheregionsinFigure6arereliablyactivatedontask-switchtrials.Theprefrontalcortexissensitivetochangesindemandsinvolvedinswitchingbetweentasks(Christoff&Gabrieli,2000;MacDonald,Cohen,Stenger,&Carter,2000)withmorecomplexworkingmemorydemandsassociatedwithrightfrontalactivation(Simmonds,Pekar,&Mostofsky,2008).Theanteriorcingulatecortexissensitivetochangesintasksandtoerrorsconsistentwithitsroleinmonitoringandinadaptivecontrolinresponsetoerrors(e.g.,Hyafil,Summerfield,&Koechlin,2009).Parietalareasarealsoinvolvedinremappingstimulitoresponseaccordingthenewtask(e.g.,Corbetta&Shulman,2002;Dosenbachetal.,2006).Finally,thebasalgangliaplayaroleinshiftingresponse.Inastudyinwhichparticipantstrackedacontinuoussinewavebycontrollingacursor,activationincreasedintheleftcaudatewhenthecurrenttrialrequiredamovementoppositetothatusedpreviously(Lungu,Binenstock,Pline,Yeaton,&Carey,2007).Languageswitchinginbilinguals.Inmonolingualparticipants,theregionsidentifiedinFigure6wereshowntocontributetotaskswitching.DotheyalsocontributetolanguageswitchingBilingualMinds andinterferewithlinguisticbehaviorinbilingualpatients?Patientreportsindicatethatdamagetotheprefrontalcortex,inferiorparietalcortex,orbasalgangliastructuresaffecttheabilityofbilingualpatientstovoluntarilyswitchfromonelanguagetoanother.Astheanteriorcingulatecortexislesssusceptibletostroke,therearefewerreportsforthisstructure,butalltheotherregionsindicatedinthiscontrolnetworkshowaclearroleinlanguageswitching.Damagetoeithertheleftprefrontallobe(Stengel&Zelmanowitz,1933;Zatorre,1989;Fabbro,Skrap,&Aglioti,2000)orleftinferiorparietallobe(Herschmann&Po¨tzl,1920;Po¨tzl,1925,1930;Leischner,1948/1983)canyieldpathologicalswitching,thatis,unintendedorinappropriateswitchingbetweenlanguages.Lesionstotheheadofthecaudateeliciteitherselectiverecoveryofthecurrentlanguage,asifitisnolongerpossibletodisengagefromit(Aglioti&Fabbro,1993;Aglioti,Beltramello,Girardi,&Fabbro,1996),orpathologicalswitchingbetweenlanguages(Abutalebi,Miozzo,&Cappa,2000;Marie¨n,Abutalebi,Engelborghs,&DeDeyn,2005).InthecasereportedbyAbutalebietal.,A.H.,atrilingualspeakerofArmenian(L1),English(L2),andItalian(L3),wasunabletoavoidswitchinglanguageswhennamingsimplepictures.Forexample,althoughhenamedthepictureofaclockcorrectlyinArmenianinanArmeniantestingsession,henameditinItalianintheEnglishnamingsessionandinEnglishintheItaliannamingsession.Thatthecircuitsunderlyinglanguageswitchingarewidespreadisalsoindicatedbydatafromtransientcorticalandsubcorticalelectricalstimulationofthebrainduringsurgeryfortreatinggliomatumorsorepilepticfociwhenthepatientisawake.Inthecaseofbilingualspeakers,thisstimulationcanleadtoinvoluntaryswitchingfromnamingpicturesinonelanguagetonamingtheminanother,reflectingthetemporarydisruptionofcontrol(Moritz-Gasser&Duffau,2009a,b).Neuroimagingstudiesofbilingualswithoutbraindamageprovidecomplementarydata.InastudywithearlySpanish-Englishbilingualspeakers,Hernandezetal.(2000)reportedmoreactivationinleftdorsolateralprefrontalcortexwhenswitchingbetweennamingpicturesinEnglishandSpanishthanwhennamingpicturesinjustonelanguage(seealsoHernandez,2009;Hernandez,Dapretto,&Bookheimer,2001;Chee,Soon,&LingLee,2003).Price,Green,andvonStudnitz(1999)usedsinglewordsandfoundthatswitchingbetweenlanguagesincreasedactivationinregionsassociatedwithphonologicalprocessing(aleftinferiorfrontalregion,Brocasarea,andparietalcortices).Takentogether,thesedataindicatethatlanguageswitchingormixinginduceincreasedfrontalandparietalactivityconsistentwiththerequirementtoinhibitongoingactivityassociatedwithonetaskandselectarelevantresponseinthefaceofcompetition.Morerecentresearchprovidesafullerpictureofthecontrolregionsinvolvedinlanguageswitching.Abutalebiandcolleagues(2008)studiedGerman-FrenchbilingualswholearnedFrenchrelativelylate(around12yearsofage)andwereenrolledinatranslationcourse.ThetaskwastonamepicturesintheirL1underoneoftwoconditions.Inthesingle-languagecondition,acuesignaledwhethertheyweretonamethepicture(e.g.,cup)orgenerateanassociatedverb(e.g.,drink).Inthedual-languagecondition,thecuesignaledwhethertheyweretonamethepictureintheirL1orintheirL2.Inthisdualcondition,thenontargetlanguageisveryactive.ThekeyanalysisisthecontrastbetweennamingapictureinL1inthesingle-languageconditionandnamingitinL1inthedual-languagecondition.Abutalebietal.foundthatnamingpicturesinthedual-languageconditioninducedmoreextensiveactivationintheleftprefrontalcortex,theanteriorcingulatecortex,andtheleftcaudatenucleusthandidnamingthesamepicturesinthesingle-languagecondition.Furthermore,thestudyconfirmedmoreextensiveactivationintheseregionswhenindividualswereusingtheirweakerL2.Theseresultsarestrongsupportfortheimportanceoftheseregionsinselectingalanguageinthefaceofinterference.Otherstudieshaveusedneuroimagingtoexaminetheneuralbasisoftheasymmetriccostinswitchingbetweenalanguageinwhichoneismoreproficientandalanguageinwhichoneislessproficient(Meuter&Allport,1999).Weillustratethiswithafunctionalimagingstudy,butthereisotherworkusingevokedreactionpotentialsthatisconsistentwiththeideathatswitchingbetweenlanguagesinvolvesaprocessofactivelyinhibitingtheotherlanguage(Jackson,Swainson,Cunnington,&Jackson,2001)evenifthatdoesnotinvariablyleadtoanasymmetryinswitchingcost(e.g.,Christoffels,Firk,&Schiller,2007;Verhoef,Roelofs,&Chwilla,2009,2010).Wang,Xue,Chen,Xue,andDong(2007)examinedthecostofswitchingintoL1(Chinese)versusanewlyacquiredL2(English).Inlinewiththeviewpresentedherethatthesameregionsareusedforcognitivecontrolandlanguagecontrol,Wangetal.reportedincreasedactivationintheregionsassoci-atedwithcontrolwhensubjectsswitchedintoL2.ThepatternagainisconsistentwiththeideathatbilingualsmustinhibittheirL1tospeakintheirL2whentheyareswitchingbetweenthetwolanguages.ThepersistingsuppressiondelaysnamingtimewhenindividualsswitchbackintoL1.Theeffectsoflanguageswitchinghavealsobeenexaminedincomprehension,and,surprisinglyperhaps,thereisalsogoodevidencefortheinvolvementofcontrolprocesses.Languageswitchingelicitsaleftcaudateresponseinlatebilinguals(German-English/Japanese-English)whentheymakesemanticdecisionsaboutthemeaningsofwords(Crinionetal.,2006).Theleftcaudateisalsoactivatedwhenbilingualsencounteralanguageswitchwhilelisteningtoanarrativeandmakenoovertresponseatsuchajuncture(Abutalebietal.,2007).TheparticipantsinthisstudywereItalian-FrenchbilingualswhohadacquiredFrenchbeforetheageofthreeandwerelivingatthetimeoftestinginanItaliancommunityinGeneva,whereFrenchpredominates.Switchingelicitedbilateralinferiorfron-talactivity(alongwithactivationinalanguagearea).Mostinterestingly,aswitchintotheless-exposedlanguage(Italian)elicitedactivationoftheleftcaudateandtheanteriorcingulatecortex.Suchaneuralresponseindicatestheneedtodistinguishbetweentheprocessesresponsibleforimplementingcontrolfromprocessesassociatedwithovercomingtheeffectsofsuchcontrol.Inthepresentcase,switchingintothelessdominantBialystoketal. languageinacomprehensiontaskappearstodemandmoreneuralresourcestoovercome(suppress)theactivationofthemoreexposed(dominant)language.Inaproductiontask,suchaneuralresponsemaygiverise,aswehaveseen,toslowernamingwhenswitchingbackintothemoredominantlanguageinordertoovercomeitsearliersuppression.Finally,aspecialtypeoflanguageswitchingoccurswhenbilingualstranslatefromonelanguagetoanother,andthistaskalsoinvolvesthecorticalandsubcorticalstructuresdepictedinFigure6.Priceetal.(1999)reportedthat,incontrasttoreadingindifferentlanguages,translatingactivatedmainlytheanteriorcingulatecortexandbilateralsubcorticalstructuresincludingtheheadofcaudate.Inthatstudy,ifparticipantsdidnotknowthetranslationequivalenttheyrespondedNoorNein.However,inotherstudies,leftinferiorfrontalactivationwasfoundwhenthatoptionwasnotavailable,bothinsingle-wordtasks(Klein,Milner,Zatorre,Meyer,&Evans,1995)andinauditorilypresentedtexttranslationbysimultaneousinter-preters(Rinneetal.,2000).Further,Rinneetal.(2000)reportedthat,sincetranslationintothenonnativelanguageisthemoredifficulttask,leftdorsolateralactivationwasmoreextensivewhentheinterpreterstranslatedintotheirnonnativelanguage.Theinvolvementofsubcorticalstructuresalongwithactivityintheleftprefrontalcortexisalsoreported(Lehtonenetal.,2005).LehtonenandcolleaguesstudiedFinnish-NorwegianbilingualswhohadlearnedNorwegianasadults(21 36years).Participantscompletedatranslationtaskandacontroltask.Inthetranslationtask,theysilentlytranslatedvisuallypresentedFinnishsentencesintoNorwegianandthendecidedwhetherapresentedNorwegianprobesentencewasacorrecttranslationoftheFinnishsentence.Inthecontroltask,theysilentlyreadaFinnishsentenceanddeterminedwhetheraFinnishprobesentencewasidenticaltoit.Thecontrastbetweenthetranslationandcontroltaskyieldedsubstantialactivationintheleft(ventrolateral)prefrontalcortexandinaregionofthebasalganglia(globuspallidus)thatisactivatedinsuppressingcompetingresponses(Atallah,Frank,&OReilly,2004;Alietal.,inpress).Takentogether,thesedataprovideevidencefortheinvolvementofthecorticalandsubcorticalregionsofthecontrolnetworkinataskspecialtobilinguals.Localswitchingandmixingcostsinbilingualandmonolingualperformance.ThedifferencebetweenlocalswitchcostsandmixingcostswasdiscussedinSection2,withmoststudiesreportingsmallermixingcostsforbilingualsandwithmorevariedevidenceforlocalswitchcosts.Thisdistinc-tioncanalsobeexaminedusingevidencefromneuroimaging.Fromacontrolpointofview,thesetwotypesofcostareinterestingbecauselocalswitchcostsreflecttransientcontrolprocesseswhereasmixingcostsreflecttheneedforsustainedcontrol.Intask-mixedblocks,individualsneedtokeeptwotasksactiveandmonitortheworldforcuesastowhichonetoperform.Dosenbachetal.(2006)provideadetailedanalysisoftheregionsinvolvedininitiatinganewtask,sustainingitoverasequenceoftrials,andrespondingtoerror.Theyarguethattheanteriorcingulatecortex,togetherwithanotherbilateralfrontalregion(theanteriorinsula/frontalopercu-lum)formacoreregionforimplementingandsustaininganewtask.Asyet,therearenocomparableanalysesforlan-guageswitchinginbilinguals,soweillustratewithevidencefromtwostudiesthatcomparelocalswitchingandmixingcostsinlanguagetasks.Braver,Reynolds,andDonaldson(2003)askedparticipantstoclassifywordsaccordingtowhethertheyreferredtoobjectsthatwerenaturalversuscreatedorwhethertheobjectsreferredtowerelargeversussmall.Participantscarriedoutthesetaskseitherinseparateblocksoftrialsormixedinthesameblockoftrials.Theanteriorcingulatecortexandprefrontalregionsoftherighthemispherewereactivatedinthemixedblocksbutshowednovariationwithlocalswitching.Incontrast,localswitchingwasaccompaniedbyactivationinleftprefrontalandparietalregions.Wang,Kuhl,Chen,andDong(2009)extendedtheseideastolanguageswitching.NativespeakersofChinesewhostartedlearningEnglisharound12yearsandwhoratedthemselvesasbeingoflowtomoderateproficiencyinEnglishnameddigitssilentlyeitherinsingle-languageormixed-languageblocks.Languageofresponsewassignaledbyaverbalcuepresented400msbeforethestimulusdigit.Consistentwithpreviousresearch(e.g.,Meuter&Allport,1999),ittooklongertoswitchbackintoChinesethantoswitchintoEnglish(43msvs.8ms.).TherewasalsoamixingcostthatwassimilarforChineseandEnglish(butseeChristoffels,Firk,&Schiller,2007;Krolletal.,2006,fordatashowingthatanL1canrevealgreatermixingcosts).Importantly,however,localswitchingandmixingcostswereassociatedwithdifferentbrainregions.Formixingcosts,therewasactivationinbilateralprefrontalandfrontalregions.Unlikeotherstudies,Wangandcolleaguesreportednodifferentialactivationoftheanteriorcingulatecortex,adifferencetheyattributetothemoreautomaticretrie-valofnumeralnames.Incontrast,andinlinewiththedataofBraverandcolleagues(2003),localswitchcostsactivatedleftfrontalregions(alongwithothercorticalandsubcorticalregions).Basedonananalysisofindividualdata,WangandcolleaguesalsoproposedthataleftparietalregionplaysaroleinovercominginhibitionorinreactivatingthepreviousBilingualismandtheneuralnetworksforcontrolWehavesummarizedresearchshowingtheneuralregionsinvolvedwhenindividualscontrolinterferenceinusingoneoftheirlanguagesandtheregionsinvolvedwhentheyswitchbetweenlanguages.Inbothcases,thesetofregionsdepictedinFigure6isactivated.Thesedatasuggestextensiveoverlapwiththeregionsmediatingcognitivecontrolwhenmonolin-gualspeakersresolveinterferenceorswitchbetweendifferenttasks.Suchacorrespondencesupportstheproposalthatthebilingualadvantageinnonverbalinterferencetasksandintaskswitchingarisesfromtheiruseofneuralregionsrecruitedinlanguagecontrol.BilingualMinds Wehavereliedoncommonalitiesintheresponseofthecontrolregionsinbilingualandmonolingualspeakersfacedwithdifferenttasks,buttheremaybesubtledifferencesthataremissedinsuchcomparisons.Itisimportanttohavestudiesthatdirectlycomparebilingualandmonolingualspeakers(matchedonconfoundingvariablessuchasIQandsocioeconomicclass)performingthesamenonverbalconflictorswitchingtask.Onesuchstudyhasidentifieddifferencesbetweenbilingualsandmonolinguals(Bialystok,Craik,etal.,2005).Theresearcherscontrastedtwogroupsofearlybilinguals(French-EnglishandCantonese-English)withamonolingualEnglishgroupperformingaSimontask.Bialystokandcolleaguesusedmagnetoencephalography(MEG)toidentifytheneuralbasisofprocessingdifferencesbetweenthelanguagegroupsandana-lyzedtwobandsofsignals:oneassociatedwithattentionalcon-trol(thetaband)andtheotherassociatedwithsignalprocessing(alphaband).Thedataindicatedthatthereisacommonnetworkusedbyallparticipantsbutwithwithsubtledifferencesinhowinterferenceiscontrolled.Fasterrespondinginthebilingualgroupswasassociatedwithmoreactivationinthesignal-processingbandintwoleftfrontalregionsandtheleftanteriorcingulatecortex,asdistinctfromtheleftmiddlefrontalregionassociatedwithfasterrespondinginmonolingualspeakers.Itwillbeimportanttoextendsuchresearchtoothertasks.Why,then,mightbilinguals,atleastthosewhousebothlanguagesonaregularbasisandwhoacquiredthemearlyinlife,showanadvantageinovercominginterferenceandintaskswitching?Thepositionthatwehavesoughttoestablishisthatitisduetotheneedtocontrollinguisticinterferencewiththecorrespondingdemandstomonitorandadaptbehavior.Suchcontrolisrequiredwhenindividualsspeaktwolanguages.Itmayalsoberequiredwhenindividualsusetwosignlan-guagesbutappearsnottobeimportantwhenindividualsspeakonelanguageandsigninanother.Consistentwiththisview,Emmorey,Luk,Pyers,andBialystok(2008)foundthatspeech-signbilingualsrespondedcomparablytomonolingualsanddidnotshowtheadvantagedemonstratedbyagroupofspeech-speechbilingualsonaflankertask;andKovelmanetal.(2009)confirmedthatbilingualswhospokeonelanguageandsignedanothershowednoincreaseinprefrontalactivationwhentheyswitchedbetweenthetwo,althoughtheydidshowincreasedactivationinlanguageregionsassociatedwithmappingmeaningtoform.Asnotedearlier,whetherthesourceofthebilingualadvantageisthevoluntaryortheinvoluntarynatureofcontrolisanopenquestion,thoughitmayprovetobetheformer(cf.Fernandez-Duque&Knight,2008).Butgiventhatthereissuchanadvantage,thecontrolnetworkinbilingualsmaybemoreefficientoverall,orbilingualsmayadoptamoreeffectivestrat-egyinperformingnonverbaltasks.Forexample,ininterfer-encetaskstheymightbebetteratmaintainingthetaskgoalandsoreducetheimpactofconflictinginformation.Intaskswitching,theymayrespondmoreefficientlytoataskcueandretrievetaskgoalsmoreeffectively.Ifthisisthecase,switch-ingcostsanddemandontransientcontrolprocesseswouldbereduced.Longitudinalstudieswillbeimportanthere,becauseitisknownthatolderadultsshiftfromacontrolstrategythatisproactiveandmaintainstask-relevantgoalstoonethatisreac-tiveandretrievesrelevantinformationonlywhenrequired(Jimura&Braver,2010;Paxton,Barch,Racine,&Braver,2008).Thebilingualadvantageshowninolderadultsmayreflecttheircontinueduseofaproactivecontrolstrategysupportedperhapsbyleftfrontalstructuresandtheanteriorcingulatecortex.Bilingualexperiencemayalsoalterthecapacityofthecontrolnetworkbyalteringthedensityofgreymatter(i.e.,thenervecellbodiestogetherwithaxonsanddendrites)inoneormorecontrolregions(e.g.,anteriorcingulatecortex;caudate).Itmayevenaffectthewhitematterconnections(i.e.,themyelinatedaxonsthatconnectregionsofgreymatter).Priorresearchindicatesthatcognitive,linguistic,andmotorabilitiescancorrelatewithdifferencesinbrainstructure,(e.g.,Crinionetal.,2009;Draganski&May,2008;Gaser&Schlaug,2003;Leeetal.,2007;Maguireetal.,2000;Mechellietal.,2004).Ifoneortworegionsshowmarkeddifferencesthenthiswouldconstrainaccountsoftheneuralbasisofthebilingualadvantage.Longitudinalstudiesareimportant,astheycanruleoutpreexistingindividualdifferencesratherthanbilingualexperienceasthesourceofthedifference.Inthiscontext,studiesoftheagingbrain(seeSection2)mayproveparticularlyrevealing,becauseage-relateddeclinescanberelatedtochangesinspecificbrainstructures.Oursuppositionisthatdeterioratingperformancefoundinnonverbal-conflicttaskswillalsobefoundintasksinvolvinglanguagecontrol.4.ImplicationsofBilingualismforClinicalThebehavioralstudiesreviewedinSections1and2revealanumberofdifferencesbetweenbilingualsandmonolingualsinavarietyofcognitivedomains.Thesedifferenceshaveproventobeusefulforunderstandingtheimplicationsofbilingualismforcognitivedevelopmentandcognitiveaging.Moreover,therecentworkinneuroimagingandrelatedfieldsdescribedinSection3isbeginningtoelucidatetheneuralcorrelatesthatunderlieproficientlanguageuse.Thequestionposedinthepresentsectioniswhetherthesefindingscanbeappliedtohelppractitionersintheareasofneuropsychology,educationalpsychology,andspeech/languagepathologydealwiththeproblemsofbilingualclientsandpatients.Thechallengetoprofessionalsintheseappliedfieldsisthatbilingualindividualsvaryenormouslyintheirlanguageskills.Afewofthemanyfactorsthataffectthedegreeoflanguageproficiencyinbilingualsareageandmannerofacquisitionofeachlanguage,degreeofuseofeachlanguageoveralifetime,andliteracyandlevelofformaleducationineachlanguage.Itseemslikelythatthesesamefactorswillalsoaffecttheextenttowhichbilingualismmodifiescognitiveprocessingmechan-isms.Itisdifficulttoobtainacomprehensiveassessmentofallrelevantfactorsineachindividualcaseyetsuchassessmentisnecessarytointerprettestperformanceaccurately.Thisuncer-taintyaboutthedetailsofindividualbilingualismcombinedBialystoketal. withthelackoftestsdevelopedspecificallyforusewithbilin-guals,thelackofknowledgeabouthowbilingualismaffectsperformanceonstandardizedteststhatweredevelopedformonolinguals,andthestrongemphasisonlanguage-basedassessmentinclinicalsettingsmakesitdifficulttoanswersomeofthemostcommonreferralquestionsaboutbilinguals.Tosimplifythefollowingdiscussion,weassumethatthebilingualindividualshadearlyexposuretotwolanguagesandthatEnglishisthedominantlanguagespokenbythemajorityofpeopleintheenvironment.However,muchofthediscussionwouldapplyequallywelltoproficientbilingualswhoacquiredoneoftheirlanguageslateinlife,tobilingualswholiveinbilingualcommunitiesinwhichonelanguageisnotclearlyinthemajority,andcertainlytosituationsinwhichEnglishisnotthemajoritylanguage.Threegeneralthemesarecommonwhenbilingualindividu-alsarereferredtoaclinicianforinterventionortherapy.Althoughthespecificquestionsdiffer,thesesamethemesareevidentforchildren,adults,andagingbilinguals.Thefirstthemeistoestablishwhetherthereisacognitiveimpairmentorlanguageimpairment.Inchildren,thisquestionoftentakestheformofaskingwhetherthechildislearningEnglish(thesecondlanguage)asquicklyassheorheshouldbe,andifnot,ifthereisalanguageimpairmentormoregeneraldevelopmentaldelay.Foradultstheconcernisoftenlinkedtotestresults.AswesawinSection1,testsofverbalfluencyandnaminggenerallyreveallowerscoresforbilingualsthanformonolinguals,andtheseverbalscoresarefrequentlylowerthanindicatorsofverbalmemoryornonverbalfunctioningforbilinguals.Inaclinicalsetting,thispatternraisestheconcernaboutthepossibilityofbraininjuryordevelopmentalimpair-mentpreciselywhatthosetestsweredesignedtodiag-noseratherthanthehistoryofbilinguallanguageuse.Forbothchildrenandadults,iflanguageimpairmentisidentified,thereareinevitablyquestionsaboutthebeststrategyforaccommodatingtheimpairmentandforfacilitatingcommuni-cationandrecovery.Forexample,shouldtreatmentbepro-videdinjustoneorinbothlanguages?Woulditbebesttotrytouseprimarilyonelanguagetoeasetheloadonthecom-promisedcognitivesystembyavoidingbilingualism(e.g.,byswitchingtousingonlythemajoritylanguageathome)?AsecondthemeistheneedforadviceonthebestwaytopromoterapidacquisitionofEnglishasthepersonssecondlanguage.Forchildrenthequestionisfrequentlyframedintermsofeducationaloptions:IstotalimmersioninEnglishbest,orisitbettertoencourageparalleldevelopmentofbothlanguagesbyincludingbothaspartoftheacademiccurriculum?Inyoungadults,theconcerniscenteredmoreonacademicachievement,andquestionsattempttodeterminetheroleofbilinguallanguageuseinacademicoutcomes.Inmiddle-agedandolderadults,thefocusagainshiftstolearningthelanguage.Someindividualsareconcernedaboutthelengthoftimeitisrea-sonabletoliveinacountrywithoutlearningtheenvironmentalThethirdthemeismorespecialized.ClinicalinterventionissometimessoughttoassesstheadequacyofEnglishproficiencyforaspecificpurpose,suchasfunctioninginschoolorinaprofessionalsetting.Adequateproficiencyisalsoessentialforsafetyandsecurity,asinunderstandingthecon-versationinamedicalinteractionordiscussingtherisksofamedicalprocedure.Linguisticlevelsthatmaybeperfectlyade-quateforsomepurposesmayfailtosupporttheabilitytounderstandcomplexinformationforwhichcarefulthoughtandcautiousdecisionmakingarerequired.Thesesituationsmayalsorequiretheservicesofaclinician.Thereareanumberofreviewsoncognitiveandlanguageassessmentofbilingualsthatprovideusefulinformationonthechallengesthatarise,onthekindsofquestionstoaskinclinicalsettingstoobtainthenecessaryinformationtointerpretbilingualperformanceonlanguage-basedtests,andonhowbilingualismcanaffectperformanceonspecifictests(e.g.,Altarriba&Heredia,2008;Baker,2000;Cummins,2000;Kohnert,2007;Paradis,2008;Paradis&Libben,1987;Pen&Bedore,2009;Ponto´n&Leo´n-Carrion,2001;Rivera-Mindtetal.,2008;Valde´s&Figueroa,1994).Hereweattempttoconnectquestionsaboutassessmentofbilingualsmorespecifi-callywiththeexperimentalliteraturereviewedabove.Beforeconsideringhowbilingualsdifferfrommonolingualsintheirperformanceonneuropsychologicaltests,itishelpfultoreviewwhattypicallyhappensduringacognitiveassess-ment.Neuropsychologistsreceivereferralsfromparents,schools,andphysicians,usuallywithaveryspecificquestionattached(e.g.,Istherealanguagedisability?IsthepersonbeginningtoshowsignsofearlyAlzheimersdisease?).Theneuropsychologistwillsubsequentlyreviewthepatientsacademicrecordormedicalchartandscheduleanappointmenttoobtainacasehistoryandadministercognitivetests.Thegen-eralquestionsrelatedtocasehistoryarethesameforbilingualsandmonolinguals:Werethereanycomplicationsatbirth?Wasalearningdisabilityeversuspected?Whatwasacademicper-formancelikethroughschool?Whatwasthehighestlevelofeducationattained?Whatistheemploymenthistory?Werethereanylossesofconsciousness?Isthereanyhistoryofsubstanceabuseorotherpsychiatricconditions?Insomecases,therewillalsobeadetailedlanguagehistoryforbilinguals,todeterminewhichlanguageisdominant,whenandhowbothlanguageswerelearned,theextenttowhichbothlanguagesarecurrentlybeingused,andotherfactors(e.g.,Marian,Blumenfeld,&Kaushanskaya,2007).Subsequently,theneuropsychologistwilladministeraseriesofteststoassessavarietyofcognitivedomains(e.g.,mentalstatus,IQ,language,memory,executivefunctions,andvisuospatialskills),usuallywithheavieremphasisonteststhatwillbeusefulinansweringthespecificreferralques-tion.OftenvocabularytestsareusedtoestimateverbalIQ,picturenamingtestsareusedtoidentifythepresenceofcog-nitiveimpairment,andtimedverbalfluencytestsaregiventolookforfrontallobepathology(Lezak,1995).Verbalfluencyperformanceissometimesalsousedtolookforpatternsofperformancethatareassociatedwithcertaintypesofdisease(e.g.,deficitsinsemanticfluencyareassociatedwithAlzhei-mersdiseasewhereasdeficitsinletterfluencyareassociatedBilingualMinds withHuntingtonsdisease;Rohrer,Salmon,Wixted,&Paulsen,1999).Assessmentofbilingualsiscomplicatedbytheproblemthatbilingualismitselfinfluencesperformanceonthesemeasures,anditisoftennotclearwhatadjustmentsshouldbemadetointerpretperformancerelativetothatofmonolingualsonthesametests.AssessingvocabularyknowledgeinbilingualsAstapleofneuropsychologicaltestingistheassessmentofvocabulary,butaswehaveseeninSection1,bilinguals,especiallybilingualchildren,oftencontrolasmallervocabu-laryineachlanguagethancomparablemonolingualsdo,evenintheabsenceofothercompromisingfactors.Howcanclinicalassessmentmakereliablejudgmentsaboutthepotentialforadisabilityordiseaseincontrasttoanormaloutcomeinthecontextofbilinguallanguageuse?Theapproachtakentotestingandinterpretationoftendependsonthenatureofthereferralquestion.Insomecases,relativelysimplereferralquestionsthatcanbesuccessfullyaddressedwithoutmuchknowledgeaboutbilingualismarise.Forexample,parentsmaywonderhowtheirchildsEnglishvocabularyknowledgecomparestothatofhisorhermonolin-gualpeers(notethatinbilingualsocietiesthisquestionmaybelessrelevant,particularlyifmonolingualsarefewinnumber).Insuchcases,itisobviouslyappropriatetoadministeratestthatwasdevelopedforusewithmonolingualEnglish-speakingchildren,andthescoreobtainedwillprovideavalidanswertothequestionbeingasked.However,thepossibilityofinterpretingthatsametestscorewillnotextendbeyondtheanswertothisonesimplequestion.Asagroup,bilingualchildrenwhospeakaminoritylanguageathome(e.g.,anon-EnglishlanguageinanEnglish-speakingenvironment)willobtainlowerreceptiveEnglishvocabularyscoresthanwillmono-linguals,eveniftheirparentsreportthattheyareproficientspeakersofEnglish(Bialystok,Luk,etal.,2010).TheselowerEnglishvocabularyscoresmaybefoundeveninchildrenwithoutmuchproficiencyintheminorityhomelanguageiftheparentsarenotnativespeakersofEnglish,becausesuchchildrenhavereducedexposuretoEnglishvocabularyathome,atleastcom-paredtochildrenwhoseparentsarenativeEnglishspeakersanduseEnglishexclusively.Thedifferenceinvocabularysizeinbilingualsisprobablyabetterreflectionofexperiencethanofabilitytolearn.In6-year-olds,thevocabularydeficitassociatedwithbilingual-ismseemedtoberestrictedtotestitemsclassifiedasunlikelytooccurinaclassroomcontext(Bialystok,Luk,etal.,2010).Similarresultsmaybeobtainedinolderbilingualchildrenandinbilingualadultsand,ifso,suchinformationcouldultimatelybeusefulfordevelopingvocabularyteststhatcatertospecificprofilesofbilinguallanguageexposure.Inaddition,itemanalysesmaybeusefulforinterpretingindividualtestscores.Forexample,ifabilingualchildmissesahome-contextitem(e.g.,toaster)itmaysimplymeanthattherehavebeennoopportunitiestolearnthiswordinEnglishbecauseitisunlikelytocomeupinaschoolcontext.Althoughagroupofbilingualswill,onaverage,scorelowerthanagroupofmonolinguals,individualscoreswillnotnecessarilybelower.Inthelarge-scalestudyoffluentEnglish-speakingbilingualchildrenbetweentheagesof3and10years(Bialystok,Luk,etal.,2010),thedistributionsofbilingualandmonolingualscoresoverlappedmuchmorethannot.Thismeansthatalthoughtheaveragebilingualscorewasabout10standardscorepoints(2/3ofastandarddeviation)lowerthantheaveragemonolingualscore,onlyasmallnumberofbilingualsscoredcompletelyoutsidetherangeofperformanceformonolinguals.Thus,themajorityofbilingualchildrendescribedasfluentinEnglishwillobtainnormalscoresontestsdevelopedformonolinguals.However,itisalsoprobablethatthesesamenormalscoreswillfailtoprovideanaccuraterepresentationoflearningpotential.Vocabularyscoresreflectthecombinedforcesofthetolearnnewvocabularyandthetolearnnewvocabulary.Bilingualswhoscorewithintheaveragerangeformonolingualsmayhavebetter-than-averageabilitytolearn,whichhasallowedthemtoachieveanaveragemonolingualscoredespitehavingfewerlearningopportunities.Animpor-tantconsiderationinsuchcasesisthatcomparisonsbetweenmonolingualandbilingualchildrenwithmatchedvocabularyscoresmaybeinvalidbecausebilingualchildrenwithmonolingual-likevocabularyscoresmaybeprecociouslearners.Conversely,bilingualswhosevocabularyscoresfall2standarddeviationsbelowthemonolingualaveragecouldbelearningdisabled,ortheymaysimplyhavehadlessopportunitytolearnEnglishthantheircasehistoriessuggesttwoconclusionswithverydifferentimplicationsbutwithequallyseriousconsequences.Bilingualswhoscorebelowaveragemaybeinaccuratelydiagnosedwithimpairmentwhennoneispresent,orcouldbediagnosedasnormalforabilingualeventhoughimpairmentisinfactpresentandtreatmentisneeded.Theless-frequentcasesinwhichbilingualsobtainscoresthatarehigherthanaretypicalformonolingualsmayindicateexceptionalabil-itytolearnvocabularyormoreopportunitiestolearnEnglishthanthecasehistoriessuggestagain,twoconclusionswithverydifferentimplications.Muchofthisdiscussionlikelyappliesaswelltobilingualadults,whoalsotypicallyobtainlowervocabularyscoresthandomonolingualadults(e.g.,Bialystoketal.,2008a;Portocarreroetal.,2007).Thisdiscussiondemonstratesthetremendouschallengeininterpretingindividualtestscoresinbilinguals.Evenwiththeavailabilityofnormativedataaboutbilingualperformanceonagiventest,severalfactorscontinuetocomplicateinterpreta-tion.Furtherdifficultyarisesifoneconsidersabroaderrangeofbilingualsatdifferentproficiencylevels.Thepreviousdis-cussionappliesonlytochildrenwhoarejudgedbytheirparentstobefluentinEnglish.SuchchildrencanreasonablybetestedinEnglish(andspecificallyshouldbetestedinEnglishifEnglishistheirdominantlanguage).However,eveninsuchcases,amoreaccurateestimationoflanguageskillswillemergeifbothlanguagesaretested.Parentsmaysometimesoverestimatethedegreeofmajority-languagefluencythattheirchildrenhaveachieved.BilingualswhoarenotdominantinBialystoketal. Englishmustbetestedintheirdominantlanguage,butoftentestsforthoselanguageshavenotbeendeveloped,andtherearevirtuallynotestsfordifferentcombinationsofbilingualtypes.Oneexceptionthatisavailableinmanydifferentlan-guagecombinationsistheBilingualAphasiaTest(theBAT;Paradis&Libben,1987).However,theBATwasdesignedtoassessfluentadultbilingualsforpossiblelanguageimpairment(i.e.,aphasia),anditisnotknownhowbilingualchildrenshouldperformonthistestorevenifthetestisusefulinasses-singbilingualadultswhodonthaveahighdegreesoffluencyintheirtwolanguages.Finally,thesesimplercasesofrelativelyfluent-in-Englishbilingualsareperhapsleastlikelytopresentforreferralinaclinicbecausetheyhavealreadybeensuccessfulinattainingsecond-languagefluency.Amoretypicalpresentationwillbesomeonewhoseemstobehavingtroubleacquiringsecond-languagefluency.ParentsofyoungpreschoolchildrenmaysuspectaproblemiftheirchildseemstobeavoidingEnglishspeakersintheclassroom,preferringinsteadtosocializeonlywiththesmallnumberofotherchildrenwhohappentospeakthesameminoritylanguageathome.Parentsofolderschool-agedchildrenmaybecomeconcernedaboutlowacademictestscoresorlargediscrepanciesbetweenverbal(e.g.,reading/writing)andless-verbal(e.g.,math)academicdomains.(Here,lessverbalismeanttoemphasizethatallacademicsubjectsrequireatleastsomeverbalskills;forexample,mathproblemssometimescomeinparagraphformatorrequireabilitytoreadinstructions.)Insuchreferralcases,itisneces-sarytoassesswhattheopportunitiestolearnEnglishhaveactuallybeensometimeschildrenhaveactuallyhadlessexposuretoEnglishthanisassumedandwhetherornotnor-malamountsoflearninghavetakenplacegiventhoseoppor-tunities.Evenwithadequateassessmentsofopportunitiestolearn,testinterpretationisdifficultbecauselittletonoinfor-mationaboutexactlyhowmuchexposureisneededtoper-formwithinaparticularrangeonanygiventestisavailabletoclinicians.Acreativeapproacharoundtheseproblemshasbeentoprovidealearningopportunityduringtheassessmentsessionitselfandthentodeterminehowmuchlearningtakesplace,anapproachsometimescalledDynamicAssessment(Gutie´rrez-Clellen&Pena,2001;Pena,Iglesias,&Lidz,2001).Thisapproachisbasedoninteractionbetweentheclinicianandthechild.Threetypesofdynamicassessmentare(a)testingthelimits,inwhichfeedbackisprovidedanderrorspursuedthroughfurtherquestioning;(b)graduatedprompting,inwhichthelevelofcontextualsupportismanipulated;and(c)test-teach-retest,inwhichalternativeversionsoftestsofthesamematerialarerepeatedafterteachingtoareasofweakness,inordertoassesslearning(Gutie´rriez-Clellen&Pena,2001).Withthesemethodstheamountofexposureiscontrolleditisprovidedduringthetestingsessionitself.Childrenwhofailtolearn(i.e.,donotshowsignificantimprovementonmea-suresofmodifiability;Pena,Resendiz,&Gillam,2007)areflagged,withahighrateofaccuracy,asprobablecasesofdevelopmentaldelay.Suchtechniquesareextremelyusefulforbilingualsandmonolingualsalike,andtheyprovideameansforobtainingaccurateassessmentswithlessconcernabouthowtointerpretpastopportunitiestolearn.Intheory,bilingualdisadvantagesinvocabularyknowledgeshoulddecreasewithageastheirtimetolearnwordsinbothlanguagesincreases.Althoughvocabularyknowledgecontin-uestoincreasewellintoolderage(Verhaeghen,2003),newwordsmaybelearnedatafasterratebeforeknowledgereachesaparticularpoint(perhapsatypicaladult-vocabularyreper-toire).Inotherwords,bilingualsshouldcatchuptomonolin-gualsasyearsofimmersioninEnglishaccumulate.Onewaytotestwhetherthisisindeedthecaseistoaskwhetherthevoca-bularydeficitassociatedwithbilingualismdecreasesinchil-drenastheyprogressthroughschoolandbeyondthatacrossthelife-span.Indeedtherehasbeensomesuggestionthatbilin-gualchildrenachievemonolingual-likevocabularyscoreswithincreasedtimeinschool(Hamers&Blanc,2000).However,thecatchingupnotionisbesttestedwithalongitudinaldesign,andtoourknowledgesuchstudieshavenotbeenreported.Moreover,bilingualsmayappeartobecatchinguponlybecausethetestmaterialsarenotdifficultenoughtorevealpersistentdifferencesbetweenbilingualsandmonolin-guals.Whentestedexclusivelyfortheirknowledgeofvery-low-frequencywordsintherelativelydominantlanguage,forexampleinstudiesofthetip-of-the-tonguephenomenon,adultbilingualsconsistentlyreportrecognizingfewerofthetargetedvocabularywordsthanmonolingualsdo(e.g.,Gollan&Silverberg,2001;Gollan&Brown,2006).Tip-of-the-tongueexperiencesareretrievalfailuresinwhichpartialphonologicalinformationisavailable;theygenerallyoccurforlow-frequencywordsbutappeartobemorebroadlybasedforbilinguals.Thus,differencesbetweenbilingualsandmonolin-gualsinopportunitiestolearnvocabularywillbelessapparentinsettingsthatonlyrequireknowledgeofrelativelyeasy,frequentlyoccurringwordsthantheywillbeinsettingsthatrequireknowledgeofdifficult,low-frequencywords(Gollanetal.,2008).Thismaybebecause,byvirtueofusingeachlanguageonlypartofthetime,bilingualswillhavehadrelativelylessexposuretowordsineachlanguagethanwillmonolinguals(theweaker-linkshypothesisdescribedinSection1),althoughtheywillhavehadsufficientexposuretolearnfrequentlyencounteredwords.ConfrontationnamingConfrontationnamingisatestingmethodinwhichpicturesarepresentedtoparticipants,whoareaskedtonamethemasrapidlyaspossible.OneofthemostcommonlyusedsuchneuropsychologicaltestsistheBostonNamingTest(BNT;Kaplanetal.,1983).Thistestcontains60black-and-whitelinedrawingsthatshowasingleobjectthatspeakerstrytoname.Thepicturesareeasyatthebeginningofthetest(e.g.,abed)butbecomeprogressivelymoredifficult,endingwithuncom-monobjectsencounteredinlimitedcontexts.TheabilitytonamepicturesissensitivetochangesincognitivefunctioningandisthereforeusefulfordetectingsubtlebraininjuriesBilingualMinds (Lezak,1995).Unfortunately,thistestmayhavemorelimitedutilityforassessingbilinguals,becausecognitivelyintactbilin-gualsobtainlowerscoresthanmonolingualsontheBNTandotherstandardizedtestsofpicturenaming(e.g.,Robertsetal.,2002)suchastheExpressiveVocabularyTest(e.g.,Portocarreroetal.,2007).Outsideofclinicalsettings,studiesofpicturenamingmeasurebothnamingsuccess(thenumberofcorrectretrievals)andthetimeneededtonamepictures.Suchstudiesrevealaverysubtlebilingualdisadvantage(e.g.,itmaytakebilinguals60millisecondslongerthanmonolingualstonameapicture;Gollan,Bonanni,&Montoya,2005).Thisresultappliestobilingualsimmersedinadominantbutsecond-learnedlanguage(e.g.,Gollanetal.,2008)andtobilingualslivinginabilingualsociety(Ivanova&Costa,2008).Picture-namingdeficitsinbilingualscouldariseforthesamereasonsasreceptivevocabularydeficitsnamely,lessfrequencyofuseofspecificwordsthanformonolinguals.Alternatively,itmaybebecauseofdual-languageactivationthatis,theneedtoselectonelanguageinthefaceofcompetitionfromtheotherone.Itisalsopossiblethatbothfactorsmaybeoperating.Someoftheburdenassociatedwithbilingualismseemstobebettermanagedwithincreasedagearesultthatisconsistentwiththenotionofafrequencylagforbilinguals.Inonepicture-namingstudy,olderbilingualswererelativelyfastertoproducelow-frequencypicturenamesinanondominantlanguagethanwouldbeexpectedbasedontheirotherwiserelativelyslownamingtimesrelativetoproficiency-matchedyoungbilinguals(Gollanetal.,2008).Becauselow-frequencywordsinthenon-dominantlanguagewillbemostvulnerabletothefrequency-of-uselagassociatedwithbilingualism,thesewordsarealsomostlikelytobenefitfromtheincreasedexposuretolanguageassociatedwithage.Theage-relatedadvantageforproducinglow-frequencywordsisalsoevidentinstudiescomparingoldertoyoungermonolingualspeakers:Likeolderbilinguals,oldermonolingualsconsistentlyproducenamesforpictureswithverylow-frequencywordswithgreatersuccessthanmatchedyoungmonolinguals(forreviewseeGollan&Brown,2006).Itmaybethatagingallowsfortheaccumulationofexperiencetodealwithlow-frequencywords.Thefindingthatolderbilingualsareinsomewaysbetterbilingualsthanyoungerbilingualsmayseemunexpectedfromtheperspectiveofbilingualismasanexerciseincognitivecontrol.Ifthefrontallobes(Raz,2000;West,1996)andexecutivecontroldeclineinolderageandareneededtosuppressthedominantlanguageduringretrievalofthenondominantlanguage,thenolderbilingualsshouldhavemoredifficultythanyoungbilingualsinproducinglow-frequencywordsinthenondo-minantlanguage.Itmightbeaskedwhetherolderbilingualsperformbetterbecausethelow-frequencywordsarearchaicwordsmorefamiliartoolderthantoyoungerparticipants.However,controlledstudiesselectmaterialsthatarehighlyfamiliartobothyoungandoldadults,andinthetimedpicture-namingstudywithbilinguals,thelow-frequencytargetswereallhighlyfamiliarandcurrent(e.g.,crutches,awhistle,ascarf,adustpan;seeappendixinGollanetal.,2008).Mostimportantly,therelativeage-relatedadvantageappearedonlyinthenondomi-nantlanguage,whereasthesameconceptsandwordsdidnotdemonstrateanyage-relatedadvantageinthedominantlanguage(orinmonolinguals).Thus,itseemsthataccumulateduseoveralifetimehasitsgreatestinfluenceontheverylowest-frequencywords,therebyoffsettingsomeaging-relateddeficitsinretrieval.Anumberoffactorshavebeenshowntoreduceoreveneliminatethebilingualdisadvantageinpicturenaming,andthisraisesthequestionofwhatwouldbethebestwaytoadjusttestsofpicturenamingtoaccommodatebilingualabilityandenableclinicianstoperformreliableassessments.Theanswertothisquestionmayvarywiththereferralquestion,andtheimplica-tionsofthesefindingsfordiagnosisandtreatmentofbilingualsarenotyetestablished.Forexample,bilingualsnamepicturesmorequickly(Costa,Caramazza,&Sebastia´n-Galle´s,2000;Hoshino&Kroll,2008)and,insomecases,withnodisadvan-tagerelativetomonolinguals(Gollan&Acenas,2004)ifthetestconsistsofpictureswithcognatenames.Cognatesreducebilingualdisadvantagesviajointactivationoftargetphonemes(sounds)throughseparatelexicalrepresentationsineachlanguage(forareview,seeCosta,Santesteban,&Can2005;forresearchshowingincreasedactivationforcognates,seeBroersma&deBot,2006).Toillustrate,thelexicalrepre-sentationsofanditsSpanishtranslationmanysharedsounds,butanditstranslationactivatenosharedsounds.Asimilarreductioninbilingualdisadvantagemaybeobtainedbyaskingparticipantstoretrievenamesofpeople(Gollan,Bonanni,&Montoya,2005).Bilingualsrelativeeaseatproducingpropernamesmayhaveadifferentmechanismfromcognateeffects;bilingualsmayeffectivelybemonolingualforproper-nameproductionbecausepropernamesaregenerallysharedbetweenlanguages(e.g.,isbasicallythesameinHebrew,English,Spanish,etc).Thefindingthatbilingualsarebetterabletonamepictureswithcognatenamescouldbeusefulclinically.Onepossibilityisthatbilingualpicture-namingtestsshouldfocusoncognates(orpropernames)forwhichbilingualsperformmuchlikemonolinguals.However,removingthedisadvantagemaycom-promiseatestasanassessmentinstrument.Forexample,thepresenceofcognateeffectsondominant-languageproductionimpliesthepresenceofdual-languageactivationevenwhenbilingualsaretestedexclusivelyintheirrelativelymoredomi-nantlanguage.Thus,apossibleproblemwithusingcognatesisthatcognatesmayincreasetheextenttowhichbothlanguagesareactive,andthismayhaveotherundesiredeffectsontestperformance(notethatcognate-facilitationeffectshavealsobeenfoundinbilingualchildren,butthisliteraturehasfocusedprimarilyonreceptivevocabularyratherthanonpicturenaming;August,Carlo,Dressler,&Snow,2005;MendezPerez,Pena,&Bedore,inpress).Similarconsiderationsapplytoanotherwaytoreducebilingualdisadvantagesinatestingorassessmentsituation:toallowbilingualstouseeitherlanguagetonamepictures(Kohnert,Hernandez,&Bates,1998;Gollan&Silverberg,2001).Thisapproachissometimescalledcompositeorconceptualscoring.ThescoringmethodimprovesBialystoketal. bilingualspicture-namingscoresinyoungadults(Kohnertetal.,1998),inelderlybilinguals(Gollanetal.,2007),andeveninbilingualswithAlzheimersdisease(Gollan,Salmon,Montoya,&daPena,2010).Thus,whennamingisuntimed,thecompositescoringoptionisnotassociatedwithanyobservableprocessingcostandonlyfacilitatesnamingperfor-mance.Intimedpicturenaming,theoptiontouseeitherlan-guageproducessignificantlanguage-switchingcostsbutalsorevealscompellingfacilitationeffects(Gollan&Ferreira,2009).Specifically,whengiventheoptiontouseeitherlan-guage,unbalancedbilingualsswitchlanguagesinamannerthatresemblesamorebalanced-bilingualprofileoflanguageswitching(i.e.,noswitch-costasymmetry;Costa&Santeste-ban,2004;Costaetal.,2006).Inaddition,olderbilingualsperformmuchmorelikeyoungbilingualsinvoluntarylan-guageswitching,whereastheyhaveconsiderabledifficultywithcuedlanguageswitching(Hernandez&Kohnert,1999).Thus,althoughlanguagemixingmightallowbilingualstocom-municatebetterinnaturalsettings,itisnotnecessarilythecasethatallowinglanguagemixingandswitchinginaclinicalsettingwillleadtomoreeffectivediagnosisandtreatment,becausetheeither-languagescoringmethodmayactuallyobscuredifferencesbetweenpatientsandcontrols(Gollanetal.,2010),whichiscoun-terproductiveifthegoalistoidentifyimpairmentsinbilinguals.Inbilinguallanguageassessment,thecostsassociatedwithlan-guageswitchingandmixingcanbeavoidedbytestingeachlan-guageinaseparatetestingblock.Theoppositeoutcomemaybefoundforcognates.Itmaybe,forexample,thatlanguage-impairedbilingualchildrenarelessabletobenefitfromcognatemanipulationsthantypicallydevelopingbilingualchildrenare.Ifthisisso,thentheabilitytobenefitfromcognatestatusitselfcouldfunctionasakindofbilingual-specificlitmustestforcognitiveimpairment.Inotherwords,failuretodemonstrateimprovedlexicalaccessforcog-natewordsrelativetotypicallydevelopingbilingualchildrenwouldsignalsometypeoflanguageimpairment.Importantly,however,itisnecessarytoconsidertherelativedominanceofthetwolanguagesforthebilingualchildandtherelationbetweenthatdominanceandthelanguageofassessment.Inrelativelybalancedbilinguals,cognatescanreducebilingualdisadvantagesinboththedominantandthenondominantlanguages(Gollan&Acenas,2004;Gollanetal.,2007),butsuchreductionsaremostrobustwhenbilingualsaretestedintheirnondominantlanguage(e.g.,Costaetal.,2000;Gollanetal.,2007).AstudybyvanHellandDijkstra(2002)usinglexical-decisionandword-associationtasksshowedthathighlevelofproficiencyeveninanL3caninfluenceprocessingspeedinthedominantlanguage.TheclinicalsignificanceisthatitisnotpossibletodiscountnondominantlanguageknowledgebecauseevenanL3canhaveaneffectonL1ifthedegreeofproficiencyintheL3ishighenough.Therefore,itispossiblethatcognateeffectsinthedominantlanguageoccuronlyinrelativelybalancedbilingualswhoarealsocognitivelyintact.Alternatively,cognateeffectsinthenondominantlanguagemightbemagnifiedincognitivelyimpairedbilinguals.Additionalstudiesareneededtodeterminetherelationsbetweencognateeffectsontheonehand,andlanguageandcognitiveassessmentofbilingualchildrenontheother.VerbalfluencyinclinicalpracticeResearchusingtheverbalfluencytestasanexperimentaltoolwasdescribedinSection1.Theresultsshowedconsistentbilin-gualdisadvantagesonsemanticfluency(exceptwhenreceptivevocabularyknowledgeismatched),withsomewhatlesssevereorlesscertaindisadvantagesonletterfluency.Clinically,thegreaterbilingualdisadvantageinsemanticfluencythaninletterfluencycanbemisleading,becausethisisthesamepatternoffluencyperformancethatisfoundinmonolingualswithearlyAlzheimersdiseaseascomparedwithnormals(Butters,Granholm,Salmon,Grant,&Wolfe,1987).Thiscreatesadilemmaforneuropsychologists:IsanindividualshowingsignsofearlyAlzheimersdiseaseorisshesimplyshowingtheeffectsofbilingualismonfluency?Theverbalfluencytestisanimportantinstrumentinthebatterytoassesspatientsforcogni-tivedecline,sotheambiguityoftheresultsobtainedfrombilin-gualspresentsaclinicalproblem.Todevelopfluencytestsforbilingualspeakers,itisnecessarytounderstandwhysemanticfluencyismoreaffectedbybilingualismthanletterfluencyis.Asweexplainedearlier,letterfluencyrequiresgreaterrecruit-mentofexecutivecontrol,perhapsoffsettingbilingualsdisad-vantagesinlexicalretrieval.Adifferentapproachtoassessingolderbilingualsistouseataskrelatedtoverbalfluency,onethatreflectssemanticprocessingyetdistinguishesthecognitivemechanismsthatunderlietheeffectsofbilingualismfromthosethatareinvolvedinAlzheimersdisease.Inthesemantic-associationtask(deGroot,1989),speakersaregivenacue(e.g.,bride)andareaskedtoproducethefirstresponsethatcomestomindinrelationtothecue.Theoverwhelmingmajorityofresponsesinthistaskaresemanticallyrelatedtothecues,andthisistrueforallspeakers,whethertheyaremonolingualorbilingualandwhetherornottheyarecognitivelyimpaired.However,bilingualsproduceslightlybutsignificantlydifferent(orlesstypical)responsesthanarenormallyfoundinmonolinguals.Forexample,giventhecuebride,theymightsayprettyinsteadofthemoretypicalgroom(Anto´n-Me´ndez&Gollan,inpress).AsimilareffectwasreportedinmonolingualswithAlzheimersdiseaseascomparedtocognitivelyhealthycontrols(Gollan,Salmon,&Paxton,2006).Tothispoint,therefore,thereisthesameinterpretationproblemasthereisforverbalfluency,becausebothbilingualismandAlzheimersdiseaseproducethesameoutcome.However,furtherexperi-mentswiththesemantic-associationtaskdemonstratedthatonlythebilingualeffectismodulatedbylexicalfrequency.Bilingualsproducedthesameassociationsasmonolingualsdowhenthecueswerestronglyassociatedtohigh-frequencywords.Incontrast,speakerswithAlzheimersdiseaseproducedatypicalresponsesregardlessofassociatefrequency(Anto´n-´ndez&Gollan,inpress).ThisevidenceisconsistentwiththenotionthatAlzheimersdiseaseimpairssemanticrepresentationsthemselves(Butters,Salmon,&Heindel,BilingualMinds 1990),whereasinbilinguals,difficultywithlexicalaccesscansometimesleadsthemtoperforminwaysthatimplysemanticdeficitswhennonearepresent.Aswithconfrontationnaming,thereisanimportantroleforcognatestatusintheperformanceofverbal-fluencytests,sotheinterpretationofresults,especiallyforclinicalassessment,needstoaccountforthisfactor.Specifically,inbothsemanticandletterfluency,bilingualswhospeaklanguageswithmanycognatesspontaneouslyproduceasmanycognateresponses(e.g.,lemon)asmonolingualsdobutfewerresponsesforwordsthatarenotcognates(Sandovaletal.,2010).Putanotherway,wordsthatarecognatesacrossthetwolanguagesaregeneratedasoftenbybilingualsastheyarebymonolingualswhoonlyknowtheminonelanguage,butuniquewordsareproducedlessoftenbybilinguals.Inthissense,thegreatestdifferenceinperformanceisinthelowerproductionofnoncog-natewordsbybilinguals,whoappeartohaveeasieraccesstowordsthatoccurinboththeirlanguages.Thesefindingssuggestthatbilingualswhospeaklanguageswithanextremelyhighpro-portionofcognates(e.g.,Catalan-Spanishbilinguals)mayexhibitnofluencydisadvantage,evenforsemanticfluency.Anothersimilaritybetweenverbalfluencyandconfrontationpicturenamingisthatbilingualsretrieveagreaternumberofconceptnamesiftheyaretestedinbothlanguages(Bedore,a,Garc´a,&Cortez,2005).However,unlikepicturenamingintheBNT,fluencyscoresdonotincreaseifbilingualsareallowedtousewhicheverlanguagecomestomindduringasingletrialandsotoswitchbetweenlanguages(Gollanetal.,2002;DePicciotto&Friedland,2001).Thelackofanimprove-mentinfluencyscoreswhenbothlanguagesareusedmayreflectthecostsoflanguageswitching.ThetimingallowedtonameeachpictureintheBNT,about6seconds,istoolongtodetectthemillisecondcostoflanguageswitching,soonthistasknoswitchingcostsarereported.Presumably,onamoretightlytimedpicture-namingtaskallowingresponsesineitherlanguage,bilingualswouldnamefewerpicturesthanwouldmonolingualsinafixedamountoftime(e.g.,60seconds),becauseoftheadditionaltimeneededtocarryoutthelanguageswitch(Gollan&Ferreira,2009).Becausebilingualismaffectsverbalfluencyinanumberofinterestingways,therearevariouspossibilitiesforreducingthebilingualfluencydisadvantage.However,reducingthisdisad-vantagemaycompromisethereliabilityoftheinstrumentasanassessmenttoolforbilinguals,soitisnotclearwhatcombi-nationoffluencytestswouldbemostusefulfordiagnosisofcognitiveimpairmentinbilinguals.Minimally,interpretationofthetestscoresneedstobemodifiedtoaccommodatethesys-tematicdifferencesthataccompanybilingualperformance,butultimatelyitmaybepossibletodevelopfluencyteststhatarespecificallytargetedtoabilingualpopulation.TheassessmentofexecutivefunctionsManyofthelinguisticskillsthatbilingualsgenerallyperformmorepoorlythanmonolinguals(reviewedinSection1)areincludedintypicalassessmentbatteries,oftenusingthesameinstrumentsasthoseusedinresearch.Therefore,understandinghowtointerpretbilingualperformanceonthosetestsisacrucialconcernforneuropsychologists.However,inSection2wedescribedavarietyofnonverbalcognitivetasksonwhichbilingualsgenerallyperformbetterthanmonolinguals.Thesetasksweremeasuresofexecutivecontroland,aswehaveargued,theexperienceofbilinguallanguageusehasthebeneficialout-comeofenhancingtheselevels.Whataretheclinicalimpli-cationsofthisadvantage?Theimplicationsofthisbilingualadvantageforclinicalassessmentaremorelimitedthanthebilingualdisadvantageinlexicalretrievalforseveralreasons.Perhapsmostimportantisthegreatemphasisonverbalskillsinclinicalassessments,withamoreminorrolefornonverbalcognitiveperformance.Therefore,thebilingualadvantagesfoundinnonlinguistictaskswillhaverelativelylittleeffectonthecognitiveprofilesgeneratedinclinicalsettings.Anotherimportantpointisthatmanyofthetasksshowingbilingualadvantagesinexperimen-talstudies(e.g.,theSimontaskandtheAttentionalNetworkTask)arenotusedinclinicalsettings.AnimportantexceptionistheStroopcolor-word-namingtask,whichiscommonlyusedtomeasureattentionandisdiag-nosticofavarietyofconditionsassociatedwithcognitiveimpairment(e.g.,Lezak,1995).Aswehaveseenearlier,bilin-gualsgenerallysufferlessStroopinterferenceandgreaterStroopfacilitationthanmonolingualsdo(Bialystoketal.,2008a;Herna´ndezetal.,2010).Severalconsiderationsmakeitdifficulttointerpretthesedifferences,however.Forexample,performanceontheStroopisaffectedbylanguageproficiency(Tzelgov,Henik,&Leiser,1990;Rossellietal.,2002).Becauseofthis,itispossiblethatonlyhighlyproficientbilin-gualswillexhibittheadvantageintheirdominantlanguageandthatdisadvantagesmaybefoundifbilingualsaretestedinalessdominantlanguage.Equally,itmaybethatasmallerStroopeffectwouldbefoundfor-proficientbilinguals,sincethemeaningofthecolorwordwouldbelessautomati-callyactivatedandthereforelessinterfering.However,Bialystoketal.(2008a)consideredthatpossibilityanddividedeachofthemonolingualandbilingualgroupsintosubgroupsbasedonthespeedwithwhichtheyreadthenameofthecolorwordwhenitwaswritteninblackink.TheideawasthatfasterreadingtimesshouldleadtomoreinterferenceandthereforealargerStroopeffect.Therefore,comparingthefastbilingualreaderswiththeslowmonolingualreadersshouldreducethesizeoftheStroopeffect,possiblyreversingthedirection.Nonetheless,theanalysisshowedthatbilingualscontinuedtorecordasmallerStroopinterferenceeffectthandidmonolin-guals,evenwhenconsideringonlythebilingualsforwhomreadingtheEnglishwordswasthemostautomatic.ThefacilitationeffectsfoundforbilingualsintheStrooptaskmightbeinterpretedasabilingualdisadvantage.IncreasedfacilitationeffectshavebeenfoundinmonolingualswithAlzheimersdiseasewhencomparedwithhealthycontrols(Spieler,Balota,&Faust,1996)andinchildrenwhencomparedwithadults(Wright&Wanley,2003).Thedisadvan-tageviewoffacilitationisthattheseeffectsindicateincreasedBialystoketal. inadvertentfocusofattentiononthewordduringcolornaming(MacLeod&MacDonald,2000;Spieleretal.,1996).Note,however,thattheversionoftheStrooptaskusedinexperimentalresearchisnotexactlythesameastheversionusedintheclinic.Forexample,experimentalstudiestypicallyuserawinterferencescoreswhereasclinicassessmentreliesonaspeed-adjustedinterferencescore.Similarly,congruenttrialsaretypicallynotadministeredinclinicalsettings.Therefore,moreinformationaboutpreciselywhattypesofbilingualsexhibitaStroopadvantage,theoriginofbilingualeffectsontheStrooptask,andperhapsmostimportantlythedistributionofscoresisneeded.5.BilingualismintheWorldTheconstantuseoftwolanguagesisanexperiencethatleavesitsmarkfarbeyondtheimmediateandobviousdomainofcommunication.Aswehaveseeninthisreview,itmodifiestheleveltowhichsomefeaturesoflinguisticsystemsmaybelearnedandthewayinwhichtheyareused;itenhancesaspectsofcognitiveprocessing,particularlythoseinvolvedintheexec-utivecontrolsystem;itrecruits,andmostlikelyadapts,theneuralnetworksinvolvedinthecontrolofnonverbalprocessestomodifytheiruseforverbalprocesses;anditintervenesinclinicalassessmentbypresentingaprofilethatmaynotbeaccuratelycapturedbymonolingualnorms.Thesearesignifi-cantconsequencesthatcoverbothindividual(e.g.,cognitivedevelopmentanddecline)andpublic(e.g.,assessmentanddementia)outcomes.Giventhiscontext,thequestionsposedinthisfinalsectionconcerntheimplicationsofbilingualismforpublicpolicydecisions,especiallyperhapsintheareasofeducationandhealthcare.Thecurrentprevalence(andrapidgrowth)ofbilingualismintodayshighlyinterconnectedworldmakethesequestionsrelevantandurgent.InlightofthedramaticnumbersnotedintheIntroduction,weconcludebyaddressingspecificquestionsaboutbilingualismthatconcernbothindividualandsocialissues.BilingualeducationNotallparentshavetheopportunitytoexposetheirchildrentoasecondlanguageathome,yetmanyunderstandthevalueofbeingabletocommunicateinanotherlanguage.Oneoptioninthesecasesistofindalternativesinformaleducation.Apopularprograminthisregardisimmersioneducation.Intheseprograms,schoolinstructiontakesplaceinalanguagethatisnotthelanguageofthehomeorthecommunity(e.g.,FrenchinstructioninEnglishCanada,SpanishinstructionintheUnitedStates)andchildrenareexpectedtousethislan-guageinalltheircommunicationwithteachersandfriendswhileatschool.Therefore,childrendevelopfairlyhighcompe-tenceinthislanguage,eventhoughtheydonottypicallyachievethelevelofanativespeaker(forreview,seeGenesee,1985;Johnson&Swain,1997).Butdoesthislimitedschoolexposuremakethesechildrenbilingualbythecriteriausedinthisreviewand,therefore,affectedbythecognitiveandlin-guisticoutcomeswehavedescribed?Thequestioncanbecastmorebroadlyasaninquiryregardingthedegreeofbilingualismnecessaryfortheoutcomesobservedformorefullyfunctioningbilinguals.Thereislittleevidenceonthispoint,buttheavailablestudiessuggestthatthereisacorrela-tionbetweenthedegreeofbilingualismandtheextentoftheimpactofbilingualismoncognitiveandlinguisticprocessing.EarlystudieswithchildreninFrenchimmersionprogramsshowedthatbothmetalinguistic(Bialystok,1988)andcognitive(Bialystok&Majumder,1998)outcomesforthesechildrenwerebetweenthosefoundformonolingualchildrenandthosefoundforbilingualchildrenwhowerefullyfluentinbothlanguages.Moregenerally,Luk(2008)compared120bilingualadultswithvaryingdegreesofbilingualismtoagroupof40monolingualsonlinguis-ticandcognitiveoutcomesandagainfoundlargereffectstobeassociatedwithgreaterdegreeofbilingualism.Extendingthispatterntoeducation,itisreasonabletoassumethatthereisacumulativeeffectoflearninglanguagethat,atleastintheintenseenvironmentofimmersionpro-grams,conferssomeofthecognitiveadvantagesonchildreneveniftheydonotbecomehighlyfluentspeakers.Importantly,therearefewifanycostsofimmersioneducationformostchil-dren,althoughindividualcasesmaypresentspecialchallengesthatneedtobeconsidered.Morelanguages,morebenefits?Bilingualism,aswehaveexplained,leadstospecificbenefitsincognitiveprocessing,andeventhelimitedbilingualismthatcomesfromimmersioneducationproducessomeminimalformofthiseffect.Bythesamelogic,then,doestrilingualismleadtoevengreaterbenefitsthanbilingualism,actingassomethinglikesuper-bilingualism?Theevidenceonthispointisscant.AninterestingstudybyKave´etal.(2008)comparedgeneralcognitivelevelinalargesampleofolderadultslivinginIsraelasafunctionofhowmanylanguagestheyspoke(therewerenomonolingualsinthegroup).Theyreportedsignificantlyhighermaintenanceofcognitivestatusinolderageintrilingualsthaninbilinguals,andevengreatermaintenancebymultilingualswhospokefourormorelanguagesthanbytrilinguals,althoughthemeasureofcognitiveleveltheyusedwasnotveryprecise.Similarly,othershavereportedlaterageofonsetofAlzheimersdiseaseinmultilingualsascomparedwithbi-andtrilinguals,aswewilldescribe(Chertkowetal.,2010).How-ever,perhapsforbilingualsbutalmostcertainlyformultilinguals,itispossiblethatpeoplewhoareabletomaintainknowledgeofmultiplelanguagesmaystartoutadvantagedincertainways.Itistooearlytoconcludewhattheeffectofknow-ingmorethantwolanguagesmightbeoncognitiveoutcomes.Adifferentkindofoutcomecanbefoundinlanguagelearning.Monolingualchildrenlearningtheirfirstlanguagesometimesuseastrategyofdisambiguationtorapidlyfigureoutthemeaningofnewwordsbyassumingthateachobjecthasoneuniquename,asdiscussedinSection1.However,Byers-HeinleinandWerker(2009)extendedthisideaandBilingualMinds compared1½-year-oldchildrenwhowerebeingraisedinmonolingual,bilingual,ortrilingualhomes.Theresultsshowedastrongrelianceonthisdisambiguationstrategybymonolingualchildren,amarginalandnonsignificantuseofthestrategybybilingualchildren,andnoevidenceatallforthisstrategyintrilingualchildren.Thus,thenumberoflanguagesintheenvironmentmodifiedchildrensexpectationsaboutwordsandtheirmeanings,possiblysettingthestagefordifferentpathsoflanguagelearning.BilingualaphasiaanditstreatmentAphasia(word-findingdifficulties)isthecommonestoutcomeofstroke,andyetourunderstandingislargelyrestrictedtomonolingualspeakers,whereasasignificantportionofstrokepatientsarebilingualaproportionthatissettoincrease.Clinicalmanagementishamperedbecausethereisnocurrentbasisforpredictingspeech-productiondifficultiesfollowingstrokeinbilingualspeakers.Recoverypatternsarediverse(Green,2005;Paradis,2004):Forinstance,bothlanguagesmayrecovertothesamerelativepremorbidlevel(parallelrecov-ery),onemayrecoverbetterthananother,ortheprogressiverecoveryofonelanguagemayimpairtherecoveryoftheother.Withoutanunderstandingofthecausalbasesoftheserecoverypatterns,includingthenatureofthecontrolprocessesinvolved,therecanbenoprincipledbasisfortreatmentandnorationalbasisforidentifyingtheresourcesrequiredfortreatment.Forinstance,iftreatmentinonelanguage(e.g.,theL1orcurrentdominantlanguage)transferstoanother,thenmonolingualspeechtherapycouldhelpintherecoveryofbothlanguages.Howeverevidenceonthispointisequivocal,largelybecausetherearefewwell-controlledstudies(seeKohnert,2009,forarecentreview).Eventhedecisiontotreatinonelanguageratherthantworeflectsanuntestedassumptionthatmayormaynotbeappropriatetotheindividualcase.Forinstance,individ-ualswithaparallelrecoverypatternfrequentlyself-cueandproduceacorrectwordinthenontargetlanguageinordertoretrievetheintendedword.Proscribinguseofthenontreatedlanguagemaynotbejustified(Ansaldo,Marcotte,Scherer,&Raboyeau,2008).AcasestudyreportedbyAnsaldo,Saidi,andRuiz(2010)exemplifiesthevalueofusingthepatientsbeha-viorinbothlanguagesandofconsideringthecontrolprocessesinvolved.TheytreatedahighlyproficientSpanish-Englishbilingualwithasubcorticallesionthatincludedtheleftcau-date.Hehadword-findingdifficultiesinbothlanguagesandinvoluntarilyswitchedbetweenlanguageswithinconversationswithmonolingualpartners.Onthesuppositionthatdistinctcontrolprocessesmediatetranslationandspeechinjustonelanguage(Green,1986),Ansaldoetal.developedanelegantprocedure(switchbackthroughtranslation)thatmadeuseoftheseinvoluntarylanguageswitchesandtreatedthepatientOurreviewindicatestheintimaterelationshipbetweenlanguagecontrolandtheprocessesofcognitivecontrol.Weexpectthatsuccessfullanguagerecoverywillbeassociatedwithatightercouplingbetweenregionslinkedtolanguageprocessingandregions(frontalandsubcortical)associatedwithcontrol(Green,2008).Preliminarydatausingfunctionalneuroimagingtoexaminechangesinregionalcouplingduringrecoverysupportthisconjecture(Abutalebi,DellaRosa,Tettamanti,Green,&Cappa,2009).Ifcontrolfunctionsareastrengthofbilingualpatients,thentreatmentshouldmakeuseofthem(Penn,Frankel,Watermeyer,&Russell,2010).Moregenerally,treatmentsaimedatenhancingormakingmoreeffectiveuseofcognitive-controlprocessesmayprovetobeausefuladjuncttoconventionaltreatmentderivedfromresearchonmonolingualpatientswithaphasia.ProtectionagainstdementiaInprevioussections,wereviewedtheevidenceshowingthatbilingualchildrenandadultsenjoyanadvantageovertheirmonolingualcounterpartsinaspectsofattentionandcognitivecontrol.Insomecases(e.g.,Bialystoketal.,2004),thisbilin-gualadvantageactuallyincreasesinolderadulthood,inthesensethatperformancefallsoffmoresteeplywithincreasingageinmonolingualsthanitdoesinbilinguals(seeFig.3b).Thisresultmaybeinterpretedasshowingthatbilingualismservestoprotectagainstsomeaspectsofage-relatedcognitiveloss,andpromptsthequestionofwhetherbilingualismmightoffersomeprotectionagainstpathologicaldecline,specificallyagainsttheonsetofdementia.Suchprotectionmightbeconsideredoneformofcognitivereservetheprotectionofcognitivefunctionbystimulatingactivities(Stern,2002).Bialystok,Craik,andFreedman(2007)conductedastudyofhospitalrecordsandfoundthatasampleof93lifelongbilingualsexperiencedtheonsetofsymptomsofdementiasome4yearslaterthanacomparablesampleof91monolingualpatients.Thetwogroupswereessentiallyequivalentonotherfactorsthatmighthaveinfluencedtheresult.Thisinitialstudywasfollowedbyanother(Craik,Bialystok,&Freedman,2010)inwhichapproximately100bilingualand100monolingualpatientsdiagnosedwithprobableAlzheimersdiseasewerequestionedaboutageofonsetandotherrelevantfactors.Inthissample,thebilingualgrouphadtheirfirstclinicvisitmorethan4yearslaterthandidthemonolingualsandhadexperiencedsymptomsofdementiamorethan5yearslaterthantheirmono-lingualcounterparts.Asinthefirststudy,thegroupswereequivalentincognitivelevel(MMSEscore)andthemonolin-gualshadthegreateradvantageintermsofeducationandoccu-pationalstatus.Therewerenodifferencesintheseresultsinsubgroupsofimmigrantsandnonimmigrants.ArecentstudyfromaMontrealgroup(Chertkowetal.,2010)hasgivenpartialsupporttothesefirstfindings.Intheirinvestigation,Chertkowandcolleaguesfoundabilingualdelayintheonsetofsymp-tomsinanimmigrantgroup,aswellasinanonimmigrantgroupwhosefirstlanguagewasFrench,butnotinanonimmi-grantgroupwhosefirstlanguagewasEnglish.Forpeoplewho(definedasspeakingthreeormorelan-guages),thedelayofonsetwasagainfound.Takingadifferentapproach,Schweizer,Ware,Fischer,Craik,andBialystok(2010)examinedsmallersamplesofBialystoketal. monolingualandbilingualpatientsdiagnosedwithprobableAlzheimersdiseasewhohadalsoreceivedaCTscan.Thesampleswerematchedoncognitivelevel,soifbilingualismboostscognitivereservemaintainingcognitivefunctionsdespiteaccumulatedbrainpathologythebilingualgroupshouldshowevidenceoflesionburden.Thiswasexactlytheresult:Thebilingualgroupshowedsubstantiallymoreatrophyintemporalregionsthandidtheirmonolingualcounterparts,althoughthebilingualpatientswerestillabletofunctionatthesamecognitivelevel.Thesestudiessupportthepossibilitythatthebilingualadvantageincognitivecon-trolextendstobenefitpatientssufferingfromAlzheimersdiseaseandalsopossiblytootherformsofdementia.Ifconfirmed,thesefindingswouldmakebilingualismonefactorthatcontributestocognitivereserve,witheffectssimilartothosefoundforsocial,intellectual,andphysicalactivity.Howexactlycognitivereserveactstoprovidecom-pensationforbrainpathologyisanexcitingquestionforfutureresearch.Asdescribedearlier,bilingualismisalreadycommoninmanypartsoftheworldandiscertaintobecomeevenmorecommonasthe21stcenturyunfolds.Wehavesummarizedthecurrentstateofknowledgeaboutlanguagedevelopmentandcognitivecontrolthroughoutthelifespan,associatedchangesinthebrain,andtheimplicationsofbilingualismforclinicalpractice.Muchremainstobelearned,butitisalreadyclearthattheconsequencesofspeakingtwoormorelan-guagesareprofound,insomecasesdramaticallyso.Asoneexample,ifthefindingthatbilingualismdelaystheonsetofAlzheimersdiseaseby4to5yearsisconfirmedbyfurtherresearch,therearepotentiallyimportantimplicationsfortheconceptofcognitivereserve.Howexactlydoesbilingualismchangethebrain,forexample,andwhichaspectsofthesechangesconferprotectionagainsttheonsetofdementia?Oncethisisknown,findingsfrombilingualismresearchmayhelptofocusthesearchforotherenvironmentalconditionswithcomparableeffects.Inthesamevein,whataboutcoun-triessuchasBelgiumandtheNetherlands,wheresubstantialproportionsofthepopulationspeakmorethanonelanguage?IsthisassociatedwithagenerallylateronsetofAlzheimersdiseaserelativetocountriesthatarelargelymonolingual?Otherintriguingquestionsincludeonesconcerningthelengthoftimethatapersonisbilingual:Doeslearningasec-ondlanguagefrominfancyprovidespecialbenefits,forexample,orisitsufficienttospeaktwolanguagesconsis-tentlyfromtheteenageyearsorevenlater?Whataboutthesimilaritiesofthetwolanguages?Isthebilingualadvantagegreater(orless?)followingtheacquisitionofhighlysimilarlanguagessuchasSpanishandItaliancomparedtosuchdis-similarlanguagesasChineseandEnglish?Giventherapidlyacceleratinginterestinbilingualismasaresearchtopic,answerstotheseandmanyotherquestionsshouldbeavail-ableintheverynearfuture.PreparationofthismanuscriptwassupportedbyGrantR01HD052523fromtheNationalInstitutesofHealthtoEB,GrantMOP57842fromtheCanadianInstitutesofHealthResearchandaGrantfromtheAlzheimersSocietyofCanadatoEBandFIMC,Grant089320/Z/09/ZfromtheWellcomeTrusttoDWG,andGrantR01HD050287fromtheNationalInstitutesofHealthtoTHG.Abutalebi,J.,Annoni,J.M.,Seghier,M.,Zimine,I.,Lee-Jahnke,H.,Lazeyras,F.,etal.(2008).Languagecontrolandlexicalcompeti-tioninbilinguals:Anevent-relatedfMRIstudy.CerebralCortex,1496 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