Language, Gesture, and the Developing Brain

DevelopmentalPsychobiology,40,293-310,2002Language,Gesture,andtheDevelopingBrainElizabethBatesandFredericDickCenterforResearchinLanguageandDepartmentofCognitiveScience,UniversityofCalifornia,SanDiegoABSTRACT:Dolanguageabilitiesdevelopinisolation?Aretheymediatedbyauniqueneuralsubstrate,amentalorgandevotedexclusivelytolanguage?Orislanguagebuiltuponmoregeneralabilities,sharedwithothercognitivedomainsandmediatedbycommonneuralsystems?Herewereviewresultssuggestingthatlanguageandgestureare“closefamily”,thenturntoevidencethatraisesquestionsabouthowrealthose“familyresemblances”are,summarizingdissociationsfromourdevelopmentalstudiesofseveraldifferentchildpopulations.Wethenexamineboththeseveinsofevidenceinthelightofsomenewfindingsfromtheadultneuroimagingliteratureandsuggestapossiblereinterpretationofthesedissociations,aswellasnewdirectionsforresearchwithbothchildrenandadults.Keywords:language;gesture;languagedevelopment;motor;parietal;imaging;fMRI;aphasia;contextDolanguageabilitiesdevelopinisolation?Aretheymediatedbyauniqueneuralsubstrate,a“mentalorgan”devotedexclusivelytolanguage?Orislanguagebuiltuponmoregeneralabilities,sharedwithothercognitivedomainsandmediatedbycommonneuralsystems?Formanyyears,developmentalscientistshaveaddressedthesequestionsbystudyingbehavioralassociationsanddissociationsbetweenlanguageandgestureacrosstheperiodinwhichbothsystemsarefirstacquired.Somecompellinglinkshavebeenobserved,involvingspecificaspectsofgesturethatprecedeoraccompanyeachofthemajorlanguagemilestonesfrom6to30monthsofage.Thesebehavioralresultsarecompatiblewithanexpandingadultneuroimagingliteratureattest-Correspondenceto:E.BatesContractgrantsponsor:NIH/NIDCDContractgrantnumbers:O1-DC00216.T32DC00041.1T332MH20002-02Contractgrantsponsor:NOHNIHNGAContractgrantnumbers:5P50DC01289105P50NS22343–15ingtothelargelydomain-generalneuralsystemsunder-pinningmeaningfulactionandperceptioninadynamicandinformationallyrichenvironment.However,datafromanumberofstudiesofnormallyandatypicallydevelopingchildren’sgesturalandlanguageabilitiespresentcomplicating,ifnotoutrightcontradictoryevidencerelativetothedomain-generalaccount.Inkeepingwiththe“convergingmethods”themeofthisspecialissue,wewillcomparebehavioralandlesionstudiesoflanguageandgestureininfantswithrecentneuralimagingstudiesoflanguageandgestureinadults,inthehopeoffindingaunifyingexplanatoryframework.Webeginbyreviewingresultssuggestingthatlanguageandgestureare“closefamily”:wefirsttracethecoemergenceofmilestonesingestureandlanguageacrossearlydevelopment,thendiscusslesionandim-agingstudiesofmovement,gesture,andimitationinadultsthatarecompatiblewiththislockstepdevel-opmentalpicture.Afterthis,weturntoevidencethatraisesquestionsabouthowrealthose“familyresem-blances”are,describingsomemysteriousbutrobustdissociationsfromourdevelopmentalstudiesoftypi-Language,Gesture,andBrainDevelopment2callydevelopingchildren,childrenwithfocalbraininjuries,andchildrenwhoare“latetalkers”.Atfirstglance,thesedissociationsseemtoprecludeatrans-parentmappingbetweengesturalandlinguisticdo-mainsandtheirneuralsubstrates.Butwhenweenlargeourwindowofenquirytoincludesomenewfindingsfromtheadultneuroimagingliterature,amoreinterest-ingstorypresentsitself,onethatmayofferapossiblereinterpretationofthesethornydevelopmentaldissocia-tions,andsuggestsnewdirectionsforresearchwithbothchildrenandadults.“ALLINTHEFAMILY”PARTI:CODEVELOPMENTOFLANGUAGEANDGESTURESincethe1970s,developmentalscientistshaveinves-tigatedlinksbetweenearlylanguagedevelopmentandseveralaspectsofmanualactivity,withspecialempha-sisoncommunicativeandsymbolicgesture(forre-views,seeBates&Snyder,1987;Bates&Thal,1991;Bates,Thal,&Marchman,1991;Iverson&Thelen,1999).TheinitialmotivationforthisworkgrewoutofPiaget’sideasaboutthesharedsensorimotororiginsoflinguisticandnonlinguisticsymbols(Piaget,1954,1962,1970;alsoWerner&Kaplan,1963),althoughinvestigatorsalsowereinfluencedbyideasfromBru-ner,Vygotskyandothersonthesocialscaffoldingofmeaningandcommunicationininfancy(Bruner,1983;Vygotsky,1987;Wertsch,1985).ResearchinthePiagetiantraditionfocusedoncorrelationsbetweenspecificlanguagemilestonesandspecificcognitiveevents,includingdifferentlevelsofcomplexityingesturalcommunicationandinsymbolic(pretend)playoutsideofacommunicativeframework.Table1summarizesaseriesofearlylanguagemile-stoneswiththeirproposedandattestedgesturalcorre-lates(withapproximateages,andsupportingreferen-ces).IncontrastwiththePiagetiantraditionsum-marizedinTable1,workonlanguageandgestureintheVygotskianframeworkhasfocusedmoreontheemergenceofjointattention[howchildrenlearntoattendtoobjectsandeventsthatadultsarewatching,orindicatinginsomefashion(Butterworth&Cochran,1980;Tomasello&Akhtar,1995)].Despitedifferencesinemphasis,resultsinbothtraditionshaveshownthatindividualdifferencesinjointattentionskills(bothrateofdevelopmentandfrequencyofuse)arecorrelatedsignificantlywithconcurrentandsubsequentabilitiesinbothgestureandlanguage(forreviewsandforfurtherevidence,seeCarpenter,Nagell,&Tomasello,1998).Jointattention,symbolicplayandlanguageskill