Schema-driven facilitation of new hierarchy learning in the transitive inference paradigm.

2013·0.29 MB·English

by  Kumaran, Dharshan

Research
Schema-driven facilitation of new hierarchy learning
in the transitive inference paradigm
Dharshan Kumaran1
InstituteofCognitiveNeuroscience,UniversityCollegeLondon,LondonWC1N3AR,UnitedKingdom
Priorknowledge,intheformofamentalschemaorframework,isviewedtofacilitatethelearningofnewinformationina
rangeofexperimentalandeverydayscenarios.Despiterisinginterestinthecognitiveandneuralmechanismsunderlying
schema-drivenfacilitationofnewlearning,fewparadigmshavebeendevelopedtoexaminethisissueinhumans.Herewe
developamultiphaseexperimentalscenarioaimedatcharacterizingschema-basedeffectsinthecontextofaparadigmthat
hasbeenverywidelyusedacrossspecies,thetransitiveinferencetask.Weshowthatanassociativeschema,comprisedof
priorknowledgeoftherankpositionsoffamiliaritemsinthehierarchy,hasamarkedeffectontransitivityperformance
andthedevelopmentofrelationalknowledgeofthehierarchythatcannotbeaccountedforbymoregeneralchangesin
taskstrategy.Further,weshowthatparticipantsarecapableofdeployingpriorknowledgetosuccessfuleffectundersur-
prisingconditions(i.e.,whencorrectivefeedbackistotallyabsent),butonlywhentheassociativeschemaisrobust.Finally,
ourresultsprovideinsightsintothecognitivemechanismsunderlyingsuchschema-driveneffects,andsuggestthatnewhi-
erarchylearninginthetransitiveinferencetaskcanoccurthroughacontextualtransfermechanismthatexploitsthestruc-
tureofassociativeexperiences.
Priorknowledge,intheformofamentalschemaorframework Rapp et al. 1996; Dusek and Eichenbaum 1997; Delius and
of associative information, is thought to facilitate the learning Siemann 1998; Greene et al. 2001; Frank et al. 2003, 2005;
ofnewinformationinarangeofexperimentalandeverydaysce- Heckers et al. 2004; Titoneet al. 2004; Smith and Squire 2005;
narios (Bartlett 1932; Brandsford 1979; McClelland et al. 1995; Moses and Ryan2006; Moses et al. 2010; Kumaran et al. 2012;
Maguireetal.1999;Tseetal.2007;Kumaranetal.2009;vanKes- Zeithamovaetal.2012).
terenetal.2010a,b,2012;Tseetal.2011).Inrecentyears,there Inthisthree-phasestudyinvolving30participants,weused
hasbeenincreasinginterestinspecificneuralmechanismsthat aversionoftheTIparadigm,whichfollowsthelinesoftheorig-
underliethisprocess(Tseetal.2007;Kumaranetal.2009;vanKes- inalparadigmdevelopedbyBryantandTrabasso(1971),andhas
terenetal.2010a,b,2012;Tseetal.2011).Forexample,aninflu- been shown to ensure the development of robust transitivity
entialstudyinrodentsfoundthatthelearningofnewassociations performanceacrossagroupofparticipants,underpinnedbyrela-
(i.e.,anewflavor–placepairedassociate)wasmarkedlyenhanced tional knowledge of the hierarchy (see Materials and Methods)
inthepresenceofanassociativeschemaconsistingofprevious- (Cohen and Eichenbaum 1993; Eichenbaum 2004; Smith and
ly acquired flavor–place associations, experienced in a similar Squire 2005; Kumaran et al. 2012). Our experimental design
context (i.e.,thesameeventarena)(Tseetal.2007).Strikingly, (Fig.1;MaterialsandMethods)allowedustoaskwhetherprior
this speeded (i.e., one-trial) associative learning became rapid- knowledge about the position of items in a previously learned
lyhippocampal-independent,providingevidenceforaschema- seven-itemhierarchy(i.e.,associativeschemaacquiredinphase
driven shift in the neural mechanisms underlying the learning 1) would facilitate learning of the position of novel items in a
ofnewinformation. new nine-item hierarchy (i.e., during phase 2). Critically, the
Despite the surge of interest in the cognitive and neural useofacontrolconditionduringphase2,whichinvolvedlearn-
mechanismsunderlyingthefacilitatoryeffectsofanassociative ingofanentirelynovelnine-itemhierarchy,enabledustoiden-
schemaonnewlearning,thereisapaucityofexperimentalpara- tify the presence of specific schema-driven learning effects,
digmsspecificallydesignedtoaddressthisquestioninhumans. uncontaminatedbygeneralchangesinstrategy.Finally,inphase
Inthisstudy,weexamineschema-basedeffectsinthecontextof 3, we probed the underlying mechanism of schema-driven fa-
thetransitiveinference(TI)paradigm—anexperimentalscenario cilitatory effects—specifically, a contextual transfer mechanism
which provides a well-controlled setting in which to examine wherebyrankinformationspreadsfromfamiliaritemsinthehier-
theinfluenceofanassociativeschema(i.e.,priorknowledgeof archy(i.e.,theschema)tonovelitemssimplythroughtheirasso-
the rank position of items in the hierarchy) on the learningof ciation(e.g.,fromAtoBduringanABtrainingtrial)—byasking
newinformation(i.e.,relatingtotherankpositionofnovelitems). whetherparticipantscouldlearnnewinformationevenintheab-
Tothebestofourknowledge,however,theTIparadigmhasnot sence of corrective feedback. Furthermore, we manipulated the
been employed with this purpose in mind, though it has been strengthoftheassociativeschema(i.e.,betweensubjectgroups;
widelyusedacrossspeciestostudythemechanismsthatsupport seeMaterialsandMethodsandbelow),andaskedwhethersuc-
inferentialbehaviorandgeneralization,andinparticularthespe- cessfulperformancethrough contextualtransferwouldonlybe
cificcontributionofthehippocampus(BryantandTrabasso1971; possibleinthe“strongassociativeschema”group(i.e.,GroupII).
McGonigleandChalmers1977,1992;HarrisandMcGonigle1994;
Results
1Correspondingauthor
[email protected]
Articleisonlineathttp://www.learnmem.org/cgi/doi/10.1101/lm.030296.113. During all three experimental phases, participants completed
FreelyavailableonlinethroughtheLearning&MemoryOpenAccessoption. blocks of training trials, which were followed by blocks of test
20:388–394#2013,PublishedbyColdSpringHarborLaboratoryPress 388 Learning&Memory
ISSN1549-5485/13;www.learnmem.org
Schema-drivenhierarchylearning
alltrainingtrialblocksandanalyzedusingamixed-designANOVA
withonewithin-subjectfactoroftrainingpairtype(sixlevels:Avs.
B,Bvs.C,...,Gvs.H),andonebetween-subjectfactorofgroup.
For % correct responses, we observed a significant main effect
oftrainingpairtype(F ¼8.3,P,0.001),withasignificant
(5,140)
quadratic effect (F ¼28.9, P,0.001) (Fig. 2B). For RT we
(1,28)
alsoobservedamaineffectoftrainingpairtype(F ¼3.4,
(1.2,32.7)
P,0.01), with a significant quadratic effect (F ¼21.5, P,
(1,28)
0.001).Noeffectofgrouporgroupbytrainingpairinteraction
was observed (P.0.1). These results, therefore, are consistent
with the operation of associative learning mechanisms during
trainingtrials(MosesandRyan2006;Zeithamovaetal.2012).
Wenextexaminedhowperformanceontestpairsvariedasa
functionofthedistancebetweenthepositionofitemsinthehier-
archy(i.e.,symbolicdistance,e.g.,equaltotwoforaBvs.Dtrial,
andfourforaBvs.Ftrial)(Fig.2C).Relatingtopercentageofcor-
rectresponses,anANOVAwithfactorsdistance(two,three,four)
andgroupshowedasignificantmaineffectofdistance,F ¼
(1.5,41.2)
10.9,P,0.001,characterizedbyalineareffect,F ¼15.4,P,
(1,28)
0.001. No other significant effects were observed (P.0.1). We
Figure1. Compositionofhierarchiesusedinphases1–3.Familiaritems founda similarpatternintermsofRT:maineffectofdistance,
surroundedbysquareboxesindicatethosethathavebeenseenbeforein
F ¼9.7, P,0.001, characterized by a linear effect,
apreviousphase.Novelitems areshownunboxed. Very familiaritems (1.6,44.8)
(i.e.,itemsintheGroupIIphase3hierarchyseeninbothphases1and F(1,28)¼10.3,P,0.001.Thoughwedidnotaskparticipantstoex-
2) are shown enclosed in bold square boxes. Specifically, the phase 2 plicitlyrecalltheunderlyinghierarchyattheendofphase1—so
FAMILIAR hierarchy comprised five items (i.e., A, C, E, G, I) that had astoavoidbiasingparticipants’strategyduringphase2—thepro-
beenpreviouslypartofthephase1hierarchy(i.e.,intheB–Fpositions). fileoffindingsobserved,inconjunctionwiththoseofprevious
Inphase3,hierarchycompositionvariedaccordingtoparticipantgroup:
studies (e.g., Kumaran et al. 2012), suggests that by the end of
InGroupI,fiveoftheitems(i.e.,A,C,E,G,I)inthephase3hierarchywere
thisexperimentalphaseparticipantshadacquiredrobustrelation-
derivedfromtheNEWhierarchyinphase2(i.e.,theB,C,D,E,Fitems,
respectively). In Group II, five of the items (i.e., A, C, E, G, I) were alknowledgeoftheunderlyinghierarchy(seeDiscussion).
derived from the FAMILIAR hierarchy in phase2 (i.e., the A, C,E, G,I
items,respectively).Forbothgroups,theotherfouritems(i.e.,B,D,F,
Phase2
H)werenovelandhadnotbeenpreviouslyexperienced(seeMaterials
andMethodsfordetails).Notethattheletterlabels(e.g.,“A”)denote Inthisphase,participantswere exposedtotwonine-itemhier-
ordinal positions, and are shown purely for explanatory purposes— archies: One hierarchy, termed “NEW,” was comprised en-
theselabelswerenevershowntoparticipants.Notealsothatitemsarede- tirely of novel items that had never before been experienced
pictedingrayscale,butwerepresentedincolor.
(Fig. 1; Materials and Methods). The other hierarchy, termed
“FAMILIAR,”wascomprisedoffiveitemsthathadbeenpartof
the phase 1 hierarchy, and four novel itemsthathad not been
trials.Trainingtrialsinvolvedthepresentationofadjacentitems
seenbefore.Critically,therelativeorderofthefivefamiliaritems
(i.e.,galaxies)inthehierarchy(e.g.,phase1:sixpremisepairsA
was preserved between the phase 1 and FAMILIAR hierarchies,
vs.B,Bvs.C,Cvs.D,Dvs.E,Evs.F,Fvs.G);participantswere
suchthattheyeffectivelyformedapre-establishedscaffold(i.e.,
required to select the item which they thought was “older,”
with corrective feedback issued in phases 1 and 2 (though not
phase3).Testtrialsalsorequiredparticipantstochoosethegalaxy
whichtheythoughtwas“older,”butdifferedfromtrainingtrials
intwoprincipalways:First,nonadjacentitemsinthehierarchy
werepresented(e.g., phase1: B–D, B–E, B–F, C–E, C–F, D–F).
Second,correctivefeedbackwasnotpresentedduringtesttrials.
Assuch,participantswererequiredtouseacapacityfortransitive
inferencetodeducethecorrectitemduringtesttrials.
Phase 1
Bytheendofthisphase,participantsreachedhighlevelsofperfor-
manceonbothtraining(mean89.5%,SEM3.0)andtest(mean
86.0%, SEM 4.7) trials (Fig. 2A). Data were analyzed using an
ANOVA with within-subject factors of block (20 levels), trial
type (two levels: train, test). Though both participant groups
were treated equivalently in this phase, a between-subjects
factorofgroupwasalsoincluded.Intermsofpercentageofcor-
rect responses, we observed a significant main effect of block Figure2. Phase1performance.(A)Trainingtrial(lightgray)andtest
(F ¼29.2,P,0.001),indexingtheimprovementoftrain- trial (dark gray) performance shown across the 20 blocks. (B) Training
(6.9,194.4)
ingandtesttrialperformanceovertheexperimentalsession(Fig. trialperformanceasafunctionofpair.(C)Testtrialperformanceasafunc-
tionofsymbolicdistance(e.g.,aB–Dtesttrialhasadistanceoftwo).Note
2A).Nosignificanteffectswereobservedinrelationtoanyofthe
thattesttrialblocksalsoincludedtrainingpairs(e.g.,AB),denotedbya
otherfactorsorinteractionsbetweenfactors(allP’s.0.1).
distanceofone—theseareshownforcompletenesshere,butnotincluded
Wenextconsideredtheperformanceofparticipantsontrain- inthestatisticalanalysisofthesymbolicdistanceeffect(seeResults).Data
ingtrialsasafunctionoftrainingpair.Datawerecollapsedacross averagedacrossall30participants.ErrorbarsreflectSEM.
www.learnmem.org 389 Learning&Memory
Schema-drivenhierarchylearning
A,C,E,G,I),inbetweenwhichthenovelitems(i.e.,B,D,F,H)were comparedtotheNEW,conditionwasconfirmedinsubsequent
inserted (see Materials and Methods for details). Further, this ANOVAs that examined training and test trials separately. As
methodof constructing the FAMILIAR hierarchy (i.e., inserting such,therewasasignificantmaineffectofhierarchytypeinrela-
novel items between familiar items) ensured that new learning tiontotrainingtrials(P,0.01),andtesttrials(P,0.05).
was required to determine the correct choice for each training Itisinterestingtonotethattesttrialperformance(i.e.,aver-
pair—andalsothatalltestpairsinvolvedchoicesbetweenitems agedacrossphase2)wassignificantlyhigherthantrainingtrial
thatwerenovelforphase2.Notethatbothparticipantsgroups performance,inbothFAMILIARandNEWconditions(Fig.3A),
were treated identically during this phase, with the exception evidenced by the significant main effect of trial type in the
thatthoseinGroupIwereexposedtotheFAMILIARhierarchyin ANOVApresentedabove(P,0.001).Thiscontrastswithageneral
thefirsttrain–testcycle,whereasthoseinGroupIIwereexposed trendintheliteraturefortrainingtrialperformancetobenumer-
totheNEWhierarchy(i.e.,tocontrolforpossibleordereffects). icallysuperiororcomparabletotesttrialperformance(e.g.,Moses
Further,theallocationofindividualstimuliwascounterbalanced and Ryan 2006), as well as the pattern of findings observed in
suchthattheitemsmakinguptheFAMILIARhierarchyforone phase 1. Specifically, in phase 1, training and test trial perfor-
subjectgroupwereusedintheNEWhierarchyfortheothergroup mances(i.e.,averagedacrossthephase)werecomparable(mean
(andviceversa). trainingtrial,72.5%[SEM2.0];testtrial,70.6%[SEM3.6];nosig-
Theexperimentaldesignofphase2,therefore,wasconfig- nificantdifference,P.0.1)(Fig.3B).Indeed,whenperformance
uredtoexamineparticipants’abilitytouseapriorschema(i.e., wasdirectlycomparedbetweenphases1and2(i.e.,anANOVA
therankpositionsoffamiliaritemsinthephase1hierarchy)tofa- withfactorsphase(1,2)andtrialtype[training,test]),therewas
cilitatenewlearningintheFAMILIARcondition,ascomparedto a significant interaction between phase and trial type (F ¼
(1,28)
theNEWcomparisoncondition.Performanceaveragedacrossall 8.2, P,0.01) that reflected the superiority of test trial perfor-
blocksfortheFAMILIARhierarchyfortrainingandtesttrialswas mance (cf. training) in phase 2 but not phase 1. Importantly,
63.0%(SEM2.2)and72.4%(SEM3.7),respectively(Fig.3A).For thisfindingcannotbeaccountedforbyadifferenceintheaverage
theNEWhierarchy,trainingtrialperformancewas55.2%(SEM symbolicdistancerelatingtotesttrialsinphases1and2—thispa-
1.8)andtesttrialperformance64.0%(SEM3.1).Datawereana- rameterwasequatedbyonlyincludingtesttrialswithasymbolic
lyzed using a mixed-design ANOVAwith within-subject factors distanceoftwo(e.g.,Bvs.D)inbothphases.Althoughitisimpor-
ofhierarchytype(FAMILIAR,NEW),block(12levels),andtrial tanttobearinmindthatphases1and2involvedhierarchiesof
type(twolevels:train,test)withonebetween-subjectsfactorof differing lengths(i.e., seven vs. nine) and different amountsof
groupalsoincluded.Intermsof%correctresponses,weobserved training(e.g.,12vs.20blocks),thesignificantsuperiorityoftest
asignificantmaineffectoftrialtype(F ¼14.5,P,0.001),and trial performance in phase 2 could potentially reflect a change
(1,28)
ofblock(F ¼27.4,P,0.001),withalineareffect(F ¼ in learning strategy. One possibility is that having completed
(3.5,96.8) (1,28)
84.0,P,0.001).Critically,therewasasignificantmaineffectof phase1participantswerebiasedtowardsearchingforanunderly-
hierarchytype(F ¼10.6,P,0.01).Assuch,participantsper- inghierarchicalstructureinphase2,consistentwiththenotionof
(1,28)
formedsignificantlybetteronbothtrainingandtesttrialsinthe an“overhypothesis”thatcanconstrainthelearningofnewinfor-
FAMILIARcondition,ascomparedtotheNEWcondition.Nooth- mation(e.g.,Kempetal.2007).
ereffects,includingtheeffectofgroupandinteractions,weresig- We next examined how performance on test pairs during
nificant(P’s.0.1).ThesuperiorperformanceintheFAMILIAR,as phase2variedasafunctionofthedistancebetweentheposition
ofitemsinthehierarchy(e.g.,Bvs.H¼symbolicdistanceofsix)
(Fig.3C).Relatingto%correctresponses,anANOVAwithfactors
hierarchytype(FAMILIAR,NEW),distance(two,four, six), and
group showed a significant main effects of hierarchy type
(F ¼5.1, P,0.05), and distance (F ¼12.7, P,0.001).
(1,28) (2,56)
The effect of distance was characterized by a linear effect
(F ¼25.4, P,0.001). No other significant effects were ob-
(1,28)
served(P.0.1).
Participants’abilitytoaccuratelyrecalltheorderofitemsin
the two hierarchies was tested at the end of phase 2 (see
MaterialsandMethods).Nine/30participantswereabletoperfect-
lyrecalltheFAMILIARhierarchy,comparedto4/30participantsin
theNEWhierarchy.Theaveragenumberofrecallerrorsmadewas
9.1(SEM1.8)and13.8(SEM1.9)fortheFAMILIARandNEWhier-
archies, respectively (Fig. 3D). Data were analyzed in a mixed-
design ANOVA with factors hierarchy type (FAMILIAR, NEW)
andgroup.Therewasasignificantmaineffectofhierarchytype
(F ¼4.5,P,0.05),butnoeffectofgrouporinteraction(P.
(1,28)
0.1),affirmingthesuperiorhierarchyrecallaccuracyrelatingto
performanceintheFAMILIAR,ascomparedtoNEW,conditions.
Thefindingsfromphase2provideevidencethatthepresence
Figure3. Phase2performance.(A)Trainingtrial(lightgray)andtest
ofanassociativeschemaintheFAMILIARconditionhasaspecif-
trial(darkgray)performanceshownforNEWand FAMILIARconditions
(i.e.,performanceaveragedacrossallblocksinphase).(B)Trainingtrial ic effect on facilitating performance in the TI paradigm, and
(light gray) and test trial (dark gray) performance shown for phases 1 ultimately results in more robust relational knowledge of the
and2(i.e.,performanceaveragedacrossallblocksinaphase).(C)Test hierarchy.
trialperformanceasafunctionofsymbolicdistance,NEW(lightgray),
FAMILIAR(darkgray).(D)PerformanceonhierarchyrecalltestinNEW
and FAMILIAR conditions. See Materials and Methods for scoring Phase 3
scheme. Note, chance performance has mean 26 errors (SD 6) based
onsimulation(involving1000randomlygeneratedhierarchies).Dataav- In phase 3, we examined whetheran associative schema could
eragedacrossall30participants.ErrorbarsreflectSEM. support successful transfer under “extreme” conditions—we
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Schema-drivenhierarchylearning
removedtheprovisionofcorrectivefeedbackfromtrainingtrials ingthesuperiorperformanceofparticipantsinGroupII(i.e.,the
(seeMaterialsandMethods),suchthatnofeedbackofanykind strongschemacondition).Indeed,theperformanceofGroupIdid
waspresentedduringthisphase.Assuch,successful(i.e.,above notrisesignificantlyabovechanceperformanceduringanyofthe
chanceperformance)ontrainingandtesttrials—aswellasthehi- sixtrainingortestingblocks(one-samplet-test,P.0.1).Further,
erarchy recall test that followed the end of the experimental theaveragetrainingandtesttrialperformanceduringphase3of
phase—was only possible by generalizing (or transferring) the GroupIIshowedarobustcorrelationwiththenumberoferrors
rankof familiaritemsin the hierarchy to novel itemsthat had madewhenaskedtorecalltheFAMILIARhierarchyattheendof
notbeenexperiencedbefore.Furthermore,wemanipulatedthe phase 2 (i.e., training trial, r¼20.65, P,0.01; test trial, r¼
strengthoftheassociativeschema(i.e.,abetween-groupmanipu- 20.77,P,0.001).
lation;seeMaterialsandMethodsandbelow),andaskedwhether We next examined how performance on test pairs during
successfulperformancewouldonlybepossibleinthe“strongas- phase3variedasafunctionofthedistancebetweenthepositions
sociativeschema”group(i.e.,GroupII). ofitemsinthehierarchy(Fig.4B).AnANOVAwithfactorsdis-
In this phase, participants were exposed to one hierarchy, tance(two,four,six)andgroupshowedtheexpectedmaineffect
whichconsistedoffiveitemsthathadbeenpartofahierarchy ofgroup(F ¼7.5,P,0.01).Further,therewasasignificant
(1,28)
learned during phase 2 (Group I, items derived from phase 2 group×distance interaction (F ¼27.0, P,0.01), that was
(2,27)
NEWhierarchy;GroupII,itemsderivedfromtheFAMILIARhier- characterizedbyalineareffect(P,0.01),reflectingthatthesupe-
archy),andfouritemsthathadneverbeforebeenexperienced. rior performance of the strong schema group (cf. weak schema
Inbothsubjectgroupstherelativeorderofthepreviouslylearned group)becamemoreapparentwithincreasingsymbolicdistance.
itemswaspreservedbetweenthephase2andphase3hierarchies. Participants’ ability to accurately recall the order of items
Note that the procedure for constructing the hierarchy during in the two hierarchies was tested at the end of phase 3 (see
phase3followeda similarmethodasthat usedduringphase2 Materials and Methods). One/15 participants in Group I were
(i.e.,novelitemswereinsertedbetweenfamiliaritems).Asprevi- abletoperfectlyrecallthehierarchy,comparedto3/15partici-
ously,therefore,thisensuredthatalltrainingpairsinvolvedanov- pantsinGroupII.Theaveragenumberofrecallerrorsmadewas
elandafamiliaritem—andalsothatalltestpairsinvolvedchoices 22.1(SEM2.9)and13.7(SEM2.6)forGroupsIandII,respectively
betweenitemsthatwerenovelforphase3. (Fig.4C).Notably,thehierarchyrecallperformanceofGroupII
Critically,priorhierarchyknowledgecouldbeconsideredto (t ¼24.9P,0.001),butnotofGroupI(P.0.1),wasfound
(14)
bestrongerinGroupII,ascomparedtoGroupI,forthreereasons tobesignificantlyabovechanceperformance(i.e.,meannumber
(seeMaterialsandMethods):First,inGroupII,thepreviouslyex- oferrors26[SD6],generatedusingasimulationof1000randomly
perienceditemshadnotonlybeenpartofthephase2(FAMILIAR) generatedhierarchies).
hierarchybutalsoofthephase1hierarchy.Second,inGroupII, Datawereanalyzedinaone-wayANOVAwithfactorgroup.
the previously experienced items occupied exactly the same There was a significant main effect of group (F ¼6.1 P,
(1,28)
rankpositions(i.e.,A,C,E,F,H)astheyhadinthepreviousphase 0.05),confirmingthehigheraccuracyofhierarchyrecallinthe
(i.e.,intheFAMILIARhierarchy).Finally,hierarchyrecallaccura- strong schema group (i.e., Group II), as compared to the weak
cywasfoundtobesignificantlygreaterfortheFAMILIARhierar- schemagroup(i.e.,GroupI).Indeed,thiseffectremainedsignifi-
chy,ascomparedtotheNEWhierarchy,attheendofphase2. cant when the hierarchy recall analysis was restricted solely to
Averageperformanceacrossthephaseontrainingandtest consideringtherelativeorderofitemsthatwerenoveltophase
trialswasGroupI55.8%(SEM3.4)and51.1%(SEM4.9),respec- 3(i.e.,theB,D,F,Hitemsinthehierarchy).
tively,andGroupII69.6%(SEM3.6)and67.8%(SEM5.8),respec-
tively (Fig. 4A). A one-way ANOVA with factors group showed
asignificantmaineffectofgroup(F(1,28)¼8.5,P,0.01),confirm- Discussion
Despiterecentinterestinthecognitiveandneuralmechanisms
underlyingschema-drivenfacilitationofnewlearning,fewpara-
digms have been developed to examine this issue in humans.
Ourstudyprovidesanewparadigmtostudytheseeffectsusinga
well-established experimental scenario, the transitive inference
task.Wedemonstratethatanassociateschemahasamarkedand
specificeffectonthelearningofanewhierarchythatcannotbeac-
countedforbyless-specificchangesingeneralstrategy.Further,we
showthatparticipantsarecapableofdeployingpriorknowledgeto
successfuleffectundersurprisingconditions(i.e.,whenfeedback
isentirelyabsent),butonlywhentheassociativeschemaisrobust.
Finally,ourresultsprovideinsightsintothecognitivemechanisms
underlyingsuchschema-driveneffects,andsuggestthatnewhier-
archy learning can occur through a contextual transfer mecha-
nismthatexploitsthestructureofassociativeexperiences.
Although we intentionally did not require participants to
explicitly recall the underlyinghierarchyat the endof phase1
(to avoid influencing participants’strategy during phase 2) the
Figure4. Phase3performance.(A)Trainingtrial(lightgray)andtest patternofdataobservedsuggeststhatbytheendofphase1par-
trial(darkgray)performanceshownforsubjectGroupsIandII(i.e.,per- ticipantshadacquiredrobustrelationalknowledgeoftheunder-
formanceaveragedacrossallblocksinphase).(B)Testtrialperformanceas lying hierarchy. Although associative learning mechanisms are
afunctionofsymbolicdistance,GroupI(lightgray),GroupII(darkgray).
known to produce a linear symbolic distance effect, the high
(C) Performance of each subject group on hierarchy recall test. See
levelsoftransitivityperformanceachievedinthecontextofarel-
Materials and Methods for scoring scheme. Note chance performance
hasmean26errors(SD6),basedonsimulation(involving1000randomly ativelylong(i.e.,seven-item)hierarchystronglyfavorsanunder-
generatedhierarchies).ErrorbarsreflectSEM. lyingrelationalhierarchyrepresentation(Franketal.2003;Moses
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Schema-drivenhierarchylearning
and Ryan 2006; Kumaran et al. 2012; Zeithamova et al. 2012). necessarily involve knowledge, be it “implicit” or “explicit,” of
Further,thisconclusionisalsoconsistentwiththeresultsofother the structure of training trial presentation (i.e., that B appears
studiesthathaveusedananalogousversionoftheTIparadigm onlywithAandC,CwithBandD,etc.).Ifthescheduleoftraining
(i.e.,Kumaranetal.2012),wheresimilarpatternsofbehavioral trialpresentationwasdifferent—forexampleinvolvingeachitem
performanceweredemonstratedinassociationwithhighlyaccu- (e.g., A) appearing with all others (i.e., B–I)—then contextual
raterecalloftheunderlyinghierarchy. transferofthisnaturewouldnotbeaviablemechanism.
Ourfindingsfromphase2provideevidencethatthepresence Interestingly,thoughmultiplemechanismsmaycontribute
ofanassociativeschemaintheFAMILIARconditionhasaspecific totransitiveinferenceasafunctionofthespecificexperimental
effect on facilitating performance in the TI paradigm, and ulti- setting underconsideration (Zeithamova et al. 2012), it should
matelyresultsinmorerobustrelationalknowledgeofthehierar- be noted that a contextual transfer effect favors the operation
chy. Importantly, in both FAMILIAR and NEW condition, new of “encoding-based” models in this experimental setting (e.g.,
learningwasrequiredtosupportsuccessfulperformanceduring thetemporalcontextmodel[TCM)][Howardetal.2005;Polyn
trainingandtesttrials;further,testtrialsinbothconditionswere andKahana2008]),over“retrieval-based”models(Kumaranand
restricted to the novel items. Furthermore, through the use of McClelland2012)(e.g.,seeZeithamovaetal.(2012)foroverview
theNEWbaselineconditionwewereabletoshowthatthiseffect ofbothclassesofmodels).ThoughTCMwasoriginallydeveloped
cannot be explained by less-specific effects such as a change toaccountforbehavioraldataintasksinvolvingfreerecall(Polyn
in overall learning strategy, as could potentially have been the andKahana2008),ithasmorerecentlybeenproposedtoaccount
caseifwehadsetouttoelicitschema-driveneffectsthroughcom- fortransitivitybehaviorintheTIparadigm(Howardetal.2005).
paringperformanceacrossdifferentphases(e.g.,phases1and2). Briefly, TCM argues that the contextual representation of each
Further,thesuperiorperformanceintheFAMILIARascompared iteminatrainingpair(e.g.,AandB)comestosharecommonfea-
totheNEWconditioncannotbeareflectionofordereffects,or tures due to their temporal co-occurrence. On the assumption
merestimulus-specificdifferences:Orderandstimulusallocation thatrankinformationcanbeconsideredpartofanitem’scontex-
wascounterbalancedbetweensubjectgroups(seeMaterialsand tual representation, TCM might naturally produce the kind of
Methods). contextual transfereffect observed—though it wouldbe poten-
Future studies are required to examine the neural mecha- tiallyilluminatingforquantitativesimulationstudiestoexplore
nismsunderlyingtheschema-drivenfacilitationofnewlearning thisissueingreaterdetail.
intheFAMILIARcondition.However,arecentstudypointstoward Insummary,thecurrentstudydevelopedaparadigmtochar-
ahippocampallymediatedeffect,byprovidingevidencethatthis acterizetheeffectsofpriorknowledgeinfacilitatingnewlearning
brain region supports the acquisition of linear hierarchies in a usingawell-establishedexperimentalscenario,thetransitivein-
domain-generalfashionandgeneratesaneuralsignalthatlinearly ferencetask.Ourfindingsdemonstratethatanassociateschema
codesforrankinformation(Kumaranetal.2012).Assuch,itis hasastrikingeffectonthelearningofanewhierarchy,evenin
worthbearinginmindthattheneuralrepresentationofassocia- surprisingconditions(i.e.,whencorrectivefeedbackisentirelyab-
tiveschemas—andthereforetheneuralmechanismsofschema- sent),andprovidesinitialinsightsintotheunderlyingcognitive
driven facilitatory effects on new learning—are likely to differ mechanismsofsuchschema-driveneffects.Inthefuture,itwill
depending on the experimental scenario under consideration. be interesting to further characterize the underlying cognitive
Forinstance,thestudybyTseetal.(2007)suggeststhatneocorti- and neural mechanisms using quantitative modeling studies
cal-basedschemasarisefollowingextensivetraining(e.g.,weeks) andfunctionalneuroimaging,respectively.
on flavor–place associations in an environment through sys-
tems-levelconsolidation, contrastingmarkedlywiththe hippo-
campal-dependence of a schema-driven enhancement of new Materials and Methods
learning that was based on a set of associative rules that had
beenrecentlyandrapidlyacquired(Kumaranetal.2009). Stimuli
Thefindingsfromphase3demonstratethatsuccessfultran- Picturesofgalaxieswereobtainedfromvarioussitesontheinter-
sitivity, training trial, performance, was possible, even in the net(includinghttp://hubblesite.org/gallery/album/nebula)(Fig.
absence of any corrective feedback, but only under conditions 1).Theallocationofindividualpicturestopositioninthehierar-
where prior knowledge was robust (i.e., strong schema, Group chywasrandomizedacrossthegroupofparticipants.Stimuliwere
presentedusingCogentGraphicstoolbox(http://www.vislab.ucl.
II).Further,thiswasassociatedwiththedevelopmentofrelational
ac.uk/cogent_graphics.php) operating in a Matlab 7 environ-
knowledgeoftheunderlyinghierarchy,asmeasuredbythehier-
ment.
archyrecalltest,whichwasfoundtobepresentevenwhenonly
novelitemswereconsidered.Theseresultsprovideinsightsinto
thecognitivemechanismsunderpinningsuchschema-drivenen- Participants
hancementsoftransitivityperformanceandrelationalhierarchy
Thirty healthy individuals participated in this experiment (age
knowledge. Specifically, our findings support the hypothesis
range19–33,16female).Allparticipantsgaveinformedwritten
thatpriorknowledgeconcerningtherankpositionsofthefamil-
consenttoparticipationinaccordancewiththelocalresearcheth-
iar(i.e.,A,C,E,G,I)itemsfacilitateslearningoftherankposition icscommittee.
ofthenovelitems(i.e.,B,D,F,H)throughaformof“contextual Eachgroup(GroupsIandII)comprised15participants.There
transfer”(cf.Howardetal.2005;WimmerandShohamy2012).As werenosignificantdifferencesbetweensubjectgroupsintermsof
such,participantsmightlearnthattheBitemislowerinrankthan ageoryearsofhighereducation(P’s.0.1).NotethatGroupsIand
A,buthigherthanC,throughthespreadofrankinformationdur- IIweretreatedidenticallyinphase1,andonlydifferedwithre-
ingtrainingtrials(e.g.,fromthefamiliarAitemtothenovelB gardstotheorderofhierarchypresentation(i.e.,whetherthefirst
train–testcyclewasFAMILIAR[GroupI]orNEW[GroupII])(see
item, during an AB trial). According to this mechanism, new
below).Thecriticaldifferencebetweengroupswasduringphase
learningoccurssimplybyviewingtheBiteminassociationwith
3:ParticipantsinGroupIwereexposedtoahierarchywhichcon-
theAandCitemsduring(i.e.,A–B,B–C)trainingtrials,rather
taineditemsderivedfromthephase2NEWhierarchy(i.e.,a“weak
than through the provision of corrective feedback during trial- schema”condition),whereasthoseinGroupIIwereexposedtoa
and-error learning (i.e., A+B). Notably, however, learning the hierarchycontainingitemsderivedfromphase2FAMILIARhier-
rank position of novel items through contextual transfer must archy(i.e.,“strongschema”condition).
www.learnmem.org 392 Learning&Memory
Schema-drivenhierarchylearning
Experimental design stinct. Note that we’ll still score your responses and perfor-
Therewerethreeexperimentalphases(i.e.,1–3)(Fig.1),allin- manceduringtrainingandtesttrialswillcounttowardfinal
volving the TI paradigm—these were divided into five sessions payout.Thethirddifferencefrombeforeisyoualsowon’tbe
(twosessionseachforphase1and2,andonesessionforphase shown cumulative totals and the end of each block, but as
3)separatedbyabreakof1–2mineach. mentionedbefore,we’lltellyouatendhowyoudid.”
Inphase1,allparticipantscompleted20trainingand20test
blocksoftheTIparadigm,involvinganewseven-itemgalaxyhi- Thecriticalmanipulationwasthathierarchycompositionvaried
erarchy(i.e.,A–B–C–D–E–F–G,whereAisthehighestranking according to participant group: In Group I, five of the items
itemandGthelowest).Eachtrainingblockcomprisedsixtraining
(i.e., A, C, E, G, I) in the phase 3 hierarchy were derived from
trials(e.g.,Avs.B,seebelow)andsixtesttrials(e.g.,Bvs.D,see
theNEWhierarchyinphase2(i.e.,theB,C,D,E,Fitems,respec-
below), with order of training and test trial presentation being
tively).InGroupII,fiveoftheitems(i.e.,A,C,E,G,I)inthephase
pseudorandom.
Inphase2,participantscompleted12trainingand12testing 3hierarchywerederivedfromtheFAMILIARhierarchyinphase2
blocksinvolvingtwonine-itemgalaxyhierarchies(i.e.,A–B–C– (i.e.,theA,C,E,G,Iitems,respectively).Forbothgroups,theoth-
D–E–F–G–H–I). Prior to the start of phase 2, participants re- erfouritems(i.e.,B,D,F,H)werenovelandhadnotbeenprevi-
ceivedinstructionsasfollows:“Youwillseetwosetsofgalaxies. ouslyexperienced.Inthisphase,nofeedbackwaspresentedon
Onesetofgalaxieswillbeentirelynew.Theothersetofgalaxies training(ortest)trials—norwascumulativefeedbackattheend
willcontaingalaxiesyouhavepreviouslylearnedabout,aswell ofeachblockprovided.Theset-upofphase3,therefore,allowed
asnewones.Whatyoulearnedaboutgalaxiesyouhavelearned
ustoexaminewhetherthepresenceofapriorschemaissufficient
aboutbeforewillstillholdtrue,butyouneedtoalsolearnabout
tosupportsuccessfultransitivityperformanceevenintheabsence
thenewgalaxies.”
ofcorrectivefeedback.Further,weassessedtheeffectonperfor-
Critically,therefore,fiveoftheitemsinthe“FAMILIAR”hi-
erarchy(i.e.,A,C,E,G,I)hadbeenpartofthehierarchylearned mance of manipulating the strength of the associativeschema;
duringphase1(i.e.,theB,C,D,E,Fitems,respectively)(Fig.1). asdescribedabove,inGroupII,previouslyseenitemsinthephase
Theotherfouritems(i.e.,B,D,F,H)inthe“FAMILIAR”hierarchy 3hierarchywerebothmorefamiliar(i.e.,hadbeenseenduring
werenewitemsthathadnotbeenseenbefore.Incontrast,allnine phase1)andoccupiedexactlythesamepositionsinthehierarchy
itemsinthe“NEW”hierarchy(i.e.,itemsA–I)werenovelitems asinthepreviousphase(i.e.,phase2)(Fig.1).
thathadnotbeenpreviouslyexperienced.Duringphase2,partic- Inallphases(includingphase3),thestartofeachblockwas
ipantscompletedalternatingtrain–testcyclesofeachofthetwo precededwiththerelevantinstruction(i.e.,“Getreadyfortrain-
hierarchies.ParticipantsinGroupIviewedtheFAMILIARhierar- ingtrials,”“Getreadyfortesttrials”).Followingtheendofeach
chy in the first train–test cycle, and those in Group II viewed blockinphases1and2,ascreenshowingthepercentageofcorrect
theNEWhierarchyinthefirstcycle(tocontrolforpotentialorder responsesachievedwasdisplayed.
effects).Theaccuracywithwhichparticipantscouldreconstruct
thehierarchies(thehierarchyrecalltest,seebelow)wastestedaf-
Training and testtrials
terphases2and3.
Inphase3,participantscompletedsixtrainingandtesting Duringatrainingtrial,adjacentitemsinthehierarchywerepre-
blocksinvolving one nine-item galaxy hierarchy (i.e., A–B–C– sentedoneithersideofthescreen(i.e.,phase1,sixpremisepairs
D–E–F–G–H–I).Priortothestartofphase3,participantswere Avs.B,Bvs.C,Cvs.D,Dvs.E,Evs.F,Fvs.G;phases2and3,eight
told that they would be exposed to a new set of galaxies, and premisepairs,i.e.,Avs.B,Bvs.C,Cvs.D,Dvs.E,Evs.F,Fvs.G,G
that:(1)previouslyacquiredinformationabouttheoldnessofgal- vs.H,Hvs.I).Theleft–rightpositionofanitemonthescreenwas
axieswouldstillholdtrue;(2)therewouldbenofeedbackofany randomizedacrosstrials.Participantshadupto3secinwhichto
kind(i.e.,nocorrectiveorcumulativefeedback);and(3)theway choose,viabuttonpress(i.e.,leftorright,indexormiddlefinger
inwhichgalaxiesarepresented(e.g.,duringtrainingtrials)would oftherighthand,respectively),theitemwhichtheythoughtwas
bethestructuredasinpreviousphases. “older.”Inphases1and2(butimportantlynotphase3),corrective
Participantswereinstructedasfollows: feedbackwasissuedaftertheparticipant’schoicehadbeenmade.
Thisconsistedofagreensquareborderwhichindicatedthepartic-
ipant’schoicetogetherwitheither“+20points”or“220points”
“Inthisphaseoftheexperiment,youwillonceagainhaveto
foracorrectorincorrectresponse,respectively.Afixationcross
learn about one new set of galaxies—some galaxies will be
precededtheonsetofthenexttrial.
ones you haven’t seen before, and some will be familiar to
Notethatouruseofarelationthatistransitiveinnature(i.e.,
youfromphase2. “older”)followstheoriginalversionoftheTIparadigmdeveloped
“Thetasksetupwillbesimilartobeforebutthereareafewkey byBryantandTrabasso(1971).Inotherwork,weshowthatthe
differencestobearinmind:Asbefore,whatyoulearnedbefore useofawell-specifiedtransitiverelationduringtheinstructions,
aboutwhichgalaxiesareolderisstilltrue;forexampleifgalaxy as opposed to one that is ambiguous in meaning and typically
XwasolderthangalaxyY,thenthiswillstillbethecaseinthis used in TI experiments(i.e., “correct”), increasesthe success of
transitivityperformanceandensuresthedevelopmentofrobust
phase.Soyou’llbeabletouseknowledgegainedfromphase2
knowledge of the hierarchy across a subject group (Kumaran
tohelpyouhere.Therewillalsobetrainingtrialsandtesttrials.
etal.2012).
However,youwon’tbegivenfeedbackduringtrainingtrialsin
Testtrialsinvolvedthepresentationofnonadjacentitemsin
thisphase.Whatthismeansisthatyou,ofcourse,won’tbe
thehierarchy.Asintrainingtrials,participantshad3secinwhich
able to learn about which galaxies are older from the feed- tochoose,viabuttonpress(i.e.,leftorright),thegalaxywhich
back—we can’ttell you exactly howto learn which galaxies theythoughtwas“older.”Thecompositionoftesttrialsdiffered
areolderbutwecantellyouthatitisstillpossibletodopretty acrossphases:Inphase1,thefollowingsixtesttrialtypeswerepre-
well,andwecangiveyouafewhints: sented:B–D,B–E,B–F,C–E,C–F,D–F.Inphases2and3,thesix
“Youshouldpaycloseattentiontothewayinwhichgalaxies testtrialtypeswere:B–D,B–F,B–H,D–F,D–H,F–H.Critically,
therefore, items presented during test trials in phases 2 and 3
arepresented,i.e.,whichgalaxiesareappeartogetheraspairs.
had not been experienced in a previous phase (i.e., were novel
Wecanalsotellyouthatthewayinwhichgalaxiesarepaired
itemsinthatphase).
togetherwillremainthesameasinpreviousphasesoftheex-
Importantly, feedback was notpresentedduring testtrials,
periment.Soeventhoughyoumayfindthisphasedifficult,
thoughparticipantswereinstructedthattheirchoiceswouldstill
justdoyourbest,andyoushouldtrytousethisinformation counttowardtheirfinalpayout.Instead,ascreenappearedwhich
to guide your performance, both during training trials and requiredparticipantstorate(onascaleof1to3)theirconfidence
also duringtest trials.If you’reunsure, gowithyour gut in- intheirdecision:Participantswerecarefullyinstructedtoentera
www.learnmem.org 393 Learning&Memory
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Acknowledgments
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I thank Hans Melo for assistance with data collection and two
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